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Sıvı kristal esaslı termosetlerin hazırlanması
Uzay/uçak endüstrisi, devre elemanları, elektrik yalıtım malzemeleri, yapıştırıcılar, kaplamalar ve mikroelektronik endüstrisi gibi yüksek performans gerektiren uygulamalarda kullanılan termoset polimerlerin özelliklerinin iyileştirilme çalışmaları giderek artmaktadır. Özellikle epoksi reçineler ve siyanat esterleri üzerlerinde en çok çalışılan polimerler olarak göze çarpmaktadır. Tüm üstün özelliklerine rağmen bu iki malzeme de kırılgan olduğundan dolayı kullanım alanları kısıtlıdır. Bu nedenle yapısal olarak modifiye edilmeleri ya da farklı termoset reçineler ile karıştırılarak alaşım halinde kullanılmaları gerekmektedir. Bu amaçla yapılan çalışmalarda ticari epoksi reçineler çeşitli siyanat monomerleri ile kürleştirilerek epoksi/siyanat alaşımları hazırlanmıştır. Ancak bu çalışmalarda ticari epoksilerin kullanılması ile elde edilen alaşımların özelliklerinde bazı kısıtlamalar ortaya çıkmıştır.Bu çalışmanın amacı, ticari epoksi reçinelerin yerine kullanılacak daha üstün özelliklere sahip sıvı kristalin epoksi reçinelerin (LCE) ve farklı özelliklerdeki siyanat esterlerinin sentezlenmesi, sentezlenen reçinelerin birbirleri ile belirli oranlarda karıştırılarak kürleştirilmesidir. Bunların literatürde yer alan benzer ürünlerden daha kolay uygulanabilir, mekanik performansları daha iyi ve geliştirilmiş ürünler olması tasarlanmaktadır.
Fotokimyasal yöntemlerle polihedral oligomerik silseskuokzan (POSS) esaslı nanokompozitlerin sentezi ve karakterizasyonu
Nanokompozit malzemelerin kullanımı, üstün optik, termal, elektronik, fotonik, manyetik, reolojik, yapısal ve mekanik niteliklerinden dolayı her geçen gün artmaktadır. Plastik sektöründe büyük paya sahip olan, otomotiv, kaplama, biyomedikal ve paketleme sanayileri en önemli kullanım alanlarıdır. Genel bir tanımla; iki veya daha fazla malzemenin, iyi özelliklerini bir araya toplamak ya da ortaya yeni bir özellik çıkarmak için, mikro veya makro seviyede heterojen karışımıyla oluşan malzemeye kompozit malzeme denir. Nanokompozitler, sürekli bir polimer matris içerisine dağılmış en az bir boyutu 100 nanometreden küçük olan parçacıkları içeren heterofazlı kompozit yapılardır. Nanoteknoloji araştırmaları, malzemenin yapısını molekül düzeyinde değiştirme şansını verir. Nanoboyutuna inildiğinde artan yüzey alanı/hacim oranı maddeyi çok daha aktif yaparak çevredeki diğer atom ve moleküllerle farklı etkileşimlerine neden olur. Bu farklılıklar, daha saydam camlar, daha hafif, daha dayanıklı arabalar, daha temiz giysiler, daha uzun ömürlü boyalar, gibi güncel yaşamımızı doğrudan etkileyen birçok nanomalzemelerin üretilmesine olanak sağlar. Özellikle nanokompozitlerde kullanılan malzemelerin fiyatlarının düşmesiyle ve kompozitlerin hazırlanmasındaki teknik zorlukların çözülmesiyle birlikte polimer nanokompozitlerinin kullanımı son yıllarda artmaya başladı. Nanokompozit üretiminde kullanılan katkı maddeleri nanoyapılarına göre üç ana kategoriye ayrılmaktadır. Bunlar tek nanoboyutlu killer, iki nanoboyutlu karbon nanotüpler ve nanoteller, ve son olarak da üç nanoboyutlu silika, metal partiküller ve kuantum taneciklerdir. Fotopolimerizasyon, fotoaktif moleküllerin aydınlatılmasıyla oluşan reaktif türlerin vasıtasıyla gerçekleşen çevreye duyarlı bir polimerizasyon tekniğidir. Termal polimerizasyona göre fotopolimerizasyon tekniğinin, oda sıcaklığında yüksek hızda tepkime gerçekleştirilebilme, daha az enerji tüketilmesi ve çözücüsüz formülasyonların hazırlanabilmesi gibi bir çok üstün özellikleri vardır. Tepkimeye girecek formülasyondaki monomer ve diğer kimyasalları düzenleyerek tepkime sonrasındaki sertlik, renk, çözünürlük, geçirgenlik, yapışkanlık, elektriksel iletkenlik gibi malzemenin performansına etki eden özellikler kolaylıkla ayarlanabilmektedir. Bu noktadan hareketle, fotopolimerizasyon tekniğinin kullanımı, istenilen özelliklere sahip nanokompozit malzemelerin hazırlanmasında son derece etkin bir yöntem olacağından tercih edilmiştir. Özetle, bu tezde fotopolimerizasyon tekniği kullanılarak polimer/POSS nanokompozitler sentezlenmiş ve bu nanokompozitlerin yapıları spektroskopi ( FT-IR), termal (DSC, TGA) ve mikroskop (TEM) gibi değişik analiz yöntemleriyle aydınlatılmıştır.
Yara/yanık örtü materyali olarak antibakteriyel özellik taşıyan gözenekli polimerik membranların hazırlanması ve karakterizasyonu
Bu tez çalışmasında, bir travma ya da yanma sonucu oluşan ve kendiliğinden iyileşmesi uzun süren deri dokusu kayıplarının doku mühendisliği yaklaşımı ile daha hızlı ve kaliteli bir şekilde tedavisini sağlamak için çift katmanlı ipek fibroin doku iskeleleri tasarlanmıştır. Doku iskelelerinde hücrelerin yayılmasını ve çoğalmasını hızlandırmak için, doku iskelelerinin birbiriyle bağlantılı yüksek gözenekli yapılara sahip olmaları istenmektedir. Bu amaca uygun olarak, liyofilizasyon yöntemiyle yüksek gözenekli yapıya sahip ipek fibroin süngerler üretilmiştir. Elde edilen ipek fibroin doku iskelelerine yara iyileşme sürecini hızlandırmak amacıyla heparin immobilize edilmiştir. Elde edilen ipek fibroin süngerlerin yapısal özellikleri SEM'de incelenmiştir. Yara/yanık iyileşmesi süresince bakteriyel atakların minimuma indirilmesi gerekmektedir. Bu çalışmada doku iskelelerine antibakteriyel özellik kazandırmak için antibakteriyel ajan olarak, gümüş sülfadiazin kullanılmıştır. Heparin immobilize edilmiş ipek fibroin süngerlerin üzeri elektroeğirme yöntemi kullanılarak gümüş sülfadiazin içeren nanofibröz ipek fibroin film tabakasıyla kaplanmıştır. Böylelikle alt katmanı heparin yüklü sünger, üst katmanı da gümüş sülfadiazin içeren ince nanofibröz tabaka olmak üzere çift katmanlı doku iskeleleri elde edilmiştir. Anahtar Kelimeler: Deri doku mühendisliği, ipek fibroin, antibakteriyel yara örtüleri.
Karbon elyaf takviyeli yüksek yoğunluklu polietilenin ısıl ve mekanik özelliklerinin incelenmesi
Günümüzde elyaf takviyeli polimer matrisli kompozitlerin kullanımı yaygınlaşmaktadır. Elyaf takviyesi olarak en çok kullanılan cam elyaf yerini karbon elyaf takviyesine bırakmaktadır. Karbon elyaf diğer tüm elyaflar arasındaki en önemli özelliği yüksek çekme direnci ve elastik modülüdür. Matris malzemesi olarak ise en çok kullanılan termoset matrisler yerini termoplastik matrislere bırakmaktadır. Termoplastik matrislerin termoset matrislere göre en önemli özelliği geri dönüştürülebilir ve hammaddelerinin raf ömrünün daha uzun olmasıdır. Bu çalışmada matris malzemesi olarak termoplastikler arasında en çok kullanılanlardan biri olan yüksek yoğunluklu polietilen seçilmiştir. Takviye malzemesi olarak seçilen karbon elyaf ise kesikli olarak kullanılmıştır. Seçilen yüksek yoğunluklu polietilen matrise karbon elyaf ağırlıkça değişik yüzdelerde takviye edilmiştir. Tez çalışmasında karbon elyaf takviyeli yüksek yoğunluklu polietilenin ısıl ve mekanik özelliklerinin incelenmesi amaçlanmıştır. Bu amaçla malzemeler ekstrüzyonla harmanlama ve enjeksiyonla kalıplama teknikleriyle kompozit haline getirilmiştir. Hazırlanan kompozit numunelerin mekanik karakterizasyonu için darbe, sertlik ve çekme testleri yapılmıştır. Kompozit numunelerin ısıl özelliklerin belirlenmesi için diferansiyel taramalı kalorimetre (DSC) ve yüzeylerinin karakterizasyonu için ise taramalı elektron mikroskobu (SEM) kullanılmıştır. Karbon elyaf polimerik matrise ağırlıkça % 5, 10, 15 ve 20 olmak üzere 4 farklı oranda takviye edilmiştir. Ayrıca karşılaştırma esaslı olması için cam elyafta polimerik matrise ağırlıkça % 10 ve 20 olmak üzere 2 farklı oranda takviye edilmiştir. Ağırlıkça karbon elyaf miktarının artmasıyla sertlik, darbe direnci ve elastik modülü değerlerinde paralel bir artış, kopma uzaması değerlerinde ise paralel olarak bir azalış gözlenmiştir. Ağırlıkça karbon elyaf takviyesinin artması ise DSC sonuçlarını pek fazla etkilemediği gözlenmiştir. SEM görüntülerine bakılacak olursa da matris ile elyaf arasında yapışmanın çok iyi olmadığını görülmektedir. Çekme testleri sonucunda çekme direncinin elastik modülü kadar etkilenmediği gözlenmiştir. Bunun sebebi olarak ise elastik modülünün karbon elyaf takviye oranına bağlı olduğu, ancak çekme direncinin ise karbon elyaf takviye oranından ziyade son elyaf boyundan daha çok etkilendiği belirtilmiştir. Yapılan araştırmalarda elyaf takviyesinin artmasıyla bahsedilen son elyaf boyunun daha da kısaldığı bulunmuştur. Ayrıca karbon elyaf takviyesinin cam elyaf takviyesine oranla son elyaf boyunu daha da kısalttığı bulunmuştur. Anahtar Kelimeler: YYPE, karbon elyaf, karakterizasyon, kompozit
Yenilenebilir kaynaklar kullanılarak ambalaj malzemesi için kaplama malzemesi hazırlanması
Yenilenebilir bir kaynak olmayan ve giderek tükenen petrol ürünleri yerine, yenilenebilir ve doğal kaynaklardan elde edilen çevre dostu ürünlerle ilgili çalışmalar son yılların en önemli araştırma konuları arasındadır. Ülkemizde yüksek miktarlarda üretilen tarım ürünlerinin meydana getirdiği tarımsal atıklar, yüksek katma değerli çeşitli ürünlerin üretilmesinde yenilenebilir ham madde olarak kullanılabilir. Bu şekilde hem ekonomik değeri olmayan bu tür çeşitli atıklardan biyobozunur ürünler elde edilmesi, hem de bu atıkların yok edilmesinin yarattığı sıkıntının giderilmesi mümkün olacaktır. Bilindiği gibi bitki hücre duvarı üç ana polimerden oluşmuştur; selüloz, hemiselüloz ve lignin. Selülozun kullanım alanı geniştir. Lignin için de kullanım alanı daha kolay bulunabilmektedir. Fakat heterojen bir biyopolimer olan hemiselüloz için kullanım alanı pek yoktur. Değişik polimerleri içinde bulunduran hemiselülozun başlıca bileşeni ksilan olup, bu biyopolimer tarımsal atıklarda kuru ağırlığın %20-35? ini oluşturmaktadır. Dolayısıyla, tarımsal atıkların değerlendirilmesinde ksilan için kullanım alanları bulunması ekonomik açıdan önemlidir. Söz konusu çalışmada, tarımsal bir atık olan ayçiçek sapı kullanılarak ambalaj kaplama malzemesi hazırlanacak ve özellikle gıda paketlerinde kullanılan ambalaj malzemesinin yağ, nem ve toza karşı bariyer özelliklerinin geliştirilmesi ve böylece ambalaj içindeki ürünün bozulmasının önlenmesi sağlanacaktır.
Polihıpe ve polimıpe nanokompozitlerinin sentezi, karakterizasyonu ve mekanik özelliklerinin geliştirilmesi
Makro gözenekli ve açık hücresel yapılı polimerler, yüksek gözenekli ve geniş yüzey alanlı yapıları ve birbirine bağlı iç içe geçmiş gözeneklerin sağladığı avantajlar nedeniyle pek çok farklı alanda kullanım olanağına sahiptirler. Emülsiyon kalıplama yöntemi yüksek ve orta iç fazlı emülsiyonlar (High Internal Phase Emulsion-HIPE, Medium Internal Phase Emulsion-MIPE) kullanılarak açık hücresel yapılı polimerlerin hazırlanmasında kullanılan en basit ve etkili yöntemdir. HIPE?ler büyük hacimlerde iç faz veya dispers (dağılan) faz içeren konsantre sistemler olarak adlandırılır. Bir HIPE?de iç faz hacim oranı (Ø) toplam emülsiyon hacminin en az 0.74?ünü oluşturur. MIPE?lerde ise Ø 0.50 ile 0.73 aralığında değişir. Her iki emülsiyon türünde de fazlardan birisinin (veya her ikisinin) monomerik türler içermesi durumunda emülsiyonların çapraz-bağlanması ile poliHIPE veya poliMIPE olarak adlandırılan açık hücresel yapılı polimerler elde edilir. PoliHIPE ve poliMIPE'ler geniş yüzey alanları ve düşük yoğunluklarının sağladığı avantajlardan dolayı çok farklı alanlarda (iyon değişimi, filtrasyon, doku mühendisliği, katalizör destek malzemelerinin üretilmesi, v.b.) kullanılabilirler. Ancak açık hücresel morfolojinin neden olduğu zayıf mekanik özellikleri nedeniyle gerçek anlamda endüstriyel uygulamalarda kullanımları sınırlıdır. Bu tez çalışmasında poliHIPE ve PoliMIPE?lerin mekanik özelliklerinin geliştirilmesi amacıyla iki farklı yaklaşım kullanıldı: (i) sürekli fazın monomer bileşimi değiştirilerek ve (ii) sürekli faza bu faz ile uyumlu nanokil katılarak. Bu kapsamda, HIPE ve MIPE?lerin sürekli fazına belirli oranlarda nanokil katılarak doymamış poliester reçinesi-ko-divinilbenzen (Pes-ko-DVB), glisidil metakrilat-ko-1,3-bütandiol dimetakrilat (GMA-ko-BDDMA) ve stiren-ko-divinilbenzen (S-ko-DVB) poliHIPE ve poliMIPE nanokompozitleri hazırlandı. Hazırlanan nanokompozitlerin morfolojik, mekanik ve ısıl özellikleri sürekli faz bileşimi ve oranı, emülgatör türü ve oranı, iç faz oranı ve nanokil oranının değişimine bağlı olarak araştırıldı. Bu amaçla sentezlenen poliHIPE ve poliMIPE nanokompozitlerinin morfolojik özellikleri taramalı elektron mikroskobu (Scanning Electron Microscope, SEM) ile incelenirken yüzey alanları ve gözenek boyutları Brunauer-Emmet-Teller (BET) yöntemi ile ölçüldü. Elde edilen nanokompozitlerin ısıl ve mekanik özellikleri ise sırasıyla termal gravimetrik analiz (TGA), diferansiyel taramalı kalorimetre (Differential Scanning Calorimetry, DSC) ve mekanik test cihazı araştırıldı.
Doymamış poliester-tabakasal silikat nanokompozitlerin hazırlanması ve karakterizasyonu
Bu projede, in-situ serbest radikal polimerizasyon tekniği kullanılarak doymamış polyester (UPE) matrisi ve nano-boyutlu montmorillonit (MMT) kili ile polimer-kil nanokompozitlerinin sentezlenmesi amaçlanmıştır. Organofilik MMT dolgusu, yapısında reaktif stiren grubu bulunduran, kuaterner kokoamin tuzunun interkelant olarak kullanılması ile elde edilmiştir. Elde edilen nanokompozitlerin karakterizasyonu X-ışını difraksiyon (XRD) tekniği ve geçirimli electron mikroskobu (TEM) ile yapılmıştır. Nanokompozitlerin ısıl ve mekanik özelliklerine, nano-dolgu yükleme derecesinin etkisi incelenmiştir. Hazırlanan nanokompozitlerin, saf UPE ile karşılaştırıldıklarında, gelişmiş ısıl ve mekanik özeliklere sahip olduğu bulunmuştur. Bu özelliklerdeki iyileşmenin, nano-dolguya bağlı interkalantın çapraz bağlanma reaksiyonuna olan katkısından dolayı olduğu düşünülmüştür. Eksfoliye yapının baskın olduğu, kısmi eksfoliye nanokompozit yapısı, ağırlıkça % 1 oranında MMT dolgusu ilavesi ile sağlanmıştır. Bu nanokompozit, en yüksek derecede ısıl kararlılık, dinamik mekanik özellik ve çapraz bağ yoğunluğu sergilemiştir. Elde edilen bu iyileşmelerin, stiren moleküllerinin, % 1 dolgulama derecesinde, optimum miktarda ve homojen bir dağılımla MMT tabakalarının arasında ve dışında var olmasından kaynaklandığı muhtemeldir
Sitrik asit esaslı biyobozunur polimerlerin sentezi ve karakterizasyonu
Biyobozunur polimerler, ilaç salınımı ve doku mühendisliğinin de dahil olduğu bir çok biyomedikal mühendislik alanında oldukça önemli bir yere sahiptirler. Özellikle hücre ekilmiş yapı iskelelerinin hasta ya da hasarlı dokularla değiştirilerek gerçekleştirilen tedaviler giderek yaygınlaşmaktadır. İdeal olarak doku mühendisliğinde kullanılacak bir yapı iskelesinin doğal dokunun fiziksel özelliklerini taşıması, yeni gelişecek dokuya yapısal kararlılık kazandırması, toksik olmaması, mekanik darbelere karşı dayanıklı olması, vücut içine yerleştirildikten sonra da yeni oluşacak dokunun ihtiyacı olan materyalleri iletebilmesi gerekir. Dünyada sağlık örgütleri tarafından vücut içerisinde kullanımına izin verilen polilaktonlar, polilaktik asitler, poliglikolik asitler ve bunların kopolimerleri başta olmak üzere az sayıda polimer bulunmaktadır. İzin verilen bu polimerler ise yumuşak doku uygulamaları için yeterince yumuşak olmamaktadır. Biyobozunur elastomerler zorlu mekanik etkilere maruz kalan bölgelerde çevre dokulara zarar vermeden işlevlerini yerine getirirler. Parçalanan sentetik matristen gerilimi aşamalı olarak yeni oluşan dokuya aktarılmasıyla, üzerine dairesel mekanik gerinim uygulanmış yapı iskelelerinin vasküler kas hücrelerinde kolojen ve elastin üretimini arttırdığı da bilinmektedir. Birçok biyobozunur elastomerler doku mühendisliği uygulamaları için üretilmiş ve kan damarları, kalp kapakçıkları, sinirler, kıkırdak ve deri gibi şekillerde kullanılmıştır. Bu tür elastomerlerin sentezi incelendiğinde en yaygın olarak kullanılan monomerin Krebs çevriminin metabolik ürünü olan, toksik etki göstermeyen ve Gıda&İlaç örgütlerince kullanımına izin verilen sitrik asit olduğu görülür. Son zamanlarda yapılan çalışmalarda üstün mekanik özelliklere sahip, farklı çapraz bağlanma yöntemlerinin uygulanabildiği, nanogözenekli ve fotoluminesan etkili sitrik asit esaslı polimerler üzerine yoğunlaşılmıştır. Bu çalışmada, özellikle doku mühendisliği alanında kullanım potansiyeline sahip sitrik asit esaslı yeni bir biyobozunur elastomerlerin sentezi ve karakterizasyonu gerçekleştirilecektir. Elde edilecek malzemenin toksik özellik taşımaması, üstün mekanik özelliklerinin olması, biyobozunur malzeme olması, kolay işlenebilir olması, hücrelerle uyumlu olması ve ekonomik olması sağlanacaktır.
Yenilenebilir kaynaklardan elde edilen matris ve reaktif interkelanta sahip polimerik nanokompozitler
Son yıllarda polimer nanokompozitler, mikrokompozitler ve saf polimerlere nazaran sergiledikleri gelişmiş mekanik, ısıl ve optik özelliklerden dolayı büyük ilgi toplamaktadır. Bu projede, soya yağından elde edilen polimer matris ve montmorillonit (MMT) kili bazlı ve yüksek performanslı polimer nanokompozitlerin in situ serbest radikal reaksiyonu ile sentezlenmesi ve daha sonra sentezlenen nanokompozitlerin ısıl, dinamik mekanik özellikleri ve morfolojisinin karakterize edilmesi amaçlanmıştır. İlk aşamada, nano-boyutlu MMT kilinin modifikasyonu, reaktif metakrilat çift bağı içeren yenilenebilir kaynaklı ve biyo-bazlı interkelant ile yapılmıştır. Daha sonra, elde edilen organofilik MMT kili (OrgMMT), akrilatlanmış epokside soya yağı (AESO)/stiren monomer karışımında dağıtılarak, serbest radikal başlatıcı ilavesi ile polimerizasyon reaksiyonu gerçekleştirilmiştir. Sonuç polimer nanokompozitlerinin yapısal karakterizasyonu, X-Işını difraksiyonu (XRD) ve geçirimli elektron mikroskop (TEM) teknikleri ile yapılmıştır. Polimer nanokompozitlerin ısıl ve mekanik özelliklerine, nanodolgunun yükleme derecesinin etkisi, ısıl gravimetrik analiz (TGA) ve dinamik mekanik analiz (DMA) yöntemleri ile araştırılmıştır. AESO bazlı nanokompozitlerin, saf AESO bazlı polimer matris ile karşılaştırıldığında, iyileşmiş ısıl ve mekanik özelliklere sahip oldukları saptanmıştır. MMT dolgusu ağırlıkça % 1 ve % 2 oranında kullanıldığında, eksfoliye nanokompozit yapısı elde edilirken, % 3 dolgulama derecesi kısmi interkelasyona/eksfoliasyona yol açmıştır. %2 OrgMMT nanodolgusu içeren eksfoliye nanokompozitin, saf polimer matrise göre, camsı geçiş ve kauçuğumsu bölgelerde sırasıyla % 400 ve % 500 daha fazla depolama modülüne sahip olduğu bulunurken, % 3 dolgulama ile elde edilen kısmi interkele nanokompoziti ile en düşük ısıl bozunma hızı elde edilmiştir.
Foto "click" kimyasıyla yıldız polimerlerin sentezi ve karakterizasyonu
Polimer zincirlerinin tek bir çekirdeğe bağlı olarak oluşturdukları yapılara yıldız polimer denir. Yıldız polimerler doğrusal polimerlere oranla daha kompakt yapılara (düşük viskozite ve hidrodinamik hacim) ve daha fazla fonksiyonel gruplara sahip olmalarından dolayı daha çok tercih edilmektedir. Özelikle bu polimerler ilaç sanayi, kozmetik, boya sanayi, membran veya baskı dahil olmak üzere bir çok potansiyel uygulama alanına sahiptir. Yıldız polimerlerin sentezi çekirdek ve kolların oluşum sırasına göre üç ana kategoriye ayrılabilir; i) çekirdek-öncelikli, ii) kol-öncelikli ve iii) kenetlenme tepkimesidir. Her yöntemin kendine göre avantaj ve dezavantajları bulunmaktadır. Sharpless ve Meldal tarafından bulunan bakır katalizörlüğünde gerçekleşen azid ve alkin gruplarının Huisgen 1,3-dipolar siklokatılma reaksiyonu (CuAAC) en çok tercih edilen "Click" kimyası reaksiyonudur. Bu reaksiyon sayesinde organik kimya, supromoleküler kimya, ilaç kimyası, biyokonjugasyon ve malzeme bilimi gibi bir çok uygulama alanında bir araya gelmesi çok zor gözüken gruplar kolaylıkla birleştirilmektedir. Fotokimyasal tepkimeler ısıyla gerçekleşen tepkimelere göre, daha düşük enerji ihtiyacı, hızlı gerçekleştirilmeleri ve hem konum hemde zaman olarak kontrol edilebilmelerinden dolayı önemli avantajlara sahiptirler. Son zamanlarda fotouyarılmış tiyol-en ve tiyol-in, fotouyarılmış 1,3-dipolar siklokatılması, fotouyarılmış gerilmiş halkalı sikloalkin ve azidlerin siklokatılması, fotouyarılmış benzodioksinon ve alkollerden ester oluşumu ve fotokimyasal diels-alder tepkimeleri foto "Click" tepkimeri olarak geliştirilmiştir. Özellikle fotouyarılmış tiyol-en ve tiyol-in tepkimeleri uygun koşullarda (oda sıcaklığı, hava atmosferinde) çok hızlı olmalarına rağmen radikal mekanizması yüzünden dış etkenlerden çok çabuk etkilenmektedir. Bununla beraber çifte bağların kendi içerisinde katılma tepkimesi vermelerindan dolayıda polimer-polimer birleştirmelerinde düşük etkinliğe sahiptirler. Diğer foto "Click" tepkimelerinde ise özellikle etkin grupların çok basamaklı sentezlerden elde edilmelerinden dolayı yeterince pratik ve kullanışlı olamamışlardır. Tez kapsamında, ışıkla indirgenen CuAAC "Click" kimyası ve atom transfer radikal polimerizasyon (ATRP) yöntemlerinin birleştirilmeyle yıldız polimerler sentezlendi. Bu amaçla, öncelikle yıldız polimerlerin düz zincirli kolları ATRP ve nükleofilik yerdeğiştirme reaksiyonlarıyla elde edilecektir. Bu polimerler ile çok fonksiyonlu çekirdek-molekülleri arasında gerçekleşen bakır katalizli foto-"click" tepkimeleriyle üç ve dört kollu yıldız polimerler sentezlenecektir. Çalışma boyunca üretilen yıldız polimerlerin spektroskopik (FT-IR ve NMR), kromatografik (GPC) ve termal (DSC ve TGA) özellikleri değişik analiz yöntemleriyle aydınlatıldı.
Terpen-esaslı mikrokürelerin foto-başlatılmış süspansiyon polimerizasyonu ile hazırlanması
Fosil yakıtlardan elde edilen kaynakların yakın zamanda tükenmesi, günümüzün büyük bir endişe kaynağıdır. Bu nedenle yenilenebilir kaynaklara dayalı yeni malzemeler bulma zorunluluğu vardır. Yenilenebilir plastiklerin üretimi için terpen kullanımı, son yıllarda yaygın bir araştırma konusu olmuştur. Terpen-esaslı polimerlerin tasarımı ve hazırlanması, terpen moleküllerindeki kimyasal işlevsellikten (örneğin; konjuge çift bağlar, hidroksil ve karboksil grupları) yararlanarak farklı kimyasal stratejilerin ve çok çeşitli polimerizasyon tekniklerinin uygulanmasını içermektedir. Mikroküreler çapı 1 ile 1000 𝜇𝑚 arasında olan küçük küresel parçacıklardır. Özellikle süspansiyon polimerizasyon prosesleri, mikrokürelerin üretimi için uygundur. Bu teknikte hem başlatıcı hem de monomer polimerizasyon ortamında çözünmezken, başlatıcı monomer içinde çözünür ve polimerizasyon monomer damlacıklarında gerçekleşir. Monomer fazı, bir karıştırıcı ve uygun bir süspansiyon maddesi vasıtasıyla ortam içinde küçük damlacıklar halinde süspanse edilir. Bu tez çalışmasında farklı oranlarda doğal kaynaklı terpen-esaslı β-Mirsen (My) ile 1,4-bütandiol dimetakrilat'ın (BDDMA) süspansiyon polimerizasyonu yöntemi kullanılarak polimerik mikroküre sentezi gerçekleştirilmiştir. Polimerik mikroküreleri verimli ve hızlı elde edebilmek için ise polimerizasyon, fotobaşlatıcı varlığında UV-ışıma ile gerçekleştirilmiştir. Monomer bileşiminin etkisi, yağ fazı bileşiminde My oranı hacimce %10 ila %90 arasında değiştirilerek araştırılmıştır. Tez çalışması süspansiyon polimerizasyonu yöntemi kullanılarak polimerik mikroküre sentezi ve sentezlenen mikrokürelerin karakterizasyonu olmak üzere iki aşamada gerçekleştirilmiştir. Hazırlanan mikrokürelerin kimyasal yapısı Fourier Transform Infrared (FT-IR) Spektroskopisi ve Nükleer Manyetik Rezonans (NMR) spektroskopisi ile, yüzey morfolojisi ve boyutu ise Taramalı Elektron Mikroskobu (SEM) ile incelendi. Spesifik yüzey alanları ise N2 adsorpsiyon/desorpsiyon izotermlerine Brunauer-Emmett-Teller (BET) izortermi uygulanarak tayin edildi. Partikül boyutları ise optik mikroskop ile saptandı ve Zetasizer ile partikül boyutu dağılım analizi yapıldı. Ayrıca, mikrokürelerin şişme davranışları araştırıldı ve Flory-Rehner Teorisi kullanılarak çapraz bağ yoğunluğu (q) ve çapraz bağlar arasındaki ortalama molekül ağırlığı (Mc) hesaplandı. Sonuç olarak, My oranını değiştirerek monomer besleme bileşimini değiştirmenin partikül morfolojisi, boyutu ve dağılımının değiştiği sonucuna varılabilir.
Polihedral oligomerik silseskioksan içeren polilaktit nanokompozitleri üzerine çalışmalar
The main purpose of the first part of this thesis was to investigate influences of three parameters on the mechanical and thermal properties of the polylactide (PLA) matrix nanocomposites filled with polyhedral oligomeric silsesquioxane (POSS) particles. For the first parameter of "Filler Content", nanocomposites with 1, 3, 5, 7 wt% basic POSS structure were compared. For the second parameter of "Functional Group", basic POSS structure having only nonpolar isobutyl groups were compared with three other functionalized POSS structures; i.e. aminopropylisobutyl-POSS (ap-POSS), propanediolisobutyl-POSS (pd-POSS) and octasilane-POSS (os-POSS). For the third parameter of "Copolymer Compatibilization", all specimens were compared before and after their maleic anhydride (MA) grafted copolymer compatibilization. Specimens were produced with twin-screw extruder melt mixing and shaped under compression molding. Various tests and analyses indicated that the optimum filler content for the improved mechanical properties was 1 wt%; while the optimum structure for strength and modulus was pd-POSS structure, in terms of fracture toughness it was basic POSS structure. Additional use of MA compatibilization was especially effective for the basic POSS and os-POSS particles. Because of the biocompatible and nontoxic character of both PLA and POSS nanoparticles, recently being a significant alternative for biomedical parts; the main purpose of the second part of this thesis was to investigate performance of the 3D-printed PLA/POSS nanocomposites with respect to the compression molded PLA/POSS specimens. Due to the higher uniformity and higher homogeneity in the distribution of POSS nanoparticles in each PLA matrix layer, mechanical tests (tensile, flexural, toughness) revealed that the improvements in the strength, elastic modulus and fracture toughness values of the 3D-printed specimens were much higher compared to their compression molded counterparts, the benefits starting from 13% increasing up to 78%. It was also observed that there was almost no deterioration in the physical structure and mechanical properties of the 3D-printed specimens, even after keeping them 120 days at 37°C in a physiological solution prepared by using the standard PBS (Phosphate Buffered Saline) tablet. It is known that electrospinning is the most practical technique to obtain unique properties of polymer based nanofibrous structures, such as neat PLA and PLA filled with POSS particles. On the other hand, due to the so many different process parameters to consider, production of these fibers are extremely difficult and time consuming. That is, use of a certain statistical optimization technique in the design of experiments would be necessary. Therefore, the main purpose of the third part of this thesis was to determine the optimum electrospinning parameters by applying the Taguchi technique first to neat PLA and then to reveal the applicability of these parameters for the electrospinning of PLA/POSS nanofibers. It was observed that instead of conducting 81 experiments to determine the most significant 4 optimum process parameters for PLA, use of Taguchi L9 orthogonal array experiment matrix, i.e. conducting only 9 experiments, reduced time, labor and material consumption considerably. Moreover, it was generally concluded that these same parameters could be also used for the electrospinning of PLA/POSS nanofibers after addition of only 3 wt% KCl salt into the polymer solution.
Yüksek sıcaklık pem yakıt hücreleri için düşük maliyetli ve yüksek performanslı (Co-n/mwcnt) ve polibenzimidazol (pbı) ile modifiye edilmiş (Pt-pbı/mwcnt) elektrokatalizörlerin geliştirilmesi
Due to the extremely high cost of platinum group metals, the development of highly efficient, non-noble electrocatalysts, especially for the oxygen reduction reaction (ORR) is essential for the commercialization. In recent studies, state-of-the-art Metal-N-C (Metal = Fe or Co) catalysts are considered as promising alternatives to expensive Pt/C catalysts because of their excellent electrochemical and physical properties. They can somehow provide decent mass activity and electrochemical performance with considerably low material and synthesis cost. In this thesis, the main course is the development of a non-noble, high-performance Co-N/MWCNT electrocatalyst for high-temperature proton exchange membrane fuel cell (HT-PEMFCs) application, and the second course is the development of polybenzimidazole (PBI) modified carbon-nanotubes as a support material for platinum-based electrocatalysts to increase catalytic durability at elevated temperatures. Upon completion of the studies, synthesis of the Co-N/MWCNT catalyst with a high-temperature pyrolysis method was successfully demonstrated by XPS, ToF-SIMS, XRD, Raman, and HR-TEM analysis. Results showed that the uniform dispersion of Co nanoparticles and the formation of active pyridinic Co-N4 sites were appropriately achieved. It is believed that the formation of stable Pyridinic-N sites could promote more electron pathways through the ORR, and increases the catalyst's stability. Rotating disc electrode (RDE) analysis demonstrated that the kinetics of the Co-N/MWCNT catalyst is sufficient enough to operate as a cathode for a typical PEM fuel cell operation. From the HT-PEMFC test results, at the 150C and 160C, the peak current/power density of the cobalt-based MEA was somehow higher than that of the commercial Pt/C. The only drawback is the stability issue at higher temperatures (170C or more) in an acidic medium. Results partially confirmed that the Co-N/MWCNT catalyst could be the promising alternative to replace noble Pt/C catalysts at the cathode side. In the sub-study, polybenzimidazole wrapped carbon-nanotubes and microwave-assisted reduction of Pt nanoparticles were successfully characterized by TGA, XPS, XRD, and TEM analysis. Modifying carbon-nanotubes through the polybenzimidazole film ensured fine (about 2 – 5 nm) and uniform dispersion of Pt nanoparticles. Cyclic voltammetry (CV) analysis concluded that the Pt-PBI/MWCNT catalyst had a 43 m2·g-1 of electrochemically active surface area (ECSA) to catalyze hydrogen oxidation, which is parallel to the literature but slightly lower than that of commercial Pt/C and Pt/MWCNT catalysts due to hydrophobic behavior of PBI molecules in an aqueous electrolyte. On the other hand, it has shown superior durability compared with the commercial Pt/C and Pt/MWCNT. After the 1000th CV, it has retained almost 80% of its initial ECSA, which makes the Pt-PBI/MWCNT is much more durable than the Pt/C and Pt/MWCNT. However, HT-PEMFC tests indicated that the peak current/power density values of the PBI-modified catalyst were lower than that of commercial-grade Pt/C, suggesting that some balance between durability and performance has to be taken into consideration.
Çeşitli katkı maddeleri içeren polibenzoksazinin hazırlanması ve karakterizasyonu
Polybenzoxazines, a class of phenolic offering excellent mechanical and physical properties, have been developed to overcome the shortcomings of the traditional phenolic resins. The features of these polymers such as no requirement for harsh catalysts, releasing no by-product, molecular design flexibility and low melt viscosity make this class of polymers a promising candidate for various industrial and academic applications. Several methods such as preparation of alloys with other high performance polymers, designing of novel monomers and incorporation of additive compounds were employed to improve the performance of polybenzoxazines. In this work, polybenzoxazine composites involving various types of additives namely aromatic diboronic acid, boric acid, clay, zirconium diboride and diglycidyl ether bisphenol-A epoxy resin were prepared to improve thermal properties. In the first part, phenol and aniline based benzoxazine monomer, in the second part, difunctional benzoxazine monomer were synthesized and their composites were prepared. The structural and thermal characteristics of the benzoxazine monomers, polybenzoxazines and polybenzoxazine composites were analyzed by NMR, FTIR, DSC, TGA, XRD, DMA and DP-MS techniques. Improvement in the thermal characteristics were recorded by the incorporation of additives of the benzoxazine monomers.
Polimerik membrane uygulamaları için yeni malzemelerin sentezi
The polymeric membranes for antimicrobial applications are in high demand nowadays, since the bacteria had developed the resistance against the antibiotics. The membrane technology could become an efficient tool to cope with the antibiotic resistant bacteria which are becoming an unevitable problem on the health and pocket of a common man. To address this issue, the current research is carried out to synthesize polymer with antibacterial properties. Norbornene and oxonorborne monomers with special modification to achieve antimicrobial properties through N-halamine functional group of hydantoin was synthesized in this thesis. The monomers were polymerized using Ring Opening Metathesis Polymerization (ROMP). The polymer norbornene dicarboximide hydantoin P(NDH) and polymer oxonorbornene dicarboximide hydantoin P(ONDH) were saturated to s-P(NDH) and s-P(ONDH) with p-toluenesulfonyl hydrazide. Polymer s-P(NDH) sucessfuly fabricated into membrane. While s-P(ONDH) could not be fabricated into membranes by itself, the s-P(ONDH) was blended with the polyether sulfone (PES). The s-P(NDH) was also blended with PES, along with PES modified cyanuric acid for comparisons. Hence four membranes were studied, one was pure and three were the blend membranes. The synthesized polymers and the blend membranes were characterized using NMR, IR, DSC, and TG/DTA respectively. The properties of membranes were measured: with SEM, pore sizes were determined: with contact angle measurements, hydrophobocity of surface was determined. Besides, tests for the pure water permeance PWP and BSA protein rejection were conducted. The membranes were studied for their antimicrobial properties against E. coli and S. aureus. The respective membranes were efficient enough to give 100% kill of both bacteria, providing the controlled release of active chlorine and restricted the biofilm formation at the surface of membrane.
Boron bileşiklerinin, ester bağı içeren polimerlerin ısıl bozunum davranışları üzerindeki etkileri
Interest in polymer nanocomposites is growing exponentially across various scientific and engineering disciplines owing to their remarkable improvements in their properties compared to micro- and macro- conventional composites. Although polymers having good physical properties are commercially available, they are mostly hampered by their low melting temperatures, poor mechanical or barrier properties. Therefore, there is a considerable work on improvement of the properties of polymers, and development of polymer nanocomposites. Several studies were concentrated on boron compounds in polymer composites in order to enhance thermal properties of polymers. Trans-esterification and/or condensation reactions between the boron compounds and the polymers involving COO, OH or CONH groups may take place and support to improve thermal characteristics. Boronic acid groups release water upon thermolysis and behave like condensed phase flame retardants and lead to the generation of boronic anhydrides and boroxines. They form a cross linked-boroxine network through water loss by assisting intermolecular interactions and so they are good char-yielding compounds. In this study, composites of polymers having ester group along the main change such as poly(lactic acid), PLA and poly(caprolactone), PCL, or along the side chain such as poly(methyl methacrylate), PMMA and poly(n-butyl methacrylate), PnBMA with methyl tallow bis-2-hydroxyethyl ammonium modified montmorillonite, Cloisite 30B (C30B) and Cloisite 15A (C15A) and boron compounds (benzene-1,4-diboronic acid (BDBA), boric acid (BA) and zinc borate (ZB)) were prepared and characterized with the use of transmission electron microscopy (TEM) and x-ray diffraction (XRD) analyses. Dispersion of clay in the polymer matrices and intercalated and partially exfoliated clay layers were analyzed by both techniques. Thermal characteristics of the nanocomposites were investigated by direct pyrolysis mass spectrometry (DP-MS) and thermal gravimetric analysis (TGA) techniques. The increase in thermal stabilities of PLA and PMMA were associated with generation of a crosslinked structure. On the other hand, the decrease in thermal stability of PCL upon incorporation of BDBA and/or C30B was attributed to lower probability of crosslinking in the presence of long alkyl chains along the polymer backbone. Generation of boron network structure was detected for PMMA-BDBA and PCL-BDBA composites. For PnBMA, although addition of C30B increased the thermal stability, addition of clay with BDBA caused any noticeable change in thermal stability. Trans-esterification reactions between BDBA and C30B and ester groups of polymer matrices were also determined.
Amidoksim fonksiyonel grubu içeren pamuk kumaşların aşı polimerizasyonu ile hazırlanması
Bu tez çalışmasında, deniz suyunda eser miktarda bulunan uranyum iyonlarının geri kazanımında kullanılacak, amidoksim grubu içeren aşılanmış dokumasız pamuk kumaşlar, plazma ile başlatılan aşı polimerizasyonu yöntemi kullanılarak akrilonitril (AN) aşılanması ile hazırlanmıştır. Aşı polimerizasyonunu gerçekleştirebilmek amacıyla optimum plazma muamele koşullarının belirlenmesi için uygulanan güç ve plazma muamele süresi gibi farklı parametrelerle çalışılmıştır. Aşılama derecesini arttırmak için plazma ile muamele edilmiş dokumasız pamuk kumaşların AN ile aşılanması farklı reaksiyon sıcaklıklarında (40, 60 ve 70oC) ve farklı derişimlerde %10(w/w), %30(w/w), %50(w/w) ve %70(w/w), hazırlanan emülsiyon çözeltileri 24 saat aşılama sürelerinde gerçekleştirilmiştir. Uranyum iyonlarına seçici adsorbent malzeme hazırlanması amacı ile, optimum şartlarda elde edilen AN aşılanmış dokumasız pamuk kumaş yapısında bulunan nitril grupları, hidroksilamin ile modifiye edilerek amidoksim gruplarına dönüştürülmüştür. AO grubu içeren modifiye edilmiş dokumasız pamuk kumaş adsorbentin U(VI) iyonları adsorpsiyonu için pH, adsorpsiyon kinetiği ve başlangıç derişimi etkisi çalışılmıştır. Optimum pH 6.00 ortamında U(VI) iyonu adsorpsiyonunun 90 dakikada dengeye geldiğini ve 250 ppm U(VI) çözeltisinden adsorplanan miktarın 530,46 mg U(VI)/g adsorbent olduğu bulunmuştur. Uranil iyonlarını adsorplamış dokumasız pamuk kumaşların desorpsiyon çalışması %3 HNO3 ile gerçekleştirilmiş ve U(VI) iyonlarını yaklaşık %100'ü desorbe edilmiştir. Tekrar kullanılabilirlik çalışmaları sonucunda U(VI) iyonları adsorpsiyonunun beş adsorpsiyon desorpsiyon döngüsü boyunca korunduğu gözlenmiştir. Ayrıca 10 mL deniz suyu ile adsorpsiyon çalışması yapılmış ve 24 saat sonunda adsorpsiyon miktarı 0,17 mg U(VI)/g adsorbent olarak tespit edilmiştir. Dokumasız pamuk kumaş, AN aşılanmış, AO grubu modifiye edilmiş ve U(VI) iyonu adsorplamış dokumasız pamuk kumaşların kimyasal yapıları, yüzey morfolojileri ve termal özellikleri, FTIR, XPS, SEM, EDX ve TGA teknikleri kullanılarak karakterize edilmiştir.
Elektromanyetik dalga engeli tekstil ürünleri üzerine bir araştırma: Polimer kaplama ve yüzey–arayüzeyler ile ilgili yapısal incelemeler
Günümüzde yaşadığımız ortamlarda, yüksek gerilim hatları, haberleşme ve radar sistemleri, tıpta teşhis ve tedavi amaçlı kullanılan sistemler gibi pek çok uygulamaların neden olduğu radyasyon kirliliği gittikçe artmaktadır. Özellikle, havayolu ulaşımında etkin olan, uzaydan dünyamıza gelen (kozmik ışınlar başta olmak üzere) zararlı elektromanyetik dalga (EMD) ların varlığı, ozon tabakasındaki incelmenin artması ve var olan deliğin büyümesi vb. olumsuz gelişmeler, ileride insanoğlu için daha fazla zararlı EMD etkileri ile karşılaşılacağının da bir göstergesidir. Bu tür zararlı radyasyondan korunma amacının yanında, güvenlik amacı ile farklı EMD yalıtımlarının da yapılma istekleri, yeni EMD engelli malzemelerin geliştirilmesine yol açmaktadır. Bu tür teknolojik istekler sonucunda bazı tekstil firmaları, önemli Ar-Ge faaliyetleri gerçekleştirmeye başlamıştır. Bu öncü Ar-Ge çalışmaları sonucunda, organik/organometalik özellikler taşıyan, EMD engeli olabilen pek çok kompozit ve nanofiber malzemeden üretilmiş tekstil ürünleri, yüksek maliyetlerle tüketim piyasasına kazandırılmaktadır. Üniversitemiz, Fizik Mühendisliği Bölümü, SWAXS Araştırma Grubu'nda gerçekleştirilen bu tez çalışması ile öncelikle, tüketime sunulan EMD engeli tekstil ürünlerinin karmaşık yapıları nanoskopik ölçekte Small Angle X-ray Scattering (SAXS, küçük açı x-ışını saçılması) yöntemi ile incelenmiştir. Yapılan öncü çalışmalar ile, iki tip SG (Steel Gray) ve ST (Silver Twin) kodları ile tanımlanan tekstil ürünü üzerine odaklanılmıştır. Bu iki ürün seçilirken, EMD kalkan özellikleri ve antibakteriyel özellikleri en güçlü olan ürünler olmasına dikkat edilmiştir. Ayrıca, yüzey özelliklerinin polimer kaplama işlemlerine uygun olup olmadıkları da Atomik Kuvvet Mikroskobu (AFM) yöntemi kullanılarak belirlenmiştir. Ardından karbon nanotüp (CN) ve grafen ile katkılanmış sanayi tipi bir polimer olan plastomer (Plasti-Dip) malzemeler hazırlanarak, farklı oranlarda iki boyutlu (2B) ve 3B nano parçacıklar içerecek şekilde, CN ve grafenle katkılanarak tekstil ürünlerini kaplayacak forma getirilmişlerdir. Sanayi tipi kullanıma uygun, basınçlı sıvı kompozit tüpleri ile püskürtme yöntemi kullanılarak kumaş kaplama işlemleri yapılmıştır. Kaplama işleminden sonra, ara yüzey ve dış yüzey bilgilerini içerecek şekilde birkaç Angström büyüklükten, nanometre ve mikrometre ölçeklerine kadar yapılar incelenerek yapı-özellik ilişkileri kurulmaya çalışılmıştır. Yüzey ve ara yüzey yapı incelemelerinde, ağırlıklı olarak SAXS yöntemi kullanılmıştır. Elde edilen kaplanmış kumaşların EMD ye karşı kalkan etkisi oluşturup oluşturmadıkları, Dalga Kılavuzu Metodu kullanılarak test edilmiştir. İnsan kullanımına doğrudan sunulabilecek bu malzemelerin sağlık açısından bir sorun oluşturup oluşturmayacaklarını belirlemek için de araştırmalar başlatılmış ve kaplama öncesi/sonrası kumaş biyo aktiviteleri incelenmiştir. Displinler arası bir çalışma olan bu tez kapsamında, Üniversitemiz, Mühendislik Fakültesi, Elektrik-Elektronik Mühendisliği Bölümü ve Fen Fakültesi, Biyoloji Bölümü bilim insanları ile iş birliği yapılmıştır. Çalışmanın sonucunda, bu tür tekstil malzemeleri ile ilgili ilk kez nano ölçekli yapısal Ar-Ge faaliyetleri gerçekleştirilerek, yapılan CN ve Grafen katkılı polimer kaplama işlemleri ile 8-13 GHz aralığında EMD kalkanlama özelliklerinin ve antibakteriyel etkilerin yapı ile ilişkilendirilebildiği nano kompozit ürünler elde edilebilmiştir. Grafen katkılı polimer kaplanan kumaşların yüzeyinde nano fraktal yapıların oluştuğu, CN katkılı kaplamalarda ise, Çekirdek-Kabuk Silindir (Core Shell Cylinder) formunda nano yapıların bulunduğu belirlenmiştir. Fraktal model ile yüzeye dağılan grafen nano oluşumlar, yüzey üzerinde daha pürüzsüz ve düzgün bir dağılımın elde edilmesine neden olmuş ve EMD kalkanlama özelliğinin, yüzeyin her bir noktasında daha uniform elde edilmesine katkıda bulunmuştur. ST kumaş üzerine yapılan kaplamalar hem CN, hem de grafen katkılamalar için çok daha düzgün ve homojen elde edilmiştir. Bu durum AFM ve EMD etkileşim testleri ile de doğrulanmıştır. %4 CN–SG tekstil ürününde, kaplamasız SG'ye göre, 11-13 GHz frekanslı EMD için soğurma en yüksek değerde olup, yansımanın da en az olması, bu malzemenin bu frekans bölgesinde görünmezlik çalışmalarında kullanılabileceğini göstermiştir. Kaplama işlemi ile soğurma değeri, 0,2 den 0,3'e artarak %50 oranında geliştirilmiştir. Ayrıca, 8-13 GHz aralığında geçirgenliğin en az olması, CN-SG nin SG ye göre kalkanlama özelliğinin de artırıldığının delili olmuştur. %4 Grafen–SG, 8,5-13 GHz aralığında EMD ler için kaplanmış kumaşın yansıtma özelliğinin en fazla, geçirgenliği ve soğurmasının ise en az olduğu belirlenmiştir. Kaplama işlemi ile geçirgenlik değeri 1,2 den 0,5'e düşerek %33 artırılmıştır. Yani başlangıç malzemesi olan SG ye göre daha iyi bir kalkanlama özelliği elde edilmiştir. %2 CN-ST malzemesi, 8-13 GHz aralığında, yansıtıcılığı en yüksek, soğurma ve geçirgenliği en düşük olması nedeni ile EMD kalkanı olarak önemli bir ürün olma özelliğine sahiptir. Kaplama işlemi sonrası geçirgenlik değeri 2,2 den 0,5'e düşerek %77 artırılmıştır. %2 Grafen-ST, 9,8-13 GHz aralığında daha az geçirgenlik göstermiş ve ortalama geçirgenlik değeri 2,8 iken 1,4 değerine düşerek %50 oranında kalkanlama özelliğindeki artışına neden oluştur. Bu ürünün aynı zamanda, Gr(+) mikroorganizma olan Staphylococcus aureus ve Gr (-) Escherichia coli üzerinde etkin bir biyoaktiviteye sahip olduğu da gözlenmiştir. CN katkılı ST malzemeler için CN katkılama oranı arttıkça, nano ölçekte Rg yarıçap değerlerinin (8,96 – 11,80 nm) ve oluşan küme boyutlarının (24,63 - 34,29 nm) arttığı belirlenmiştir. Bu çalışma sonucunda elde edilen en değerli ürün fiziksel, kimyasal ve biyolojik özellikler açısından %2 CN-ST malzemesidir. 8,96 nm yarıçaplı, homojen dağılımlı, nano globular parçacıklara sahip bu malzeme iyi bir EMD engeli olup aynı zamanda çok iyi bir mikroorganizma karşıtı özelliğe sahiptir.
Enjekte edilebilir hemostatik fibroin mikrojellerin geliştirilmesi
daha sonra doldurulacaktır
Yeni nesil sünek dökme demir malzemenin basamaklı polimerizasyon yöntemi ile hazırlanan epoksi reçinelerle korozyona karşı korunması
Son yıllarda dökme demirlerin önemi metalurji ve malzeme bilimi sektöründe oldukça artmıştır. Birincil nesil dökme demirlerden farklı olarak, 20. Yüzyılın sonlarında ikinci nesil adı verilen, yeni bir sfero dökme demir sınıfı ortaya çıkmıştır. Katı çözelti ile güçlendirilmiş ferritik sfero dökme demir (solid solution strengthened ferritic ductile iron, SSF) olarak adlandırılan bu malzemeler, yüksek mukavemete dayanımının yanı sıra yüksek uzama değerleri de göstererek çeliğin kimyasal yapısı kadar kompleks olmayan, çelik benzeri özellikler taşıyan, işleme kabiliyeti yüksek, metalurji sektörü için oldukça avantajlı ve üretimi çeliğe nazaran ucuz olan bir malzeme sınıfı haline gelmiştir. Bu tez çalışmasında yeni nesil sfero dökme demir malzemelerinden biri olan ve üretimi henüz yaygınlaşmamış olan EN-GJS-600-10 kodlu malzemenin kimyasal bileşimini, standartta verilen mekanik test değerlerini sağlayacak şekilde oluşturmak ve sonrasında savunma sanayi gibi sektörlerde kullanımında korozyona ve aşınmaya karşı dirençli hale getirmek için uygun bir polimer malzemeyle yüzeyini modifiye etmek amaçlanmıştır. Tez çalışması kapsamında hazırlanan sünek özelliklere sahip yeni nesil sfero dökme demir malzeme, başta demir (Fe) olmak üzere, silisyum (Si), mangan (Mn), karbon (C), magnezyum (Mg) gibi toplam 16 farklı elementin uygun oranlarda karıştırılması ile elde edilmiştir. Bu elementler farklı oranlarda bir araya getirilmiş ve neticede hem kimyasal bileşime hem de mekanik özelliklere yönelik olarak standartlarda tanımlanan kriterleri karşılayacak optimum oranlar tespit edilmiştir. Hazırlanan dökme demir malzemenin dünyada üretimi yaygın değildir. Ülkemizde ise endüstriyel üretimi henüz optimize edilmemiştir. Tez çalışması kapsamında, çelikten daha ucuz ve daha hafif ancak çelikle benzer mekanik özellikler gösteren, yapısında 16 element içeren metal malzemelerin hazırlanması ve yüzey özelliklerinin modifikasyonu ile korozyon ve aşınmaya dayanıklı hale getirilmeleri adına önemli sonuçlar elde edildiği düşünülmektedir. Yüzey modifikasyonu, akademik ve endüstriyel çalışmalarda ihtiyaç duyulan yüzey özelliklerinin elde dilebilmesi için sıklıkla başvurulan bir yöntemdir. Özellikle, metalik malzemelerin korozyona karşı yüzeylerinin modifiye edilmesi pek çok uygulamadaki kullanımları açısından zaruridir. Tez kapsamında, metal yüzeylerde basamaklı polimerizasyon yöntemi ile epoksi reçine oluşumu sağlanmış ve korozyona karşı yüzeylerin dirençleri araştırılmıştır. Korozyon testleri, metal yüzeylerde dikkat çekici düzeyde korozyona karşı direncin sağlandığını göstermiştir. Çalışılan 5 monomerden alkol türündeki etilen glikol yüzey modifikasyonunda istenen performansı gösterememiştir. 4 amin monomer içinde en zayıf direnç bir diamin olan etilen diamin (EDA) varlığında tespit edilmiştir. -Tri, -tetra ve -penta (bilhassa -tetra ve -penta) aminler kullanılarak sentezlenen reçinelerin bariyer özelliklerinin daha iyi olduğu; korozif gaz, sıvı ve çözünmüş türlerin polimer matrisi boyunca iç kısımlara doğru difüzyonuna engel olarak metalin korozyona uğramasına karşı daha şiddetli direnç gösterdiği kanaatine varılmıştır. Bunun temel sebebinin çapraz bağlar arasındaki zincir uzunluklarının daha kısa olması ve/veya yüksek dallanma oranına bağlı olarak çapraz bağlar arasındaki serbest hacim bölgelerinin daha sık doldurulması ve böylece daha yüksek bariyer özelliklerinin elde edilmesi olduğu düşünülmüştür. Basamaklı polimerizasyonun gerçekleştirildiği monomerler arasındaki stokiyometrik oranın iyi ayarlanmasının, korozyona karşı dirençli bir reçine elde edilmesinde oldukça önemli olduğuna dair sonuçlar elde edilmiştir. EDA hariç diğer tüm numunelerde di-epoksi:amin momoner oranı 2:1 olan örnekler korozyona karşı daha yüksek direnç göstermiştir. 2:1 mol oranının, reçine yapısında daha sık çapraz bağ oluşumuna sebep olmuş olabileceği, çapraz bağlar arasındaki zincir uzunluklarının kısalması ile bariyer özelliklerinin artmış olabileceği düşünülmektedir. Korozyon testi sonrasında metalik yüzeylerin mikroskobik incelenmesi neticesinde yüzeylerin hiçbirinde blisterleşme tespit edilmemiştir. Bu durum, yüzey kaplamasının dayanıklılığını ve yüzeylerde boya kabarmalarına sebep olarak korozyonu attıran blisterleşmenin olmadığını göstermesi açısından önemli bir bulgudur. Bir korozyon inhibitörü olarak Benzotriazol'ün (BTA) korozyona etkisi incelenmiş; BTA'nın korozyonu önlemede olumlu bir etki yarattığına yönelik sonuçlar elde edilmiştir. BTA'nın metal yüzeyde ince bir tabaka oluşturduğu ve/veya reçine içerisinde BTA moleküllerinin bir araya gelip kümelenerek bariyer benzeri yapılar oluşturmuş olabileceği düşünülmektedir. Tez kapsamında geliştirilen metalik malzemelerin, başta savunma sanayi olmak üzere ülkemiz için önem arz ettiğine ve ekonomik değere sahip olduğuna inanılmaktadır. Anti-korozif polimerik kaplamanın hazırlanması ile ilgili kısmın özellikle bazı temel kriterlerin ortaya konulması açısından önem arz ettiği düşünülmektedir.
Silikon sünger kauçuğun hazırlanması içinoptimum proses koşullarının belirlenmesi
Silikon sünger kauçuk yüksek ve düşük sıcaklığa ve havaya karşı mükemmel direnç gösteren bir polimerdir. İyi elektriksel özellikler, şok emilimi ve elastikiyete sahiptir [1]. Bu avantajlı özellikleri göz önüne alındığında silikon sünger kauçuk, sızdırmazlık contası, süspansiyon conta, termal yalıtım malzemesi gibi özel uygulamalar için endüstride yaygın şekilde kullanılmaktadır. Aydınlatma, kombi kazanı, beyaz eşya uygulamaları, ısıtıcı, fırın ve taşımacılık en sık kullanıldığı sektörlerdendir [2]. Bu çalışmada silikon sünger kauçuğun Colmec marka, her biri 6 metre olan 2 fırınlı, ekstrüzyon hattında 2x8 mm kesitindeki bir fitilin optimum proses parametreleri belirlenmeye çalışılmış ve ekstrüde edilen fitilin sıcaklık akış profili J tipi ısıl çift ile ölçülmüş ve kaydedilmiştir. Kaydedilen sıcaklık akış profili TA-Elite marka Kauçuk Proses Analizörü (Rubber Process Analyzer (RPA)) ile proses koşullarının ve kür kinetiğinin simülasyonu için kullanılmıştır. Silikon sünger kauçuk olarak Elkem Silicone SPG 955 D/SM kullanılmış ve kullanılan bu silikon kauçuk iki farklı katalizör sistemine göre ısıl kararlı kılıcı malzeme, dolgu amaçlı kuartz, karbon siyahı boya ile 16 farklı karışım oluşturacak şekilde hazırlanmıştır. Kauçukların çapraz bağ yoğunluğunu belirlemek amacıyla non-izotermal frekans taraması yapılarak, farklı katkı malzemeleri, dolgu maddeleri ve katalizörler kullanılarak hazırlanmış silikon sünger kauçuğun reolojik davranışları, pişme eğrileri elde edilmiştir. Tüm bu çalışmaların sonucunda ekstrüzyon prosesinde sıcaklık akış profilinin silikon sünger kauçuğun kür karakteristiği üzerindeki etkisi belirlenmeye ve optimum koşulları oluşturmak hedeflenmiştir.
Bor içeren polimerlerin sentezi ve karakterizasyonu
Boron is a Group 13 element that has properties which are borderline between metals and non-metals (semimetallic) which atomic number is 5. Boron compounds have specialized roles in high strength, low weight structuralmaterials. For example, boron is used in glass and ceramic industry for making material resistant to heat. Especially because of its flame retardant properties, usage of boron in polymers is increased in past few years. According to the studies, reactions between boron element and acrylic polymers resulted with acrylic polymers containing boron. Acrylic polymers can be used in many industries, primarily in dye industry, and also it has many copolymer derivatives. In this study, boron containing acrylic monomers was synthesized and characterized. Afterwards, homopolymers and copolymers were synthesized from the boron containing acrylic monomer. Free radical polymerization is choosen as the polymerization method and finally, polymers are characterized with different methods. In this thesis, firstly with esterification reaction boron acrylic monomer is synthesized. Boric acid, neopentyl glycol and as for acrylic monomer HEMA (2- hydroxyethyl methacylate) are reacted to obtain boron containing acrylic monomer. Characterization is made by FT-IR, 13C-NMR, 1H-NMR ve 11B-NMR and results of synthesized monomer is compared with HEMA. After the characterization, homopolymer and copolymers with styrene (St) and methyl methacylate (MMA) are synthesized by free radical polymerization. Properties of copolymer synthesized with St is examined detaily. Monomer reactivity ratios for the studied monomer pair were calculated by using extended Kelen-Tudos (EKT) method. Copolymerization composition and reactive ratios show that the copolymerization is occured randomly. Thermal behaviors of synthesized polymers are studied by TGA and DSC methods. Homopolymer has one glass transition temperature at 72.3 oC. In addition the styrene homopolymer glass transition temaparature at 74.2 oC. Depending on the copolymer composition, the glass transition temperatures of boron acrylic-styrene copolymers have between at 62.9 oC and 97.2 oC. As a result of TGA analyzes, TGA diagrams of copolymers were determined to be in between TGA diagrams of pBAc and pSt . Based on these results, while St copolymer has one decomposition, BAc homopolymer has two decomposition.
ATRP ile ftalosiyanin içeren polimetilmetakrilat sentezi
Since their accidental discovery in 1930s, the phthalocyanines have been one of the most studied classes of organic functional materials because of their unusual chemical and physical properties Their diverse functionality comes from its 18-π electron aromatic system and their ability to coordinate with most of the metal atoms in the periodic table.Phthalocyanines can be incorprated whitin the the macromolecular structure as either network, main-chain or sidechain polymers. In addition, they can also be present as end-groups, pendant groups or as a core of a polymer which is an active area of research. ATRP is one of the very versatile and convenient techniques for polymer synthesis with good control of the molecular weight and relatively low polydispersities. ATRP also allows the synthesis of a variety of polymers with well-defined compositions, architectures, functionalities, and chain topology.In this study, methyl methacrylate is polymerized by ATRP using brominated phthalocyanines as macroinitiator. Therefore, hydroxy end group containing phthalocyanines are brominated to form reactive bromine groups. Structure of the phthalocyanines were examined by NMR, FT-IR and electrochemical studies. Bromine functional group take part in initiating the poly(methyl methacrylate) chain growth. Polymerization characteristics, chemical structure, thermal, UV-Vis, fluoresence and transmittance properties were examined by analysis.
Tris(Hidroksimetil)aminometan ile modifiye edilmiş reçinenin sulu çözeltilerden bor giderilmesinde kullanılması
Boron compounds are used in the glass and ceramic industry to produce borosilicate glass, insulation fiberglass, flame retardant fiberglass, ceramic glazes, neutron absorbers, porcelain enamels, herbicides or fertilizers.Boron presents in groundwater or surface water in various locations where it occurs mainly in the form of boric acid. Common boron sources in water are urban wastewater containing detergents and cleaning products and also industrial effluents from a great number of industrial waste and diverse chemical products used in agriculture.There is no easy method available for the removal of boron from water and wastewater. One or more methods may be applied according to boron concentration in the medium. Adsorption is a very useful and economical technique at low boron concentration. In this study, glycidyl methacrylate (GMA) and ethylene glycol dimethacrylate (EGDMA,10%) were copolymerized to obtain crosslinked poly GMA by using suspension polymerization method. The resin was reacted with excess of tris(hydroxymethyl)aminomethane to obtain tris(hydroxymethyl)aminomethane modified methacrylate based crosslinked bead polymers.The resin was used to remove boron from water. Therefore, loading capacity of the boron was studied depending on different boron concentration and pH. Batch kinetic sorption experiments were performed with highly diluted boric acid solution (4.9x10-3 M) to investigate the efficiency of the resin in the presence of low boron concentrations. Sorption kinetic models were applied to the resin. Loaded polymer samples, when treated with HCl, become almost boron-free.
Akrilik emulsiyon polimerlerinin sentezi ve boya formülasyonunda kullanımı
Formed on the metal surface from corrosion due to the atmospheric conditions, causes the loss of the mechanical properties of the metal, reduce the lifespan and seriously affect the country's economy. For these reasons, metals have to be protected against atmospheric conditions. One of the precaution methods is isolated metals from water and air with a coating material. Solvent-based system is the leader of the metal coatings, but recently solvent-based product usage limitations and volatile organic compounds (VOC) regulations make popular water based coating for protection of metal. For that matter, solvent based products usage, which have negative effect on human health and environment because of toxic and flammable material inside can be reduced with water-based products. With the project, emulsion polymers performance which has ketonic resin as a co-binder will be tested on water based metal paint to evaluated corrosion and adhesion properties. Ketonic resins can be added to the emulsion polymer to prolong coating life because it increases adhesion and corrosion performance. Ketonic resins are the family of thermoplastic resins and have low moleculer weight. They work as an adhesion promoter when combine with co-polymers. Cyclehexanone formaldehyde resin is used in this thesis because of high amount –OH functional group in its backbone. It gives better compability with water borne systems. Choosing right polymer is one of the important criteria for corrosion protection. Emulsion polymerization system is can be used in the metal corrosion. 2-Ethylhexyl acrylate and methyl methacrylate can be choosen for polymerization due to their hard monomer properties. Cyclehexanone formaldehyde resin is obtained solid state and it dissolved in proper solvent. This emulsion is added on pure acrylic polymer which, obtained from water based emulsion polymerization method, as 5% rate and tried to getting homogeneous blend under high-speed mixture. Acrylic polymer – ketonic resin blend is used for water-based metal coating formulation. Water based metal paint is applied on 4 different metal types such as aluminum, galvanized, stainless steel and cold rolled steel for checking adhesion and corrosion performances. The aim of the study is evaluating ketonic resin adhesion and corrosion performance on metal formulation with comparing ketonic resin-acrylic polymer combination and pure acrylic polymer emulsion without ketonic resin. For this study, 3 different paint is prepared one is has only pure acrylic polymer as a binder, second one is acrylic polymer – ketonic resin blend and last one is commercial product of ketonic resin is blended with acrylic polymer as a binder and cheching performance between 3 of them. According to adhesion and corrosion performances show that ketonic resin is enhance adhesion on some metal types: adhesion affects corrosion performance in long term. During the synthesis part, when added ketonic resin on the system, some stability problem is observed. Although added some surfactant into the system for preventing agglomeration, is not clear off the problem. Preventing the system against to stability problem, resin will be connected with acrylic polymer as chemical bond during the polymerization stage and than they are tested on paint formulation is planned for next study. In this way, foreseeing that ketonic resin will be integrated the acrylic emulsion polymer and getting better adhesion and corrosion performances.
Vida dönüş hızının, uyumlaştırıcı ve R-PET miktarının R-PET/HDPE harman özelliklerine etkisi
This thesis aimed to study the low mechanical properties of High Density Polyethylene (HDPE) was mixed Recycled Polyethylene Terephthalate (R-PET) to obtained high mechanical properties. Also we aimed to increase the processebility of R-PET with the helping of HDPE. Ethylene Ethylacrylate Glycidyl Methacrylate Terpolymer (E-EA-GMA) was used a compatibilizer. First of all to see the effect of screw speed, the R-PET/HDPE/E-EA-GMA (30/67/3) blends were prepared at five different screw speed (5-8-10-12-15-18 hertz). Than R-PET/HDPE blends were prepared at various R-PET compositions of 10, 15, 20, 25, 30, 35, 40 and 50wt% in a twin screw extruder. In addition R-PET/HDPE/E-EA-GMA compatibilized blends were prepared with 3wt% and 5wt% E-EA-GMA. All process parameters were kept constant during the preparing all of blends. Then, the samples were moulded by using injection moulding machine for measuring of mechanical properties. First of all the Young Modulus of R-PET/HDPE blends were increased by concentration of R-PET without compatibilizer. On the other hand the increase of amount R-PET badly affected in tensile stress because of weak interaction between R-PET and HDPE polymers. This weak interaction between polymers were examined by scanning electron microscopy (SEM)analysis. The two polymers are immiscible and need to be compatibilized in order to be used in commercial applications. So 3wt% and 5wt% E-EA-GMA were added in the blends to solve the problems. Addition of compatibilizer decreased the droplets size and interphase tension. The more homogenous morphology was obtained and tensile strength was increased. The result of study, optimal parameters were tried to determine for the blend can be used in pipe production
Gümüş nitrat içeren poliakrilonitril kompozit nanoliflerin geliştirilmesi
Nowadays polymer composite nanofiber materials including silver nano particles have been drawn attention due to their attractive properties which are used in several areas. Silver nitrate (AgNO3) loaded polymer composite nanofibers have been used in wound-healing application, filtering media, chemical and biological protective materials, industrial dust collection systems, air filters or water filters, photonic and electric sensors, artificial tissues, protectivetextiles etc.. Polyacrylonitrile (PAN) is one of the important engineering material that is used to produce synthetic nanofibers. PAN/Ag composite polymers provide opportunity to obtain functionally fibers due to their gained optical, mechanical, electrical, antibacterial properties. Also providing high specific surface area and high interpenetrating capacity, high electrical conductivity. Although various properties was obtained from silver nanoparticles embedded polymer composite, dispersion of the silver ion has great importance in the PAN/Ag nanofibers. The properties of these nano composites are related with the size, amount and dispersion quality of the silver nitrate nano particles that embedded into polyacrylonitrile matrix. There are different methods for obtaining a polymer composite matrix. The mechanical mixing of polymer solution and silver nano particles (AgNO3) is one of the easiest methods. Although its simplicity, this method has a major disadvantage that agglomeration of the silver nano particles. Also the homogeneous dispersion of the silver nano particles into the polymer matrix is quite difficult because of the high viscosity of the polymer solution. In chemical reduction method, the reduction of the silver salt could be done in the presence of a suitable stabilizer that required to obtain stable, monodispersed nanoparticles. Poly(N-vinylpyrrolidone) (PVP) is the one of the best stabilizer that used in this area. Owing to these disadvantages some recent methods that are based on in situ reduction of metal ions and in situ polymerization of monomers have drawn interest. In these methods, silver ions have been provided from metal salt that have been reduced into Ag0 in the polymeric matrix. Obtaining of the silver metallic nano particles could be done by different reduction methods such as chemical reduction using sodium borohydrate, heat treatment, reflux method, UV radiation, Xenon arc reduction etc. Electrospinnig is the most used technique among the researchers for the production of polymer fibers containing metal nano particles. In this thesis the effect of the loading different amounts of the silver nitrate into polymer composites, different dispersion methods, different ratio of PVP loading, the effect of the reduction methods were investigated on the mechanical, electrical properties and antibacterial efficiency of the composite nanofibers.
ADMET polimerizasyonu yöntemi kullanarak poli-(5,6-izopropiliden-L-Askorbik asit) sentezi
Ascorbic acid is a naturally occurring organic compound with antioxidant properties. It is a white solid, but impure samples can appear yellowish. It dissolves well in water to give mildly acidic solutions. The overwhelming majority of species of animals (but not humans or guinea pigs) and plants synthesize their own vitamin C. Therefore, some animal products can be used as sources of dietary vitamin C. Vitamin C is most present in the liver and least present in the muscle. Since muscle provides the majority of meat consumed in the western human diet, animal products are not a reliable source of the vitamin. There are three main types of biological activity distinctive to L-ascorbic acid in plants and animals. These are (1) its function as an enzyme co-factor; (2) as a direct physiological radical scavenger and finally; (3) as a donor/acceptor in electron transport in both plasma membrane and chloroplasts 1) Function as an enzyme co-factor L-ascorbic acid is involved in the modulation of a number of important enzymatic reactions such as in the metabolism of several amino acids which lead to the formation of hydroxyproline, hydroxylysine, norepinephrine, serotonin, carnitine and homogenistic acid. It has also been found to be essential for the normal functioning of the osteoblasts,fibroblasts, adrenal hormones and carnitine biosynthesis. 2) Function as a direct radical scavenger Since oxygen is required for cell viability in both plant and animal systems, it is essential that a mechanism be available to control the reactive oxygen species (ROS) generated during cellular metabolism and from exogenous sources and environmental chemicals. L-ascorbic acid interacts enzymatically and non-enzymatically with ROS and their derivatives to neutralize their cellular damaging effects 3) Function as a donor/acceptor in electron transport The biochemical and physiological functions of L-ascorbic acid primarily depend on its reducing properties and its role as an electron carrier.35, 115 L-ascorbic acid and its single-electron oxidized product, semidehydro-L-ascorbate functions as a cycling redox couple in various electron transport reactions and changes the activities of cytochromes, the electron membrane-protein carriers. In addition, simple derivatives of L-ascorbic acid have been shown to possess important pharmacological properties. For example 5,6-Omodified ascorbic acid derivatives have been found to be effective anti-tumor agents for various human cancers, and induce apoptosis in tumor cells and C2 alkylated derivatives have been shown to have immuno-stimulant activity. Recently, the chemistry of ascorbic acid has also been exploited to develop strategies for central nervous system drug delivery. Because of using in drug industries lots of scientists are interested in L-Ascorbic Acid. However there are huge studies in L- Ascorbic Acid area, there is no investigation about polymerization of the structure. Because of having antioxidant and redox properties which are closely associated with the electron rich 2, 3-enediol moiety of the molecule, free radical polymerization can not be used. We thought that polymerization type should be one of the step-growth polymerization. Acyclic diene metathesis is considered to be a step-growth polycondensation-type polymerization reaction, which makes strictly linear chains from unconjugated dienes.10-14 As such, ADMET requires very high monomer conversion rates to produce polymer chains of considerable size. Therefore, the more active 2nd generation catalysts such as 2 and 3 are usually better suited for ADMET than bisphosphine ones. Since the loss of ethylene is the main driving force behind the cross metathesis of terminal olefins, the efficient removal of this volatile gas from the reaction vessel is also crucial. Consequently, although olefin metathesis with ruthenium catalysts is, in general, very mild and does not require stringent air removal, ADMET greatly benefits from conditions which promote the diffusion and expulsion of ethylene (i.e., higher reaction temperatures, application of vacuum, and rigorous stirring). In addition, the use of concentrated or even neat solutions of monomers is usually helpful to polycondensation reactions but, in the case of ADMET, a very viscous solution might be detrimental to efficient stirring and ethylene removal. Furthermore, as a consequence of the poor molecular weight control of stepgrowth reactions, the polydispersity index (PDI) of polymers obtained by this method is usually quite large. However, an important advantage of ADMET is that it allows a large variety of monomers to be polymerized since terminal olefins are quite easy to install. Many functional groups and moieties of interest can be incorporated into such polymers directly through monomer design, due to the excellent tolerance of ruthenium catalysts. In this study Polyvitamine is synthesised from L-Ascorbic acid backbone monomer via ADMET method using both bulk and solution polimerization. In bulk polimerization monomer was reacted with each catalysts G-1 and GH-2. For mixing reactants DCM was used then evaporated from reaction mixture. Both two catalysts were reacted three different temperatures at 40oC, 60oC ve 80oC to see temperature effects. Also in solution polymerization monomer was reacted with each catalysts G-1 and GH-2. O-DCB was used asa solvent. These reactions were happened at just 60oC. The composition and molecular weight of the polyvitamines were characterized by 1H NMR and GPC.
Emülsi̇yon poli̇meri̇zasyonu i̇le doğal kauçuk üzeri̇ne sti̇ren aşılanması
NR has unique and special properties, including high tensile strength, high elongation, and outstanding resilience. It has gained more importance in industry due to its environmental preservation and being renewable source. However, natural rubber is weak in oil resistance, weather resistance, and ozone resistance because of unsaturated carbon double bonds. Some curing techniques and physical and chemical modifications have been developed to get better weathering stabilization of natural rubber. The chemical modification of NR by grafting with vinyl monomers combines the properties of NR and the monomer grafted. The most widely used vinyl monomers are methyl methacrylate, styrene, acrylonitrile. Many research in literature about the graft copolymerization of natural rubber have confirmed that St is one of the most suitable monomers when polymerized to give a high level of grafting, and also provides better ozone, heat, and weathering resistance. Graft copolymerization of St onto NR molecule has been performed by free radical polymerization in emulsion states using various initiator systems including thermal and redox initiators. This work deals with the graft copolymerization of St onto NR in emulsion state by free radical polymerization. The aim of this study was the graft copolymerization of Styrene (St) onto unsaturated carbon double bonds of Natural Rubber (NR) to improve the environmental resistance (UV, heat). The graft copolymerization of St onto NR was performed using ammonium persulfate (APS) as initiator in the emulsion polymerization at a temperature of 85 0C for 4 hours. The graft copolymerization was also carried out by varying the concentrations of initiator and reaction temperature. The grafting efficiency, graft ratio, particle size, and monomer conversion results were compared. The obtained copolymer composition was determined by nuclear magnetic resonance spectroscopy (NMR) and fourier-transform infrared spectrophotometer (FT-IR). The percentage of residual monomer was analyzed by gas chromatography (GC). The Styrene grafted Natural Rubber (St-g-NR) was applied as antislip carpet back-coating. The UV resistance and heat resistance of St-g-NR was tested by using accelerated weathering tester according to ASTM G154 Standard Practice for Operating Fluorescent Ultraviolet Lamp Apparatus for Exposure of Nonmetallic Materials.
Pirina kompozit reçine sentezi
In this study melamine-formaldehyde, urea-formaldehyde and melamine-urea-formaldehyde resins which are thermoset amino resins are modified with olive pomace which is a natural product. Olive pomace, which is taken from Edremit region of Balikesir/Turkey, which has been a waste of olive industry and has been used as fuel or fertilizer by local farmers. The aim of this study is to utilize olive pomace in industry by modifying the amino resins which are synthesized at basic environment with olive pomace. Therefore, resin will be more lightweight, cheaper and will have a wood-like appearance. This study consists of two parts. First part is the synthesis of melamine-formaldehyde and urea-formaldehyde resins which are classified as thermosetting amino resins and their pomace composites. The desired Formaldehyde/Melamine and Formaldehyde/Urea molar ratios are 2 and the synthesis reactions takes place at basic environment. To make a wood-like resin-pomace composite, resins are in situ modified with olive pomace while they are synthesized. The weight of pomace is determined as 10%, 20% and 50% of the weight of melamine and urea in melamine-formaldehyde and urea-formaldehyde resins respectively. In the second part a combination of melamine and urea is used. Melamine-urea-formaldehyde resin is synthesized with a pomace amount of 20% of the total weight of melamine and urea. Resins are characterized using Fourier Transform Infrared Spectroscopy. Water absorption percentage, solubility in water and solubility of in organic solvents are determined. They are resistant to solvents, they either insoluble or slightly soluble. They have wood-like appearance as intended. Moreover, they have different characteristics based upon olive pomace ratio. In low olive pomace weight ratios colour of the composites are light and it gets darker as olive pomace ratio increases. Also, in low olive pomace weight ratios composites are hard and rigid while in higher olive pomace ratios they become softer and sticky. They all have homogeneous appearance which makes them suitable for direct use in many applications.
Polipirol ile tiyenil sonlu etoksile nonil fenolün demir (III)klörür varlığında heterofaz polimerizasyonu
This study presents synthesis of novel block copolymers of thienyl end capped ethoxylated nonyl phenol and pyrrole via chemical oxidative polymerization, by iron (III) chloride (FeCl3). Ethoxylated nonyl phenol (ENP) was reacted with 2-thiophenecarbonyl chloride in order to synthesize a macromonomer containing thienyl end-group (ENP-ThC). Then copolymers of ENP-ThC and pyrrole were synthesized by chemical oxidative polymerization using iron (III) chloride as an oxidant. ENP-ThC served both as a macromonomer and an emulsifier for pyrrole with poor solubility in water.
Poliakrilonitril/karbon nanotüp kompozit nanolif özellikleri üzerine karbon nanotüp ve polianilin etkisi
PAN is the most widely used precursor for processing high performance fibers due to its combination of tensile and compressive properties as well as its high carbon yield. CNTs are ideal reinforcing materials for polymeric matrix. Some important interactions exist between PAN chains and CNTs and these ones lead to a higher orientation of PAN chains during the heating process. It was reported that the PAN macromolecular orientation increases with increasing CNT orientation in the polymer. Some difficulties must be overcome before producing a homogenous dispersion of CNTs in a polymer matrix, including modification for CNTs and processing methods for fabrication CNTs/polymer composites. Modification for CNTs may be succeed by lots of methods including the use of surfactants and chemical functionalization which has been shown to be effective in improving dispersion because the functional groups on the CNTs surface counteract the van der Waals attractive forces between CNTs and then enhance interaction of the matrix phase. Pristine and functionalized CNTs can be dispersed in a lot of polymer matrix systems. Among the conductive polymers, polyaniline (PANI) is widely used in polymer matrix to improve conductivity thanks to ıts low cost, ease of synthesis and good compability with other polymers. Nanofibres can be prepared from a polymer solution utilizing electrospining. Electrospinning is one of tools for preparation of nanofibers and also ıt provides a straightforward and cost-effective approach to produce fibers from polymer solutions or melts having various diameters. In this thesis, PAN-CNT and PAN-CNT-PANI composite fibers were produced. Characterization of composite nanofibers is made by FT-IR, DSC, XRD, SEM, tensile tester and conductivity meter. With the addion of PANI and CNT, tensile strength improved to 10.85 N/mm2 from 8.64 N/mm2. Also electrical conductivity and crystallization were improved with PANI and CNT.
Kompozit resol reçinelerinin sentezi ve cam elyaf üretiminde kullanımı
This study can be divided into two parts. The first part aims to synthesis resol nanocomposites that can be used for thermal insulation materials, coatings, molding compounds, foundry materials, wood products and aerospace components due to their high strength, thermal stability, heat resistance and solvent resistance. In this study, resol resins were modified with alendronic acid and sepiolite in the presence of base catalyst. Sepiolite is a needle like clay that improves the thermal stability, mechanical properties of polymers and used in the matrix of polyethylene, polypropylene, polyurethane, polyamide, polyvinylalcohol and epoxy resins, however there is not any research that include sepiolite and resol. Alendronic acid that is a phosphorus compound mostly used in drug sector for treatment of hypercalcemia, Paget's disease, parasitic diseases, hypercholesterolemia and atherosclerosis. On the other hand phosphorus containing compounds used as flame retardant materials in engineering plastics, polyurethane foams, phenolic resins, polyamides, coatings and textiles. The influence of sepiolite content and alendronic acid content on spectroscopic, thermal and microscopic properties of resins have been researched and determined. For this reason, with adding the different clay amounts of sepiolite (3wt%, 5wt%, 8 wt%, 10wt%, 15wt%, 20 wt%, 30 wt% and 50wt%) and different amounts of alendronic acid (5wt% and 10wt%) were synthesized. Furthermore, the synergist effect of sepiolite and alendronic acid were studied with 5wt% sepiolite and 5wt% of alendronic acid. In this part the synthesized resins formed the structure of nanocomposites. The characterization of the resin nanocomposite samples have been researched and determined. The characterization of the resin samples were performed by Fourier Transform Infrared Spectroscopy (FTIR-ATR), Thermogravimetric Analysis (TGA), X-ray Diffraction (XRD) and Scanning Electron Microscope (SEM). In addition, the solvent behaviour of these resins were investigated with the solvents of acetone, methanol, tetrahydrofuran (THF), dimethylformamid (DMF), chloroform and dimethyl sulfoxide (DMSO). In FTIR-ATR measurements, with the characteristic peaks of neat resol (PFR), Si-O-Si vibrating characteristics of sepiolite and phosphorus peaks of alendronic acid were obtained in nanocomposite resin samples. The DSC technique was used for determining the maximum cure temperatures and onset of cure temperatures. The cycle was heated from 30°C to 200°C with 10 °C/min heating rate. Due to sepiolite clay and alendronic acid loading, the curing temperarutres were enhanced. The thermal attitude of resins were determined by TGA analysis. All resin samples heated at linear heating rate of 10 oC/min up 30oC to 700oC temperature. The weight loss of the resins were calculated with TGA. The obtained all residues at 700oC were higher than 50%wt of initial resin. The structures and the variations of spacing of the PFR, SEP, PFR-AAs, PFR-SEPs and PFR-AA-SEP were detected by X-ray diffraction. The d-spacings were calculated by Bragg's Equation. All of the PFR-SEPs exhibited intercalated structure. As the loading of sepiolite was increased, the interlayer distance did not change very much due to the layers of sepiolite were bonded covalently and resol has thermoset structure even before curing. In PFR-AAs the nanocomposite structure was changed from exfoliated to intercalated with increasing alendronic acid content. Distribution of clay particles in polymeric resol resin matrix and morphology of resin samples were determined with SEM analysis. The sample that contained 10wt% sepiolite loading had good dispersion in resol matrix that supports the strong interaction between silanol (Si-OH) groups of sepiolite and methylol (-CH2OH) groups of resol. The solubility tests were done with six different solvents that were acetone, methanol, THF, chlorofom, DMF and DMSO. All of the resin samples were not solve in acetone, methanol, THF and chloroform. The neat PFR were soluble in DMF and DMSO. Alendronic acid including nanocomposite resins were soluble in DMF however sepiolite including nanocomposite resins were not soluble in DMF. In DMSO not only PFR-AAs but also most of PFR-SEPs and PFR-AA-SEP were soluble. However, increased sepiolite contents of PFR-SEPs reduced the solubility. The second part of this study aimed to obtain production of glass wool insulation materials with sepiolite and alendronic acid modified phenol formaldehyde resol resins to improve thermal properties. Glass wool that is a fluffy material of discontinuous fibers in random lenghts is very useful in thermal insulation sector. For producing glass wool composites of resol samples in a batch mixer the major ingredients (silica sand, limestone, soda ash, cullet) were blended at 1100oC-1300oC. From the reactor the molten glass was poured into the spinner that consisted of 2000 small holes. The fluid mixture were constrained and fibers were manufactured, owing to the centrifugal force of spinner. To bind glass wools the synthesized liquid nanocomposite resol resins were sprayed. After this step, the glass wool was dried in the curing oven at 180-250oC to obtain composite glass wool – modified resol resin product. Length and width trimmers were cut the size of the composite glass wool insulation product At the end of process glass wool composites gained the colour of resin samples.
Polipirol ve tiyenil uç gruplu polisülfon kopolimerleri
Polysulfone (PSU) is a specialty engineering polymer having various industrial applications. PSU is especially used in waste water treatment membranes due to its good mechanical properties, structural and chemical stability. But it is a hydrophobic material and therefore its surface aim to pollute easily, which can be solved by preparetion PSU copolymer or nanocomposite. Polypyrrole (PPy) is a conductive polymer, which has extremely chemical resistance, high surface energy and it is insoluble in many organic solvent. In the membrane field, PPy based membranes used in gas separation and pervaporation. And sepiolite is one of the natural clays, which is a hydrate magnesium silicate fiber, also one of the well known layered clays of the montmorillonites where has several unique channels and pores within. It has also moisture durability, strength and low price. Sepiolite channels give great capacity of absorption and good surface properties, that is bebeficial for hydrophoby of PSU. In this thesis study PSU was synthesized from bisphenol and bis (p-chlorophenyl) sulfone in presence of potassium carbonate by polycondensation and the nanocomposite of PSU with sepiolite were synthesized by in situ method. Their end goups were functionalized with 2-thiophenecarbonyl chloride in order to obtain macromonomers containing thienyl end-group (PSU-ThC and PSU/Sepiolite-ThC), which are capable of giving redox polymerization with pyrrole monomer. Finally copolymers of PPy with these two product were obtained via chemical oxidative polymerization by iron (III) chloride. The synthesized block copolymers were characterized by spectroscopic analysis and the electrical conductivities were investigated with four point probe technique. The obtained samples were also characterized by Scanning Electron Microscope (SEM) and X-Ray Diffraction (XRD).
Çitosan/polipirol/kil nanokompozitlerinin sentezi ve karakterizasyonu
Many researchers studying on discovering new materials to enhance the quality of human life in all aspects. The challenging part of this quest is to find all desired properties in a single material. A composite material is composed of two or more constituents to unite all desired properties in one material. The goal of this study is to discover and produce a high conductivity nanocomposite which is biodegradable, biocompatible, and biofunctional so that it can be used in biomedical applications. Chitosan (CS) is chosen as one of the most attractive polymer due to its' specific properties; such as biocompatibility, biodegradability, and biofunctionality, etc. One of the most investigated conducting polymers is polypyrrole (PPy) because of its characteristics such as; easy synthesis and high conductivity. Recently, there have been many attempts to synthesize composites of CS and PPy to investigate what combined functionality can be obtained. Combination of pyrrole with cerium (IV) ammonium salts (Ce+4) exhibits better solubility than PPy. In aqueous media, redox systems of Ce+4 and reducing agents such as acids are well known initiators for vinyl polymerization. Polymerization reaction in aqueous media has many technical advantages than other methods. Additionally, the preparation of polymers with clay minerals has been extensively studied topic due to understand the synergistic effect of them. In this work, Chitosan/Polypyrrole composites and Chitosan/ Polypyrrole/ Sepiolite (Cs/PPy/Sep) Nanocomposites (NC) were synthesized via redox polymerization in aqueous media with magnetic stirrer system in presence of ammonium cerium (IV) nitrate (Ce+4) at room temperature. The roles of the oxidant/monomer mole ratio, on the yield, conductivity and morphology of the resulting products were investigated. Chitosan /Polypyrrole composites and Chitosan/ Polypyrrole/ Sepiolite Nanocomposites (Cs/PPy/Sep NC) were prepared with the oxidant to pyrrole mole ratios as 0.67:1, 0.8:1, and 1:1 for comparison. In addition, to understand the effect of inorganic agents to Cs/PPy/Sep nanocomposites, Silver (Ag) ions were added to blend. Ag particles has some unique characteristics increased optical, electromagnetic, and catalytic properties. The yield and electrical conductivity of the products (polymer) were investigated as physical characteristics. The electrical conductivities of Cs/PPy/Sep NC were determined by four point probe technique. In addition, the resulting NC were characterized with spectroscopic method that was Fourier Transform Infrared Spectroscopy (FTIR), and also morphological method, which was Scanning Electron Microscopy (SEM). According to conductivity results, Polypyrrole/Chitosan (PPy/CS) composite polymers showed conductivity between 1.8x10-6 and 1.4x10-2 S/cm. Polypyrrole-Chitosan/Sepiolite (Ppy-CS/Sep) nanocomposite polymers showed conductivity between 3.0x10-4 and 6.41x10-4 S/cm. Polypyrrole/AgNO3 nanocomposite polymers had a conductivity between 0.755 and 7.2 S/cm. According to SEM results, PPy/CS-1 sample has average size of 28.90 nm and PPy-CS/Sep-1 sample has average size of 28.63 nm. In future, many applications will benefit from conductive materials like PPy/CS, PPy-CS/Sep and PPy/Ag in biosensors, bioactuators and many other biomedical applications which will be very important in next century.
Köpük poliüretan için yanma geciktirici poliol olarak kil modifiye nanokompozit ketonik reçineler
Cyclohexanone formaldehyde resin is modified with clays, which are sepiolite and montmorillonite, and alendronic acid which contains of phosphate group in its structure. The modified resins are added to rigid foam polyurethane for fire retardancy.
PANI/CeO2 nanokompozit kaplamalar ile karbon çelik ve alüminyum metallerinin korozyonunun önlenmesi
Carbon steel and aluminium are the most common metals for industrial applications. Corrosion is one of the biggest drawbacks of using these metals in equipments. Corrosion may be defined as a destructive phenomenon, chemical or electrochemical, which affects the appearance of an object, and in extreme cases may cause structural failure. Economic losses resulting from metallic corrosion costs billions of dollars per year worldwide. In addition to the economic costs, there are times when corrosion is responsible for the even greater costs of human life and safety. Polymers have already replaced most of the materials we use in our daily life. Innovations on polymeric materials allow them to be used in corrosion inhibition. The use of organic coatings is one of the most common method for minimizing corrosion losses. Conducting polymers have been increasingly investigated for their use in organic coatings. Many studies showed that conducting polymers improve the corrosion inhibition properties of coatings. Polyaniline (PANI) is one of the most widely used conducting polymer because of its superior properties. Inorganic nanoparticles are a class of new materials having wide variety of applications in many fields. To obtain the materials with synergetic or complementary behavior between polymer and inorganic nanoparticles, various composites of polymer with inorganic nanoparticles have been synthesized in recent years. Among those inorganic nanoparticles, cerium oxide (CeO2) nanoparticles have been intensively studied due to their unique catalytic, electrical, and optic properties, as well as their extensive applications in diverse areas. The main objective of this study is to investigate the corrosion behaviour of PANI/CeO2 nanocomposite and pure PANI coatings on carbon steel and aluminium metals in corrosive environments such as 0.1 M H2SO4 and 3.5 % sea water. In the first part of the study, synthesis of PANI and PANI/CeO2 nanocomposite were carried out and they were characterised by Fourier Transform Infrared Spectroscopy, UV-Visible Spectroscopy, conductivity measurements and SEM analysis. It is confirmed by the analysis results that the polymer and nanocomposite were sucsessfully synhesized. Coatings including pure PANI and PANI/CeO2 nanocomposite were prepared at different concentrations and coated on carbon steel and aluminium electrodes and they were investigated for their corrosion protection properties. In addition to emeraldine salt forms of the polymers, emeraldine base forms of both species were used in order to have more concentrated polymer solutions due to better solubility which increased PANI content of coatings. It is evident from the SEM images of the coatings that PANI/CeO2 nanocomposite formed a more uniform coating which can lead to a better corrosion protection efficiency; whereas pure PANI polymer formed a rough and curved coating. Since corrosion occurs via electrochemical reactions, electrochemical techniques are ideal for the study of the corrosion processes. The electrochemical impedance spectroscopy (EIS) is one of the most effective and reliable method to extract information about electrochemical characteristics of the electrochemical system. Electrochemical measurements, including potentiodynamic polarization curves and EIS were performed in a three-electrode cell. EIS data is also analyzed by fitting it to an equivalent electrical circuit model and experimental results were confirmed. Steady-state current-voltage curves and electrochemical impedance spectroscopy measurements of the coatings in 0.1 M H2SO4 for carbon steel and aluminium and in 3.5 % seawater for carbon steel were conducted. The initial measurements were conducted in 0.1 M H2SO4 both for carbon steel and aluminium electrodes after 1 hour immersion to corrosive media. It is evident that both coatings inhibit corrosion of bare electrodes. The increase in polymer concentration effects the corrosion protection efficiency of the coating positively. PANI/CeO2 polymer coatings showed slightly better corrosion protection efficiency over pure PANI coatings both for carbon steel and aluminium electrodes, which shows the advantage of CeO2 nanoparticle contrubition in the coating. It is evident from the polarization curves that the coatings retard both anodic and cathodic reactions. In other words, they reduce the anodic dissolution and also retard the hydrogen evolution reaction. PANI/CeO2 nanocomposite coating with 1,62 % showed the best corrosion protection performance on carbon steel and aluminium electrodes in 0.1 M H2SO4. The corrosion protection efficiencies of the coatings including emeraldine base form of polymers were also measured with increasing exposure time. It was observed that the coating degradetion increased and consequently corrosion currents and corrosion rates increased as the exposure time to corrosive media increased. The differnace in corrosion protection property of the coatings became close to each other by increasing exposure time, which may be due to the effect of corrosion product formation on the electrode surface. EIS measurements were also supported by equivalent circuit models and it is observed that a reasonable accuracy of the fitting was obtained. Chi-square is in the order of 10-3 and 10-4 for all the experimental data. Rp values obtained by equivalent circuits and experiments are in agreement with each other. In order to see the protection performance of coatings in different corrosion media, measurements in 3.5 % seawater for carbon steel electrodes were also carried out. Results suggest that the same concentration of PANI/CeO2 nanocomposites have better corrosion protection efficiency compared to pure PANI coatings even in emeraldine salt form which has lower concentration owing to the contrubition of CeO2 nanoparticles in the coating.
Poliviniliden florür temelli aşı kopolimeri
During the last three decades, many special fluoropolymers have been developed, due to their chemical resistance, weathering elements and oxidants, low surface free energy properties and also oil/water repellence due to their hydrophobic properties. Fluoropolymers represent a rather specialized group of polymeric materials. Amphiphilic fluorinated graft copolymers are of considerable interest for proton exchange membrane applications. Poly(vinylidene fluoride) (PVDF) has commercial importance due to its excellent properties as well as for special properties such as resistance. Because of its commercial importance, various synthetic approaches for the preparation of graft copolymers from PVDF have been reported. The limitations of the commercial fuel cell membranes are a susceptibility to chemical degradation at elevated temperature, including poor ionic conductivities at low humidity or elevated temperatures, finally, membrane expensiveness. Thus synthesizing alternative membranes for fuel cells is still a challenging goal. Atom transfer radical polymerization (ATRP) is controlled free radical polymerization technique. The technique also permit advanced fluorinated polymers to be synthesized. They are one of the best route for the preparation of these well-defined amphiphilic graft copolymers with controlled molecular weight, polydispersity, terminal functionalities, and chain architecture composition due to the relavite ease of synthesis and their compability with a wide range of solvents. Here are reported that PVDF backbone was grafted by methyl methacrylate (MMA) and 3-sulfopropyl methacrylate potassium salt (SPMAK) by using atom transfer radical polymerization (ATRP). First, PVDF was functionalized to obtained ATRP macro-initiator by 2-bromo-2-methylpropionyl bromide via lithiation reaction. Second MMA and SPMAK was grafted to PVDF backbone using PVDF-Br as a macroinitiator by ATRP. Then the graft copolymers were characterized by FT-IR, 1H NMR and DSC methods. Then the proton conductivity and thermal stability in grafted polymer have been investigated for PVDF based membranes.
Elektrostatik boyamaya uygun iletken poliamid/ karbon siyahı, karbon lif ve karbon nano tüp kompozitleri
Conductive polymer composites (CPCs) coming out from the combination of an insulating polymer matrix with conductive fillers exhibit several interesting features and many applications. In automotive industry metal parts can be replaced by CPCs which means a vehicle with the lower weight and lower fuel consumption.The motivation behind this study was to produce an engineering plastic in order to use in the automotive industry with cost reduction, to improve mechanical properties and production efficiency. For this purpose, this study was aimed to find a conductive polyamide compound (CPAC) formula in order to use as raw material to produce hubcap (wheel cover) which is suitable for electrostatic painting (EP) system. The CPAC was prepared by extrusion methods by using commercial polyamide (Minlon) and carbon based conductive materials such as carbon black (CB), carbon fiber (CF), and carbon nano-tube (CNT). Compatibilizer was also added to the formula to obtain the suitable CPAC, which covers the requirements for the resulting composite. Formulations with different carbon filler contents were prepared and then produced and tested. They were compared with commercial product of Noryl, which have been used for EP applications. The disadvantage of Noryl is poor mechanical properties for some applications such as wheel cover. There are types of method to produce the conductive polymer composites (CPCs) such as; solution, melt mixing etc. In this study, the extrusion, which is one of the melt mixing method, was used. After compounding materials, electrical conductivity of composites was measured by a 4-point probe method. ATR-FTIR, DSC, SEM and mechanical properties tests were also performed on the samples. Wheel cover was produced from the samples that have the desired properties and after electrostatic painting the basic tests such as cross cut, hardness, drop weight impact were carried out on the final product. The results of all these tests suggested that, the suitable composites for EP were prepared and these composites fit the requirements of the wheel cover.
Düşük yoğunluklu polietilen ve polimetil penten polimerlerinden taze gıda ambalaj malzemesi üretimi
As a result of population growth and global warming, fertile soil lands are decreasing and occurrence rate of natural disasters such as drought and flood are increasing. Because of these reasons millions of people around the world cannot reach the staple food products. Therefore, food supply is one the most urgent problems which is awaiting a solution nowadays. In order to overcome that problem, agricultural harvest is needed to increase or shelf lives of harvested products are needed to extend. Despite the limited arable soil lands, the quantity of product per unit area can be already increased due to increase in fertilisation. In spite of this enormous increase in fertilisation, the food requirements of population growth cannot be met. The main reason of this situation is the loss of post-harvest products which is said approximately 40% by weight. In order to overcome this problem completely, this losses should be eliminated. In order to eliminate these losses, new searches have been focused on new packaging methods. Active packaging and modified atmosphere packaging are new methods which were recovered from these studies. Fundamental principle of these methods is obtaining a balanced internal atmosphere between the respiration rate of preserved product and the gas permeabilities of packaging materials in order to extend the shelf lives of post-harvest products. However, the commercial plastics which are used in packaging industry cannot provide these high gas permeability values and because of this reason they cannot offer longer shelf lives. In accordance with this purpose, in order to obtain high gas permeability values and selectivity properties of packaging material, polymethylpentene (PMP) copolymer was added in different loading levels into low density polyethylene (LDPE) matrix by using a laboratory scale co-rotating twin screw extruder. In this study, LDPE/PMP copolymer blends which were containing 10%, 25%, 50%, 75%, and 90% PMP copolymer ratios were prepared by using extrusion. Also, for blends' structural, morphological, thermal and mechanical evaluations, neat LDPE and PMP copolymer were extruded under the same conditions in order to obtain standard materials which were exposed the same thermal treatment. The package samples were produced by using cast film extrusion method. The most important parameter of this study is O2 and CO2 permeabiltiy values of the package samples. In order to investigate this property entirely, under 90% relative humidity conditions, O2 and CO2 permeability values were determined at 3 different temperatures. Beyond these analysis, according to loading ratio of PMP copolymer into LDPE matrix was increased gas permeability values up to 600%. Increase in gas permeability values can be explanied with DSC and XRD analysis. The tetragonal symmetry of PMP copolymer and phase separations between PMP copolymer and LDPE which can be seen in SEM images led to obtain high gas permeability values in our opinion. The results of shelf life analysis was indicated that the package sample was containing 25% PMP copolymer could extend the shelf lives of banana and marrow fruits 2 times. Thus, the extension of shelf life of preserved products used in this study could be achieved.
Foto düzenleyicilerin pamuk lifi takviyeli düşük yoğunluklu polietilen kompozit malzemelerin mekanik özelliklerine ve yüzey analizine etkisinin incelenmesi
Fiber reinforced composites have gained much acceptance in recent years. Synthetic fibers like glass, carbon and aramid are widely being used in polymer based composites because of their high stiffness and strength properties. However, these fibers have serious disadvantages in terms of their biodegradability, costs, recyclability, energy consumption etc. Although synthetic fibers currently dominate the polymer industry, the use of natural fibers as reinforcing substance in the thermoplastic industry has become more accepted. The use of cotton fiber could be an alternative reinforcement in the replacement of wood fiber, especially in the outdoor environment. The natural fiber composites expose outdoors undergo expecially photo-oxidation degradation caused by ultraviolet radiation. This degradation takes place primarily in the lignin substance, which is responsible for the characteristic color changes. The presence of 0.7-1.6% lignin content in the cotton structure is advantage for the cotton fiber. Cotton fiber have very promising physical properties as a fiber in plastic/fiber composites but there have been few studies about plastic/cotton fiber composites. Thermal stability, moisture resistance, fungal resistance and ultraviolet exposure (UV) are included in the outdoor durability of composites. UV exposure is one of the important concern about the durability of these composites when exposed to outdoor environment. For example, UV exposure can cause the composites to undergo photo-degradation leading to undersirable effects, including a loss in mechanical properties and surface quality, i.e. surface micro-cracking and color change. To prevent the photodegradation and extend service life of cotton fiber reinforced polyethylene (CF/LDPE) composites, various stabilizers were introduced to eliminate or delay the UV light exposure on the CF/LDPE composites, or dissipate the enegry of molecules in the excited state. In this study, the use of photo-stabilizers such as UV absorbers (UVA), hindered amine light stabilizers (HALS-free radical scavengers) and antioxidants were used to minimize the effect of UV exposure in the cotton fiber reinforced low density polyethylene composites.. Cotton fiber reinforced LDPE (CF/LDPE) composites were manufactured by using a custom made single screw extruder. After the manufacturing process, composite plates were pressed to maintain constant thickness and flatness. Samples were cut out by using a desktop CNC milling machine for tensile and impact testing. Composite materials were exposed to both Ultraviolet (UV) light exposure for the time periods of up to 240h. To investigate the effect of photostabilizers on mechanical properties of stabilized and unstabilized CF/LDPE composites, tensile testing was applied to the all composites and compared to each other. Tensile strength, modulus of elasticity and strain at break were calculated from the tensile testing. Fourier transform infrared (FTIR) spectroscopy has been used to study changes in the surface of chemistry of polyethylene. Carbonyl index of all composites were determined to investigate the degradation of composites upon UV weathering. DSC analysis were determined for obtaining the thermal properties of CF/LDPE composites. The crystallinity values were calculated from DSC curves. The crystallinity values of composites indicates that the chain scission mechanism of polyethylene matrix during photo-degradation. Color measurement of CF/LDPE composites were determined. The lightness (L*) and chromaticy coordinates (a* and b*) were measured and color change (∆E*) was calculated.
PES/PCz kompozitinin sentezlenmesi ve karakterizasyonu
In recent years, conductive polymers have been used in various field and become an important alternate instead of metals. This approach causes an increase in improvement regarding conductive polymers. Conductive polymers are used as body area network (BAN), antenna, sensor, electrode, cathode material obtained by coating onto PET and glass, electrocardiography (ECG), electromiyography (EMG), electromagnetic shielding applications in military and on the sports field. Conductive textiles are one of the applications of conductive polymers. Polypyrrole (PPy), polyaniline (PANi), polythiophene (PTh), polydioxythiophene(PEDOT):paratoluenesulphonicacid(PTSA), PEDOT:PSS copolymers and Poly(3-methyl thiophene) (P3MTh) nano application are within application of conductive polymers. In this study, it is aimed to synthesize PCz by in situ polymerization onto polyester (PES) textile substrate with using different oxidants and solvents. Most studies have been focused on in situ polymerization to produce conductive textile since this method does not require the destruction of the substrate and provides reasonably good conductivity. The final form of PCz is that of a long conjugated backbone. The polymer has resonance structures. In this neutral state the polymer is not conducting and only becomes conducting when it is oxidized. FeCl3 and CAN were used as oxidant. Acetonitrile (ACN), water and toluene was used as solvent. It was investigated the effects of different concentration of monomer, oxidant, solvent and polymerization time and also the order of immersion of Cz monomer and oxidant solutions to electrical conductivity. Electrical conductivities and capasitive values were measured by disc probe. PES/PCz composites were characterized by Color analysis, Scanning Electron Microscopy (SEM), Fourier Transform Infrared Spectroscopy (FT-IR), Dynamical Mechanical Analysis (DMA) methods. As a result, PCz was coated onto PES tekstile in the presence of FeCl3 and PES/PCz composites were obtained with 0.32 Ω electrical resistance.
Cam elyaf katkılı polibütilen tereftalat kompozitin alev dayanımı ve mekanik özelliklerinin geliştirilmesi
The objective of this study is the improvement of mechanical and fire retardant properties of poly(butylene terephthalate) composite. In order to investigate flame resistance efficiency of PBT and glass fiber reinforced PBT (GF-PBT) composites, boron phosphate (BP), triphenyl phosphate (TPP), zinc borate (ZB) and calcium sulphate dihydrate (CSD) additives were used at 5 % and 10 % loading levels, also different binary combinations were examined. PBT compounds were prepared by using a co-rotating twin screw extruder and injection molding machine. The composites were characterized in terms of flammability and mechanical properties. In this study, it was observed that TPP is the most successful flame retardant additive for PBT and GF-PBT in terms of flammability properties. Highest LOI values were obtained when 10 % TPP was added to PBT matrix and LOI increased to 27.2. However, TPP additive was decreased some mechanical properties like tensile strength and flexural strength values. So as to increase mechanical properties TPP combined with BP flame retardant additive. Even though some decreases in LOI value occurred compare to TPP base formulation, combination of TPP with BP showed high LOI results with higher mechanical properties. Furthermore, combinations of BP with ZB additive showed a significant synergistic effectiveness from the point of flammability. 30 % glass fiber reinforced PBT (GF-PBT) provided to reach higher mechanical properties, but lower LOI values than that of GF free PBT composites. On the other hand, the optimization between mechanical and flame retardant properties of PBT was achieved, in this study.
Poliüretan filmlerde yüzey pürüzlülüğü ve kristalinitenin protein adsorpsiyonuna etkilerinin incelenmesi
Accelerating developments for human health care necessitate need for biocompatible devices to be used inside the body and for outside applications. There has been an increasing trend to use biocompatible polymeric materials in biomedical field. Among biopolymers, polyurethanes are widely used in many fields such as prosthesis, implants and in controlled drug delivery systems due to their excellent chemical and mechanical properties. The most important factor in determining and developing a biomaterial is to examine the relationship between polymeric structures with blood proteins. Thus, a clear understanding of protein adsorption is crucial to design new biomaterials. It is known that protein structure, protein solution and surface properties are major components that determine adsorption kinetics. In this point of view, important surface properties such as crystallinity, hydrophilicity and roughness were investigated in the context of thisstudy using both experimental and computational approaches. In this study, six different polyurethane films were synthesized by using castor oil (CO), hexamethlyene diisocyanate (HDI) and 1,4-butandiol (BDO). Among these polyurethanes, poly(ethylene glycol) (PEG) was also used as polyol in the synthesis of three polyurethane samples. Polymers were synthesized at different CO/PEG weight ratios (50/50, 60/40, 70/30, 100/0) by bulk polymerization. In order to obtain chemically identical surfaces with different roughness, tetra hydrofuran (THF) or dimethylacetamide (DMAc) were used during the polymer sythesis for two PEG free samples. Structural characterization of films was carried by Fourier transform spectroscopy (FT-IR).Thermal and mechanical characterization were performed by thermal gravimetric analyses (TGA), differential scanning calorimeter (DSC) and dynamic mechanical analyses (DMA). Crystallinity of films was determined by x-ray diffraction (XRD), hydrophilicty of films was calculated by contact angle measurements and surface properties were analyzed by atomic force microscopy (AFM). Effect of each surface property on protein adsorption kinetics was investigated using Brownian dynamics simulations for albumin-polyurethane system. Brownian dynamics enabled the simulation of the coarse-grained polymer-protein system in three-dimension comparable with experimental findings. For this purpose, polymeric film was modeled as lattice surface with protein binding regions predetermined according to the experimental results on crystallinity. Furthermore, the polymeric film was modeled as a flat or rough surface, which actually depended on the solvent evaporation rate employed in the experiments. Bovine serum albumin proteins were described as uniform spheres interacting with the polymeric surface. Various protein concentrations were considered in order to reveal the effect of macromolecular crowding on protein adsorption rate. The model system represented quarter of one-micrometer square polymer film interacting with proteins at real molar levels, which provided an effective comparison with experimental observations. Considering the effect of surface roughness, hydrophilicity, crystallinity and protein adsorption results together, computational results indicated that the molecular crowding, i.e. high concentrations had the biggest impact on protein adsorption, then degree of surface crystallinity and finally roughness. Observation from simulations suggested the roughness had an implicit effect on protein adsorption by providing higher surface area compared to smooth surfaces. In other words, if high surface area revealed more crysttaline regions, more proteins adsorbed on the surface. In contrary, if high surface area revealed more amorphous regions, protein adsorption rate diminished.
İletken polimerlerin sentezi ve elektriksel özelliklerinin incelenmesi
This thesis is consisting of two parts. First part concerning with synthesis of new conducting polymers. For this purpose, chemical polymerization of aniline in the presence of propiolic acid as dopant and synthesis and polymerization of chalcone substituted aniline, and the other one is preparation of the poly (N-vinyl carbazole)- co-poly (2-(dimethylamino) ethyl methacrylate) based hydrogen bonded side-chain liquid crystal copolymer. Among the conducting polymers, polyaniline is one of the important electronic materials because of its easy synthesis, environmental stability, reversible proton dopability, redox recyclability, cost-effectiveness, and reasonable electrical conductivity. Polyaniline is one of the most promising conducting materials for applications in optoelectronics and microelectronics devices. In the present work, polyaniline (PANI) was synthesized in the presence of propiolic acid. The effects of the dopant on the course of oxidation and properties of final products have been studied by Fourier Transform Infrared Spectroscopy (FTIR) spectroscopy, and conductivity measurements. The dielectric properties of PANI and doped PANI were investigated using the impedance spectroscopy (IS) dependency of the frequency and the temperatures. New chalcone substituted aniline derivative, was synthesized by starting from 3-aminoacetophenone and 4-pyrridinecarboxyaldehyde in the presence of NaOH. The obtained chalcone containing aniline was polymerized oxidatively in water in the presence of dopant such as methanesulfonic acid, formic acid, HBr and acetic acid using ammonium persulfate as oxidant at room temperature for 24h. Chalcone containing polyaniline (Cs-PANI) was characterized by using FTIR and physical methods. Side-chain liquid crystalline polymers (SLCPs), which represent a combination of liquid crystalline behavior and polymeric properties, have been the subject of intensive research during the last decade since these polymers are regarded as materials with promising optical and electro-optical properties for potential applications in optical switching and image storage. The liquid crystallinity and physical properties of LCPs depend on the molecular structures chosen for polymer design. In this study, new side chain liquid crystalline copolymers were prepared from N-vinyl carbazole (NVC) and 2-(dimethylamino) ethyl methacrylate) (DMAEM) as a hydrogen bond acceptor copolymer and 8-(4-cyanobiphenyl-4'-oxy) octan-1-ol (LC8) by molecular self-assembly processes via hydrogen bond formation between nitrogen of (DMAEM) and hydroxyl group of the LC8.The formation of H bond was confirmed by using FTIR spectroscopy. The liquid crystalline behavior of the copolymers and homopolymer of the (DMAEM) was investigated using a differential scanning calorimeter (DSC) and polarized optical microscopy. The dielectric relaxation properties of H-bonded Side Chain LC Copolymers (HB-LCP) doped 8-(4-cyanobiphenyl-4'-oxy) octan-1-ol(LC8) and pure LC8 liquid crystals have been investigated by the dielectric spectroscopy (DS) method. The second part of the thesis, conducting polymer composites was prepared physical and chemical characterizations were performed. PANI was interacted with nanoclay, magnetite and graphite to obtain its composites. The thermal stability, mechanical strength, gas barrier, fire retardant properties, processability, etc. can be enhanced by the synthesis of the composites. The formation of polyaniline composites with inorganic materials provides new synergistic properties that cannot be attained from individual materials. The combination of clays and functional polymers interacting at atomic level constitutes the basis for the preparation of an important class of inorganic–organic nanostructured materials. In this study, aniline was polymerized oxidatively in the presence of boric acid as dopant and nanoclay with different weight percentage. The electrical properties of polyaniline nanoclay composite were studied using impedance spectroscopy. The magnetic nanoparticles were synthesized by mixing a water solution of FeCl2.4H2O (1.0 M) and FeCl3.6H2O (1.5 M). Composites of poly (aniline) and magnetite were prepared by using oxidative polymerization of aniline in the presence of different weight percentage of magnetite (2%, 5% and 10%). Field Emittion Scanning electron microscopy (FESEM) and FTIR analyses were performed to understand the structure of PANI-magnetite composites. The magnetic and electric properties of PANI, magnetite, magnetite doped PANI were investigated by electron paramagnetic resonance and impedance spectroscopy techniques, respectively. Also, dielectric properties were investigated by impedance spectroscopy for undoped PANI, magnetite and different weight percentage of magnetite doped Polyaniline–magnetite composites. In this work, synthesis and characterization of composite materials based on graphite (GH) and boric acid doped PANI were studied. PANI + GH composites were prepared via a simple in situ polymerization of aniline in graphite dispersion. The resulting composites of the PANI + GH were characterized by using spectroscopic, morphologic and physical methods. Polythiophene-boron nitride composites were prepared and characterized accordingly. Polythiophene/different weight percentage of Boron nitride (BN) (1% and 2%) (BN) composites were prepared via in situ oxidative polymerization of thiophene by using FeCl3 as oxidant at room temperature for 48 h. FESEM and FTIR spectroscopy were used to characterize the morphology and structure of the samples. Also, electrical characterizations of the composites have been investigated by impedance spectroscopy.
Bor içeren metil etil keton formaldehit reçinelerinin sentezi ve karakterizasyonu
Methyl ethyl ketone formaldehyde resins are modified in situ and after the polymerization with different modifiers to increase their physical and chemical performances by changing their chemical structures. In this thesis study, methyl ethyl ketone formaldehyde resins including nitrogen and/or boron are synthesized and their phycical and chemical properties are analyzed in a comperative way. The resins are prepared by alkaline-catalysed condensation of methyl ethyl ketone and formalde in a molar ratio of 1: 2 in a batch process. NaOH is used as catalyst for this reaction. During all of the reaction pH value should been kept around 10-11. The medium is kept at 80-90oC. After 4h, the reaction is completed, and yellow resin is formed. For in sitı modifications, the modifer is added to the reaction medium in the beginning of the reaction. For boric acid modification, of resin sample is dissolved in toluene, and boric acid is added. Using deanstag systam, the medium is heated to 150oC, refluxed for about 2h until no water is collected any more. Ten different types of methyl ethyl ketone formaldehyde resins are synthesized for this study, five of which include nitrogen, one includes boron and three include both nitrogen and boron: methyl ethyl ketone formaldehyde resin (MEKFR), MEKFR modified with alendronic acid at a ratio of 5wt% (MEKFR-AA), MEKFR modified with cyclic urea which is synthesized from alendronic acid at a ratio of 5wt% (MEKFR-CUAA), MEKFR modified with diethanolamine at ratios of 5wt%, 10wt% and 20wt% (MEKFR-DEA), MEKFR and three MEKFR-DEA modified with boric acid (MEKFR-BA and MEKFR-DEA-BA, respectively). After the synthesis and modifications of resins, their chemical structures are analyzed, and Fourier Transform Infrared Spectroscopy (FTIR) and Nuclear Magnetic Resonance Spectroscopy (NMR) are used for this purpose. When the spectums of resins obtained are looked through the characteristics peaks and their corresponding functional groups, it is concluded that the estimated chemical structures as the product of synthesis and modification reactions match with the results obtained. In the terms of physical properties, solubility analyses are carried out in five different solvents, namely ethanol, acetone, dichloromethane (DCM), tetrahydrofuran (THF) and dimethylsulfoxide (DMS), and it is seen that depending on the modifier type and ratio, the solubility of resins change, as a result of the changes in the chemical structures. Lastly, in order to get information about thermal behaviour of the resins and effects of modifications on thermal degradation of them, thermogravimetric analyses (TGA ) and Methyl ethyl ketone formaldehyde resins are modified in situ and after the polymerization with different modifiers to increase their physical and chemical performances by changing their chemical structures. In this thesis study, methyl ethyl ketone formaldehyde resins including nitrogen and/or boron are synthesized and their phycical and chemical properties are analyzed in a comperative way. The resins are prepared by alkaline-catalysed condensation of methyl ethyl ketone and formalde in a molar ratio of 1: 2 in a batch process. NaOH is used as catalyst for this reaction. During all of the reaction pH value should been kept around 10-11. The medium is kept at 80-90oC. After 4h, the reaction is completed, and yellow resin is formed. For in sitı modifications, the modifer is added to the reaction medium in the beginning of the reaction. For boric acid modification, of resin sample is dissolved in toluene, and boric acid is added. Using deanstag systam, the medium is heated to 150oC, refluxed for about 2h until no water is collected any more. Ten different types of methyl ethyl ketone formaldehyde resins are synthesized for this study, five of which include nitrogen, one includes boron and three include both nitrogen and boron: methyl ethyl ketone formaldehyde resin (MEKFR), MEKFR modified with alendronic acid at a ratio of 5wt% (MEKFR-AA), MEKFR modified with cyclic urea which is synthesized from alendronic acid at a ratio of 5wt% (MEKFR-CUAA), MEKFR modified with diethanolamine at ratios of 5wt%, 10wt% and 20wt% (MEKFR-DEA), MEKFR and three MEKFR-DEA modified with boric acid (MEKFR-BA and MEKFR-DEA-BA, respectively). After the synthesis and modifications of resins, their chemical structures are analyzed, and Fourier Transform Infrared Spectroscopy (FTIR) and Nuclear Magnetic Resonance Spectroscopy (NMR) are used for this purpose. When the spectums of resins obtained are looked through the characteristics peaks and their corresponding functional groups, it is concluded that the estimated chemical structures as the product of synthesis and modification reactions match with the results obtained. In the terms of physical properties, solubility analyses are carried out in five different solvents, namely ethanol, acetone, dichloromethane (DCM), tetrahydrofuran (THF) and dimethylsulfoxide (DMS), and it is seen that depending on the modifier type and ratio, the solubility of resins change, as a result of the changes in the chemical structures. Lastly, in order to get information about thermal behaviour of the resins and effects of modifications on thermal degradation of them, thermogravimetric analyses (TGA ) and Methyl ethyl ketone formaldehyde resins are modified in situ and after the polymerization with different modifiers to increase their physical and chemical performances by changing their chemical structures. In this thesis study, methyl ethyl ketone formaldehyde resins including nitrogen and/or boron are synthesized and their phycical and chemical properties are analyzed in a comperative way. The resins are prepared by alkaline-catalysed condensation of methyl ethyl ketone and formalde in a molar ratio of 1: 2 in a batch process. NaOH is used as catalyst for this reaction. During all of the reaction pH value should been kept around 10-11. The medium is kept at 80-90oC. After 4h, the reaction is completed, and yellow resin is formed. For in sitı modifications, the modifer is added to the reaction medium in the beginning of the reaction. For boric acid modification, of resin sample is dissolved in toluene, and boric acid is added. Using deanstag systam, the medium is heated to 150oC, refluxed for about 2h until no water is collected any more. Ten different types of methyl ethyl ketone formaldehyde resins are synthesized for this study, five of which include nitrogen, one includes boron and three include both nitrogen and boron: methyl ethyl ketone formaldehyde resin (MEKFR), MEKFR modified with alendronic acid at a ratio of 5wt% (MEKFR-AA), MEKFR modified with cyclic urea which is synthesized from alendronic acid at a ratio of 5wt% (MEKFR-CUAA), MEKFR modified with diethanolamine at ratios of 5wt%, 10wt% and 20wt% (MEKFR-DEA), MEKFR and three MEKFR-DEA modified with boric acid (MEKFR-BA and MEKFR-DEA-BA, respectively). After the synthesis and modifications of resins, their chemical structures are analyzed, and Fourier Transform Infrared Spectroscopy (FTIR) and Nuclear Magnetic Resonance Spectroscopy (NMR) are used for this purpose. When the spectums of resins obtained are looked through the characteristics peaks and their corresponding functional groups, it is concluded that the estimated chemical structures as the product of synthesis and modification reactions match with the results obtained. In the terms of physical properties, solubility analyses are carried out in five different solvents, namely ethanol, acetone, dichloromethane (DCM), tetrahydrofuran (THF) and dimethylsulfoxide (DMS), and it is seen that depending on the modifier type and ratio, the solubility of resins change, as a result of the changes in the chemical structures. Lastly, in order to get information about thermal behaviour of the resins and effects of modifications on thermal degradation of them, thermogravimetric analyses (TGA ) and differential scanning calorimetry (DSC) analyses are carried out for each of resins. T50 values and residue amounts of them obtained from TGA curves as well as glass transition and melting temperatures obtained from DSC curves are the crucial parameters used during the evaluation of thermal properties of the resins.
Çapraz bağlanabilen polietilenin geri kazanılması
Polyethylene (PE) has excellent electrical insulating properties, stable mechanical properties, good fatigue resistance and resistance to chemical attacks. Because of these properties, polyethylene is one of effective and important insulating material in the cable production. PE is suitable till 75°C working temperature. Moreover, many power cables require 90°C for working temperature. Therefore, thermoplastic PE is not suitable for this kind of cables, which require 90°C working temperature. PE has molecular structure, which has linear chains of independent polyethylene molecules loosely held together by weak molecular bonds. This molecular structure of PE can be converted in to more thermal stable thermosetting compound by the process of crosslinking. Perpendicular chemical bonds are formed between parallel chains of the polyethylene molecules by crosslinking process. The parallel loose two-dimensional molecular structure is converted into a cellular three-dimensional polymeric structure. Crosslinked polyethylene (XLPE) shows superior insulation properties and high thermal stability over conventional thermoplastic insulating materials. The desirable properties of polymers are achieved through proper molecular weigth and molecular weigth distribution. Any change to the original molecular structure will change these properties and usually is considered degradation. Antioxidants are very important additives whose role it is to maintain the chemical and physical properties of polymer during transportation, storage, processing, and serving conditions. Antioxidants are chemical substances, which are added to polymers in small amounts with generally 1-2% and are capable in the course of autoxidation of trapping emerging free radicals or unstable intermediate products such as hydroperoxides and to transform them into stable end products. Primary antioxidants act by trapping or deactivating radicals after they are formed. Secondary antioxidants prevent the formation of free radicals through non-radical decomposition of hydroperoxides. In general, primary antioxidants can be used alone more or less successfully, whereas secondary are used to enhance the performance of the primary antioxidant and are not used alone. Molecular network of XLPE gives high thermal stability but makes recycling nearly impossible. Thus, the waste of XLPE is mainly burnt as a fuel or disposed in landfills. Some recycling attempts are also known, such as grinding in small particuls and put into road fillers. Some works are known in which the XLPE is tried to plasticize by various techniques. One of them applies alcoholysis of the silane crosslinked polymer in supercritical reactor. The others apply suitable heating and shearing process for partially decomposition of polymers. Commercially crosslinkable polyethylene compounds (CPEC) which contains crosslinking agent inside are ready to crosslinking. They can crosslinked easily when they faced proper condition such as high temperature. One of the main applications of CPEC is cable insulation. Some amount of CPEC needs to be bleeded from the dies of the extruders due to the providing of required process condition before starting the process. Bleeded material becomes scrap because of presence of crosslinking agent inside which limits reuse of material. Terminate crosslinkability of bleeded material will be it is reusable and prevents it to be a scrap. In this study, for recovery of commercial crosslinkable polyethylene compound (CPEC) was studied. CPEC has crosslinking agent inside and is ready to crosslinking when appling to appropriate conditions such as high temperature. Phenolic antioxidant (AO1), blend type of antioxidant (AO2), which has primary hindered phenolic and secondary phosphite, and amine class antioxidant (AO3) be on the point of being three different types of commercial antioxidants were used. Each type of antioxidant was added 1%, 3% and 5% into CPEC of separately. Another sample was prepared without adding any antioxidant into CPEC as blank sample. The samples with 1.5% AO1 + 1.5% AO2 and 2.5% AO1 + 2.5% AO2 were prepared to check the synergetic effects of AO1 and AO2. Laboratory plasticorder was used for mixing. All samples were mixed at 110°C with 50 rpm. The effect of antioxidants on crosslinking characteristics of samples were investigated structurally, mechanically, and thermally. Crosslinking characteristics minimum torque (ML), maximum torque (MH) of the compounds were obtained by using rubber process analyser (RPA) at 185 °C. While MH values decreasing, while the ML values were about stable when the types and the amounts of antioxidants were changed. The difference between MH and ML (MH-ML) can be expressed cure extend which gives information about degree of crosslinking of the compounds due to torque values are close to each other. The smallest crosslinking degrees, which was 0.36 and 0.37, obtained when CPEC mixed with 5% AO1 and 2.5% AO1 + 2.5% AO2 respectively. Mechanical property analysis of the samples showed that amount of antioxidants had a pronounced effect on the tensile properties of samples. The maximum tensile strengths decreased approximately 30% when all type antioxidants were used with 5%. Maximum decrease in elongation at break was observed when 5% of blend type of antioxidant AO2. Minimum change at tensile strength and elongation break values observed, when phenolic antioxidant used as 1%. Differential thermal calorimetry was used to measure the melting temperatures and enthalpy of fusion of the samples. There were not significant changes in melting temperatures (Tm), when any type and amount of antioxidants were added. Results of Tm values of all samples were obtained between 107 °C to 109°C. Although addition of AO1 and AO2 increased enthalpy of fusion of the samples, while those of AO3 decreased. The highest value was 117.7 J/g when 1% of AO2 was added into CPEC. On the other hand, the lowest value of enthalpy was 79.7 J/g with 1% of AO3. Hot-set test is special test for cable sector that represents mechanical resistance of XLPE by controlling its crosslinking degree. Positive result in hot-set test means polyethylene chains crosslinked each other under specified conditions. On the other hand, crosslinking is not satisfactory when negative results are obtained. Hot-set test was performed to check that CPEC can crosslinkable after antioxidant addition. According to hot-set results CPEC, CPEC with 1% blend antioxidant (AO2) and CPEC with 1% amine class (AO3) antioxidant passed the test. The other combinations failed in hot-set test. It means that, the addition of antioxidants to CPEC prevented the crosslinkability of the other samples.
Organik-inorganik hibrit malzemelerin sentezi ve karakterizasyonu
Organic–inorganic hybrids that combine the advantages of both kinds of materials, such as mechanical strength and thermal stability with the processability and flexibility of an organic polymer matrix, exhibit multifunctional characteristics. Hybrid materials with the desired properties can be obtained in many forms such as bulk, powder, nanocomposites, coatings, glasses, fibres, foams etc., depending on the forming process and a wide variety of components of hybrids such as metal oxides, alloys, ceramics, clay, rubber, resins, elastomers, natural materials. Through the combinations of different inorganic and organic components with appropriate processing methods hybrid materials can be developed with new properties for electrical, optical, biomedical, structural, or related applications. In principle two different approaches are used for the formation of hybrid materials: First approach, well-defined preformed building blocks are applied that react with each other to form the final hybrid material in which the precursors of blocks still at least partially keep their original integrity and second approach, one or both structural units are formed from the precursors that are transformed into a novel (network) structure as in-situ method. There are mainly two classes of hybrid materials; the one with weak interactions between the two components of hybrid materials, such as van der Waals, hydrogen bonding or weak electrostatic interactions and no strong interaction such as covalent bonds and the second having strong chemical interactions between the components of the hybrid materials such as covalently bonding. Silica has attracted much interest due to their low toxicity, ease of formation in a wide range of sizes and morphologies, high stability, and the surface that can be further functionalized. This thesis based on the study of incorporation of silica nanoparticles and silicon dioxide network domains, as the inorganic components, with organic polymeric structures leading the formation of hybrid materials and, the characterization of the such materials. The interactions between the inorganic silicon dioxide and organic components were based on the strong chemical interaction as covalent bonding. Silica nanoparticles leading to an extreme increase in interfacial area have been considered as a challenging reinforcement with a wide range of properties for hybrid materials. Their efficiency in polymeric matrices requires uniform dispersion and strong interfacial bonding between two component of the hybrids. Common strategies are being developed to improve the poor dispersion of nanoparticles in polymer matrices and also organic solvents for advanced interfacial bonding of nanoparticles and matrices. Coupling reactions of silica nanoparticles with silane coupling agents having functional groups is one of the most common approaches for the modification of the surface of the silica particles. As the first step of the coupling reaction, silane coupling agents hydrolyze to form silanols and during the hydrolysis step, condensation can also take place between silanols resulting in ormation of siloxane bridges (Si-O-Si). The condensation between the silanol groups of coupling agents decrease the number of free silanols of silane coupling agents that reduce the rate of possible condensation with the silanol groups of the silica particles. Hence, the formation of a siloxane network layer on the surface of the silica nanoparticles may also results in a variety of concentration of functional groups of silane coupling agents. In the second step of coupling reaction of silica particles, the possibility of different type of condensation reactions between free silanol groups of coupling agents and silanol groups of silica nanoparticles may also result in inadequate concentration of functional groups grafted on the surface of silica particles. Seemingly effective coupling reactions of silica nanoparticles over the silane coupling agents may become challenging due to the such disadvantages. Direct functionalization of the surface of silica particles with reactive organic moieties can overcome such problems of silane coupling reactions and the limitation of high concentration of functional groups on the surface of silica particle. 2,4-toluene diisocyanate (TDI) having two reactive isocyanate groups takes the place of being a very effective organic moiety for reacting with the hydroxyl groups of silica particles resulting in surface grafting and also for bringing the ability for further reactions on the surface of silica particles. Grafting of end-functional polymers on the surface of silica nanoparticle as "grafting to" method has been described as one of the main approaches and the "grafting from" method, where polymers are grown from either monomer functionalized or initiator functionalized surfaces of silica nanoparticles, has been described as another approach. By a free radical manner, in most of silica nanoparticles functionalized with the organic monomers, the polymerization proceeds both by surface monomers of nanoparticles and by the free monomers existing in polymerization medium resulting a high ratio of ungrafted polymer formation. For this reason, initiator grafted nanoparticles may be considered for the higher grafting ratios of polymers onto the nanoparticles surfaces. In this study, firstly, well defined, mono-dispersed silica nanoparticles within desired size range was synthesized according to Stöber method as depicted in Figure 1. Physical and chemical structure of the nanoparticles such as particle size, specific surface area and hydroxyl number characterized clarifying their surface properties for the modification of silica nanoparticles. Figure 1 : Synthesis of silica nanoparticles by Stöber method. After the definition of the silica nanoparticles, surface modification of the nanoparticles was achieved with the reaction over isocyanate groups of toluen di-isocyanate (TDI) in order to gain both improved dispersion in organic phase and further attachment possibility of benzoin photoinitiator moieties onto the surface of silica nanoparticles as represented in Figure 2. Figure 2 : Grafting of TDI and benzoin moeities onto the surface of silica nanoparticles In the second stage, photopolymerization of methyl methacrylate (MMA) was achived over the benzoin photo-initiator attached succesfully onto the surface of silica nanoparticles. Since it was discovered by Dupont, photoinitiated polymerization has become an important industrial process. The main positive attributes of photochemical processes are that they offer a rapid conversion of formulated reactive liquids to solids by radical or cationic means. The photopolymerization of MMA by grafting from method was simply performed under UV radiation in the presence of benzoin functionalized silica macroitiators. Well-defined, spherical silica nanoparticles grafted with TDI was also incorporated into preformed epoxy-acrylate resin over the covalent bonding between hydroxyl groups of epoxy resin and free isocyanate groups of Si-TDI by the formation of urethane linkage. Epoxy-acrylate resin forming networks with chemically incorporated silica naoparticles (EA-Si hybrid resin) was cured under UV treatment in the form of film. The effect of uniform, well-dispersed, covalently incorporated silica nanoparticles on the thermal, morphological and mechanical behavior of cured EA-Si hybrid film was also investigated. In this thesis, the design of alkoxysilane precursor of aromatic amide-urethane structure was also aimed for the formation of silicon dioxide network domains and polymeric matrix together as hybrid material. For this purpose, preformed terephthalic acid chloride was reacted with m-amino phenol yielding aromatic amid containing dihydroxy monomer, N1,N4-bis(3-hydroxyphenyl), and the reaction of the synthesized monomer with amino propyl trimethoxysilane (IPTES), formed alkoxysilane containing aromatic amide-urethane macromonomer, over the urethane linkage. Synthesized macromonomer (Figure 3) characterized by 1HNMR indicating the high purity, has the potential to form hybrid materials by owning the organic and inorganic precursor in the same macromonomer. Aromatic amide-urethane alkoxy silane based sol-gel was prepared and incorparated into epoxy acrylate resin formulations following UV curing process. The resulting epoxy acrylate hybrid material was determined and thermal and morphological properties of the hybrid material were characterized. Figure 3 : Alkoxysilane modified aromatic amide-urethane precursor.