Preparation Of New Bioactive Materials By Cellulose/Chitosan Graft Copolymerization Initiated By Laccase/TEMPO Oxidation System

Research has focused on the modification of natural cotton fibers through a green,non-polluting biological and chemical method to prepare a cellulose derivative to expand the application value and fields of cellulose.Firstly,the catalytic system of laccase/TEMPO was used to selectively oxidize the cotton fibers so that the primary hydroxyl groups on the cellulose C-6 were oxidized to aldehyde groups.Secondly,the Schiff base reaction was used to graft chitosan onto the modified cotton fiber,so that the cotton fiber and the chitosan are chemically bonded together to form a novel functional material having a Schiff base structure.This new material not only has the characteristics of natural cellulose,but also has the characteristics of chitosan,while also having the features of Schiff base.Oxidation reaction conditions,characterization of the grafted product and performance of the grafted product were studied by experiments.Firstly,the effect of concentration of TEMPO and oxidation time on the content of aldehyde groups in the laccase/TEMPO-catalyzed cellulose oxidation system was studied.The optimum reaction conditions were determined as follows:the pulp concentration was 1%,the TEMPO concentration was 40 mmol/L and the reaction time is 12 hours.Secondly,the surface and structure of the cotton fiber and the grafted product were analyzed by infrared spectroscopy(FT-IR),scanning electron microscopy(SEM),Scanning electron microscopy-X-ray energy spectrum(SEM-EDXA),X-ray diffraction(XRD)and thermogravimetric analysis(TGA).It was found that a new absorption peak appeared at 1637 cm-1 on the infrared spectrum of the grafted product,which was the stretching vibration of-C=N-;Scanning electron microscopy showed that the surface of oxidized cotton fiber showed obvious signs of candle,the grafted product showed a unique surface morphology,the surface of the small particles attached to the more obvious,and by Scanning electron microscopy-X-ray energy spectrum on the surface attachment of the small particles of elemental analysis,were detected N elements,it showed that the covalent bond structure of Schiff base is produced between oxidized cellulose and chitosan;XRD analysis shows that the crystallinity of the oxidized cotton fiber increases,while the crystallinity of the grafting products decreases.Thermogravimetric analysis shows that the thermal stability of grafted products slightly decreased compared with cotton fiber.At the same time,the content of chitosan in grafted products was calculated throug formula by detect the content of nitrogen,which help us to explore the best conditions of schiff base reaction:the reaction temperature is 80 ? and the reaction time is 3 h.Finally,the antibacterial properties and antioxidant properties of grafted products were studied in order to explore the application of grafting products.The antibacterial activity showed that the grafted products had good antibacterial activity against Escherichia coli and Staphylococcus aureus,and the effect on Staphylococcus aureus was slightly worse than that of Escherichia coli.Antioxidant experiments show that the grafted products have good oxidation resistance.These properties show that the grafted product has a high application value in the fields,such as papermaking,medical treatment,textiles,daily chemical industry,and packaging.