Methods to increase the energy density of biofuel feedstock for shipment are important towards improving supply chain efficiency in upstream processes. Towards this end, densified pretreated lignocellulosic biomass was produced using hot-pressing. The effects of fiber hornification induced by hot-pressing on enzymatic digestibilities of lodgepole pine and poplar NE222 wood chips pretreated by sulfite pretreatment to overcome recalcitrance of lignocelluloses (SPORL) were examined. Pretreated wood chips were pressed at 25, 70, 90, 110, and 177°C. The cellulose accessibilities of the pressed and unpressed substrates were evaluated using water retention value and direct cellulase adsorption measurements. Hot-pressing below 110°C produced a degree of hornification (DH) below 0.26 and had limited effect on cellulose accessibility and enzymatic digestibility. Hot-pressing at 177°C produced a DH of 0.86 that substantially hornified the fibers and resulted near zero saccharification. The saccharification results were consistent with cellulose accessibility data. Ethanol fermentation studies at 18 % solids suggest that a pressing below 110°C is preferred to reduce its effect on biofuel yield.

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