Preparation Characterization And Acetylation Of Different Allomorphic Cellulose Nanocrystals

As the most abundant biopolymer resource in the world,cellulose utilization is further enhanced in recent years.The structure of cellulose is complex.The allomorphic transformation of cellulose has a great influence on its crystallinzation,solubility,chemical reacrtion,enhancement as reinforcing fillers and applications.However,the reseaches based on different allomorphic cellulose was only limited to their macroscopic or submicroscopic state,the allomorph of cellulse nanocrystals(CNCs)was significantly insufficient.CNCs are normally prepared by sulphuric acid hydrolysis of native cellulose.It has played a significant role in the enhancement of some hydrophilic polymers due to its excellent hydrophilic property,but largely limited in the application of hydrophobic polymors.In this paper,the hydrophobic acetylation of CNCs with different allomophs was studied as follows:1.CNC Ⅱ and Ⅲ were obtained from CNCs prepared by sulfuric acid hydrolysis through alkali treatment and ethylenediamine treatment.The results showed that the morphology of CNC Ⅲ was similar to that of CNC I,while CNC Ⅱ showed great differences,such as shorter length,larger width,greater flocculation and poor dispersion performance.2.This study investigated the impact of CNC allomorphs on the acetylation.CNC samples with different allomorphs(cellulose I,Ⅱ and Ⅲ)were surface modified by acetylation in heterogeneous system.It was found that all obtained ACNC allomorphs kept their original intact crystal forms and rod-like structure.The degree of substitution(DS)of ACNC I was the highest and up to 1.98,followed by ACNC Ⅲ’,and ACNC Ⅱ’ was the lowest which only came to 0.32 after the reaction of 3 hours.The crystallinities of CNC allomorphs decreased,in which CNC Ⅱ dropped least and CNC Ⅲ dropped most.Both allomorphic transformation and acetylation improved the thermal stability of native CNC I.3.In order to further simplify the process and reduce the damage to the original morphology and structure of CNCs,a one-step method for the preparation of ACNCs was developed from the traditional acetylation of cellulose on the basis of the two-step method above.The results showed that this method could achieve hydrolysis and and acetylation of cellulose in a synergetic process,avoiding secondary damage of structure in the modification process,and maintaining high crystallinity of ACNCs,about 70% at most.