Polymeric Additive
Synthetic water-soluble polymers modified with pendant aldehyde functionalities supply temporary wet strength and dry strength to paper and paperboard. Cationic backbones synthesized from acrylamide and diallyldimethylammonium chloride undergo partial derivatisation with glyoxal to form glyoxylated polyacrylamide. Cationic charges promote rapid retention onto anionic cellulose surfaces without requiring secondary anchoring chemistries.
The free aldehyde groups form hemiacetal bonds with cellulose hydroxyl groups as the sheet dries through the press and dryer sections. Hemiacetal linkages are reversible in the presence of liquid water, causing the wet tensile resistance to decay after prolonged soaking. This temporary wet strength profile satisfies flushability mandates for hygienic tissue while preserving web integrity against short-term moisture exposure.
Decay Mechanism
Contact with liquid water hydrolyses the hemiacetal linkages, dissociating the polymer-cellulose bridge over predictable durations. Initial wet tensile levels provide sufficient wet web strength during converting operations or brief consumer use. Submersion initiates rapid loss of tensile resistance, with significant decay occurring within ten to thirty minutes under neutral or alkaline conditions.
Acidic water baths decelerate the hydrolysis rate, maintaining bond integrity longer than alkaline environments. The reversible nature of the bond prevents persistent mechanical wet strength, eliminating repulping obstacles in broke processing systems.
Stock Preparation
Effective retention relies on controlled dosing into thin stock loops before sheet formation. High shear zones, such as fan pumps or pressure screens, can disrupt mechanical polymer adsorption if addition points are placed too far upstream. Elevated residual active chlorine in recycled process water oxidises aldehyde groups, degrading wet-strengthening capability.
The shelf life of concentrated liquid polymer solutions is bounded by self-crosslinking tendencies, which induce unwanted viscosity increases and gelation during prolonged storage. Temperature control during shipping and storage preserves reactive aldehyde sites prior to wet-end addition.
