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

• LVAQPO provided interesting dissolving pulp characteristics with high Fock reactivity.
• XRD showed no variation of pulp crystallinity along the biobleaching treatments.
• Fibre surface degradation caused by H2O2 was reduced with a previous L-VA treatment.
• LVAQPO presented better surface characteristics than a conventional treatment (PO).
• TGA confirmed no grafting reactions with presence of natural mediators, SA and pCA.

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.