SYMPOSIA PAPER Published: 01 March 2023
STP164220210106

Impact of Specimen Preparation Method on Thermal Analysis Testing and Derived Parameters

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Thermal analysis methods are used to obtain data for fire modeling. These milligram-scale tests require that representative specimens be produced from bulk samples. Researchers have adopted cryogenic milling as a method of specimen preparation, but it is not clear whether this process affects test results and consequently the derived kinetics and energetics parameters. In this work, six preparations each of a charring polymer, polyvinyl chloride (PVC), and noncharring polymer, polymethyl methacrylate (PMMA), were produced by varying the durations of cryogenic milling. The preparations were subjected to thermal analysis testing (thermogravimetric analysis, differential scanning calorimetry, and microscale combustion calorimetry). Kinetics and energetics were derived for each preparation and used to simulate a gram-scale gasification experiment involving these materials. PMMA was significantly affected by the specimen preparation method, with longer milling durations increasing the contribution of low-temperature reactions and decreasing the contribution of high-temperature reactions. Predictions of mass remaining after 15 min of exposure to 25 kW m−2 irradiance decreased from 66.9 ± 0.2% when the model utilized parameters determined from tests of unmilled samples to 56.5 ± 2.1% when these parameters were determined from samples milled for 10 min. PVC was less affected by the specimen preparation method, with the exception of the unmilled preparation, which exhibited a rapid increase in mass loss rate and heat flow at approximately 300°C. The predicted mass remaining after 5 min of exposure to 40 kW m−2 irradiance ranged from 57.2 ± 7.3% to 68.8 ± 5.7% among the six preparations. Due to the high variability in derived parameters, the impact of specimen preparation on model predictions was not conclusive for PVC. This work demonstrates that cryogenic milling can affect thermal analysis testing, derived parameters, and predictions based on those parameters. Additional study is needed to make recommendations for the adoption of a standardized protocol.

Author Information

DiDomizio, Matthew, J.
Fire Safety Research Institute, UL Research Institutes, Columbia, MD, US
McKinnon, Mark, B.
Fire Safety Research Institute, UL Research Institutes, Columbia, MD, US
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Pages: 64–87
DOI: 10.1520/STP164220210106
ISBN-EB: 978-0-8031-7732-1
ISBN-13: 978-0-8031-7731-4