Improvement in pulp quality and effluent properties using methanol as carbohydrate protector during ozone bleaching of wheat straw pulp

The effects of using methanol as a radical scavenger during ozone treatment on delignification efficiency (DE), bleaching efficiency (BE), selectivity, loss of pulp fractions, metal ions, hexenuronic acid (HexA) content, physical strength, morphological properties of wheat straw pulp and effluent properties were studied. The aim of the study was to protect cellulosic pulp fibres from excessive degradation with improved brightness and delignification. Using methanol during ozone treatment improved the DE by 9.5%, the BE by 12.8% and most importantly the selectivity by 32.4% compared to those of the control. Removal of 46% of the hexenuronic acid content in pulp during elemental chlorine free bleaching followed by 41% during ozone treatment and only 9% in the oxygen delignification stage occurred. Use of methanol during ozone treatment improved bleached pulp viscosity by 5.2%, and reduced pulp shrinkage by 2.6% compared to the control pulp. The morphological and physical strength properties of the pulp were comparable with the control pulp.