Effects of fiber morphological characteristics and refining on handsheet properties.

Abstract

Under a fixed wet end chemical additive regime, pulp fibers of different morphological characteristics, including 2 softwood pulps of northern softwood and radiata pine, and 3 hardwood pulps of eucalyptus, mixed Indonesian hardwoods, and acacia underwent different degrees of pulp refining and then were used individually or as a blend (1 softwood to 1 hardwood pulp) to form handsheets. The handsheet bulk, water absorption, air permeability, and dry and wet opacities properties were then compared and correlated to the fiber morphological indicators such as fiber length, coarseness, and population in order to provide a reference for furnish blending to make specialty papers and other applications. The experiment on the individual pulp fibers indicated that along with increasing degrees of refining, the fiber population increased proportionally, pulp freeness and fiber lengths changed in an inverse manner, while fiber coarseness changed irregularly. The blended furnishes, on the other hand, indicated that along with increases in the hardwood pulp proportions, the freeness, fiber lengths, and coarseness changed in an inverse trend, whereas the fiber population also increased. Thus, it is feasible to use refining and blending of softwood and hardwood pulps to adjust the stock that meets the required freeness and fiber morphological properties for paper machines. Analysis of handsheets formed from individual pulps indicated that paper bulk and both dry and wet opacities decreased with an increased degree of pulp refining and were negatively correlated. Water absorption, and air permeability, on the other hand, increased with increasing pulp refining and exhibited positive correlations. The bulk and opacity of the hardwood pulps were higher than those of the softwood pulps, whereas the water absorption and air permeability values were higher than those of the hardwood pulps. The blended furnish study indicated that along with increasing hardwood pulp proportions, the paper bulk of Indonesian hardwoods pulp containing furnishes increased proportionally, while those of eucalyptus and acacia pulps containing furnishes showed negative correlations. Water absorption and air permeability values were negatively correlated to the hardwood pulp proportions, whereas opacities showed positive correlations. In addition, paper bulk and water absorption were positively correlated with the fiber coarseness (except for the Indonesian hardwoods), Relationships between the paper air permeability value and fiber coarseness and populations were furnish-dependent; while there was a positive correlation between paper opacities and fiber populations (except for the Indonesian hardwoods). There was a linear correlation between the pulp blend ratio and handsheet opacity. Hence, the opacity of a blended paper was derived from the opacities of the individual softwood and hardwood fibers.