Relationship between Surface Properties and Fiber Network Parameters of Eucalyptus Kraft Pulps and Their Absorption Capacity

Water absorption capacity is a key characteristic of cellulosic pulps used for different commodities. This property is influenced by the affinity of the pulp fiber surface with water, chemical composition of the pulp, morphology, and organization of fibers in the network. In this study, surface properties of six industrial Eucalyptus bleached kraft pulps (fluff pulps) dry-defiberized in a Hammermill, which were obtained by wood pulping and pulp bleaching under different production conditions, were studied while employing dynamic water vapor sorption and contact angles measurements. The absorption properties of air-laid pulp pads were analyzed following the absorbency testing procedure and the relationship between these properties and pulp’s chemical composition and fiber network structure were assessed by multivariate analysis. The results showed that the accessibility of the fiber surface is related to the reduction of the contact angles, but, at the same time, to the longer absorption time and less absorption capacity of the fiber network. Therefore, the absorption properties of the pulps are not necessarily directly related to their surface properties. Indeed, absorptivity is related to the surface chemical composition, fiber morphology, and fiber network structure. Thus, surface carboxylic groups promote total water uptake, resulting in better absorption capacity. Greater fiber coarseness and deformations (curl and kink) provide a less wettable surface, but a more porous network with higher specific volume, resulting in more absorbent air-laid formulations.