Lignin-based catalysts for Chinese fir furfurylation to improve dimensional stability and mechanical properties

In order to valorize lignin from spent liquor of pulping mills, a novel catalyzing system for wood furfurylation which composed of lignin-derived acids (LDAs, i.e. lignosulfonic acid and sulfomethylated lignin acid) and buffer sodium borate was developed, and was applied to Chinese fir furfurylation for improved dimensional stability and mechanical properties. LDAs were prepared by protonating of sulfomethylated lignin and lignosulfonate through cation exchange resin. The catalyzing system was optimized by the storage duration of FA formulas with respective catalyzing system at room temperature and the curing time at elevated temperature. Then, three formulas were selected out to treat Chinese fir and their performance was evaluated by weight percentage gain, dimensional stability, and compressive strength. The results showed that LDAs, especially sulfomethylated lignin acid, penetrated into cell walls and catalyzed furfurylation reaction quite well. The best performance achieved in this study by Formula III was with weight percentage gain of 66.4%, equilibrium moisture content 12.9%, anti-swelling efficiency 61.9% and 70.6% for the conditions of high humidity and water-soaking, respectively; its parallel-to-grain compressive strength was improved by 45.4%. It hints lignin-derived acids combined with borate would be a promising catalyst system for wood furfurylation since it valorizes both the waste lignin and low-valued wood.