BLEACHING ALKALINE PULPS FROM PINUS RADIATA

Oxygen-delignified kraft, kraft-anthraquinone (kraft-AQ), and soda-AQ pulps from Pinus radiata D. Don were bleached with oxygen-based and chlorine-based treatments. Oxygen-based bleaching employed ozone (Z), alkali extraction (E), and peroxide (P) treatments in previously optimised ZEP and ZPZP sequences. Chlorine-based bleaching was with a conventional sequence. Comparative information was gathered on the effects of bleaching on pulp yield, viscosity, beating requirements, handsheet strengths, and brightness stability. In general, the responses of the three alkaline pulps were similar for each bleach sequence though bleached soda-AQ pulps had slightly lower brightnesses. The yield advantages of AQ-additive pulping were preserved after full bleaching. Except for lower chemical demands with ZPZP bleaching, no noticeable differences were found between the effects of ZEP and ZPZP bleaching. Both sequences reduced pulp viscosity, pulp beating requirements, and handsheet tear and burst properties. In comparison, chlorine bleaching resulted in higher pulp viscosity and increasing pulp strength levels mainly because of enhanced handsheet tear properties, but had no effect on beating requirements and resulted in less stable brightnesses