Integration of hemicellulose pre-extraction in the bleach-grade pulp production process

Abstract

Loblolly pine woodchips were first pre-extracted with 6 wt% (percent on original nonextracted o.d. wood weight) sodium hydroxide at room temperature overnight, then treated at 90°C for 90 min, following another 4 h extraction with the addition of 5 wt% boric acid to partially remove hemicellulose. During the subsequent bleach-grade kraft pulping process, the cooking intensity was alleviated, either by decreasing the cooking time (reduced H-factor by 35%) or decreasing the chemical charge by 30%, with the objective of obtaining similar pulp quality as the control cook. After elemental chlorine free bleaching and PFI refining, the results indicated that the pre-extracted pulp could maintain equal or similar brightness and physical strength as the control pulp through this optimization of the pulping process.