Bleached dissolving pulps applying laccase treatments

Abstract

A biobleaching sequence, using a laccase enzyme (Trametes Villosa) in combination with different mediators, was applied to softwood dissolving cellulose in order to study its bleaching efficiency and its potential in terms of kappa number, ISO brightness and viscosity. The tested mediators were classified as synthetic compounds such as HBT (1-hydroxybenzotriazole) and VA (violuric acid), and as natural compounds such as SA (syringaldehyde) and pCA (p-coumaric acid). The influence of the enzymatic stage in the bleaching sequence was compared with a control treatment and also with a conventional alkaline hydrogen peroxide stage. The contribution of L (laccasemediator) stage on the effluent properties is important for evaluating and minimizing its environmental impact. Therefore, effluent properties (COD, colour, residual enzyme activity and toxicity) were determined. Laccase-VA system showed the most promising results in reducing kappa number and increasing brightness without detriment to viscosity