Enhancing bulk and absorbency of tissue paper using softwood bleached chemi-thermomechanical pulp

Softwood bleached chemi-thermomechanical pulp (SW-BCTMP) was added in tissue paper manufacturing, focusing on bulk, absorbency and strength performance. The SW-BCTMP exhibited high fines content (52.4%), elevated polymeric cationic demand (83.0 μeq·L⁻¹), and substantial zeta potential (-93.0 mV), which initially impaired both dynamic drainage performance and first-pass retention of pulp furnishes. The optimal application of polyaluminum chloride (PAC) was found to effectively reduce the cationic demand of pulp furnishes and enhance first-pass retention. The addition of 5.0 to 10.0% SW-BCTMP consistently enhanced the bulk, water absorbency, and air permeability of the handsheets. In the absence of polyamide-epichlorohydrin resin (PAE), dry strength was well maintained or even improved when substituting the bleached hardwood kraft pulp (BHKP), despite a marginal decline upon replacing the bleached softwood kraft pulp (BSKP). However, in PAE-containing systems, a consistent reduction in both dry and wet strength was observed. This detrimental effect was more pronounced when the SW-BCTMP replaced BSKP in the furnishes, which can be attributed to the interference of the SW-BCTMP with the adsorption and effectiveness of the wet-strength resin. The SW-BCTMP showed potential for enhancing bulk and absorbency in tissue products, such as toilet paper, where wet strength agents are not used.