Effect of endoglucanases and hemicellulases in magnetic and flotation deinking of xerographic and laser-printed papers

Abstract

Laser-printed paper was treated individually and with combinations of purified endoglucanases from Gloeophyllum sepiarium (EGS) and Gloeophyllum trabeum (EGT), a xylanase from Thermomyces lanuginosus (X) and a mannanase from Sclerotium rolfsii (M). Subsequent toner removal efficiency after enzymatic and both magnetic or flotation deinking treatment was assessed by image analysis. The enzyme effect was more pronounced in magnetic deinking, demonstrating 94% removal of toner using a combination of EGS and X. The use of the pure EGT and EGS suggests that endoglucanases are responsible for most of the success in deinking. Compared to flotation deinking (89%), a higher yield of fibres (97.2%) was attained with this new combined enzymatic–magnetic technique, which consequently uses only tap water and no chemicals. While all enzyme applications increased freeness and slightly reduced intrinsic fibre strength, the resultant handsheets strength was maintained or marginally improved. The nature of the individual endoglucanase seems to play an important role since different deinking efficiencies and strength properties were measured with EGS and EGT, which are closely related enzymes in terms of molecular properties and specificities on model substrates.