Enzymatic hydrolysis of Asclepias syriaca fibers in the presence of ionic liquids

Abstract

Attempts have been made to enhance Asclepias syriaca (As) fiber saccharification by cellulase in the presence of ionic liquids. Three ionic liquids (1-butyl-3-methylimida- zolium chloride, (BMIM)Cl; 1-ethyl-3-methylimidazolium chloride, (EMIM)Cl; and 1-butyl-4-methylpyridinium chlo- ride, (BMP)Cl) were used. In comparison with conventional cellulose pretreatment processes, the ionic liquids were used under milder conditions corresponding to the optimum activity of cellulase. The structural modification and thermal properties of As fibers were analyzed by DSC, TG, DTG, and FT-IR. As fibers were hydrolyzed by cellulase more easily in aqueous ionic liquid media. For As fibers hydrolyzed in the presence of ionic liquids, saccharification rate during the first 3 h of the hydrolysis reaction was significantly improved, especially when the fibers were hydrolyzed in the presence of (BMP)Cl. FT-IR spectra revealed that As fibers undergo modification during enzymatic hydrolysis in the presence of ionic liquid. The increased rate of hydrolysis was accompa- nied by an increase in the degree of crystallinity of the As fibers. It was apparent from thermal analysis that the well ordered crystalline phase and the intermolecular regularity of carbohydrates obtained from the As fibers considered in this study were affected by the ionic liquid through changing of the fiber structure.