Preparation of high-grade dissolving pulp from radiata pine

High-grade dissolving pulp was prepared from radiata pine by the pre-hydrolysis Kraft process. The effect of the P-factor in the pre-hydrolysis stage on the properties of wood chips was investigated. With an increasing P-factor, hemicellulose was selectively removed from wood chips, and the crystallized index of the pre-hydrolyzed wood chips increased owing to the dissolution of the amorphous phase in the substrates. Further, sugars in hemicellulose could be rapidly hydrolyzed; whereas, their release became slower with a further increase in the P-factor. Comparatively, arabinose and galactose were readily removed during pre-hydrolysis for its accessibility. Additionally, accumulations of furfural and 5-hydroxymethylfurfural (HMF) were detected via acid-catalyzed dehydration of pentose and hexose, respectively. HMF can be further converted into formic and levulinic acid by acid-catalyzed dehydration. After pre-hydrolysis, the chips were subjected to Kraft cooking, and the optimal P-factor (480) for the production of dissolving pulp and the optimal H-factor (1500) in terms of the Kappa number, viscosity, and alpha-cellulose of the pulp were obtained. Then, the Kraft pulp was bleached using the (OO) D0EOPD1D2 sequence, and a final ISO brightness of 91.0% was achieved with negligible loss in alpha-cellulose. The described technique and parameters are important for the industrial production of high-grade dissolving pulp using radiata pine.