EFFECTS OF WOOD AGE ON THE PAPERMAKING PROPERTIES OF

The effects of wood age (internodes from apex, growth ring number from the pith) on the papermaking properties of kraft pulp from radiata pine are discussed. In 40-year-old trees the tear strength of pulps from 30th internode material (that which contains 30 growth rings) was almost twice that of 10th internode material. Similarly in 18-year-old thinnings, the 15th internode pulps had higher tear index than the pulps from 10th or 5th internodes. Pulps from all types of material were readily beaten to good burst and tensile strength, the ease of beating decreasing with increase in wood age. In studies of 5-ring-group material numbered from the pith it was found that the outer wood pulps from mature trees had tear strength 3 times that of pulp from growth rings 1-5; the inner wood pulps formed sheets of higher density than pulps from outer wood, since the fibres were more readily collapsed. As expected, slabwood pulps gave pulps with highest tear strength. The data on slabwood and those for internodal and ring-group pulps indicate that the strength parameter most affected by wood age is tear index. As tree age increases tear strength of pulps also increases. It is concluded that the use of slabwood pulp to supplement whole-log pulps will be necessary for both export pulp and for certain packaging grades of paper. Empirical procedures for estimating the effects of forest age on the tear index of pulps based on ring-group sampling are described