An improved TCF sequence for biobleaching kenaf pulp: Influence of the hexenuronic acid content and the use of xylanase

Enzymatic delignification with laccase from Trametes villosa used in combination with chemical mediators (acetosyringone, acetovanillone and 1-hydroxybenzotriazole) to improve the totally chlorine-free (TCF) bleaching of kenaf pulp was studied. The best final pulp properties were obtained by using an LHBTQPo sequence developed by incorporating a laccase-mediator stage into an industrial bleaching sequence involving chelation and peroxide stages. The new sequence resulted in increased kenaf pulp delignification (90.4%) and brightness (77.2%ISO) relative to a conventional TCF chemical sequence (74.5% delignification and 74.5% brightness). Also, the sequence provided bleached kenaf fibers with high cellulose content (pulp viscosity of 890 g · mL−1 vs 660 g · mL−1). Scanning electron micrographs revealed that xylanase altered fiber surfaces and facilitated reagent access as a result. However, the LHBTX (xylanase) stage removed 21% of hexenuronic acids in kenaf pulp. These recalcitrant compounds spent additional bleaching reagents and affected pulp properties after peroxide stage.