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Sep 3, 2018
Chemical heat stability of the polymer
Before discussing the polyimide thermal andthermal oxidative decomposition we should first discuss the thermal stabilityof polymer chemistry, physical heat resistance, and temperature. Chemicalthermal stability means that the polymer thermal decomposition of high and lowtemperature, generally measured by TGA. As the temperature begins to decompose,and the temperature of 5% weight loss of 10% weight loss temperature isrepresented.
The so-called "Start decompositiontemperature" refers to the TGA curve begins to deviate from the baselinetemperature. Because of this it is difficult to accurately determine the TGcurve. But the maximum rate of weight loss is difficult to accuratelydetermine. More important is the method used to determine the initialdecomposition temperature is much higher than the actual decompositiontemperatures. So lose the actual thermal stability of the polymer indicatedmeaning.
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 theloss in weight, but also the material substantially retains its basic structureand performance available. There is also more of weightlessness. E.g. 10%, 50%of the temperature. Then the structure and properties of the material haschanged 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 decompositiontemperature measured by TGA up to about 600 ℃. It is probably thelimit of organic polymer materials may reach thermal stability. But this doesnot mean that such polymers can be used at nearly 600 ℃. The actualtemperature is much lower than the decomposition temperature in TGA indicatedabout, usually because the polymer has begun to chemical changes in the 350 ~400 ℃. Such as the generation of free radicals, chain scission andcrosslinking occur.