| This study examined the concept on the fractionation of wood polymers in situ as the carboxymethyl derivatives of cellulose (CMC), hemicelluloses (CMH), and lignin (CML). CMC is a water-soluble polymer used extensively as additives in many applications ranging from food to paper industry. The extent of fractionation was evaluated based on the formation of water-soluble materials, which was generally higher for aspen than for spruce wood, i.e., 59 vs. 36% for a typical CM condition. The initial water-soluble materials formed were a mixture of CMH and CMC plus some CML (3-5%) and contained carboxylic groups (3.2 - 3.6 mmol/g), while the water-insoluble residue contained mainly the cellulose and lignin components with a lower carboxylic group content (2.4-2.7 mmol/g). Interestingly, the water-insoluble residue after another CM treatment gave a nearly pure CMC product containing less than 1% of residual lignin. Thus, the bulk of wood lignin was less reactive than the polysaccharide components toward the CM reaction.;A controlled removal of hemicelluloses by either a hot water or dilute acid pre-treatment of wood significantly facilitated the subsequent CM process especially for the cellulose component. However, the reactivity of lignin was also noticeably enhanced in case of the pre-extracted aspen wood sample. This two-stage process does provide the flexibility for converting extracted hemicelluloses to bio-based fuels or other useful materials including biodegradable polymers like polyhydroxyalkanoates.;The nature of lignin in the water-soluble materials derived from the CM of wood was evaluated by ionization difference UV spectra, which displayed the presence of phenolic hydroxyl group (PhOH) for both non-conjugated and conjugated types. A similar observation was observed for the CM of kraft pulps and kraft lignin samples. Thus, the reactivity of PhOH toward CM differs significantly from other etherification reactions. |
