Question 16.6: Design of a Polymer Insulation Material A storage tank for l......
Design of a Polymer Insulation Material
A storage tank for liquid hydrogen will be made from metal, but we wish to coat the metal with a 3-mm-thick polymer as an intermediate layer between the metal and additional insulation layers. The temperature of the intermediate layer may drop to -80°C. Choose a material for this layer.
We want the material to have reasonable ductility. As the temperature of the tank changes, stresses develop in the coating due to differences in thermal expansion, and we do not want the polymer to fail due to these stresses. A material that has good ductility and/or can undergo large elastic strains is needed. We therefore would prefer either a thermoplastic that has a glass-transition temperature below –80°C or an elastomer, also with a glass-transition temperature below –80°C. Of the polymers listed in Table 16-5, thermoplastics such as polyethylene and acetal are satisfactory. Suitable elastomers include silicone and polybutadiene.
We might prefer one of the elastomers, for they can accommodate thermal stress by elastic, rather than plastic, deformation.
| Table 16-5 Melting, glass-transition, and processing temperature ranges (°C) for selected thermoplastics and elastomers | |||
| Polymer | Melting Temperature Range | Glass-Transition Temperature Range (T_{g}) | Processing Temperature Range |
| Addition polymers | |||
| Low-density (LD) polyethylene | 98–115 | -90 to -25 | 149–232 |
| High-density (HD) polyethylene | 130–137 | -110 | 177–260 |
| Polyvinyl chloride | 175–212 | 87 | |
| Polypropylene | 160–180 | -25 to -20 | 190–288 |
| Polystyrene | 240 | 107 | |
| Polyacrylonitrile | 320 | ||
| Polytetrafluoroethylene (Teflon) | 327 | ||
| Polychlorotrifluoroethylene | 220 | ||
| Polymethyl methacrylate (acrylic) | 90–105 | ||
| Acrylonitrile butadiene styrene (ABS) | 110–125 | 100 | 177–260 |
| Condensation polymers | |||
| Acetal | 181 | -85 | |
| 6,6-nylon | 243–260 | 49 | 260–327 |
| Cellulose acetate | 230 | ||
| Polycarbonate | 230 | 149 | 271–300 |
| Polyester | 255 | 75 | |
| Polyethylene terephthalate (PET) | 212–265 | 66–80 | 227–349 |
| Elastomers | |||
| Silicone | -123 | ||
| Polybutadiene | 120 | -90 | |
| Polychloroprene | 80 | -50 | |
| Polyisoprene | 30 | -73 | |