Swelling of recycled wood pulp fibers: Effect on hydroxyl availability andsurface chemistry

The objective of this research was to examine how swelling treatments affec t the hydroxyl availability and surface chemistry of recycled fibers. It al so assessed the use of organic liquids in mitigating fiber hornification, t he loss of hydrogen-bonding ability in recycled fibers. Hardwood bleached k raft pulp fibers were recycled, swollen, and subsequently analyzed for wate r retention value (WRV), dynamic contact angle, and hydroxyl number. Result s show that the relative swelling powers of the liquids were: 12% NaOH > fo rmamide > dimethyl sulfoxide = 2% NaOH = ethylene glycol. These liquids res ulted in WRVs that were 23-72% higher than the control, i.e. the water-swol len recycled fibers (WRV 1.10). Swelling increased the hydroxyl number of t he fibers except for those treated with 12% NaOH. Fibers that were swollen to a greater extent had a higher total surface-free energy and a lower wate r contact angle. By swelling the fibers in organic liquids, polar surface-f ree energy increased with an increase in hydroxyl numbers. Such a relations hip was obscured for the alkaline treatments, which presumably altered the chemical composition of the fibers. These findings promote understanding fo r a more effective formulation of treatment methods for recycled fibers. An immediate implication from this study is the strong fiber swelling power o f formamide whose concentration and cost efficiency should be optimized in future studies.