Dynamic Vapor Sorption Mechanics in Recycled Packaging Substrates
Recycled packaging substrates exhibit non-Fickian moisture uptake and severe hysteresis, reducing compressive strength by over 20 percent under cyclic humidity.
Edge Wick Migration
Fluid Penetration
Capillary flow drives liquids into the exposed cross-section of a porous board or sheet. Package designers test for edge wick migration to evaluate how well barrier coatings protect the untreated edges of liquid packaging board. This phenomenon occurs when water or oil bypasses the surface laminate by entering through the raw cut edges of the carton.
Barrier Performance
Sizing agents are added to the pulp during papermaking to increase the hydrophobic properties of the cellulose fibres and slow down liquid absorption. The rate of capillary absorption depends on the diameter of the pores between the fibres and the surface tension of the liquid. Low viscosity liquids like fruit juices or milk penetrate the raw edges faster than high viscosity oils or fats.
Packaging converters apply polymer coatings or use skiving and hemming techniques to protect the raw edge from direct contact with the product.
Material Integrity
Moisture absorption through raw edges softens the carton walls and leads to structural failure under compression during distribution. Dry storage conditions reduce the risk but cannot eliminate the capillary draw of liquid from the food itself. Testing involves measuring the mass of liquid absorbed per unit of exposed edge area over a specified time.