Preparation And Research Of Fiuorescent Nanocellulose And Its Hydroge Based On Mchanochemical Action

With the development of economy and technology and the increasing demand for new materials,the preparation and modification of green and efficient nanocellulose have attracted people’s attention.How to use chemical means to make nanocellulose have new functions,thereby broadening the application scope of cellulose,accessing to new advanced nano-cellulose functional materials,has become the focus of research in cellulose science.This study aims to solve at the problems of complex operation,low yield,and environmentally unfriendly use of toxic reagents in the modification process of nanocellulose.It uses the nature of polyhydroxyl groups on the surface of nanocellulose to functionally modify them.The acid-catalyzed hydrolysis method prepared esterified nanocellulose(E-CNCs)to achieve green and efficient nano-cellulose esterification modification;on the basis of preparing E-CNCs,L-cysteine was added,It reacts to form a special group with a fluorescent structure,thereby obtaining fluorescent nanocellulose(F-CNCs);the F-CNCs and the hydroxyl groups in PVA form multiple hydrogen bonds to prepare a fluorescent nanocellulose intelligence with a chloride ion response hydrogel,and preliminary exploration of its formation mechanism.The main research work of the thesis is as follows:(1)Under the action of mechanochemistry,phosphotungstic acidcitric acid catalytic hydrolysis is used to prepare esterified nanocellulose(E-CNCs).This method is simple,green and environmentally friendly,and has a high yield of E-CNCs.The results show that under the action of mechanochemistry,it can significantly improve the reactivity of cellulose and accelerate the hydrolysis rate of cellulose.The ball milling time is 1.5h,the concentration of phosphotungstic acid is 6 %,the reaction time is 6h,and the ultrasonic time is 1.5 h.Under the conditions,the yield of E-CNCs is 75.6 %,the crystallinity is 80 %,the length is 180-210 nm,the diameter is 8-10 nm,the degree of substitution is 0.25,and the thermal stability is good.(2)Based on the preparation of E-CNCs,under the action of mechanochemistry,cysteine is added to react with the carboxyl group on E-CNCs to form fluorescent TPDCA grafted onto the surface of nanocellulose to obtain F-CNCs.Under the conditions of ball milling time1.5 h,reaction temperature 140°C,reaction time 6h,cysteine concentration1mol/L,the yield of F-CNCs was 66.5 % and the quantum yield was 0.32.Furthermore,ion-selectivity studies have shown that F-CNCs are most sensitive to chloride ion at relatively low p H.(3)Using polyvinyl alcohol(PVA)as a matrix,adding F-CNCs and using phytic acid as a cross-linking agent,under homogeneous conditions,the carboxyl and hydroxyl groups on the F-CNCs molecular chain are formed with the hydroxyl groups on PVA and phytic acid Hydrogen bonding prepared PVA/F-CNCs/PA composite hydrogel.Analysis using SEM,XRD,FTIR,etc.shows that a strong hydrogen bond is formed between F-CNCs and PVA,PA,so that the composite hydrogel has good mechanical properties.The fluorescence of the composite hydrogel showed good fluorescence stability,and under certain p H,the fluorescence quenching efficiency of the PVA/F-CNCs/PA composite hydrogel to chloride ion(0～0.2M)in a certain concentration range was Linear response.