Characterization of autohydrolysis aspen ( P . tremuloides ) lignins. Part 2. Alkaline nitrobenzene oxidation studies of extracted autohydrolysis lignin

Abstract

Alkaline nitrobenzene oxidation of the lignins extracted from extractive-free aspen wood meal after autohydrolysis at 195 °C for periods varying from 5 min to 2 h indicated that these lignins were structurally more condensed in terms of an increase in new carbon–carbon bonds than aspen milled wood lignin. The degree of condensation generally increased with longer autohydrolysis times. It is postulated that condensation involved materials from both the carbohydrate and lignin components of the wood which were generated during the autohydrolysis. The molar ratio of syringaldehyde to vanillin of extracted lignin on oxidation was observed to decrease with increasing autohydrolysis time. It is suggested that syringyl units are preferentially extracted as low molecular weight material.