Biobleaching of Orange Tree Pruning Cellulose Pulp with Xylanase and Laccase Mediator Systems

The biobleachability of soda-anthraquinone pulp from orange tree pruning has been evaluated in this study for the first time. Three different laccase-mediator systems (LMS) have been tested: laccase from Trametes villosa (Tv), either in combination with 1-hydroxybenzotriazole (HBT) or with acetosyringone (AS), and laccase from Myceliophthora thermophila (Mt) in combination with AS. After the LMS treatment (L), a standard bleaching sequence, comprising an alkaline extraction (E) and a hydrogen peroxide stage (P), was carried out, altogether resulting in a LEP sequence. The three LMS improved the bleaching sequence, L-Tv+AS being the LMS that provided the highest delignification and improvement of optical properties. In contrast, no significant variations were observed in the viscosity and mechanical properties of the handsheets. In order to boost the optimal L-Tv+AS sequence, a xylanase pretreatment was performed; however, no improvements in delignification, optical properties or brightness stability were observed compared with the same sequence without xylanase pretreatment.