Effect of cellulose structural features on enzymatic hydrolysis

Abstract

In cellulose-cellulase system, it has been suggested that degree of crystallinity, surface area, and lignification of lignocellulose are the most important structural features which affect the susceptibility of cellulose to enzymatic hydrolysis. Pretreatments such as compression milling, and dissolving and reprecipitation were reported to be effective to increase the cellulose reactivity which had been decreased by these structural features. In this work, the degree of crystallinity and degree of polymerization were investigated by X-ray diffraction and measuring viscosity of cellulose solution, respectively. The changes of the structural parameters by water-swelling, compression milling, phosphoric acid-swelling, and sodium hydroxide-swelling were examined. Also the effects of the parameters on the rate of enzymatic hydrolysis and the change of these during the course of the reaction were studied. It was observed that the increase in degree of crystallinity in water-swelling, could be the recrystallization effect, and the decrease in degree of crystallinity and degree of polymerization of Solka Floc SW40 and Avicel PH102, had a correlation with the increase in the initial reaction rate. It was found that phosphoric acidswelling made degree of crystallinity decrease like compression milling, and sodium hydroxide-swelling converted cellulose I into cellulose II by lattice change. Native cellulose, Sweco milled cellulose, and cellulose treated with phosphoric acid and sodium hydroxide were used as the substrates for enzymatic hydrolysis, which had the same enzyme loading. Native cellulose and cellulose treated with 5 N sodium hydroxide, with high initial degrees of crystallinity (78 and 75%, respectively) showed the similar mode of change in reducing sugar concentration, slight increase in degree of crystallinity during enzymatic hydrolysis, and little change in degree of polymerization. And Sweco 270, medium degree of crystallinity (37%), had a rapid increase...