Extended oxygen delignification of alkaline pulps from Pinus radiata. New Zealand Journal of Forestry Science 11(3): 287-97. Efficient ozone and peroxide bleaching of alkaline pulps from Pinus radiata (in prep

Extended oxygen delignification of three types of alkaline pulps from Pinus radiata D.Don was investigated. Kraft, kraft-anthraquinone (kraft-AQ), and soda-anthraquinone (soda-AQ) pulps at 40 and 60 Kappa number were treated with oxygen to remove about 60, 70, and 75 % of their residual lignin. Extended oxygen treatments resulted in less selective delignification, higher brightness at a given Kappa number, and generally less strength degradation in 60 Kappa than in 40 Kappa pulps; and in less selective delignification, lower brightness at a given Kappa number, and lower strength in soda-AQ pulps than in kraft and kraft-AQ pulps. The yields of kraft-AQ and soda-AQ pulps remained higher than those of kraft pulps after extended oxygen delignification. At 25 Kappa number use of extended oxygen treatments increased total yields by 3% over those attainable through continued pulping. With careful control, oxygen delignification of alkaline pulps could be extended to at least 60 % lignin removal before significant strength losses occurred