Influence of the Hemicellulose Content on the Fiber Properties, Strength, and Formability of Handsheets

Hemicelluloses contribute to many intrinsic fiber properties, such as the swelling, fibrillation, bonding ability, and hornification tendency. During hornification, additional cross-linking between cellulose fibrils leads to a reduction in the swelling and water-holding capacity of pulp. The specific surface area, fibrillation, and flexibility of fibers also tend to decrease. To improve the plasticity of fibers and formability of the resulting paper, effective ways to control the fiber properties and their interactions in paper are highly desirable. This work investigated the role of xylan in the plasticization of bleached birch pulp fibers, as hemicelluloses act as natural spacers and thus reduce the interfibrillar cross-linking. Controlled removal of hemicellulose from fiber cell walls was performed using alkaline extraction and enzymes. The results confirmed that the xylan content noticeably influenced fiber shape and sheet properties, such as the tensile strength, strain at break, density, and 2D formability. A 60% reduction in xylose content reduced the tensile index by approximately 65% and strain at break by 50% compared to the original sample. The reductions were proportional to the amount of xylan removed and could be attributed mainly to the reduced interfibre bonding.