Polymorph Conversion Of Cellulose Nanocrystals And Its Impact On The Adsorption And Hydrolysis Of Enzymes

Polymorphic and morphological transformations of cellulosic materials are strongly associated to their properties and applications. It was reported that cellulose resources had clear polymorphic transformation rules. But whether it was also useful in nano-sized cellulose or not was unknown. Related changes that take place upon treatment of cellulose nanocrystals(CNC) in alkaline conditions(1%~17.5%Na OH) are studied here by XRD, TEM, AFM, and other techniques. In the end of the paper, Quartz crystal microbalance(QCM) detected the cellulase enzyme adsorption and hydrolysis process among surfaces of different allomorph cellulose nanocrystals.The results indicate polymorphic transformation of CNC proceeds gradually in a certain range of alkali concentrations, i.e. from about 8% to 12.5% Na OH. In such transition alkali concentration, cellulose I and II allomorphs coexists. Such value and range of the transition concentration is strongly interdependent with the crystallite size of CNCs. In addition, it is distinctively lower than that for macroscopic fibers(12-15% Na OH). Transmission electron microscopy and particle sizing reveals that after mercerization CNC tends to associate. Furthermore, TEMPO-oxidized mercerized CNC reveals individual nanocrystal of the cellulose II type, which included some interconnected granular structures. Overall, this work reveals how the polymorphism and morphology of individual CNC change in alkali conditions and sheds light onto the polymorphic transition from cellulose I to II. The XPS results show that the hydroxyl content on the surface of the cellulose II crystals reduced and the O/C ratio decreased as well. This study provides evidences to explain the different adsorption behaviors of cellulases onto cellulose substrates which suffered different treatments, and also offers some merits to its applications.This paper compared the Trichoderma reesei adsorption and hydrolysis among cellulose allomorph I, I/II and II in nanoscale through QCM technique. In enzyme adsorption and desorption process during low temperature, cellulose nanocrystal(CNC) of allomorph II had lowest capacity that total adsorption mass was 179.20ng·cm-2,but highest reversible binding ratio of 33.72% and strongest binding with Trichoderma reesei. CNC-II presented best enzyme hydrolytic ability, and superior a lot to others during optimum hydrolytic temperature. Substrate samples' crystallinity degree was similar calculated by XRD and these morphologies were detected by AFM. The results inferred that the polymorphism of cellulose was an important factor impacting hydrolysis ability rather than enzyme adsorption and substrate's crystallinity degree.It inferred the crystalline structure and cellulose chains arrangement of cellulose II through the research about crystalline structure, morphology and surface analysis of mercerized CNCs. And two spherical cellulose nanocrystals II had wide application in follow-up development due to nano-scale and sphere. As a new technique, QCM revealed the fact that cellulose polymorph was an important factor impacting enzymatic hydrolysis, rather than enzyme absorbed mass. It explained the more efficiency of enzymatic hydrolysis from alkali pretreatment, and providing the references about cellulose adsorption and hydrolysis researches.