General Properties
Short Name:
Name:
PET
Polyethylene terephthalate
Polyethylene terephthalate is a semi-crystalline polymer; its semi-crystalline state is sometimes designated PET-C or C-PET and its amorphous state is designated PET-A or A-PET. Amorphous PET is mainly employed for beverage bottles, since it features a high transparency and resistance to breaking. For the use as a construction material, a high degree of crystallinity can be advanta- geous since this prevents shrinkage of the components due to post-crystallization.*
Structural Formula
Properties
| Glass Transition Temperature | 70 to 85°C |
|---|---|
| Melting Temperature | 245 to 260°C |
| Melting Enthalpy | 140 J/g |
| Decomposition Temperature | 425 to 445°C |
| Young's Modulus | 2100 to 3100 MPa |
| Coefficient of Linear Thermal Expansion | 80 to 100 *10-6/K |
| Specific Heat Capacity | 1.04 to 1.17 J/(g*K) |
| Thermal Conductivity | 0.24 W/(m*K) |
| Density | 1.33 to 1.45 g/cm³ |
| Morphology | Semi-crystalline thermoplastic |
| General properties | High stability and stiffness. Good abrasion resistance. Good sliding properties. Resistant to diluted acids, aliphatic and aromatic hydrocarbons, oils, fats and alcohols. Tear and weather resistant. Good electrical insulating properties |
| Processing | Injection blow molding, stretch blow molding, injection molding |
| Applications | Fibers (polyesters), e.g., for sportswear. Packing (e.g., beverage bottles). Instrument and apparatus engineering. Medical engineering |
NETZSCH Measurement
| Instrument | DSC 204 F1 Phoenix® |
| Sample Mass | 8.43 mg |
| Isothermal Phase | 5 min |
| Heating/Colling Rates | 10 K/min |
| Crucible | Al, pierced lid |
| Atmosphere | N2 (50 ml/min) |
Evaluation
Polyethylene terephthalate (PET) exemplifies how the ratio of amorphous and crystalline phases within a sample can be affected by different cooling rates. During production, the material undergoes very fast cooling, resulting in a high amorphous content. This is evident in the 1st heating (blue) from the large glass transition step (Δcp of 0.34 J/(g.K)) and subsequent cold or post-crystallization at 137°C (peak temperature). Post-crystallization is generally associated with a volume change (shrinkage). At 251°C (1st heating, blue), all crystalline phases melt.
After a controlled cooling at 10 K/min, the amorphous content of the polymer was considerably lower than before. For this reason, the glass transition step height in the 2nd heating (red) was lowered and post-crystallization was almost completely eliminated. The melting temperature in the 2nd heating (peak temperature) occurred at 249°C. The difference between peak temperatures of the 1st and 2nd heatings is due to the better contact between the sample and crucible bottom after the first melting.