Preparation of Enzymatically Liberated Lignin From Naturally Brown-Rotted Wood

Abstract

Brown rots from various conifer species were sieved (&lt60 mesh) and alcohol and water extracted to yield crude preparations of “naturally enzymatically liberated lignin” (NEL) containing 61.4–91.7Z of Klason plus soluble lignin and 0.5–2.6% ash. The <200 mesh fractions were generally best represented in <60 mesh preparations and contained highest Klason plus soluble lignin percentages (86.6–92.2Z). Carbohydrates varied in these fractions between 3.7 and 8.0% and contained glucose, mannose, galactose, xylose, and arablnose, decreasing generally in that order. Methoxyl contents were lower and oxygen contents higher than in milled wood lignin (MWL) suggesting some oxidative demethylation. Treatment with Cuoxaa increased Klason plus soluble lignin content to 93.0–95.8%, decreased carbohydrates to 1.7–5.0%, increased methoxyl and decreased oxygen contents by removal of a part of cellulose and hemicelluloses and of more degraded lignin fractions. Infrared spectra of the preparations showed a small increase in carboxyls and possibly in phenyl conjugated double bonds and a decrease in aromatic structures, as compared with MWL. In thermo-gravimetric analysis the curves for MWL and Cuoxam treated NEL preparations (CuNEL) were very similar when run in nitrogen. In air, however, MWL lost weight appreciably slower. In differential scanning calorimetry in air and oxygen, MWL exhibited less intensive exotherms below 500°C than NEL and left higher amounts of char. The different behaviour of MWL in thermal analysis in oxidative atmosphere was explained by its lower molecular weight and corresponding low glass transition temperature (Tg). It was concluded that preparation of enzymatically liberated lignin from natural brown rot represents a convenient procedure where larger amounts of lignin are required; such lignins are somewhat more degraded than MWL in terms of functional groups present, but are possibly closer to protolignin in terms of molecular weight.