Effect of internal void on the burning rate constant of PMMA

Le résumé fourni par la source

This study aims to obtain an idealized burning rate constant for polymers without internal bubble effects through a systematic investigation of the combustion behavior of spherical polymethyl methacrylate (PMMA) samples under controlled conditions. The initial void fraction, defined as the relative volumetric expansion resulting from internal bubble formation within the test specimen, was one of the key parameters in this work and was varied within the range of 10 % to 100 %. Burning tests were performed at various sub-atmospheric levels (< 101 kPa). At 100 kPa, buoyancy-induced flows led to asymmetric flame structures and localized overheating of the polymer, triggering active bubble dynamics. As a result, the specific influence of initial void fraction on the burning behavior was difficult to distinguish. By reducing the ambient pressure while maintaining the flame temperature, buoyancy effects were effectively suppressed, allowing for more stable and symmetric flame development. This condition enabled a clearer examination of the relationship between initial void fraction and the burning rate constant. At 20 kPa, for instance, a distinctive linear correlation between the burning rate constant and the initial void fraction was clearly observed, which was masked under relatively higher ambient pressures. Using the extrapolation technique, a reference burning rate constant of 0.43 mm 2 /s was obtained under conditions free of initial void effects. This value is considered an idealized burning rate constant without any void and deformation effects. Indeed, this value is less than half of the values shown in the previous literature (∼1–1.5 mm 2 /s), implying that the effect of volume expansion of the polymer specimen during the burning, accelerated by the internal bubble, is significant. Having an idealized burning rate constant is essential for systematically discussing the internal bubble effects on burning behavior, and this work has a meaningful innovative impact on the deep understanding of polymer combustion.

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