Interfacial Bond Degradation in Laminated Flexible Packaging Film
Polyurethane bond degradation in laminated flexible packaging is driven by Corona decay, slip amide migration, and moisture hydrolytic cleavage at film boundaries
Polyester Polyurethane Hydrolytic Cleavage
Chemical Breakdown
Water molecules reacting with ester groups in a polymer chain lead to the fragmentation of the molecular structure. Continuous polyester polyurethane hydrolytic cleavage reduces the molecular weight of the adhesive and destroys the bond between two layers of a laminate. This process is accelerated by high temperatures and high humidity levels.
It is a common cause of delamination in retort pouches or industrial packaging.
Reaction Mechanism
Protons from the water catalyze the splitting of the ester linkage into a carboxylic acid and an alcohol. In polyester polyurethane hydrolytic cleavage the resulting acid groups further accelerate the reaction rate in a self sustaining cycle. This degradation leads to a loss of tensile strength and the formation of sticky residues on the film surface.
Failure Prevention
Selection of polyether based systems or the addition of carbodiimide stabilizers can slow the rate of the reaction. Monitoring for polyester polyurethane hydrolytic cleavage involves testing the peel strength of the laminate after exposure to environmental stress. If the cleavage proceeds far enough, the package will lose its integrity and fail to protect the contents.
The reaction is irreversible and cannot be stopped once substantial degradation has occurred. Adhesives designed for tropical climates must be formulated to resist this specific chemical vulnerability.