Characterization of Handsheets Prepared from TEMPO-Oxidized Pulps with De-bonder

Abstract

A hardwood bleached kraft pulp was oxidized by 2,2,6,6-tetramethylpiperidine-1-oxyl radical (TEMPO)-mediated oxidation, and two TEMPO-oxidized pulps with different carboxylate but similar aldehyde contents were prepared. Handsheets were prepared from the reference and TEMPO-oxidized pulps with di(oleamidoethyl)ammonium formic acid salt (DOFAS) used as a de-bonder in handsheet-making. Density, DOFAS content and tensile strength of the handsheets were measured, and these properties were compared between the reference and TEMPO-oxidized pulps. When the TEMPO-oxidized pulps were used, sheet density was effectively decreased, but degrees of tensile strength reduction of the handsheets were diminished to some extent, in comparison with the reference pulp. Sheet density can be decreased by partial prevention of interfiber hydrogen bonds with DOFAS molecules added, although interfiber bonds are still present when TEMPO-oxidized pulps are used. Scanning electron microscopic observations of cross sections of the handsheets also supported the above hypothesis. TEMPO-oxidized pulps had significant amounts of aldehyde groups so that hemiacetal linkages are probably formed with hydroxyl groups at the interfiber bonding areas, thus resulting in higher tensile strength of the handsheets prepared thereof. Hence, an effective decrease in sheet density can be achieved with less reduction of tensile strength by preparation of handsheets from TEMPO-oxidized pulps with DOFAS. Aldehyde groups formed by the TEMPO-mediated oxidation and present on the pulp fiber surfaces are likely to contribute to higher tensile strength of the handsheets.