Swelling of Recycled Wood Pulp Fibers: Effect on Hydroxyl Availability and Surface Chemistry (2)
Publication Name: Wood and Fiber Science
The objective of this research was to examine how swelling treatments affect the hydroxyl availability and surface chemistry of recycled fibers. It also assessed the use of organic liquids in mitigating fiber hornification, the loss of hydrogen-bonding ability in recycled fibers. Hardwood bleached kraft pulp fibers were recycled, swollen, and subsequently analyzed for water retention value (WRV), dynamic contact angle, and hydroxyl number. Results show that the relative swelling powers of the liquids were: 12% NaOH > formamide > dimethyl sulfoxide = 2% NaOH = ethylene glycol. These liquids resulted in WRVs that were 23-72% higher than the control, i.e. the water-swollen recycled fibers (WRV 1.10). Swelling increased the hydroxyl number of the 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 water contact angle. By swelling the fibers in organic liquids, polar surface-free energy increased with an increase in hydroxyl numbers. Such a relationship was obscured for the alkaline treatments, which presumably altered the chemical composition of the fibers. These findings promote understanding for a more effective formulation of treatment methods for recycled fibers. An immediate implication from this study is the strong fiber swelling power of formamide whose concentration and cost efficiency should be optimized in future studies.