Effects of chlorite delignification on dynamic mechanical performances and dynamic sorption behavior of wood

Chlorite delignification is popular in preparation of advanced functional biomaterials or pulping processes. To get more knowledge about the effects of chlorite delignification on wood, the dynamic mechanical performance and dynamic sorption behavior of Populus euramericana Cv. delignified at three levels were investigated. Results showed that partial delignification whitened wood but did not break the intact integrity. Some mesopores generated, and even cell separation appeared when too severe delignification was applied, indicating the binding functionality of lignin. Delignification increased the overall crystallinity while did not destroy the crystalline structure of cellulose. The crystallinity increase compensated for the stiffness loss for delignification and helped to restrict the molecular mobility at glass transition temperature indicated by dynamic mechanical analyses. Delignified wood presented stronger dynamic vapor sorption, which was further confirmed by increased hydrated moisture and dissolved moisture analyzed by Hailwood-Horrobin theory. The increasing concentration of sorption sites and accommodation for water molecules could account for this sorption increase after delignification. Delignified wood exhibited lower sorption hysteresis primarily for the synergies of acceleration of matrix relaxation and facilitation of molecular chain slippage of hemicelluloses and amorphous cellulose caused by delignification. This study connected wood hierarchical structures with dynamic mechanical and sorption properties for better understanding the behavior of delignified wood and underlying mechanisms. The results can provide basis for wood (or other lignocellulosic biomaterial) modification and advanced biomaterial functionalization based on delignification. Graphic abstract