Influence of fungal enzyme pre-treatment on totally chlorine-free (TCF) bleaching of dimethyl formamide bagasse pulp

A study was carried out on totally chlorine-free (TCF) bleachability of dimethyl formamide (DMF) treated bagasse pulps exposed to CZ-3 and FP 90031-sp strains of white-rot fungus Ceriporiopsis subvermispora. This process involved a bleaching sequence consisting of oxygen and peroxide treatment stages. The effect of enzymatic stage on bleachability properties was studied and compared with control pulps, processed without enzyme addition. A final brightness of 79-80% International Standard Organization of brightness (ISO) was achieved after complete bleaching. The effects of direct bleaching caused pulp brightening (1.7-1.3% ISO) and delignification (>10%) immediately after the enzymatic stage. Under a peroxide charge of 3% to 9%, the improvements in brightness and the bleachability of these pulps were found to be superior to those of the control during all peroxide stages. The selective bleaching of each process was assessed by changes of intrinsic viscosity. Generally higher bleachability and bleaching selectivity of xylanase-treated pulps and the inevitable maximal gain in pulp brightness (or bleach boosting, as a main objective of xylanase application) were only achieved after the first and second peroxide bleaching stages. These substantially diminished by the end of the sequence.