Production and characterisation of biodegradable and antimicrobial gel film from waste tea pulp

The possibility of encountering an energy bottleneck in the near future due to the environmental impacts of petroleum based polymeric materials (caused by global warming or excessive CO2 emission, lack of biodegradability), having toxic effects on living beings and the limited availability of oil reserves; led to the search for alternative and sustainable raw materials for the production of polymeric products. For this reason, studies have recently been increasing on the development of methods for the production of biodegradable and environmentally friendly polymeric materials from plant and animal based sustainable sources.While there are specific studies to improve the mechanical/elastic/water resistance properties of the produced biopolymers in order to compete with the petroleum-based polymeric products in the commercial field, there are ongoing question marks on commercial-technical and sustainable economic resource. In this study, it was aimed to produce polymeric gel films which is highly mechanical/water resistant and low in water vapor permeability and moisture uptake capacity (which acts as an water vapor barrier), responsive to environmental effects (pH, temperature) biodegradable and antimicrobial from tea pulp, which is a qualified domestic field and has previously not been evaluated for the production of polymeric materials. Unlike conventional smart polymeric gels, the response of produced polymeric gel films to environmental pH change was achieved not by swelling and shrinkage but the change in the color of gel with the change in pH. The sensitivity of polymeric gel films to pH and temperature, antimicrobial and mechanical resistance properties are determined by adding to the polymeric structure the natural herbal pH indicator (extract of purple cabbage), comonomers, herbal essential oils (mint, rosemary, thyme, juniper etc.) and natural additives, (chitin, chitosan, montmorillonite, bentonite). The water resistance of the polymeric gel has been achieved with the cross-linked network structure of the gel. The study was carried out in three stages. In the first phase of the study, the waste tea pulp obtained from the local market was separated into its basic components (cellulose-hemicellulose-lignin) by extraction method followed by the pretreatment applied and then the components obtained from the tea pulp were characterized using suitable instrumental methods (FTIR, XRD and H-NMR) .In the second stage, the color pigments, which was used to provide a pH-sensitive to the polymeric gels, was extracted by water from purple cabbage and then the extract was characterized by FTIR spectrometry. In the third stage, the polymeric gel film, which was pH and temperature sensitive, was produced by polymerization from hemicellulose extracted from waste tea pulp and characterized. Polymeric gel films were produced in accordance with solution-casting technique. The influence of type and amount of co-monomer, cross-linker and initiator, the amount of natural indicator and the type of antimicrobial plants were investigated on the physicochemical properties of the gel films produced and their sensitivity to environmental stimulants. The synthesized polymeric gel films were characterized by determining the structural, morphological, physicochemical, thermal and optical properties of them. For this purpose, FTIR, SEM and DSC analyzes of the synthesized gel films were carried out. Water vapor permeability test, moisture retention capacity test, equilibrium and dynamic swelling tests, light permeability tests of the gel films were performed. Hemicellulose based gel films were absorbed maximum 1% in 100% relative humidity environment. It has been determined that the average solubility values of the polymeric films produced within the scope of the thesis vary between approximately 0.4% and 1.8%. Among the films, the lowest water vapor permeability (WVP) value (5.88×10-g/sn.Pa.m) was measured for the hemicellulose based film which is contained chitosan. It was observed that gel films prepared by adding purple cabbage extract showed reversible color change when put in different pH environments. It has been determined that the optical transparency of hemicellulose based polymeric gel films varies from about 45% to 65% and the opacity/thickness values are from 0.0027-0.0011μm-1. Polymeric films which were contained rosemary, thyme, carnation and nettle volatile oil produced within the scope of this study have been shown to have antimicrobial activity and a significant inhibitory effect on E-coli.The synthesized hemicellulose based gel films were found to be biodegradable as expected. Polymeric films produced under different conditions were determined to degradased by 80-98% in the soil after 60 days. Keywords:Biodegradable, antimicrobial, polymer, gel film, waste tea pulp, alkaline oxidative extraction, natural indicator, pH and temperature-sensitive polymers.