Modification of microcrystalline cellulose structural properties by ball-milling and ionic liquid treatments and their correlation to enzymatic hydrolysis rate and yield

Abstract

This study investigated the characteristics of cellulose Avicel PH-101 (NPA) and Avicel samples treated by either ball milling (BMA) or ionic liquid 1-ethyl-3-methylimidazolium acetate (ILA), which alter cellulose structural properties specifically and, consequently, affect the enzymatic hydrolysis of these materials differently. All materials were submitted to 48 h hydrolysis using the commercial enzymatic preparations Celluclast 1.5 L and Novozymes N188. For ILA hydrolysis, a high yield of 96.8% was observed, which was related to its high specific surface area, low cellulose crystallinity, and high cellulose II content rather than to the particle size. The hydrolysis yields of BMA and NPA were 74.4% and 41.6%, respectively. BMA crystallinity was higher in comparison to ILA and lower in comparison to NPA, whereas the BMA surface area was lower in comparison to ILA and NPA. X-ray diffraction (XRD) analysis suggested the formation of cellulose II by both pretreatments on Avicel, which was reinforced by the samples’ diffractograms and an additional characterization by XRD/crystallinity index of the partial hydrolyzed BMA insoluble residue. In the presence of amorphous cellulose, cellulose II allomorph presented higher hydrolysis recalcitrance. The set of results showed that crystallinity and surface area provided a straightforward correlation with the hydrolysis rate and yield of Avicel cellulose. In addition, the understanding of the effects that can be caused by pretreatments of cellulosic materials was improved and these findings contribute with the interpretation of the kinetics and yields of enzymatic hydrolysis.