Thermal oxidative destruction

Polyorganosiloxanes are very stable chemically the siloxane chain is preserved in many chemical reactions, whereas the thermal oxidative destruction of the molecule is generally connected only with the detachment of lateral radicals. It is essential that the decomposition product is polymer (SiC>2)x, which keeps all its dielectric properties and some strength, unlike the decomposion products of organic polymers. E.g., at 200 °C the dielec-... 

All synthesized oligomers, as shown by DTA and TGA data, are characterized by high thermal stability. Thermal oxidative destruction occurs at temperature as high as 500 °C. 

Silicone-organic pol3miers are more resistant to elevated temperatures. As a result of thermal-oxidative destruction, they release low-molecular-weight products like water and formaldehyde. 

In fact all pol uner materials release hydrogen during thermal-oxidative destruction. 

Thermal-oxidative destruction of polymer materials is accompanied by the formation of corrosion-active components that may essentially change corrosion processes in the polymer-metal contact. 

As a result of photochemical destruction, the halogen-containing polymers split off low-molecular-weight products having analogous composition to those isolated during thermal-oxidative destruction. For example, as polyvinyl chloride breaks down, the release of hydrogen chloride is observed. 

Another group of problems arising in coating deposition from polymer melts is connected with their low thermal stability. The onset temperature of thermally oxidative destruction of structural thermoplastics is much lower than the temperature of the gas flows transporting molten particles to the article. The particles undergo ablation during transportation, which means that a part of the substance is carried away from the surface layer by the... 

MDI based material (177°C) than for the sample with DBDI (>210°C). Since such a transition is a result of thermal-oxidation destruction, the difference between the storage moduli of the MDI and DBDI materials, revealed a higher thermal stability of the DBDI material. 

FIGURE 6 Thermogravimetric curves of a thermal-oxidative destruction of composites K-2 (1), K-3 (2), K-4 (3), hardened by a hardener D-1. 

Thermogravimetric curves of the studied samples have rather complex character because of overlaying different processes against each other, as the differential thermal analysis (DTA) is poorly informative. The carbon rest of samples approximately on 30% exceed maintenance Si02 in samples. Most likely the thermal thermal-oxidative destruction of the polymers, accompanied also allocation of low-molecular siliceous products mainly proceeds (Table 8). 

By study of thermal oxidation destruction of obtained composites it is established that the polymers are more high thermal proof systems in comparison with initial epoxy resin. 

Certain compounds that improve the light stability of polyamides are also stabilizers against thermal oxidative destruction. For example, hydroxyphenylbenzoxazole, which exhibits an appreciable effect as a photostabilizer [45], is also an inhibitor of thermal oxidation [42]. 

The TGA data lend support to the assumption as to the high thermal stabillity of polymers with fragments Tg in the main chain (Fig. 7). The incipient decomposition temperature in a gel medium was 460 °C, and the wieght loss at 1000 °C was 14%. Simultaneously, thermal oxidative destruction in air causes a rapid structural degradation of the polymer starting at 300 °C. Here the weight loss was several times that observed in thermal destruction and could be as high as 60%. 

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