Degradation Mechanism
A self-accelerating chemical degradation process occurs in polyester-based barrier coatings and adhesives when accumulated carboxyl end groups accelerate the rate of further ester cleavage. In moist packaging environments, acid autocatalysis occurs because the initial hydrolytic cleavage of polyester chains generates acidic carboxyl groups. These newly formed groups act as catalysts for subsequent hydrolysis reactions, leading to a cascade of bond cleavage that weakens the adhesive layer.
This mechanism is especially problematic in humid storage conditions where the adhesive is enclosed between water-impermeable barrier films, trapping the acid within the adhesive line and accelerating the decay.
Kinetic Evolution
Exponential increases in the rate of polymer degradation characterize this self-reinforcing reaction over time. As acid autocatalysis progresses, the mechanical strength of the adhesive film declines rapidly from its initial specification. This deterioration can cause sudden delamination failures in multi-layer paperboard containers where moisture has penetrated the glue line, turning a slowly occurring chemical change into a rapid structural breakdown.
Preventive Strategy
Incorporating acid scavengers or utilizing hydrolytically stable polyether backbones provides an effective defense against this self-sustaining degradation. Minimizing moisture exposure through robust foil barrier layers prevents the initial reaction from generating the catalytic carboxyl groups required for acid autocatalysis to begin. This proactive formulation strategy ensures the long-term integrity of high-performance packaging laminates.
