Studying the effects of laccase treatment in a softwood dissolving pulp: cellulose reactivity and crystallinity.

An enzymatic biobleaching sequence (LVAQPO) using a laccase from Trametes villosa in combination with violuric acid (VA) and then followed by a pressurized hydrogen peroxide treatment (PO) was developed and found to give high bleaching properties and meet dissolving pulp requirements: high brightness, low content of hemicellulose, satisfactory pulp reactivity, no significant cellulose degradation manifested by α-cellulose and HPLC, and brightness stability against moist heat ageing. The incorporation of a laccase-mediator system (LMS) to bleach sulphite pulps can be a good alternative to traditional bleaching processes since thermogravimetric analysis (TGA) showed that the laccase treatment prevented the adverse effect of hydrogen peroxide on fibre surface as observed during a conventional hydrogen peroxide bleaching treatment (PO). Although VA exhibited the best results in terms of bleaching properties, the performance of natural mediators, such as p-coumaric acid and syringaldehyde, was discussed in relation to changes in cellulose surface detected by TGA.

Investigating the structure-effect relationships of various natural phenols used as laccase mediators in the biobleaching of kenaf and sisal pulps.

Nine phenol derivatives, p-coumaric acid (PC), vanillin (V), acetovanillone (AV), acetosyringone (AS), syringaldehyde (SA), coniferaldehyde (CLD), ferulic acid (FRC), sinapic acid (SNC), and sinapyl aldehyde (SLD) were assayed as laccase redox mediators in the biobleaching of kenaf and sisal pulps. As a general behaviour, the phenolic mediators increased the kappa number (KN) and reduced the brightness of pulps. In particular, these changes were found to depend in a linear manner on the energy of the highest occupied molecular orbital (E(HOMO)) of the mediators.