Enzymatic hydrolysis of mercerized and unmercerized sisal pulp

Abstract

Enzymatic saccharification of sisal cellulosic pulp has been investigated. Brazil leads global production of lignocellulosic sisal fiber, which has high cellulose content, an important property for producing glucose via saccharification. Hence, sisal pulp can be a good alternative for use in biorefineries. Prior to enzymatic hydrolysis, the starting pulp [85 ± 2% α-cellulose, 15 ± 2% hemicelluloses, 1.2 ± 2% insoluble lignin, viscometric average molar mass (MMvis) 19,357 ± 590 g mol−1, crystallinity index (CI) 74%] was pretreated with alkaline aqueous solution (mercerization, 20 g of pulp L−1, 20% NaOH, 50 °C). The changes in the properties of the cellulosic pulp during this pretreatment were analyzed [α-cellulose content, MMvis, CI, pulp fiber dimensions, and scanning electron microscopy (SEM)]. The unmercerized and mercerized (97.4 ± 2% α-cellulose, 2.6 ± 2% hemicelluloses, 0.3 ± 0.1% insoluble lignin, MMvis 94,618 ± 300 g mol−1, CI 68%) pulps were subjected to enzymatic hydrolysis (48 h, commercial cellulase enzymes, 0.5 mL g−1 pulp); during the reactions, aliquots consisting of unreacted pulp and liquor were withdrawn from the medium at certain times and characterized (unreacted pulp: MMvis, CI, fiber dimensions, SEM; liquor: high-performance liquid chromatography). The changes in pulp properties observed during mercerization facilitated access of enzymes to cellulose chains, and the yield of the hydrolysis reaction increased from 50.2 (unmercerized pulp) to 89.0% (mercerized pulp). These initial results for enzymatic hydrolysis of sisal pulp indicate that it represents a good alternative biomass for bioethanol production.