Jun 25 2003
Polystyrene homopolymer is an amorphous thermoplastic that is rigid, brittle and relatively hard. It has excellent gamma radiation resistance, good electrical properties, and can be radiation sterilized but has poor chemical and UV resistance.
When modified by incorporating elastomers, polystyrene homopolymer becomes (high) impact polystyrene (HIPS), which is generally opaque. Therefore, a large number of polystyrene grades are available on the market.
Background
A cross-linked polystyrene copolymer which is rigid, transparent and colourless with outstanding electrical properties, including low dielectric losses up to very high frequencies, and very high radiation resistance. Cross-linked polystyrene copolymer has good dimensional stability, is easily machined and can be polished to a high optical quality.
Compared to normal polystyrene, it is harder and somewhat more temperature resistant.
Applications
Applications of polystyrene include light diffusers, glazing, packaging, containers, and housewares and for HIPs, cassette cases, take-out containers, cups, and casings. It is also extensively used as structural foam and expanded into beads for cushioning and packaging.
Cross-linked polystyrene copolymer is used primarily as a dielectric material in a wide range of components together with lenses, observation windows, x-ray equipment and radiation detectors.
Key Properties
The key properties of cross-linked polystyrene copolymer are tabulated below.
Table 1. Key properties
| Chemical Resistance |
| Acids - concentrated |
Fair |
| Acids - dilute |
Good |
| Alcohols |
Good |
| Alkalis |
Fair |
| Aromatic hydrocarbons |
Poor |
| Greases and Oils |
Fair |
| Halogens |
Poor |
| Ketones |
Poor |
| Electrical Properties |
| Dielectric constant @ 1 MHz |
2.5 |
| Dielectric strength ( kV.mm-1 ) |
27-47 |
| Dissipation factor @ 1 MHz |
0.0002 |
| Surface resistivity ( Ohm/sq ) |
>1015 |
| Volume resistivity ( Ohm.cm ) |
>1015 |
| Mechanical Properties |
| Abrasive resistance - ASTM D1044 ( mg/1000 cycles ) |
60-100 |
| Elongation at break ( % ) |
3-5 |
| Hardness - Rockwell |
R110-120 |
| Tensile modulus ( GPa ) |
1.65 |
| Tensile strength ( MPa ) |
55-70 |
| Physical Properties |
| Density ( g.cm-3 ) |
1.05 |
| Flammability |
Combustible |
| Radiation resistance - Alpha |
Good |
| Radiation resistance - Beta |
Good |
| Radiation resistance - Gamma |
Good |
| Radiation resistance - X-ray |
Good |
| Refractive index |
1.59 |
| Resistance to Ultra-violet |
Good |
| Water absorption - over 24 hours ( % ) |
0.02-0.03 |
| Thermal Properties |
| Coefficient of thermal expansion ( x10-6 K-1 ) |
90 |
| Thermal conductivity ( W.m-1.K-1 ) |
0.17 @ 23 |
| Upper working temperature ( °C ) |
93 |
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