Cellulose Nanocrystal Preparation via Rapid Hydrolysis of Wood Cellulose Fibers Using Recyclable Molten Ferric Chloride Hexahydrate

Recyclable molten FeCl3 & BULL;6H(2)Owas first proposed for the acid hydrolysis pretreatment of wood celluloseto fabricate CNCs. Cellulosenanocrystals (CNCs) are clean and sustainable materialsthat have drawn significant attention in academia and industry becauseof their unique physicochemical properties. However, realizing economicaland environmentally friendly production of CNCs remains a challenge.In this study, we proposed an innovative strategy to fabricate CNCs,which involves the acid hydrolysis pretreatment of wood cellulosefibers using innocuous and recyclable ferric chloride hexahydrate(FeCl3 & BULL;6H(2)O). During the molten FeCl3 & BULL;6H(2)O treatment, the degree of polymerization(DP) of the cellulose fibers sharply decreased, along with the transformationof cellulose I to cellulose II crystallites. Molten FeCl3 & BULL;6H(2)O quickly hydrolyzed cellulose fibers within5 min at 80 & DEG;C, inducing a rapid decrease in the DP from 922to 196, and the water-insoluble solid (WIS) retention reached 80.1%.CNCs were successfully produced from the mechanical disintegrationof the WIS with a low energy input. Hence, the yield of CNCs is consistentwith that of the WIS. Interestingly, the CNCs exhibited typical celluloseII crystallites, which were significantly different from those ofthe cellulose feedstock (cellulose I). Detailed characterization revealedthat the CNCs had tunable number-averaged heights of 10.4-26.9nm and high thermal stability (a maximal weight loss temperature of327 & DEG;C). Most notably, FeCl3 & BULL;6H(2)Owas easily recycled from the hydrolysate after hydrolysis, with ahigh recovery of 94.0-94.5 wt %, using simple concentrationand crystallization technologies. Thus, this study proposes a novelproduction technology for CNCs that is both economical and eco-friendly,providing new ideas for clean and large-scale production of CNCs.