Wet tensile strength development of PAE wet-strengthened NBSK handsheets by AKD internal sizing

Abstract

Polyamide-epichlorohydrin (PAE) is used in papermaking to increase the paper’s wet strength. High levels of PAE can make repulping of paper more difficult. PAE deposits can also impair paper machine performance by plugging the paper machine felts. The results of a preceding study indicated that the wet strength of paper containing a moderate amount of PAE (added amount 0.3 wt%) can be increased by utilizing internal alkylketene dimer (AKD) sizing. In the present study, the effects of an added amount of PAE and AKD on the wet strength of handsheets made from Nordic bleached softwood pulp (NBSK) were examined. The wet strength was measured after soaking the sheets in ion-exchanged water for up to 1 month. The improving effect of AKD sizing on the wet strength was long-lasting and it was apparent especially with a low and moderate added amount of PAE (0.15 and 0.45 wt%) resulting in higher wet strength than the highest added amount of PAE (1.35 wt%) alone. No clear sign of worsened repulpability was observed at low to moderate treatment levels. The results suggest that use of small or moderate amounts of PAE with AKD can be a viable option for paper mills facing problems related to the high usage of PAE.

Piloting wet tensile strength development of polyamide-amine-epichlorohydrin wet strengthened nordic bleached softwood pulp paper by alkyl ketene dimer internal sizing

“…The previous laboratory studies indicated that AKD internal sizing had no noticeable effect on the dry strength of handsheets that were wet strengthened using PAE (Korpela et al 2021(Korpela et al , 2022. In the studies, PAE alone had no effect on the dry strength of the handsheets either.…”

“…The Schopper-Riegler ( ○ SR) value of the delivered pulp measured according to ISO 5267-1 (1999) was 18. The wet strength agent PAE and cationic AKD dispersion for this study were the technical-grade products used in the preceding laboratory trials (Korpela et al 2021(Korpela et al , 2022. Both PAE and AKD were used as such in the pilot trials.…”

“…Another observation from previous laboratory studies was that the AKD internal sizing had very little if any effect on the dry tensile strength and density of PAE wetstrengthened handsheets (Korpela et al 2021(Korpela et al , 2022. As Hubbe (2014) suggests, AKD internal sizing does not apparently interfere with the formation of inter-fiber bonds.…”

“…Siqueira (2012) notes that PAE resins may slightly reduce the water absorption capacity of paper, which is useful in packaging products but not in tissue papers. The observed positive correlation of the watersoaked paper dry content and wet strength (Korpela et al 2021(Korpela et al , 2022 indicate that AKD is capable, one way or another, of boosting the decreasing effect of PAE on the paper water absorption capacity.…”

“…The present study examined whether the synergistic effect of PAE and AKD on the wet strength of the paper also occurred in pilot-scale papermaking, where especially the dewatering conditions in the wire section differ from those of laboratory sheet making. The idea was to carry out the pilot trials under conditions that are otherwise as close as possible to the laboratory sheet-making conditions (Korpela et al 2021(Korpela et al , 2022, and in this way obtain comparable information on the effect of the web forming conditions on the joint effect of PAE and AKD on the paper properties. In the study, a similar type of NBSK pulp, and the same PAE and AKD products were used as in the laboratory study.…”