Development of dissolving pulp from Phyllostachys pubescens stem by prehydrolysis soda cooking with 2-methylanthraquinone

Abstract

Moso bamboo (Phyllostachys pubescens) is a non-wood and non-edible biorefinery resource and is extremely important for the development of dissolving pulp as a material of regenerated cellulose fiber. However, the bamboo contains a high amount of xylan compared to hardwoods. This study aimed at finding suitable conditions for producing dissolving pulp of good quality from the moso bamboo stem using a combination of prehydrolysis non-sulfur alkali cooking and elemental chlorine-free bleaching, and separating a lignin product from the black liquor in the cooking process. Prehydrolysis at 150 °C for 7 h using soda cooking at 160 °C for 3 h with 28% active alkali and 0.06% 2-methylanthraquinone was found to give a good outcome. The xylan content of the pulp was reduced to 4.0%, and further treatment of cold caustic extraction to remove xylan was not required for producing dissolving pulp of good quality, although the pulp yield was approximately 30%. The pulp was then bleached to obtain a dissolving pulp with α-cellulose content of 95.0%, brightness of 89.9%, and viscosity of 8.8 mPa·s. Lignin dissolved in the soda cooking black liquor was easily precipitated by CO2 when employed with 35% of solid concentration and provided a yield of 42%. The precipitation by CO2 followed by purification at pH 2.9 provided a lignin product with weight-average molecular weight, polydispersity, and ash content of 1566, 2.62, and 0.6%, respectively.