Use of Bacterial Xylanase in Chlorine Free Bleaching Sequences, 1993 Pulping Conference Proceedings

The pulp and paper industry is coming under increasing customer and regulatory pressure to move towards chlorine-free bleaching sequences, especially in countries where the elimination of bleach plant waste water is becoming strictly regulated.

Recent advances in pulp bleaching research have shown that oxygen, ozone, hydrogen peroxide and various peroxygen compounds can be used in combination to bleach soft and hardwood pulps to 90% IS0 with reasonable strength properties.

This work illustrates the combination of enzymatic prebleaching with TCF sequences. In ECF sequences the enzyme application reduces the available chlorine charge required for delignification, thus reducing the chlorine-containing compounds in the bleach sequence. In TCF sequences xylanase can be used to reduce the application of expensive non-chlorine bleaching agents.

The use of xylanase in TCF sequences containing ozone yielded hardwood kraft pulps with brightnesses in the 88 + % IS0 range, higher DP values and reduced 03 applications. Position of the enzyme stage within the bleach sequence had no significant impact on final brightness or DP, but may impact the O3 application required for equivalent brightness.