Characterization of autohydrolysis aspen (P. tremuloides) lignins. Part 1. Composition and molecular weight distribution of extracted autohydrolysis lignin

Abstract

Extractive-free aspen [Populus tremuloides] wood meal was subjected to autohydrolysis at 195.degree. C for 5 min to 2 h, and the lignin extracted with 90% dioxane. Extracted autohydrolysis lignin was higher in C but lower in H and O content than aspen milled wood lignin. The methoxyl content was also lower than the reference lignin. These differences were attributed to condensation and incorporation into the lignin of non-lignin components. A lignin extractability curve with a maximum delignification at autohydrolysis time of 30-40 min was found. From MW distribution studies the ratio of high MW to low MW materials varied for the different extracted lignins and reached a maximum at autohydrolysis time of 40 min. A mechanism of depolymerization/repolymerization of the lignin via carbonium ions was proposed. p-Hydroxybenzoic acid is postulated as contributing to the extractability of aspen lignin by acting as a blocking agent.