Mechanical deconstruction of lignocellulose cell walls and their enzymatic saccharification

Abstract

Laboratory mechanical softwood pulps (MSP) and commercial bleached softwood kraft pulps (BSKP) were mechanically fibrillated by stone grind- ing with a SuperMassColloider. The extent of fibril- lation was evaluated by SEM imaging, water retention value (WRV) and cellulase adsorption. Both lignin content and mechanical treatment significantly affected deconstruction and enzymatic saccharifica- tion of fibrillated MSP and BSKP. Fibrillation of MSP and BSKP cell walls occurs rapidly and then levels off; further fibrillation has only limited effect on cell wall breakdown as measured by water retention value and cellulase adsorption. Complete (100 %) saccharifica- tion can be achieved at cellulase loading of 5 FPU/g glucan for BSKP after only 15 min fibrillation with energy input of 0.69 MJ/kg. However, the presence of lignin in MSP affects the extent of fibrillation produc- ing fibrils mainly above 1 lm. Lignin binds nonpro- ductively to cellulases and blocks cellulose thereby reducing its accessibility. As a result, the cellulose saccharification efficiency of MSP fibrils (6 h of fibrillation, energy input of 13.33 MJ/kg) was only 55 % at same cellulase loading of 5 FPU/g glucan.