Enhancing wet strength with less PAE: a study on oxygen delignified softwood pulps

This study explores the potential to reduce the use of polyamidoamine-epichlorohydrin (PAE) wet-strength additives in tissue paper by replacing fully bleached fibers with oxygen delignified softwood pulps. Laboratory isotropic 20 g/m 2 hand sheets were produced from commercial fully bleached pulp (reference pulp), unbleached kraft pulp, and oxygen delignified pulps with varying lignin contents and fiber charge levels. The impact of PAE, alone and in combination with carboxymethylcellulose (CMC) was evaluated for both unrefined and PFI refined pulps. The unbleached kraft pulps and oxygen delignified pulps characterized by different lignin contents and total fiber charge levels, exhibited significantly higher fiber swelling and enhanced wet tensile strength compared to the fully bleached pulp. Notably, the use of oxygen delignified pulps enabled up to a five-fold reduction in PAE requirement while maintaining comparable wet tensile strength. Beyond performance gains, these pulps offer sustainability advantages by reducing the extent of delignification and eliminating the need for full bleaching. The findings highlight the role of fiber chemistry – particularly lignin content and fiber charge – in wet strength development, and suggest a promising pathway toward more resource-efficient tissue products.