Anthraquinone polymer catalysts for alkaline delignification of lignocellulosic matter. Part 2. Action in soda pulping conditions on softwood and phenolic beta-O-4 lignin models

Two hydrophobic and one hydrophilic anthraquinone (AQ) polystyrene catalysts were tested under soda pulping conditions on thermomechanical fibers, and the results were evaluated based on commercial AQ. Hydrophobic and hydrophilic polymers had efficiency gains of 23%–28% and 57%, respectively, compared to AQ (100% efficiency). Hydrosolubility of AQ polymers played a major role in delignification efficiency, a property that allows a better contact with lignocellulosic fibers. Hydrophobic copolymers were stable under pulping conditions and preserved their catalytic effect entirely by contrast to the hydrophilic AQ, as demonstrated by recovery yields after pulping and catalytic action of the recovered copolymers. Studies on lignin models confirmed that the hydrophilic AQ polystyrene is a better catalyst under soda pulping conditions than the hydrophobic ones. It was demonstrated that AQ polystyrene polymers react with lignin models by electron transfer mechanisms.