Comparison of KP Pulping Properties between Heartwood and Sapwood of Popla I-69

The case was carried out to study the variance of fiber feature, chemical composition and pulping property between heartwood and sapwood of poplar I-69. As results showed, the mean fiber length in heartwood and sapwood of poplar I-69 were 770 and 1146 mu m separately, with the length-to-width ratio of 42.56 vs 51.76, and the wall-to-lumen ratio of 0.40 vs 0.59, respectively. The heartwood of poplar I-69 differed from sapwood in contents of chemical compositions, with holocellulose of 82.65% vs 81.35%, alpha- cellulose of 42.83% vs 42.82% and lignin of 18.01% vs 21.68%, respectively. Both the heartwood and sapwood of poplar I-69 were suitable for pulping material. By investigating pulp yield and Kappa number, it was proven that the caustic soda dosage and the duration of reaction temperature were major factors influencing KP pulping properties of poplar I-69 sapwood. Under the same technical conditions of pulping, the pulp of the poplar I-69 sapwood was lower in Kappa number and higher in yield and in viscosity compared with those of heartwood. The tensile index, tear index and burst index of paper made by sapwood were higher than those made by heartwood. The sapwood of poplar I-69 showed overall better pulping aptitude in comparison with heartwood.