Thermal degradation mechanism silicone

Hence, a zero percent residue from our TGA of the silicone OH fluids were obtained. GC/MS studies of the decomposed volatiles which were collected by a liquid nitrogen trap have confirmed the presence of these cyclic siloxanes. (A proposed thermal degradation mechanism is listed in Figure 4). Since oxidation... 

Flame-retardant mechanisms of PC-containing sihcone additives (FR-PC) were also elucidated by Py-GC in the presence of TMAH using a similar approach. Recently, much attention has been paid to silicone additives as flame retardants because they generate particularly smaller amounts of toxic substances even in the case of extreme fire. In order to elucidate the structure change induced in the FR-PC system during thermal degradation, the FR-PC and its control PC samples before and after thermal treatment at 380°C (for 2 h) were comparatively subjected to the Py-GC measurement using TMAH at 400°C. 

Kong et al. [115] synthesized hy melt-intercalation silicone rubber (SR)/clay nanocomposites using synthetic Fe-montmoriUonite (Fe-MMT) and natural Na-MMT which were modified by cetyltrimethylammoniumbromide, surfactant. They obtained exfoliated and intercalated nanocomposites. With TGA and mechanical performance found that with the presence of iron significantiy increased the onset temperarnre of thermal degradation in SR/Fe-MMT nanocomposites. In addition, the thermal stability, gel fraction and mechanical property of SR/Fe-MMT were different from the SR/Na-MMT nanocomposites, so the iron not only in thermal degradation but also in the vulcanization process acted as an antioxidant and radicals trap. A new flame-retardant system, SR/Fe-OMT based on an EVA matrix, was examined Fang et al. [ 116]. The experimental analyses showed that the exfoliated Fe-OMT had better dispersion in the EVA matrix than Na-OMT, and it was more effective in improving... 

Pyrolysis followed by gas chromatographic separation uses thermal energy to break down a polymeric structure to monomers and oligomers, and separation of those units for quantification. Because of the temperature limitations of the common silicone capillary column, only the dimer and trimers of the system studied can be reliably separated and detected. The major mechanism of producing dimers and trimers with pyrolysis can be attributed to thermal degradation. A relatively small amount of dimers and trimers is formed as a result of a recombination of monomers. This mechanism is demonstrated as follows. 

Patel et al. [21] also demonstrated that organotin species such as dialkyltincarboxylates have a significant influence on both the low temperature thermal stability and load bearing characteristics of elastomeric silicone foams. The presence of these catalysts is impKcated in both proposed low temperature degradation mechanisms for condensation-cured RTV silicones. It was also reported that reaction of these tin species with water leads to siloxane chain scission at temperatures >120°C. This conclusion has been further supported by the Sn Mossbauer and NMR studies carried out recently by Labouriau et al. [22]. 

The mechanism of thermal degradation is also directly related to the amount of oxygen present in the immediate environment as well as the presence of oils, chemicals or steam. When silicone elastomers are heated above 200 °C in close confinement, polymer reversion may result in softening and a loss of elastomeric properties. Usually this effect can be... 

Fillers can also be used to promote or enhance the thermal stability of the silicone adhesive. Normal silicone systems can withstand exposure to temperatures of 200 C for long hours without degradation. However, in some applications the silicone must withstand exposure to temperatures of 280 C. This can be achieved by adding thermal stabilizers to the adhesive formulations. These are mainly composed of metal oxides such as iron oxide and cerium oxide, copper organic complexes, or carbon black. The mechanisms by which the thermal stabilization occurs are discussed in terms of radical chemistry. 

Silicones possess both thermal stability and good mechanical, chemical, and electric properties between —70 and 250 C. In the absence of oxygen, many linear siloxanes degrade at temperatures greater than 350 C to give cyclic products. Oxidative degradation generally occurs at lower temperatures. 

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