Thermoplastic polyester elastomers (TPE) are a group of block copolymers with hard crystalline and soft rubber segments. This gives them both thermoplastic and elastomeric properties that are influenced greatly by the ratio of hard to soft segments and their nature. TPE is used where conditions are severe and for example require high elasticity in combination with considerable mechanical strength and long service life. Examples include shock absorbing parts, flexible couplings and tubes, seals and membranes. Glass-reinforced types are used when there are stringent requirements for the deformation temperature.
Resistance to heat and chemicals increases in step with the hardness and rigidity of the TPE. The hardest types are briefly capable of withstanding temperatures of 150°C, but for prolonged periods of time the upper limit is approximately 80°C.
The moisture absorption of TPE depends greatly on the chemical structure. A typical value is 1.1% at 23°C /50% RH and 0.5% when saturated in water at 23°C. TPE is resistant to mineral oils and greases and non-aromatic hydrocarbons, and also to diluted acids, bases and alkaline substances. The material is not resistant to hot water or strong acids and bases, alcohol and halogenated and aromatic hydrocarbons. Resistance to UV radiation is mediocre: UV-stable types are required for outdoor usage.
The most important benefit of unreinforced TPE is its corrective capability after deformation, which may be up to about 25%. The resistance to cold deformation is limited, while the strength of this material when stretched is significantly better than rubber. Impact resistance is excellent at temperatures down to -40°C to -80°C, depending on the chemical structure.