On The Sol-Gel Technique For Enzyme Immobilization On Fabrics

The sol-gel is a technology that starts with organic metal compounds or inorganic compounds and solidifies through a solution-sol-gel evolvement,finally resulting very fine particles of oxide.The modification of fabric surface using sol-gel technology has been reported to be an encouraging approach.The sol and finishing process are common factors to be considered in improving modification efficiency.However,few studies have been focused on the textile fabric,which is another key factor governing the adhesion of silica coating prepared by sol-gel technology.Therefore,it is meaningful to investigate the interaction between textiles and the sol coating.Textiles are also one of the most important immobilization carriers taking the advantages of low cost,performance stability and flexibility.Currently,the methods for enzyme immobilization on textiles include chemical modification and physical adsorption.However,there exist some unavoidable disadvantages for these methods. The sol-gel chemistry offers an access to enzyme encapsulation except textile modifications.The objective of the present study is to analyze the interaction between the sol-gel and textiles and apply the sol-gel technology to immobilize papain on fabric carriers.For this purpose,the first part is to prepare sol with tetraethyl orthosilicate(TEOS)as precursor,distilled water as solvent and hydrochloric acid in minute quantities as catalysis.The influence of the molar fraction of water and TEOS(R),temperature and electrolyte on sol system is investigated.The results show that R and temperature greatly alter the rates of hydrolysis and condensation reaction and thereby control the gelation time.In addition,when the electrolyte of Na₂HPO₄ is added to the sol system, reduce in the gelation time of sol is found from about 6 days to less than 2 hrs. Based on the above-prepared sol system,the following study is to compare the interaction and adhesion of the coating with different fabric substrates by means of the add-ons and leaching behaviours of the silica gel coating on the surface of the fabrics. The consequences of the surface changes induced are outlined and discussed,with the data derived from the surface analysis by Brunauer-Emmet-Teller(BET)specific surface area,FTIR-ATR,X-ray photoelectron spectrum(XPS),X-ray diffraction(XRD)and imaging using scanning electron microscopy(SEM).The results show that the adhesion of silica coating on the surface of fabrics is in principle influenced by the chemical composition and structure of fabric substrates.The adhesion of silica coating on the synthetic fabric substrates is mainly a result of thermodynamic affinity by dipolar-dipolar or hydrogen bond interaction.For the cellulose fabrics,except the thermodynamic affinity,there are covalent bonds(Si-O-C)formed between the end groups of silica precursor and hydroxyl groups on cellulose fibres,which make the silica coating more durable.The leaching of silica from the surface of cellulose fabrics is less than the synthetic fabrics when the treated fabrics are dipped into borate buffer (pH=9.6).There is more than 50%add-on%still conserved on the cotton and flax fabrics while the residual add-on%of silica on PET and nylon remains no more than 10%.The surface of fabrics treated with sol-gel become coarse and the BET specific surface area of all coated fabrics increases significantly in comparison with the pristine fabrics.The formed Si-O-C between the end groups of silica precursor and hydroxyl groups on cellulose fibres shows no effect on the microstructure of the fabrics.The silica presented on the surface of the treated fabrics is in SiO₂ states.The third part of this study involves the papain immobilization on cotton fabric by sol-gel technology.According to the analyses of image by SEM and chemical composition by EDS,the sol-gel technology has been successfully used for papain immobilization on cotton fabric.The immobilized papain is less sensitive to pH as compared to free papain,and the optimum medium pH value for immobilized papain is 7.0.The activity of the immobilized enzyme-pH curve shifts to the alkaline side.As expected,the reusable times for papain immobilized on cotton fabric by sol-gel technique are more improvable than that immobilized on cotton fabric by simple adsorption.A typical application of enzyme immobilization is as bioreactors.To our best knowledge,few studies on the manufacture and application of bioreactor with fabrics as carriers and papain as model enzyme have been reported in domestic.Therefore,the further research is to design such a bioreactor model.The new model could be extensively ranged from textile carriers,immobilized methods to biomolecules.The new papain bioreactor manufactured with cotton as carrier and sol-gel as immobilized method shows a certain role in hydrolyzing chitosan.After 4 uses,the viscosity decrease rate of chitosan is about 3.74%.The conclusions on the interaction between textiles and sol coating in this thesis could provide theoretical basis for the further application of sol-gel on textiles.The application of sol-gel technology in papain immobilization on fabric is beneficial to not only afford more space to improve the immobilized papain efficiency than ever,but also provide some new ideas for the engineers and researchers in this field.