Lipase Treatment for Pitch Control in Recycled Pulps: Application in a Duplex Board Mill

Abstract

This study evaluated whether lipase enzymes could control pitch contamination in recycled pulps from a duplex board mill. The pitch contents of four recycled pulp types—old magazine paper (OMG), old book paper (OB), old newspaper (ONP), and old corrugated containers (OCC)—were analyzed using Sudan IV staining and image analysis of handsheets. The reaction times of lipase at varying dosages on pitch were monitored up to one hour under controlled conditions. The pitch contents, quantified in terms of total stained area and pitch-particle count, were substantially higher in OB and OCC than in ONP and OMG, with the latter showing the lowest contamination level. Lipase activity was most effective within the first 30 min. Thereafter, the pitch area reduction plateaued, and the larger aggregates fragmented, slightly increasing the particle count. It was inferred that a 30-min treatment time optimally balances efficiency and cost. Lipase treatment effectively reduced the pitch contents in both OMG and OCC pulps but was less efficient in OMG. The enzyme activity was apparently inhibited by the ink-derived compounds in OMG but was enhanced by the many lipase-accessible lipids in OCC, enabling a stronger, dose-dependent response. Lipase emerged as a promising biotechnological solution to pitch control in a duplex board mill.