Fundamental properties of handsheets containing TEMPO-oxidized pulp in various weight ratios

A hardwood bleached kraft pulp (HBKP) was oxidized using aqueous 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO)/NaBr/NaClO at room temperature and pH 10. Different amounts of NaClO were used to prepare TEMPO-oxidized pulps (TOPs) with different carboxylate and aldehyde contents. One of these TOPs was mixed with the original HBKP at various weight ratios, and beaten using a PFI mill. The fundamental properties of handsheets made from these pulp mixtures were evaluated. The dry and wet tensile strengths, particularly the wet-tensile strengths, were significantly improved at 10-40% TOP contents. This is because of formation of interfiber hemiacetal linkages between aldehyde groups in the TOPs and pulp fiber hydroxyl groups in the fiber-bonding areas. The dry and wet tensile properties of the handsheets can therefore be controlled using 10-40% TOP; use of 100% TOP is unnecessary. The light-scattering coefficients and zero-span tensile strengths of the TOP-containing handsheets were investigated. Significant cellulose depolymerization occurred in the TOPs, and therefore the 100% TOP handsheets had no advantages in terms of improved dry or wet tensile strength. Microscopy images of the handsheets and single pulp fiber surfaces showed that the external fibrillation behavior caused by beating with the PFI mill was different between the original HBKP and TOPs.