Degradation of PET – Quantitative estimation of changes in molar mass using mechanical and thermal characterization methods

Gernot Oreski, Bettina Ottersböck, Chiara Barretta, Petra Christöfl, Simone Radl, Gerald Gerhard Pinter

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Polyethylene terephthalate (PET) films are used when mechanical strength, thermal and chemical stability, and barrier properties to atmospheric gases are required in combination with good processability. Hydrolysis leading to embrittlement of the material is a major concern as PET is used in a variety of applications with expected lifetimes of up to decades (e.g., for use in buildings, textiles, or photovoltaic backsheets). Therefore, a comprehensive understanding of the degradation processes and the effects on the molecular mass distribution is of great importance.
Usually, the direct determination of molar mass and molar mass distribution involves high effort and sophisticated equipment. Therefore, the main objective of this work is to quantify molar mass changes due to accelerated aging using thermal and mechanical methods. Two stabilized PET films were subjected to seven different accelerated aging conditions (heat; combined heat-humidity). The samples were then characterized by size exclusion chromatography (SEC), tensile tests and differential scanning calorimetry (DSC).
A linear correlation was found between crystallization temperature and average molar mass. The values of fracture stress from tensile tests indicate a ductile-brittle transition at a molar mass of 15 000 g mol−1. The study concludes that the crystallization temperature obtained from DSC measurements can be used to estimate changes in the average molar mass of PET after hydrolysis. Crystallization temperatures between 208 °C and 211 °C correspond to a critical reduction in molar mass and severe embrittlement.
Original languageEnglish
Article number108130
Number of pages8
JournalPolymer Testing
Issue numberAugust
Publication statusPublished - Aug 2023

Bibliographical note

Funding Information:
The research work was performed within the COMET-project „ Reliability of photovoltaivc system components“ (project-no.: 3.02) at the Polymer Competence Center Leoben GmbH (PCCL, Austria) within the framework of the COMET-program of the Federal Ministry for Climate Action, Environment, Energy, Mobility, Innovation and Technology and the Federal Ministry for Digital and Economic Affairs with contributions by the Chair of Material Science and Testing of Polymers at Montanuniversität Leoben. The PCCL is funded by the Austrian Government and the State Governments of Styria , Lower Austria and Upper Austria.
Publisher Copyright: © 2023 The Author(s)


  • Critical molar mass
  • Degradation
  • DSC
  • Hydrolysis
  • Molar mass estimation
  • PET

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