An enzyme-catalysed bleaching treatment to meet dissolving pulp characteristics for cellulose derivatives applications

Bleached cellulose with good end-properties (∼90% ISO brightness and 62% cellulose preservation) was obtained by using a totally chlorine-free biobleaching process (TCF). Unbleached sulphite cellulose was treated with Trametes villosa laccase in combination with violuric acid. This enzymatic stage (L) was followed by a chelating stage (Q) and then by a hydrogen peroxide stage reinforced with pressurized oxygen (Po), resulting to an overall LQPo sequence. The use of violuric acid was dictated by the results of a preliminary study, where the bleaching efficiency of various natural (syringaldehyde and p-coumaric acid) and synthetic mediators (violuric acid and 1-hydroxybenzotriazole) were assessed. The outstanding results obtained with laccase-violuric acid system fulfil most of the characteristics of commercial dissolving pulp, totally acceptable for viscose manufacturing or CMC derivatives, with the added advantage that the enzymatic treatment saved 2 h of reaction time and about 70% of hydrogen peroxide consumption, relative to a conventional sequence (Po).