Reductive Modification of Alkaline Pulping of Southern Pine, Integrated with Hydrothermal Pre-extraction of Hemicelluloses

This study was to investigate the effect of modification of the kraft cooking process integrated with hemicellulose pre-extraction on the properties of pulp produced from softwood chips. Lob lolly pine wood chips were extracted with pressurized hot water at an elevated temperature and then subjected to conventional and modified kraft pulping. A reductive pretreatment using sodium borohydride (SBH) in a mild alkaline sodium sulfide solution was adopted for a modification of kraft pulping preceded by water extraction. The presence of SBH in pretreatment caused a pronounced increase in pulp yield of the water pre-extracted kraft pulps. This reductive modification strategy for water-extracted kraft pulping was evaluated in two different ways including double extraction (SBH-alkaline extraction preceded by water extraction) followed by AQ-kraft pulping (DE-AQKP) and water extraction followed by pretreated AQ-kraft pulping (WE-SB-AQKP). The DE-AQKP using 1% SBH showed the same pulp yield as normal kraft cooking at 12% water-extraction weight loss along with approximately 3% of additional sugar extracts from the second extraction stream. In the case of WE-SB-AQKP with 1% SBFI, the same yield as the kraft control was achieved around 14% water-extraction weight loss. The SBH demand for zero-yield-loss in pretreatment was in proportion to water-extraction weight loss in kraft pulping preceded by water extraction. Pulps from the modified processes showed faster PFI mill refining responses than the corresponding kraft pulps. No significant changes in paper strength properties were observed in handsheets prepared from the modified kraft pulping preceded by water extraction except for some reductions in tear strength.