Identification of thermoplastic polymers by method of synchronous thermal analysis

Introduction. The results of research of thermoplastic polymeric materials of different chemical nature (high-­density polyethylene, polycarbonate, polyvinyl chloride), capable of melting, spreading, burning and dripping when exposed to high fire temperatures, forming secondary fire centers, are presented. The relevance of application of a highly accurate and informative method of synchronous thermal analysis to determine the chemical nature of polymers in fire conditions is substantiated.

Goals and objectives. The purpose of the research was to assess the possibility of application of the method of synchronous thermal analysis to identify polymeric materials with different degree of thermal impact on them when diagnosing the formation of secondary fires within the framework of fire-technical expertise.

To achieve the goal, the following tasks were solved: thermoanalytical characteristics to identify semi-crystalline thermoplastics in the native state and exposed to high-temperature effects of fire were determined; thermoana­lytical characteristics to identify amorphous polymeric materials with different degrees of thermal impact on them were determined.

Methods. The method of synchronous thermal analysis, including: thermogravimetric analysis, differential thermo­gravimetry and differential scanning calorimetry was used in the study. An example of combining the method of synchronous thermal analysis with the method of quadrupole mass spectrometry to solve the problem of identification of thermoplastics is presented.

Results. The regularities of thermal and thermo-oxidative degradation of polymeric materials were studied. The methodology of identification thermoplastics by the method of synchronous thermal analysis is considered. It was established that for polymers with exposure temperatures up to 300 °C, significant information about the chemical nature of the polymer is provided by the values of phase transition temperatures (melting, glass transition, thermal (thermo-oxidative) degradation). Determination of the chemical nature of thermoplastics with a high degree of burn-up is possible only in the presence of extrema in the curves of differential thermogravi­metry and differential scanning calorimetry in the high-temperature range of polymer thermolysis. The possibility of identification of thermoplastics by combining thermal analysis with mass spectrometry is demonstrated.

Conclusions. The analysis of research results has shown that the significant thermoanalytical characteristics for identification of semi-crystalline thermoplastics are the melting temperature and the temperature of the maximum mass loss rate of the process of thermal or thermo-oxidative degradation of the polymer. For amorphous thermoplastics — the glass transition temperature and the temperature of thermo-oxidative degradation of the polymer.

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