Controllable Synthesis Of Cellulose Esters By Homogeneous Transesterification And Its Application

Driven by the growing fear of the depletion of oil,coal and other non-renewable resources,and the global need to focus on renewable and earth-abundant resources,high value-added cellulose-based functional materials and polymers are now spotlighted once again and widespread concerned.A series of studies were carried out in this dissertation on the mild and rapid methods of cellulose esters preparation by controllable homogeneous transesterification in N,N-dimethylacetamide/lithium chloride(DMAc/LiCl)system,which includes the dissolution process improvement of cellulose in DMAc/LiCl system,the optimization of the reaction conditions,the analysis of product characteristics and SEC measurement.The ultimate goal is providing a theoretical basis for further research and application.The influence of solvent exchange and LiCl content on cellulose dissolving process was investigated in order to better understand the solubility characteristics of MCC in DMAc/LiCl system.After comparing the viscosity of cellulose in different LiCl concentration,the reason for the agglomeration in the solution is that the activation of cellulose could not scattered timely in DMAc/LiCl solution,thus the surface of the agglomerate has high viscosity in a certain LiCl concentration which prevent the outward spread of cellulose.By using the method of two-step to add LiCl,the raw materials including MCC,cotton,filter paper,the purified bamboo fiber and Miscanthus fiber could dissolved quickly in DMAc/LiCl system.DMAc/LiCl solution with 4-5 wt%LiCl concentration was firstly prepared.The activated cellulose was dispersed uniformly in the solution,and then a certain amount of LiCl was added to make 8 wt%as its final concentration.Finally,the high concentration of cellulose solution was obtained efficiently and the agglomeration was avoided during the dissolving process.Cellulose acetate(CA)of MCC was prepared efficiently by homogeneous transesterification in the DMAc/LiCl system with vinyl acetate as acylation reagent and 1,8-diazabicyclo[5,4,0]undec-7-ene(DBU)as catalyst.The affection reaction conditions on the substitution degree(DS)of products were investigated.Among various reaction factors,the ratio of esterification reagent or catalyst to the cellulose has a significant influence on the DS.By controlling the amount of two reagents,the degree of substitution can be adjusted.At the same time,there was nearly no affection of temperature on the reaction,so 30 ? was chosen as the reaction temperature.FT-IR,1H NMR and 13H NMR analysis confirmed that the successful preparation of cellulose acetate,SEM,XRD and TG-DSC reflected the apparent morphology,phase structure and thermal characteristics,which prove that the structure of the products were similar to the existing cellulose acetates.The priority of reactions in three positions of the cellulose acetate followed the same order of C6>C2>C3 for a homogeneous conversion.Thermal stability of cellulose acetates was better than that of MCC.Cellulose aliphatic esters(CEs)and three kinds of Mixed Cellulose Esters(MCEs)were synthesized efficiently in an DMAc/LiCl system with vinyl esters(VEs,number of carbon atoms ranging from 4 to 12)as acylation reagent and DBU as catalyst.The existence of ester bond and different number of methylene in FT-IR curve proved that the successful preparation of the cellulose aliphatic esters.The structures and properties of the products have been characterized by various analytical techniques.Generally,the DS of CEs showed a reverse trend with the length of the aliphatic chain increasing due to steric effects.Their thermal stability was also better than that of MCC.CE2,CE3 and CE4 can not be dissolved in chloroform,while CE6,CE8 and CE10 can.This research provides a novel homogeneous technology to synthesize various CEs efficiently.Cellulose acetate butyrate(CAB),cellulose acetate propionate(CAP)and cellulose acetate hexante(CAH)were prepared homogeneously.There was no decrease of molecular weight under this mild reaction.Mixed cellulose ester also shows good solubility properties in many conventional solvents.We took advantage of the excellent dissolving properties of the cellulose derivatives and dissolved it in the THF for the SEC determination of THF as the mobile phase.The mobile phase has the advantages of low molecular weight,low cost,wide adaptation,the good liquidity.When the molecular weight of different kinds of cellulose derivatives was obtained,and finally calculated the DP according its DS value.The results show that using DBU as a catalyst in homogeneous solvent of DMAc/LiCl,the synthesis and preparation process of all kinds of cellulose esters is controlled.In addition to controllable substitution degree and polymerization degree,pollution-free and fast reaction,the product has the excellent properties of high thermal stability and good solubility,and the performance have reached the optimum level in literature.The cellulose ester prepared by this new catalytic reaction system has a great application and development prospect in the field of membrane materials and optical materials.