The mechanism of fiber cutting during enzymatic hydrolysis of wood biomass

The relationship between fiber dislocations and fiber cutting during the enzymatic hydrolysis of lignin-free fibers was investigated. Dislocations are morphological changes in the microfibril direction of cellulose. It was hypothesized that enzymatic activity is concentrated at dislocation sites, resulting in fiber cutting. Bleached softwood kraft pulp was analyzed during enzymatic hydrolysis (Novozynme 188 and Celluclast 1.5L) to confirm fiber cutting and explore its relationship with dislocation sites via microscopy, fiber length, and sugar determination. Results reveal that fibers were quickly cut through during enzymatic hydrolysis, resulting in shorter fiber fragments during the initial 60% of hydrolysis. Polarized light microscopy images show a relationship between dislocations and fiber cutting during enzymatic hydrolysis. Images show fibers partially cut at dislocation sites, and that there are no dislocations on cut fibers after 6 h hydrolysis. PLM and FQA data revealed that there were about seven major dislocations per fiber and each fiber was cut through about 6, and 10 times after 4 and 6 h of enzymatic hydrolysis, respectively. In combination, this data strongly implicates dislocation sites as the location of fiber cutting.