A materials aging problem in theory and practice

Polyesters are widely used in plastic objects, films, and fabrics. A recurring mechanism of polyester aging is attack by humidity (hydrolysis), whereby the long chain molecules are cleaved and the material softens. This article offers an approach for modeling the hardness/aging behavior of commercial polyesters. The model is qualitatively consistent with exposure tests on fresh polyester plastic material made from a commercially available resin and hardening agent. It expresses the rate of polyester hydrolysis in terms of the relative humidity, and then connects the degree of hydrolysis to hardness using a relation that accounts for stabilizers that are present in commercial polymers to counter the hydrolysis. (Author)