Before discussing the polyimide thermal and thermal oxidative decomposition we should first discuss the thermal stability of polymer chemistry, physical heat resistance, and temperature. Chemical thermal stability means that the polymer thermal decomposition of high and low temperature, generally measured by TGA. As the temperature begins to decompose, and the temperature of 5% weight loss of 10% weight loss temperature is represented.
The so-called "Start decomposition temperature" refers to the TGA curve begins to deviate from the baseline temperature. Because of this it is difficult to accurately determine the TG curve. But the maximum rate of weight loss is difficult to accurately determine. More important is the method used to determine the initial decomposition temperature is much higher than the actual decomposition temperatures. So lose the actual thermal stability of the polymer indicated meaning.
To solve this problem, the proposed 5% weight loss temperature of the material to measure the thermal stability. Because the 5% weight loss temperature can be accurately determined, while the loss in weight, but also the material substantially retains its basic structure and performance available. There is also more of weightlessness. E.g. 10%, 50% of the temperature. Then the structure and properties of the material has changed too much, hard on behalf of the original structure and the state.
TGA also affected by the atmosphere, affecting the speed constant temperature, and sample status.
For polyimide, the decomposition temperature measured by TGA up to about 600 ℃. It is probably the limit of organic polymer materials may reach thermal stability. But this does not mean that such polymers can be used at nearly 600 ℃. The actual temperature is much lower than the decomposition temperature in TGA indicated about, usually because the polymer has begun to chemical changes in the 350 ~ 400 ℃. Such as the generation of free radicals, chain scission and crosslinking occur.