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