Comparison of acid sulfite (AS)- and prehydrolysis kraft (PHK)-based dissolving pulps

The processability and quality of viscose are mainly influenced by the properties of dissolving pulps. Acid sulfite (AS) and prehydrolysis kraft (PHK) are the main commercial processes for the production of dissolving pulps. In this paper, the properties of dissolving pulps obtained from the AS and PHK processes, with respect to purity, molecular weight distribution (MWD), porosity, surface area, accessibility and reactivity, were comparatively evaluated. The results indicated that the PHK pulps had higher α-cellulose, lower S₁₀/S₁₈ content, and narrower MWD than the AS pulps, which can be ascribed to the different reaction mechanisms in the acid and alkaline pulping processes. The traditional parameters (S₁₀/S₁₈, α-cellulose and intrinsic viscosity) were insufficient to evaluate the pulp quality when comparing with dissolving pulps from different pulping processes. The Fock reactivity and the Chinese filterability tests were applied to evaluate their end-use properties in the rayon production process. The AS pulps had better accessibility than the PHK pulps (larger pore size and volume and thinner primary wall), supporting the conclusion that the AS samples exhibited higher reactivity that the PHK samples. The results from the Fock reactivity and Chinese filterability corresponded well.