Investigation on the Bleachability of Bio-Kraft Pulp in Environmental Friendly ECF Method

Bio-kraft pulps made from poplar chips pre-treated by Trametes versicolor in 1, 2 and 3 weeks, were bleached in ECF method (DED sequence) for evaluation of their bleachability. In this study, pulps were characterized in lignin content, bleaching yield, Hexenoronic acids (Hex-A), viscosity and efficiency of fungal pre-treatment on chemical consumption before and after each stage of above mentioned sequence. Then laboratory handsheets were made from above bleached pulps and tested in optical properties. Results showed that kappa number was enhanced by increasing in pre-treatment time expect third phase of 3-week pre-treatment samples. It's due to non-selectivity of T. versicolor that caused more degradation of carbohydrates due to acidic groups creation specially Hexenoronic acids. This acidic groups were led to wrong measurement of kappa number as more. By progressing in bleaching from phase 1 to phase 3, bleaching yield was increased except 3-weeks pre-treatment samples. Also, after bleaching, viscosity of pulps was decreased. In total, fungal pre-treatment of poplar wood has been effected on its pulp bleachability that chemicals consumption was decreased in bleaching process and also adsorption values of chemicals of spent liquor that measured by UV-Vis in 257, 280, 289 and 355 respectively for ClO2, soluble lignin, ClO- and ClO2- increased. Paper brightness was increased by decreasing in lignin content during bleaching process.