MIRANDA G. S. CHUA and MORRIS WAYMAN. Can. J. Chem. 57, 1141Chem. 57, (1979. Extractive-free aspen wood meal was subjected to autohydrolysis at 195'C for 5 min to 2 h, and the lignin extracted with 90% dioxane. Extracted autohydrolysis lignin was found to be higher in carbon but lower in hydrogen and oxygen content than aspen milled wood lignin. The methoxyl content was also lower than the reference lignin. These differences have been 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 molecular weight distribution studies the ratio of high molecular weight to low molecular weight 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 has been proposed. p-Hydroxybenzoic acid is postulated as contributing to the extractability of aspen lignin by acting as a blocking agent.MIRANDA G. S. CHUA et MORRIS WAYMAN. Can. J. Chem.,57, 1141Chem.,57, (1979. On a soumis de la sciure de bois de tremble (ne contenant plus de produits pouvant dtre extraits) a une autohydrolyse k 195'C pour des temps allant de 5 min k 2 h puis on en a extrait la lignine par du dioxanne a 90%. On a trouvk que la lignine extraite de l'autohydrolyse contient plus de carbone et moins d'hydrogkne et d'oxygene que la lignine provenant de bois de tremble broy6. La quantitk de methoxyle qui y est contenue est aussi plus faible que celle contenue dans la lignine de rkfkrence. On a attribuk ces diffkrences k la condensation et k I'incorporation dans la lignine de composants qui ne sont pas des lignines. On a dktermink une courbe permettant d'kvaluer la facilitk d'extraction de la lignine; elle prksente un maximum de dklignification a des temps d'autohydrolyse de 30 ti 40 min. En se basant sur des Btudes de distribution de masses moleculaires, on a determine que le rapport des produits de masses molkculaires klevBes/produits de masses molkculaires plus faibles varie suivant les diffkrentes lignines extraites et qu'il atteint un maximum k un temps d'autohydrolyse de 40 min. On propose un mkcanisme de dkpolymkrisation/repolymkrisation de la lignine par l'intermkdiaire de carbocations. On croit que I'acide p-hydroxybenzoi'que facilite l'extraction de la lignine de tremble en agissant cornrne agent bloqueur.[Traduit par le journal]

Infrared and ultraviolet studies 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 functionally modified and different from aspen milled wood lignin. The extracted lignins changed from a guaiacyl–syringyl type lignin to a syringyl-deficient type lignin with increasing autohydrolysis time. Extracted lignins were also observed to contain unconjugated β-ketone groups and conjugated carboxylic acid groups. It is proposed that the unconjugated β-ketone groups resulted from the depolymerization reactions of the lignin macromolecule under acidic conditions which formed monomeric, dimeric, and oligomeric/polymeric lignin fragments with Hibbert's ketone side chains. The conjugated carboxylic acid group observed to be present was attributed to p-hydroxybenzoic acid. p-Hydroxybenzoic acid has been postulated as contributing to the extractability of aspen lignin by acting as a blocking agent in the repolymerization of lignin fragments to form insoluble lignin.

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