Abstract
Some paper and paperboard grades require strength also when rewetted. The purpose of this study was to investigate the impact of web forming method, different foaming agents, polyamideamine-epichlorohydrin (PAE) wet strength resin, and retention aids on the strength development of hand sheets. Only a slight, if any, improvement in dry tensile strength due to PAE resin was observed. PAE improved the wet strength of the water-laid sheets, and the retention systems had a minor but positive impact. Although wet strength was lower at given PAE addition levels, the trend was similar with the sheets foam-laid with an anionic foaming agent, except at high PAE levels. With the non-ionic surfactant the maximum level of wet strength was reached already at a low PAE addition level and use of retention aids decreased wet strength. Such differences between the water- and foam-laid sheets are most likely due to the chemical interactions between PAE, foaming agents, and other additives.
Acknowledgments
The authors wish to thank Metsä Fibre for providing the pulp, and all the chemical suppliers for the product samples.
Conflict of interest: The authors declare no conflicts of interest.
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