Towards Overcoming the Brightness Ceiling of Mechanical Pulps Prepared from Blue-Stained Lodgepole Pine Chips, 2008 Engineering, Pulping and Environmental Conference

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The initial brightness of TMP and CTMP prepared from chip blends containing mountain pine beetle-infested (kill date = 2-3 years), blue-stained lodgepole pine is up to 5.0 ISO points lower than that of the pulps made from the green chips. Paprican’s VIS-NIR system is capable of accurately predicting the blue-stained chip content in the chip blends on a pilot-plant conveyor.

TMP made from chip blends with various blue-stained chip contents all have lower sodium hydrosulfite (Y) bleach response than pulp made from the green chips. A method to overcome the brightness ceiling of Y-bleached TMP made from a chip blend with 25% blue-stained chip content has been developed. The method involves the addition of 0.2% (o.d. pulp) of sodium borohydride to Y bleaching of the pulp.

A high bleaching end pH (~10.0) in alkaline hydrogen peroxide bleaching removes most to all of the blue stain in TMP made from the blue-stained chips. Under optimal peroxide bleaching conditions, TMP made from 50% blue-stained chips or CTMP made from 100% blue-stained chips was bleached to the same brightness as TMP or CTMP from green chips. TMP from 100% blue-stained chips was bleached to within 0.8 brightness points of TMP from green chips.