Degradation high temperature-resistant

R. D. Ritchie, Symposium on "High Temperature Resistance and Thermal Degradation of Polymers"... 

For many years prior to the development of high-temperature thermoplastics and thermosets, such as the polyimides. polysulfones, and epoxies, phenolic molding material dominated the high temperature-resistant market. This emphasizes their ability to resist temperature degradation in the 400-500°F (204-260 C) range. Because phenolics were found to possess excellent ablative properties, it has been reported that both the American and Soviet space efforts used them in combination with certain other... 

Monomeric vinylic metal n complexes undergo polymerisation reactions to form polymers that have limited applications because of their poor thermo-mechanical properties but they absorb UV without degrading in the process. Such polymers can be used as a UV-resistant coating and act as catalysts in other monomer reactions. Metallocene methylene polymers are high temperature resistant materials and have uses as ablative materials for space capsule heat shields. These materials use Fe and Ru in their metal polymers. 

Research results have determined some increase in high temperature resistance over a single phased cordierite by combining it with a refractory phase such as mullite. However, the cordierite portion still melts at temperatures approximately 1460°C and only a marginal increase is achieved. The addition of substantially quantities of mullite in cordierite degrades the thermal shock resistance. 

W. Gerrard, High Temperature Resistance and Thermal Degradation of Polymers, Monograph 13, Society of Chemical Industry, London, 1961, p. 328. 

Nomex is a high-temperature-resistant polymer since it degrades without melting at temperatures in excess of 300 C. Furthermore, its outstanding mechanical properties are retained after prolonged exposure to elevated temperatures. Its melt intractability precludes melt spinning and it is produced by solvent spinning. 

Madorsky SL, Straus S (1961) High temperature resistance and thermeil degradation of polymers. SCI Monograph 13, pp 60-74... 

However, densely cross-linked plastics (thermosets) are sometimes deliberately used. Reasons tend to be nonmechanical increased solvent and swelling resistance, high-temperature resistance, and reduced flammability are cited. The last arises because the polymer chars rather than degrades with concomitant reduction of volatile (and flammable) components. Examples include epoxies, phenol-formaldehyde resins, and some polyurethanes see Section 14.2. 

They have excellent chemical and radiation inertness and are not subject to UV degradation. High oxidation resistance is another important property. The operating temperature range is from below —310 to 500-600 F (below -190 to 260-315 C). 

The most important properties of refractory fibers are thermal conductivity, resistance to thermal and physical degradation at high temperatures, tensile strength, and elastic modulus. Thermal conductivity is affected by the material s bulk density, its fiber diameter, the amount of unfiberized material in the product, and the mean temperature of the insulation. Products fabricated from fine fibers with few unfiberized additions have the lowest thermal conductivities at high temperatures. A plot of thermal conductivity versus mean temperature for three oxide fibers having equal bulk densities is shown in Figure 2. 

Polyamide or polyimide polymers are resistant to aliphatic, aromatic, and chlorinated or fluorinated hydrocarbons as well as to many acidic and basic systems but are degraded by high-temperature caustic exposures. 

When cured with room temperature curing system these resins have similar thermal stability to ordinary bis-phenol A type epoxides. However, when they are cured with high-temperature hardeners such as methyl nadic anhydride both thermal degradation stability and heat deflection temperatures are considerably improved. Chemical resistance is also markedly improved. Perhaps the most serious limitation of these materials is their high viscosity. 

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