The effect of wood density on the kraft pulping properties of Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco)

Graduation date: 1979Three samples of different wood densities of Douglas-fir\ud (Pseudotsuga menziesii (Mirb.) Franco) were cooked by\ud the kraft process. The yields and the Kappa numbers were\ud studied to establish the rates and the energies of activation\ud of the pulping and delignification reactions\ud respectively. Wood properties did not show significant\ud effects on the pulping reactions compared to the effects\ud of time and temperature. However, their influences on\ud delignification was greater than on pulping reactions.\ud The intermediate density wood sample which had the\ud lowest amount of lignin and the highest amount of sapwood\ud underwent the most delignification and showed the highest\ud yields. Heartwood penetrability affected the pulping\ud reactions in the beginning stages and became less effective\ud at higher temperatures and longer cooking times. Fluoro-metric analysis was used to measure the lignin in the waste\ud liquors and linear relationships between fluorescent\ud intensities and cooking tithes were found at 165° and 175°C.\ud These results agreed with the relationships of Kappa numbers\ud to cooking times for each wood sample. A non-linear relationship\ud between fluorescent intensities of waste liquors\ud to cooking times were found at 185°C which may be due to\ud lignin condensation reactions.\ud Wood density influenced the physical strength properties\ud of handsheets. Paper made from low density wood pulp\ud had higher tensile strength, bursting strength and folding\ud endurance, but the paper from high density wood pulp showed\ud higher tearing resistance