Redispersibility of Paper Under Low Agitation and How It Deteriorates over Time

In many paper applications the paper is supposed to disintegrate into its constituating fibers after disposal. This happens in water with only very little input of mechanical energy. The aim of this work is to understand the natural aging processes in different pulp types and their impact on the disintegration behavior under low agitation. We first introduce a laboratory testing method to assess the disintegration performance of various paper types in water under low mechanical energy input. Then we investigated the changes in paper disintegration and the corresponding physical properties over a nine-month period of paper storage. We measured wet strength, water retention value WRV, speed of water penetration, and contact angle. Our findings reveal substantial degradation of disintegration over time for unbleached paper. In contrast, for bleached paper the changes are much less pronounced. The best predictor of paper dispersibility turned out to be wet tensile strength. Furthermore, we found a strong relation between deterioration of dispersibility and fiber wetting (contact angle) and fiber swelling (WRV). We hence conclude that the observed decrease of low agitation paper dispersibility over time is related to a deteriorated water uptake into the fibers and fiber-fiber bonds which prevents the breaking of the bonds by the water. As potential aging mechanisms related to water uptake we identified hornification, crosslinking and lignin self-sizing as major factors influencing fiber-water interactions and ultimately the disintegration behavior.