| Chitosan and its derivatives had the excellent properties of biocompatibility,biodegradable,hygroscopicity,antimicrobial and fiber into membranous which performed a wide application prospect in medicine,food,textile,daily chemical,papermaking and other fields.However,owning to the strong intramolecular and intermolecular hydrogen bonds,chitosan only can dissolve in acid solvent and limited its application.Study had revealed that solubility in organic solvents can be increased by introduced some hydrophobic groups to widen its popularization.Strong acids solvents with strong toxicity,corrosive and difficulty subsequent processing were used in traditional chemical esterification way.What is more,the-NH2 groups and the protection groups had to be protected and moved during the reaction.Enzyme as biological catalyst have the characteristics of high efficiency catalytic,strong specificity and mild reaction conditions.Some ionic liquids were good solvent for chitosan while others were good medium for enzyme.So,the possibility of lipase catalytic synthesis of different molecular chitosan with methyl palmitate in mix ILwas were investigated;the influence of different reaction condition was also studied;Besides,the composite materials composed of palmitate chitosan/oligosaccharide and cellulose were formed and properties were tested to analyzed the effect of products.Results showed that enzyme peformed high catalytic activity for chitosan esterification in [EMIM]Ac and [BMIM][BF4].In this reaction medium,maxmium DS value of 0.214 was obtained.The optimum of quality ration of ILs,molar ratio of glucosamine/methyl palmitate,lipase dosage,reaction time and temperature for the esterification of palmitate chitosan were found to be 6:4(g/g),1:3(mol/mol),75 mg,24h and40? respectively;Meanwhile,the reaction of synthesis of palmitate chitooligosaccharide was also investigated in mix ILs.The optimum of quality ration of ILs,molar ratio of glucosamine/methyl palmitate,lipase dosage,reaction temperature and time were 4:6(g/g),1:3(mol/mol),50 mg,50? and 9 h.The maxmium DS value was 1.67.The formation of palmitate chitosan/oligosaccharide were confirmed by the presence of the carbonyl signal in the FT-IR,1H and 13 C NMR spectra.Based on the changes of signal,esterification was occurred mainly in C-6 and C-3 sites.XRD results indicated that crystalstructure of chitosan was destroyed while some new peak arised and crystallinity of chitooligosaccharide was increased after modification.TGA results showed that the thermal stability of palmitate chitosan worse than the native while palmitate oligosaccharide were better than original one.The changes of palmitate oligosaccharide in SEM further demonstrated esterification modification.The performance of the composite materials were tested to investigated the effects of modified products.FT-IR and XRD resulted that products have certain compatibility with cellulose and without obvious change of crystallinity in palmitate chitosan materials,while the crystallinity of chitooligosaccharide materials had increased 15.8%.Water contact angle measurements revealed that the hydrophobic of both products were respectively improved from 19.9°to 39.0°and39.6°.The maxmium tensile stress were 23.6MPa and 33.1MPa occurred in 6% point and respectively increased 0.56 and 1.80 times compared with pure cellulose.Antibacterial test of palmitate chitooligosaccharide showed that composite materials has better antibacterial property than pure cellulose.Antibacterial diameter reached2.39 cm at 6% and bigger than the native 14.9%. |
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