EFFECTS OF MULTIPLE PULPING VARIABLES ON THE MOLECULAR-WEIGHT AND MOLECULAR-WEIGHT DISTRIBUTION OF KRAFT LIGNIN

The effects of pulping variables on the molecular weight and molecular weight distribution of dissolved lignin have been studied. Kraft lign ins were prepared by cooking Slash pine (Pinus caribaea) wood chips in a pilot-scale batch circulation digester. Four pulping variables, eff ective alkali, sulfidity, cooking temperature, and time-at-temperature , were arranged in a very broad input space under a central composite experimental design, and their effects on the molecular weight of diss olved lignin were examined by means of fifteen-parameter quadratic mod els. It was found that, generally, the molecular weight of dissolved l ignin increases in both bulk and final phases as delignification proce eds. Prolonged cooking at the end of final phase delignification cause s degradation of lignin in the liquor and reduces the molecular weight of Kraft lignin. Discussions of pulping effects on the molecular weig ht of dissolved lignin are presented in detail.