Properties of spruce sulfite pulp and birch kraft pulp after sorption of cationic birch xylan

In this study, correlations between the charge density of adsorbed cationic xylans and the mechanical properties of selected pulps are discussed. Hand-sheet experiments were carried out using birch sulfate pulp and spruce sulfite pulp after the adsorption of 2-hydroxypropyl-trimethylammonium-4-O-methylglucuronoxylans (HPMAGXs) with different molar degrees of substitution (MS) in the range of 0.06–0.19. The charge density of the HPMAGX in water was determined by polyelectrolyte titration. Properties such as the tensile and burst index increased after HPMAGX addition and showed an optimum depending on the MS, which was 0.1 for both pulps. Other properties like the tear-index or the specific volume changed depending on the pulp. Beating experiments were also performed and showed an increasing tensile index of birch kraft pulp in the range of 53.7 to 85.7 N m g⁻¹ for a beating time of 10 min. The adsorption of HPMAGXs with different MS onto thiol-based self-assembled monolayers (SAMs) on gold and regenerated cellulose surfaces were studied using surface plasmon resonance (SPR). Electrostatic interactions were found to be the most important factors affecting HPMAGX adsorption, and a strong correlation between HPMAGX adsorption onto carboxyl-terminated SAMs (SAM-COOH) and paper strength when HPMAGX was used as a papermaking additive was observed.