Properties of Polyester Film
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Polyester film is a man-made substance using polyethylene terephthalate (PET). This film is used in a variety of applications. PET is the generic form of thin foil coverings for pouches and convenience foods. It is also the film that covers microwaveable dinners due to its high resistance to heat. Polyester film is used in the medical industry, including X-rays sheets. It is even in NASA astronaut suits to provide warmth and radiation resistance. Foil balloons available in card and gift shops are also made with the film. The scientific properties of PET film demonstrate its physical, electrical and thermal limitations.
Physical
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The physical properties of polyester film are tested by stretching and pulling the film in various ways to see how it changes. Tensile Strength (a measure of force required to pull something before it breaks) is 28,000 lbs. per square inch (psi). Strength elongation (how far it stretches) is 15,000 psi. Surface roughness (texture of surface) is 38 nanometres.
Electrical Properties
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Dielectric strength is a measurement of the electricity a material can endure before it breaks down. The units are in degrees Celsius. At 20 degrees Celsius, PET breaks down under 7,000 volts/mil (volts per million) of electricity.
Thermal Properties
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Thermal properties test the strength of the material against heat. All temperatures are in Celsius. The melting point of PET is 254 degrees Celsius. The specific heat is the heat energy required to raise the material by 1 degree. The specific heat of PET is .28 calories/grams/celsius---meaning that it takes .38 calories per gram to raise the temperature by 1 degree. Thermal expansion is the volume (size) change in the material when heat is applied. In this case, per degree PET changes 1.7 inches by 10 to the -5 power inches.
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