SIMULTANEOUS EXTRACTION OF CARBOXYLATED CELLULOSE NANOCRYSTALS AND NANOFIBRILS VIACITRIC ACID HYDROLYSIS-ASUSTAINABLE APPROACH

摘要

In this study,cellulose nanocrystals(CNC)with surface carboxylic groups were prepared from bleached softwood pulp by hydrolysis with concentrated citric acid at the concentrations of 60-80 wt％.The solid residues from acid hydrolysis were collected for producing cellulose nanofibrils(CNF)via subsequent high pressure homogenization.The citric acid can be easily recovered after hydrolysis reactions through crystallization due to its low water solubility,or precipitation as a calcium salt followed by acidification.Several important properties of CNC and CNF were evaluated,such as dimension,crystallinity,surface chemistry,thermal stability,etc.The effects of temperature and acid concentration on yields of CNC and CNF were also investigated.The resultant CNC and CNF surfaces contained carboxylic acid groups which facilitated functionalization and dispersion in aqueous processing.Disruption of crystalline structure and carboxylated cellulose surface significantly lowered the thermal stability of the CNC products.The recyclability of citric acid and surface functionality through carboxylation lead to that the renewable cellulose nanomaterial has huge potential for a wide range of industrial applications.Furthermore,the resultant CNC and CNF were used as reinforcing agent to make sodium carboxymethyl cellulose(CMC)films.Both CNC and CNF shown reinforcing effects in CMC nanocomposite films.The tensile strength of CMC filmincreased by 54.3％and 85.7％with 10 wt％of CNC and CNF inclusion,respectively.This study provided a set of detailed information on carboxylated nanocellulose prepared by critic acid hydrolysis and the sustainable approach for the preparation of CNC/CNF is of significant importance for its various uses.