Thermal Aging and Shrinkage in PET Films
Persistence Regime: Thermal
Assumption under test
PET retains dimensional stability and tensile properties under continuous moderate heat exposure for years.
Irreversible physical mechanism
Physical aging and enthalpic relaxation cause permanent shrinkage and embrittlement under sustained sub-Tg temperature exposure.
Why persistence timescales are required
Cumulative relaxation effects are undetectable in short or accelerated tests and only manifest after prolonged exposure.
MVP persistence experiment
- Free-standing PET films
- Constant exposure at 70–80°C
- Dry air environment
- Duration: 2–5 years
Binary kill condition
>10% permanent shrinkage or >40% tensile strength loss.
Estimated probability
0.6–0.8