Production of SEBS based elastomer compatibilized and nanoclay reinforced polypropylene nanocomposites

Polymer nanocomposites (PNC) attract the attention of the academy and industry with their superior features and their application areas are expanding rapidly.The properties such as mechanical, thermal, electrical, optical and gas permeability of the polymer matrix can be significantly improved by using small amount of nano filler. Polypropylene (PP) is one of the most widely used thermoplastic polymer because of its low cost, low density and easy processability. However, low impact resistance and low toughness values of PP limit its application areas. Low impact resistance and toughness values of polypropylene can be improved by reinforcing with various fillers or by addition of elastomeric polymers. In this study, nanoclays with different geometries and styrene-b-ethylene/butylene-b-styrene (SEBS) based thermoplastic elastomer compatibilizers were used to enhance the impact resistance and toughness of polypropylene. In the first part of the work, polypropylene-based nanocomposites containing halloysit nanotube (HNT) and maleic anhydride grafted SEBS (SEBS-g-MA), were prepared by two different methods and the effects of production methods on the nanocomposite properties were investigated. Halloysite is a natural inorganic nano filler having hollow tubular structure. To increase the interaction between the polymer and the nanotubes, halloysite was modified with cetyltrimethylammonium bromide (CTAB), quaternized ammonium salt using cryoscopic expansion method and organophilic surface modified halloysite (Org-HNT) was obtained. The nanocomposites were prepared in two different ways in an internal mixer by melt mixing: simultaneous melt mixing method and masterbatch based method. In the masterbatch-based process, the HNT / SEBS-g-MA ratio was selected as 1/3. The components of masterbatch were distributed in tetrahydrofuran (THF) solvent by using a centrifugal revolution/planetary rotation type high shear mixer and after removal of solvent, the masterbatch was blended with the PP matrix by melt blending. The effects of the production method on the morphological, mechanical and thermal properties of the nanocomposites were analyzed in details. The nanocomposites prepared by masterbatch method showed better nanotube and elastomer dispersion in the matrix than nanocomposites prepared by simultaneous method. Consequently the composites prepared by masterbatch based method exhibited better thermal and mechanical properties. The nanocomposite with 3 wt.% HNT and 9 wt.% SEBS-g-MA showed about 200% higher impact resistance compared to neat PP, which created a good balance between stiffness and toughness. In the second part of the study, masterbatches were produced in different Org-HNT / SEBS-g-MA ratios (1/1, 1/2 and 1/3) by using a revolution/rotation type high shear mixer and the effects of the ratio of Org-HNT / SEBS-g-MA on the mechanical and thermal properties of Org-HNT/SEBS-g-MA/PP nanocomposites were analyzed. For this purpose, polypropylene nanocomposites containing 1 wt.%, 3 wt.% and 5wt.% of Org-HNT were prepared by melt blending for each masterbatch. All nanocomposites exhibited higher storage moduli and damping at low temperatures as compared to neat polypropylene. The nanocomposites containing HNT/SEBS-g-MA ratio of 1/3 acted as effective dampers with their relatively higher damping values. In terms of short-term creep performance, 1 and 3 % Org-HNT loaded systems with low amount of SEBS-g-MA (<9 %) enhanced dimensional stability of PP with their lower creep strain and permanent deformation values. The short-term creep test results showed that the composites having 1 wt% and 3 wt% Org-HNT and less than 9 wt% SEBS-g-MA have better dimensional stability, creep strain and permanent deformation than pure PP. The nanocomposite containing 3 wt% Org-HNT and 9wt% SEBS-g-MA exhibited relatively higher storage modulus and lower permanent creep strain at low temperatures, while exhibiting effective damping in a very wide temperature range (-70°C to 50°C). In the third part of the study, firstly a new compatibilizer poly (ethylene oxide) (PEO) grafted SEBS (SEBS-g-PEO) was synthesized by modifying the maleic anhydride functional groups on the SEBS-g-MA elastomeric compatibilizer with the poly (ethylene oxide) (PEO) molecule. To evaluate the performance of the new compatibilizer againts to SEBS-g-MA, the nanocomposites containing polypropylene, elastomeric compatibilizer and montmorillonite (MMT) (PP / SEBS-g-PEO / MMT and PP / SEBS-g-MA / MMT) were prepared by melt blending. Effects of grafting of the PEO molecule onto the SEBS elastomer on morphological, mechanical and thermal properties of the nanocomposites were analyzed in comparison with SEBS-g-MA. The nanocomposites having SEBS-g-PEO exhibited higher toughness, thermal stability and creep resistance than the composites having SEBS-g-MA. The damping parameter of the SEBS-g-PEO containin nanocomposite was also found to be high in a broad range of temperature as another advantage of the SEBS-g-PEO toughener/compatibilizer. The water contact angles of the blends and nanocomposites were found to be lower than that of neat hydrophobic PP which is desirable for finishing processes such as dyeing and coating.