Application of amylases for the improvement of water drainage from recycled pulp fibre

[摘要] English: The use of recycled fibre to produce paper is increasing due to improved processes and consumer pressure. However, recycled fibre has slow drainage rates because of fines and residual starch. Slow drainage reduces machine speed, production rate, energy demands of the drying section and water consumption. Amylases have been used previously on mill scale to degrade residual starch in paper and improve drainage.This study evaluated commercial amylases to degrade starch and improve drainage. The enzymes BAN 480L, Duramyl 300L, Fungamyl 800L, Termamyl 120L and AMG 300L were used to treat recycled pulp and the influence of pH, temperature and shear forces was tested on the enzymes. BAN 480L and Duramyl 300L displayed activity over a wide temperature range, while Duramyl 300L had activity over a wide pH range. Termamyl 120L, BAN 480L, Duramyl 300L and Fungamyl 800L showed good tolerance to shear forces.The influence of BAN 480L, Duramyl 300L and Fungamyl 800L was tested on strength properties of pulp. Enzymatic treatment had no negative effect on Bursting Index, Tearing Index, Air Permeance and Handsheets Drainage Time. In some cases, strength properties improved. Laboratory-scale drainage evaluation (Canadian Standard Freeness, Drainage Time, Vacuum Drainage Time and the Water Retention Value) showed no significant improvements despite reduction of starch content.Pilot trials were conducted with different pulp grades and at different consistencies. Paper and backwater samples were evaluated for changes in moisture, starch content and Chemical Oxygen Demand (COD). The COD levels of backwater did not increase after enzymatic treatment. The reductions in starch and moisture content of paper indicated that amylases could improve papermaking, but that mill-scale trials were required to quantify possible benefits.Duramyl 300L was applied in a mill trial to treat K4 pulp for production of 195 Flute. Temperature, pH, starch, COD, Total Dissolved Solids (TDS), and moisture were measured at different sampling points. The machine speed, steam consumption, moisture and strength properties of the product were also recorded. Secondary starch degradation of 66 % was achieved and moisture of the trim and jumbo roll was reduced. Machine speed and steam consumption did not improve and no significant influence on strength properties was found. The backwater COD and TDS increased, but were still within control limits. Longer trials should be conducted in future to focus on optimisation of enzyme dosages and production of other fluting grades. The impact of the enzymatic treatment on effluent quality and microbial fouling should also be investigated.

[发布机构] University of the Free State