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To prevent the onset of osmosis from the start, it is necessary to use a resin which has both a low water transmission rate and a high resistance to attack by water. When used with reinforcements with similarly resistant surface treatment and laminated to a very high standard, blistering can then be virtually eliminated. A polymer chain having an epoxy backbone is substantially better than many other resin systems at resisting the effects of water. Such systems have been shown to confer excellent chemical and water resistance, low water transmission rate and very good mechanical properties to the polymer. 5.1.5 Other Resin Systems used in Composites Besides polyesters, vinylesters and epoxies there are a number of other specialised resin systems that are used where their unique properties are required: 5.1.5.1 Phenolics Primarily used where high fire-resistance is required, phenolics also retain their proper- ties well at elevated temperatures. For room-temperature curing materials, corrosive acids are used which leads to unpleasant handling. The condensation nature of their curing process tends to lead to the inclusion of many voids and surface defects, and the resins tend to be brittle and do not have high mechanical properties. Typical costs: £2-4/kg. 5.1.5.2 Cyanate Esters Primarily used in the aerospace industry. The material’s excellent dielectric properties make it very suitable for use with low dielectric fibres such as quartz for the manufac- ture of radomes. The material also has temperature stability up to around 200°C wet. Typical costs: £40/kg. 5.1.5.3 Silicones Synthetic resin using silicon as the backbone rather than the carbon of organic poly- mers. Good fire-resistant properties, and able to withstand elevated temperatures. High temperature cures needed. Used in missile applications. Typical costs: >£15/kg. 5.1.5.4 Polyurethanes High toughness materials, sometimes hybridised with other resins, due to relatively low laminate mechanical properties in compression. Uses harmful isocyanates as curing agent. Typical costs: £2-8/kg 5.1.5.5 Bismaleimides (BMI) Primarily used in aircraft composites where operation at higher temperatures (230°C wet/250°C dry) is required. e.g. engine inlets, high speed aircraft flight surfaces. Typi- cal costs: >£50/kg. GTC-6-0417 - 23PDF Image | GUIDE TO COMPOSITES
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