Canadian Forest Service Publications
Overcoming the brightness ceiling for mechanical pulps prepared from blue-stained lodgepole pine chips. 2008. Hu, T.; Williams, T.; Yazdi, S.; Wallbacks, L.; Watson, P.A. Natural Resources Canada, Canadian Forest Service, Pacific Forestry Centre, Victoria, BC. Mountain Pine Beetle Working Paper 2008-05. 29 p.
Issued by: Pacific Forestry Centre
Catalog ID: 28162
The initial brightness of thermomechanical pulps (TMPs) and chemithermomechanical pulps (CTMPs) prepared from chip blends containing mountain pine beetle-infested (kill date = 2-3 years), blue-stained lodgepole pine (LPP) is up to 5.0 ISO points lower than that of the pulps made from the green LPP chips; the higher the blue-stained chip content in the chip blends, the lower the initial brightness of the pulps. Paprican's VIS-NIR technique has been shown to be capable of predicting the blue-stained chip content in the chip blends accurately on a pilot-plant conveyor. TMP pulps made from chip blends with various blue-stained chip contents all have lower sodium hydrosulfite (Y) bleaching response than TMP pulp made from the green chips; the brightness of the Y-bleached, blue-stained TMP is up to 7.8 ISO points lower than the Y-bleached, green TMP. A method to overcome the brightness ceiling of Y-bleached TMP made from chip blends 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 in alkaline hydrogen peroxide (P) bleaching has been discovered to be capable of removing most or all of the blue stain in TMP pulps made from chip blends with 50-100% blue-stained chip contents. Thus, optimal P bleaching conditions (for example H2O2 ? 5.0% o.d. pulp, end pH = ~10.0) have been identified to allow the bleaching of the TMP made from chip blends with 50% blue-stained chip content to the same brightness as the bleaching of the pulp from the green chips. However, the brightness of the TMP made from 100% blue-stained chips and bleached with P under optimal bleaching conditions is still 0.8 ISO points lower than that of the P-bleached, green TMP. CTMP made from the 100% blue-stained chips can be bleached with alkaline hydrogen peroxide (P) to the same brightness as CTMP made from the green chips, due to the complete removal of the blue stain during P bleaching. The blue stain in the sapwood of mountain pine beetle-infested LPP appears to be the fungal melanin pigments. The blue stain chips have a lower triglyceride content than the green chips. The DMSO-soluble, lignin-carbohydrate-complex-poor fraction from the blue-stained chips appears to contain the blue stain as only this fraction shows significant chemical difference from that of the green chips; its SEC chromatogram contains slightly more low-molecular weight UV-absorbing material.