Improving the reactivity of kraft-based dissolving pulp for viscose rayon production by mechanical treatments

The capacity of dissolving pulp to react with carbon disulfide under the defined conditions, known as the “Fock reactivity,” is an important parameter in determining the processability, end-product quality, and environmental impact in downstream rayon production. This study was aimed at improving the reactivity of kraft-based dissolving pulp by mechanical treatments, such as grinding and PFI refining, which can induce additional accessible surfaces in the compact cellulose structure via fiber cutting and fibrillation, respectively. Results showed that the Fock reactivity of a kraft-based dissolving pulp was increased from 49.3 to 71.8 % by 6-min grinding treatment under the conditions studied. Such a treatment led to increases in the fines content and specific surface area while decreasing the fiber length, intrinsic viscosity, and the crystalline ratio of cellulose. PFI refining can also result in changes in the fiber morphology and cellulose structure; a 25,000 PFI revolution treatment led to an increase in the Fock reactivity from 49.3 to 58.3 % for the same dissolving pulp.