Chemical Agent
Synthetic polymers added to the paper pulp during stock preparation ensure that the finished paper retains up to forty percent of its dry strength when saturated with water. In paper manufacturing, wet-strength additives prevent the sheet from disintegrating when exposed to moisture by creating a water-resistant network of covalent bonds. The polymers are typically cationic, allowing them to bind electrostaticly to the anionic cellulose fibres.
This treatment is standard for liquid packaging boards and beverage carrier cartons.
Curing Mechanism
Development of water resistance in the sheet relies on the chemical reaction of these resin molecules during the drying phase of the paper machine. When wet-strength additives are activated by heat, they form crosslinks between the polymer chains and the cellulose surface. The crosslinked network protects the fibre-to-fibre bonds from being disrupted by water molecules, which would otherwise cause the sheet to lose up to ninety percent of its strength.
The mechanism is particularly effective when using polyamide-epichlorohydrin resins in neutral papermaking. This reaction continues to develop after the paper reel is wound.
Packaging Durability
Industrial boxes subjected to condensation or direct water contact rely on this chemical treatment to survive the supply chain. Incorporating wet-strength additives in the board formulation protects the box from buckling in cold storage or humid shipping containers. This stability preserves the structural integrity of the food container.
