The effects of treatment with the white-rot fungus Trametes versicolor andlaccase enzymes on the brightness of Douglas-fir heartwood derived thermomechanical pulps

Douglas-fir is a significant west coast tree species that cannot be used as a furnish in the high yield thermomechanical pulping process (TMP) because of the low brightness caused by the high chromophoric extractive content i n its heartwood. Trametes versicolor and laccase enzymes were assessed for their potential to improve the brightness of Douglas-fir heartwood derived TMP. Treatments with T. versicolor were relatively unsuccessful. Although t he application of laccase without a mediator decreased the unbleached brigh tness of heartwood pulps from 40.1 to 34.1 % ISO, after bleaching with H2O2 , it was found that the laccase treatment increased the bleached brightness from 58 to 61 % ISO. Biological treatments were performed alone and in com bination with methanol and alkaline extraction. When pulps were extracted w ith methanol prior to treatment with laccase and the mediator HBT, the hydr ogen peroxide bleached brightness increased from 63 to 64.5 % ISO compared to the non-laccase treated, methanol extracted controls.