The Effect of Hot-Water Pre-Extraction on the Properties of Soda-AQ Pulp of Wheat Straw

This research investigated the effect of hot water pre-extraction on the bleaching process and properties of wheat straw soda-AQ pulp. Preextraction experiments were carried out on wheat straw to obtain a weight loss of about 15 percent. Based on preliminary experiments, soda-AQ pulping of non-extracted straw chips was performed at 160 oC for 60 min, whereas the pre-extracted chips were pulped with lower Hfactor at 150 oC for 45 min to obtain the target kappa number of about 15. The pulps were subjected to ECF bleaching sequences, D0ED1, with 8% ClO2 consumption as active chlorine, 75% relative share of total ClO2 at D0 and 25% at D1, and alkaline extraction with 1% NaOH. The results showed that bleaching of hot water pre-extracted pulp is rather difficult due to the lignin condensation. Thereby, under the same bleaching conditions non-extracted pulp had lower kappa number, yellowness, and opacity, as well as higher brightness than pre-treated pulp at all bleaching stages. Furthermore, hot water pre-extracted pulp exhibited inferior strength properties compared to non-extracted pulp, due mostly to the fiber structure deterioration and loss of inter-fiber bonding potential.