Polybutylene Terephthalate (PBT) is one of the most frequently use semi-crystalline engineering plastics. Glass-reinforced types of this material are widely used in the automotive industry thanks to its excellent resistance to oils and greases, its thermal stability at temperatures up to 130°C to 140°C and its high wear resistance. The UV-stability also makes it suitable for exterior parts like door handles and mirror casings. The low absorption of moisture, the thermal shape stability and excellent colourability also make PBT suitable for use in electronic components.
PBT has exceptionally low moisture absorption, i.e. 0.25% at 23°C/50% RH and 0.5% when saturated in water at 23°C. Moisture absorption does not affect the dimensions. An important advantage of PBT compared with polyamides is its independence of the mechanical properties of moisture absorption. PBT is resistant to most solvents, including oils, greases and halogenated and aromatic hydrocarbons. This does not apply to strong acids, alkaline substances and hot water. At temperatures above 60°C hydrolysis begins and the material starts to become highly breakable. PBT is resistant to temperatures up to 120°C to 130°C for long periods of time, and a temperature of 180°C is permissible briefly.
Compared with most other thermoplastics, PBT’s resistance to UV radiation is exceptionally high. Nevertheless, the addition of active black carbon is recommendable for outdoor applications in order to avoid mechanical degradation. The values for ignitability and flame retarding are low: this problem can be avoided by using special types. Glass-reinforced PBT retains its shape well at temperatures up to 120°C to 130°C and is resistant to fatigue. The electrical properties are excellent and unrelated to the absorption of moisture.