Fibre size does not appear to influence the ease of enzymatic hydrolysis of organosolv-pretreated softwoods

To determine the effect of fibre size on enzymatic hydrolysis, organosolv-pretreated lodgepole pine was size-fractionated into six substrates ranging in average size from 0.20 to 3.4 mm. Other than the fines fraction (<0.2 mm) which contained most of the lignin, the fractionated substrates were more readily hydrolyzed than the original substrate with nearly complete hydrolysis after 72 h at 5 FPU g−1 cellulose. Surprisingly, fibre size was found to have little influence on enzymatic hydrolysis likely due to similarities in the substrates’ chemical composition, accessible surface area, cellulose crystallinity and degree of polymerization. To determine the influence of the fines on enzymatic hydrolysis, their content was artificially increased (from 8.9% to 55.4%) however; this did not have a noticeable effect. These results show that within the range of fibre sizes tested, other substrate characteristics likely play a more significant role in the ease of hydrolysis of pretreated substrates.