Xylanase pretreatment of wood fibers for producing cellulose nanofibrils: a comparison of different enzyme preparations
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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.
KeywordsXylanase pretreatment Microfluidization Cellulose nanofibrils (CNFs) CNF films Mechanical properties
This work was conducted at the USDA Forest Products Lab (FPL) while HZ was a visiting student under the sponsorship of Chinese Scholarship Council (CSC). We would like to acknowledge Dr. Ron Sable of FPL for conducting tensile tests of CNF films. HZ would also like to acknowledge the financial support of the National Natural Science Foundation of China (21506117), the Key Research and Development Plan of Shandong (2018GGX104015), the Applied Basic Research Programs of Qingdao (17–1-1–23-jch) and SDUST Research Fund (2018YQJH102 and 2015RCJJ008).