We quantified the effects of wood density (chip specific gravity) and wood chemical composition (cellulose, hemicellulose, and lignin) on the kraft pulp yield of 13-year-old loblolly pine trees (Pinus taeda) grown as part of a genetic selection study. Both bleachable (kappa No. 30) and linerboard grade (kappa No. 100) pulps were made from 18 trees selected for combinations of wood specific gravity and cellulose:hemicellulose:lignin ratios. Statistical analysis indicated that digester pulp yield correlated significantly with wood xylan content and cellulose-to-lignin ratio but was not strongly correlated to wood specific gravity. Near infrared (NIR) spectra were collected from wood samples and correlated with the total kraft pulp yields. The analyses for both kappa No. 30 and kappa No. 100 pulps provided strong calibration statistics, suggesting that papermakers can use NIR spectroscopy to esti-mate the bleachable and linerboard grade pulp yields of P. taeda whole-tree samples.
Results are reported on the relationships of loblolly pine tree age and wood characteristics and the yield of pulp obtained when the trees were chipped and pulped by the kraft process. Eighteen 13-year old and 18 22-year-old loblolly pine trees were selected to represent specified ranges of specific gravity and lignin content. The trees were further characterized by chemical analysis and near infrared spectroscopy before kraft pulping. The resulting pulps were characterized by measurements of yield and chemical analysis. Multiple regression analysis was used to identify wood characteristics that most influenced pulp yield and to derive equations relating pulp yield to tree age, specific gravity, and wood chemical composition. In addition, near-infrared spectroscopy calibrations were developed to allow prediction of pulp yield from analysis of wood. The results showed that wood specific gravity cannot be used to predict the yield of linerboard-grade pulp from trees of either age. The yield of pulp from 13-year-old trees can be predicted from the amounts of xylan and lignin present in the wood. The yield of pulp from 22-year-old trees decreased with increasing lignin content but was unrelated to xylan content. Thirteen-year-old trees had significantly higher xylan content and the excess xylan was lost during pulping. Regression equations were developed for estimating pulp yields from 13- and 22-year-old trees, given their xylan and lignin contents. Another equation derived from the combined data for trees of both age classes will be useful for predicting yields from trees of other ages, if it is assumed that the effect of tree age is linear.
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