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Polybutylene Terephthalate (PBT)

Polybutylene terephthalate (PBT), a strong and highly crystalline synthetic resin, produced by the polymerization of butanediol and terephthalic acid. PBT is similar in structure to polyethylene terephthalate (PET) – the difference being in the number of methylene (CH2) groups present in the repeating units of the polymer molecules. The mechanical properties of the two materials are also similar.

However, PBT has a lower melting point (223 °C [433 °F]) than PET (255 °C [491 °F]), so it can be processed at lower temperatures. This property, combined with its excellent flow when molten and its rapid crystallization upon cooling, makes PBT highly suitable for injection-molding into solid parts. Either unmodified or reinforced with glass fibers or mineral fillers, it is used in numerous applications, especially electrical and small machine parts, owing to its excellent electrical resistance, surface finish, and toughness.

PBT lends rigidity and thermoplastic properties to a synthetic rubber known as copolyester elastomer.

Chemical Resistance
Acids – dilute Good
Alcohols Good
Alkalis Poor-Good
Aromatic Hydrocarbons Good
Greases and Oils Good
Ketones Good
Electrical Properties
Dielectric constant @1kHz 3.2
Dielectric strength ( kV.mm-1) 20
Dissipation factor @ 1kHz 0.002
Volume resistivity ( Ohm.cm ) 1015
Mechanical Properties
Elongation at break ( % ) 250
Hardness – Rockwell M70
Izod impact strength ( J.m-1 ) 60
Tensile modulus ( GPa ) 2
Tensile strength ( MPa ) 50
Physical Properties
Density ( g.cm-3 ) 1.31
Limiting oxygen index ( % ) 25
Water absorption – over 24 hours ( % ) 0.1
Thermal Properties
Heat-deflection temperature – 0.45MPa (°C ) 150
Heat-deflection temperature – 1.8MPa (°C ) 60
Upper working temperature (°C ) 120

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