Acid-catalyzed Kraft lignin liquefaction for producing polyols and polyurethane foams

Abstract

This study investigates the use of acid-catalyzed lignin liquefaction for the production of polyols and polyurethane foams. The liquefaction process was carried out using a kraft lignin powder following a process similar to the Lignoboost® method, based on a previous study, with catalyst (sulfuric acid) weight contents of 0, 3 and 6 wt.% in relation to the lignin. The PU foams were prepared by the free expansion method and analyzed by Fourier transform infrared spectroscopy (FT–IR), thermogravimetry (TG), differential scanning calorimetry (DSC), dynamic-mechanical analysis (DMA), as well as contact angle and apparent density evaluations. The effect of the catalyst concentration on yield, moisture content and molecular weight of the resulting polyols was assessed, and the optimal conditions were obtained for 6 wt.%. FT–IR analysis indicated a suitable foam polymerization. The incorporation of an acid catalyst led to a more hydrophilic foam and a rigid cell structure, with thinner and more uniformly sized cells, as well as higher thermal stability and glass transition temperature.