Publications
Application of low-heating rate TGA results to hazard analyses involving high-heating rates
Thermal gravimetric analysis (TGA) combined with evolved gas analysis by Fourier transform infrared spectroscopy (FTIR) or mass spectrometry (MS) often is used to study thermal decomposition of organic polymers. Frequently, results are used to determine decomposition mechanisms and to develop rate expressions for a variety of applications, which include hazard analyses. Although some current TGA instruments operate with controlled heating rates as high as 500° C/min, most experiments are done at much lower heating rates of about 5° to 50° C/min to minimize temperature gradients in the sample. The intended applications, such as hazard analyses involving fire environments, for rate expressions developed from TGA experiments often involve heating rates much greater than 50° C/min. The heating rate can affect polymer decomposition by altering relative rates at which competing decomposition reactions occur. Analysis of the effect of heating rate on competing first-order decomposition reactions with Arrhenius rate constants indicated that relative to heating rates of 5° to 50° C/min, observable changes in decomposition behavior may occur when heating rates approach 1,000° C/min. Results from experiments with poly(methyl methacrylate) (PMMA) samples that were heated at 5° to 50° C/min during TGA-FTIR experiments and results from experiments with samples heated at rates on the order of 1,000° C/min during pyrolysis-GC-FTIR experiments supported the analyses.