8-49: Chemical and mechanical increases in fibre swelling to improve the enzymatic hydrolysis of organosolv pretreated softwoods

The organosolv process is one of the few pretreatment options capable of processing recalcitrant biomass, such as softwoods, to generate a cellulosic substrate that is amenable to cellulolytic hydrolysis. However, obtaining complete cellulose conversion at low enzyme loadings (< 5FPU g^-1 cellulose) still remains a challenge. Possible explanations for this resistance to complete and quick hydrolysis include non-productive binding of cellulases to residual lignin and the physical blocking of cellulose by precipitated lignin. Our previous work indicated that, when the chemical composition of organosolv-pretreated substrates generated with various catalysts were relatively similar, fibre porosity and swelling seemed to be controlling factors governing each substrate’s ease of hydrolysis. Therefore, to gain further insight into the potential factors that reduce hydrolysis yields at low enzyme loadings, organosolv pretreated  Lodgepole pine containing moderate amounts of lignin (18%) was subjected to mechanical refining and sulphonation to  try to increase substrate swelling. Despite decreasing particle size, increasing swelling and reducing cellulose crystallinity, refining did not result in significant increases in hydrolysis yields. However, sulphonation resulted in significant increases in hydrolysis yields at both 5 and 2.5 FPU g^-1 cellulose (from 80% to 95% and from 35% to 80% respectively) despite less pronounced effects on fibre swelling.