| Popis: |
The mountain pine beetle epidemic in British Columbia is leaving behind vast stands of dead pine trees to be harvested. Several years after death, when the needles have fallen off, the trees are referred to as gray-stage. The trees’ natural defense system when attacked is to pitch out the beetles by producing large amounts of canal resin to flood the beetles’ bore holes; hence, changes in wood resin (extractives) will accompany beetle attack. Increased extractives concentration has been shown in the final bleached pulp in a kraft mill pulping a large proportion of gray-stage pine wood killed by the mountain pine beetle. Similar to the wood extractives content in gray-stage pine chips, pulp extractives in gray-stage mill pulps are variable and can occasionally be high (e.g., > 0.05%), likely because of the composition of the extractives in the incoming chips. Although this usually does not cause pitch problems in the pulp mill and its customer paper mills, kraft mills that sell gray-stage pulp to extractives-sensitive customers should check extractives content before shipment to make sure it is not unacceptably high. |
