Xylanase pretreatment of wood fibers for producing cellulose nanofibrils: a comparison of different enzyme preparations

Abstract

Three commercial xylanases and an endoglucanase preparation were compared in the enzymatic pretreatment of bleached eucalyptus pulp for producing cellulose nanofibrils (CNFs) through subsequent microfluidization. Commercially provided xylanases X10A and X10B hydrolyzed more xylan than the X11 xylanase. Moreover, the average degrees of polymerization (DP) of the fibers after treatments using xylanases X10A and X10B (DP ~ 1000) were lower than for the fibers following treatment using xylanase X11 (DP ~ 1100). Based on protein molecular weight, the commercial xylanases X10A and X10B are both thought to be endoxylanases of glycoside hydrolase (GH) family 10 and X11, an endoxylanase of GH11. Xylanase treatment facilitated initial stage fibrillation to separate fibrils due to removal of easily accessible xylan located mainly between cellulose fibrils of micrometer size, but had no substantial effect on nanoscale fibrillation due to difficulties in removal of xylan located between nanoscale fibrils. Although electron microscopy did not show much variation among the CNF samples from different xylanase treatments, a large DP reduction associated with aggressive enzymatic treatment facilitated mechanical fibrillation and also reduced the specific tensile strength of the resulting CNF films.