Relative Thermal Stability of Polymeric Materials

The chemico-thermal stability of polymeric materials can be expressed by the mass loss at a particular temperature by thermogravimetry, since polymers are degraded by thermo-oxidative reactions. On the other hand, the thermal stability of the physical structure of materials is characterized by the softening temperature for 

Sample Temperatures of mass loss/ C Residual mass at 700 C/ % y C 

For several typical heat-resistant polymers, the temperatures of 5% and 10% mass loss and residual mass at 700 C obtained from TG curves, which were determined at a heating rate 5 C min under an N, atmosphere, are given in Table 5.1. The of each polymer is also given in Table 5.1. The structures of some heat-resistant polymers are given in Table 5.2. 

2 Estimation of Thermal Index of Electrical Insulating Materials by the Toop Method 

A test commonly used for estimating the lifetime of wire insulation is ANSI/AMTM procedure D-2307. Twisted pairs of insulated wire are aged in an oven for various time intervals (up to 50 days) at elevated temperatures (up to 240 °C) until voltage breakdown occurs. A series of such tests, performed at different oven temperatures, create a semi-logarithmic plot of lifetime versus the reciprocal of failure temperature. This procedure is useful but it is time consuming. For example, it takes many months for the 

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