The utilization rate of wastepaper in Japan has reached 58.0% in 2001. However, the use for printing and communication papers has been limited due to concerns about appearance, strength and brightness. To promote the use of recovered paper for higher-quality grades, it is necessary to understand the fundamental aspects on recycled fiber. This paper describes papermaking potentials of recycled pulp fiber.
When a kraft pulp is repeatedly defibrated in water, dewatered and dried for several times, the strength properties of papers, as well as the micro-structure of the pulp fibers, are considerably deteriorated. Morphological changes such as delamination and crack formation in cell wall of pulp fiber are enhanced by recycling treatment. On the other hand, the pore volume in cell wall of pulp fibers determined by the solute exclusion method decreases with recycling. Therefore, the shrinkage of internal pore structure under recycling is not easily reversed. The kraft pulp with a significant decrease in handsheet tensile strength during recycling tends to swell less and reduce their bonding potential.
Variations in strength properties of papers during recycling are closely related to the fiber morphological characteristics. The fiber lumen diameter : fiber width ratio is an important predictive factor of strength properties of handsheet during recycling.
Remarkable increase in water contact angle of kraft pulp fiber is observed by recycling. The recycled fiber is clearly much less hydrophilic than the virgin fiber. This relates to inactivation of the fiber surface by recycling, which is known as “irreversible hornification”.
The deterioration of neutralized recycled paper prepared from hardwood bleached kraft pulp by accelerated aging is similar to that of conventional neutralized paper.