SYMPOSIA PAPER Published: 01 January 1994

Assigning the Glass Transition Temperature in Oriented Poly(ethylene terephthalate)


Thermoplastics like poly(ethylene terephthalate) (PET) can be melt processed into sheet and film formats for a variety of applications. Fabrication of these formats often involves application of a drawing process which can include drafting, tentering, heat setting, detentering, and heat relaxation. These various components add a thermomechanical history to the PET that will influence the glass transition. Thermomechanical analysis (TMA) in both the compressive mode and the tensile mode along with differential scanning calorimetry (DSC) techniques have been applied to a series of seven PET films generated using different drawing processes applied with an Iwamoto Biaxial Stretcher on extruded sheet from a single source. These measurements were undertaken to assign a glass transition temperature for each film. The assigned temperature ranged between 70°C and 94°C. Orientation and heat setting increased the temperature assigned as Tg while detentering both increased and lowered Tg on a direction-specific basis. Both the measurement technique and the assignment protocol employed to determine Tg contributed to differences in the assigned value. DSC results suggested the presence of two amorphous domains (mobile and constrained) in the film oriented uniaxially without constraint. TMA data demonstrated the assigned Tg may be direction specific and not a bulk property in oriented PET films.

Author Information

Moscato, MJ
Eastman Kodak Company, Rochester, NY
Seyler, RJ
Eastman Kodak Company, Rochester, NY
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Developed by Committee: E37
Pages: 239–252
DOI: 10.1520/STP15378S
ISBN-EB: 978-0-8031-5287-8
ISBN-13: 978-0-8031-1995-6