The effect of enzymatic pre-treatment with amylase and refining on the physical and dewatering properties of OCC pulp

In the current research, enzymatic modification of OCC pulp with Bacillus sp. amylase was evaluated. Amylase was added at different levels of 0.5, 0.1, 0.2 and 0.3% (based on oven-dried weight of recycled paper) to OCC pulp under constant conditions included consistency of 10%, temperature of 50°C, time duration of 1 hour, and at a pH range of 6.9-7. To neutralize the residual enzyme, hydrogen peroxide 0.05% (based on oven-dried weight of pulp) was applied. The refining of pre-treated OCC pulp with different levels of amylase was done at the constant revolution of 2000. The dewatering and physical properties of amylase pre-treated OCC pulps as compared to control pulp (non-treated pulp with enzyme) for two refined and unrefined conditions were evaluated. Obtained results showed that amylase pre-treatment improved pulp freeness by 11-22% compared with the control sample. The highest freeness (600 ml, CSF) was achieved with 0.2% amylase. Refining of both amylase pre-treated OCC pulp and the control sample reduced the pulp freeness, but dewatering capability increased with an increase in amylase usage. The use of Amylase resulted in a paper with slightly higher caliper, higher bulk, but similar air resistance, compared with control run. An increase in amylase usage from 0.5% to 0.3% along with refining decreased caliper and bulk and increased air resistance of paper. Also, the results of the evaluation of different times of amylase treatment of unrefined OCC pulp (at a constant concentration of 0.1%) on a caliper, bulk as well as air resistance indicated that the duration of 90 minutes was the optimal time. In general, the combined treatment of amylase (0.05-0.1%) and PFI refining (at the constant revolution of 2000) indicated the pulps with better quality in terms of dewatering and physical characteristics in comparison with control OCC pulp.