May 27 2003
Polybutylene Terephthalate (PBT) is a white or off-white semi-crystalline polyester similar in both properties and composition to polyethyleneterephthalate (PET). When compared to PET, it has somewhat lower stiffness and strength, is slightly softer but has very similar chemical resistance and higher impact strength. As it crystallizes more quickly than PET, it is usually favoured for industrial scale moulding.
Background
The reinforcement of Polybutylene Terephthalate ( PBT ) with glass fibre results in large increases in strength, stiffness and heat distortion temperatures without loss of impact strength. The normal colour is off-white.
Applications
Applications of Polybutylene Terephthalate ( PBT )include those for unfilled polybutylene terphthalate (PBT) together with high power lighting components, ignition rotors, distributor caps etc.
Other applications include automotive and electrical components (including "under-bonnet") and power tool casings.
Key Properties
The key properties of Polybutylene Terephthalate ( PBT ) / 30% Glass Fibre Reinforced are tabulated below.
Table 1. Key properties
| Chemical Resistance |
| Acids – concentrated |
Good |
| Acids – dilute |
Good |
| Alcohols |
Very Good |
| Alkalis |
Poor |
| Aromatic hydrocarbons |
Good |
| Greases and Oils |
Good |
| Halogens |
Good |
| Ketones |
Very Good |
| Electrical Properties |
| Dielectric constant @ 1 MHz |
4 |
| Dielectric strength ( kV.mm-1 ) |
20 |
| Dissipation factor @ 1 kHz |
0.002 |
| Volume resistivity ( Ohm.cm ) |
2x1014 |
| Mechanical Properties |
| Elongation at break ( % ) |
2 |
| Hardness – Rockwell |
M93 |
| Izod impact strength ( J.m-1 ) |
70 |
| Tensile modulus ( GPa ) |
12 |
| Tensile strength ( MPa ) |
185 |
| Physical Properties |
| Density ( g.cm-3 ) |
1.63 |
| Flammability |
Self Extinguishing |
| Limiting oxygen index ( % ) |
23 |
| Water absorption - over 24 hours ( % ) |
0.15 - 0.35 |
| Thermal Properties |
| Coefficient of thermal expansion ( x10-6 K-1 ) |
20 - 70 |
| Heat-deflection temperature - 0.45 MPa (°C ) |
220 |
| Heat-deflection temperature - 1.8 MPa (°C ) |
200 |
| Thermal conductivity ( W.m-1.K-1 ) |
0.24 @ 23 |
| Upper working temperature ( °C ) |
120 - 200 |
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This information has been sourced, reviewed and adapted from materials provided by Goodfellow.
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