Effect of Mixed Hardwood Chips Thickness on Unbleached and Bleached Pulp Quality

Abstract

This paper describes the effect of chips thickness on pulping process and unbleached and bleached pulp quality including pulp yield. Mill chipped mixed hardwood chips were manually classified based on their thickness in three segments thinner chips, intermediate chips and thicker chips with an average thickness of 3.5 mm, 5.0 mm and 7.0 mm, respectively. The response of these manually classified chips during kraft pulping and subsequent ECF bleaching was compared with that of mixed control chips. Thinner chips required less cooking chemical as well as time compared to control and thicker chips to get unbleached pulp having similar kappa number. Reject content of the unbleached pulp was in the order thinner chips (0.1%) < intermediate chips (1.1%), < control chips (1.7%) < thicker chips (2.6%). Screened pulp yield of 49.2% was the highest for intermediate chips (followed by 48.8% for thinner chips and 46.8% for thicker chips. Results showed that higher kappa pulp can also be produced with less reject content from thinner chips. Bleached pulp of superior viscosity and physical strength properties was produced from intermediate chips compared to thicker and control chips.