Effect of pulp prehydrolysis conditions on dissolution and regenerated cellulose pore structure

When producing regenerated cellulose materials, e.g., fibers and films, pulp fibers are first dissolved in a solvent and then regenerated in an antisolvent. The pulp properties have a significant impact on the dissolution. This study examines the effect of pulp prehydrolysis conditions on pulp structure, subsequent dissolution in cold aqueous NaOH/ZnO solvent, and regenerated cellulose film properties. The fiber and regenerated cellulose swelling and pore structure is addressed. Once-dried kraft pulp was activated in acid hydrolysis at two temperatures, 60 and 80 °C. The hydrolysis primarily affected the cellulose degree of polymerization (DP), and its reduction dramatically improved the pulp dissolution. Surprisingly, higher hydrolysis temperature did not increase the fiber hornification. DP reduction marginally effected the pulp swelling properties but had a significant effect on the regenerated film swelling. The regenerated films contained cellulose II, and their wet porosity correlated inversely with the DP. Low hydrolysis temperature films remained more porous after critical point drying.