performance of pectinase on improving the properties of onp deinked pulp by washing method

in this research, the effect of different concentrations of pectinase has been investigated on deinking of old newspaper (onp). onp re-pulped at 5% consistency for 10 min in disintegrator (with 2650 rpm). enzymatic treatment of recycled onp pulp was done under constant conditions (10% consistency, duration time of 20 min, ph range of 4.5-5) at different pectinase concentrations (0.05, 0.1, 0.2, 0.3 and 0.5% based on oven-dry weight of waste paper). the optical and physical properties of the standard paper (60 g/m2) made from treated pulps with different concentrations of pectinase were evaluated in comparison with paper produced from control pulp (untreated onp pulp by pectinase). the results showed that using pectinase in deinking of onp led to a slight increase in the brightness and the yellowness and decrease the opacity. the brightness was improved to 43.83 iso% (about one percent increase), but the yellowness decreased to 18.61 iso% (about 3.5 percent) with increase in pectinase dosage from 0.05% to 0.2%. the brightness reduced and the yellowness increased at higher concentrations than 0.3% pectinase. the highest opacity (99.49 iso%) was achieved using 0.5% pectinase. the results of physical properties showed that, paper air resistance and density improved with increase in pectinase dosage. also treatment of pulp with 0.3% pectinase has been resulted in the papers with higher burst and tear indices compared to control pulp.