The impact of ionic liquid pretreatment on the chemistry and enzymatic digestibility of Pinus radiata compression wood

Abstract

Compression wood represents a unique challenge for biochemical processing of softwoods to biofuels and chemicals on account of its high lignin and galactan, and low glucan contents. Here we report the impact of ionic liquid pretreatment on the chemistry and enzymatic digestibility of Pinus radiata compression wood and opposite wood. Samples were pretreated using 1-ethyl-3-methylimidazolium acetate at 120 °C and 155 °C for 3 h. Hemicelluloses were preferentially extracted during the pretreatment and the recovered biomass was enriched in cellulose and lignin. The pretreatment caused structural modifications to the lignin and polysaccharides that included loss of ether linkages and formation of condensed structures in the lignin, reduced cellulose crystallinity and possible depolymerisation of polysaccharide chains. The enzymatic digestibility of the cellulose was significantly enhanced in both wood types after pretreatment. Approximately 90% of the glucan was converted to glucose after enzyme treatment for 24 h following pretreatment at 120 °C compared to only 3–8% in untreated samples. Because the ionic liquid pretreatment was equally effective on both compression wood and opposite wood the outcome of the saccharification was largely determined by the original chemical composition of the two wood types.