Impact of pulp chemical composition and fiber morphology on hygroexpansion and strength properties of kraftliner

Sammanfattning: Kraftliner is the unbleached pulp used in the outermost layer of corrugated cardboard. Like other types of paper, it is produced from wood chips as a raw material. Kraftliner is known for its high tensile strength, tear resistance, compressive strength, etc., making it suitable for packaging material for heavy objects. When paper is exposed to moisture, there is usually a dimensional change within the fiber structure as it is a porous material. Thus, paper can absorb water from the environment and swell, called hygro-expansion. When exposed to moisture, corrugated cardboard boxes used for high-quality boxes, packaging, and protective layers in transport packaging suffer as well. By boiling wood chips to different kappa numbers (lignin content) and reducing the hemicellulose content in some of the pulp samples, the influence of the chemical composition on the tensile strength, compressive strength, and hygroexpansion of the number of produced sheets was experimentally determined. A fiber test was also performed to compare fiber properties and identify any relationships between them. Tensile strength, compressive strength, and hygroexpansion were found to increase with increased sheet density. Removal of hemicellulose was shown to decrease tensile strength by up to 72% and increase hygroexpansion by up to 17%, but did not significantly affect compressive strength. Finally, the effect of lignin's chromophore groups on the brightness of the sheets was also studied, which resulted in a significant decrease of about 15-18% when removing the chromophores.