Study Of The Solid Phase Esterification Of Cellulose With Different Degree Of Polymerization By Long Chain Fatty Acids And Their Structure-activity Relationship

As the oil and other fossil-resource are increasingly scarce,more and more attention has been shifted from the fossil resource to green energy-natural cellulose.However,the features such as high crystallinity,and low accessibility,severely delay the development and adoption of cellulose.It is of great urgency to expand the scope of application of cellulose by the modification of it,such as the synthesis of the cellulose derivatives.Therefore,the research of cellulose derivatives has become a hot point in academia.With the support of National Natural Science Foundation of China,our research team has developed the technology of mechanical activation-assisted solid phase synthesis of long chain cellulose esters using co-reagent,and the effect of different long chain acids on solid phase esterification of cellulose and the properties of products was also investigated.Based on these researches,this study mainly focused on investigating the solid phase esterification reaction characteristics of the cellulose materials with different degree of polymerization(DP).The reseach contents and results are as follows:(1)Using microcrystalline cellulose(MCC)(DP?200),bagasse cellulose(DP?1300)and cotton cellulose(DP?2500)with different DP as the raw materials,octanoic acid,lauric acid and palmitic acid as the long chain esterifying agents,the synthesis of different chain length cellulose esters with acetic anhydride as a co-reagent of fatty acid was studied.The cellulose materials and the esterification products with reaction time of 90 min were characterized by means of SEM,FT-IR,XRD,1H-NMR,TG,etc.SEM analysis indicated that there had obvious difference in the morphologies of different cellulose materials,and significant changes were occurred in the morphologies of cellulose esters.FT-IR analysis showed that the spectra of esterification products exhibited a peak at 1750 cm-1,which corresponded to the stretching vibration of the ester carbonyl groups.XRD analysis indicated that the crystalline allomorph of cellulose materials was cellulose ?,and the crystallinity index was:MCC(79.72%)>cotton cellulose(78.26%)>bagasse cellulose(64.56%).It was found that the crystallinity of cellulose esters decreased,and new crystal structure was formed.1H-NMR analysis indicacted that cellulose materials and chain length of esterifying agents had remarkable effect on DS of the esterification products.The thermogravimetric analysis showed that the thermal stability of different cellulose materials was cotton cellulose>MCC>bagasse cellulose.The thermal stability of cellulose materials was influenced by both crystallinity and DP of cellulose.(2)The 1H-NMR and 13C-NMR were used for the analysis of esterification products.1H-NMR analysis indicated that the proportion of long-chain fatty acyl substituents in total degree of substitution(DS)increased with increasing the chain length of esterifying agents.With octanoic acid as esterifying agent,the maximum DS value of the product was obtained with the reaction time of 90 min.With lauric acid and palmitic acid as esterifying agents,the maximum DS values of the products were obtained with the reaction time of 120 min.In addition,the proportion of long-chain fatty acyl substituents in total DS decreased with the increase of chain length of fatty acids.13C-NMR analysis indicated that the distribution of substituents in cellulose acetate-octanoate prepared by different cellulose materials had large difference.When MCC and cotton cellulose were used as raw materials,the distribution of substituents was:C-6>C-2>C-3.When bagasse cellulose was used as raw material,the distribution of substituents was:C-3>C-2>C-6.The distribution of substituents had a close relationship with the crystallinity of cellulose materials.For the cellulose material with higher crystallinity,the higher reactive hydroxyl group was in C-6 position.For the cellulose material with lower crystallinity,the higher reactive hydroxyl group was in C-3 position.(3)The thermostability analysis of esterification products showed that the thermal stability of the products with the same cellulose material was:cellulose acetate-laurate>cellulose acetate-palmitate>cellulose acetate-octanoate,and thermal stability of the products with the the same fatty acids:cotton cellulose>bagasse cellulose>MCC.For the same cellulose material,the esterification products with higher DS had poorer thermal stability,and the thermal stability increased with the increase of chain length of esterifying agents.For the same esterifying agent,the higher DP the cellulose material had,the better thermal stability the esterification products possessed.Tg of the cellulose acetate-octanoate was the lowest for its highest DS.Cellulose acetate-laurate had the highest Tg because the chain length of lauroyl was longer than that of octanoyl,and the steric hindrance of the introduced fatty acyl had positive effect on enhancing the rigid of cellulose molecules.Tg of cellulose acetate-palmitate was between that of cellulose acetate-octanoate and cellulose acetate-laurate.On the one hand,the DS of long chain fatty acyl of cellulose acetate-palmitate was lower than that of cellulose acetate-octanoate and cellulose acetate-laurate,and on the other hand,the palmitoyl introduced in cellulose had the larger size with the longest methyl(-CH2-).Therefore,Tg of cellulose esters was influenced by both the chain length of esterifying agents and the DS of cellulose esters.(4)The analysis of the solution properties of cellulose esters indicated that the transmittance of cellulose acetate-octanoate:MCC>bagasse cellulose?cotton cellulose;the transmittance of cellulose acetate-laurate:bagasse cellulose?MCC>cotton cellulose.The transmittance of cellulose acetate-octanoate decreased with the increase in DP of cellulose materials,and transmittance of cellulose acetate-laurate decreased with the increase in crystallinity of cellulose materials.