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A Standard Methodology to Characterize Composite Materials for Pyrolysis Models

Mark B. McKinnon

Sponsor: 
The National Institute of Standards and Technology
FM Global

figure 1As manufacturing technology has improved and structural material requirements in the built-environment have become more demanding, there has been a marked prevalence of engineered polymers and composite materials replacing more conventional materials. These materials provide improvements to the built environment in terms of structural stability and costs, but the thermo-physical properties and pyrolysis behavior of these materials are currently not well documented nor well understood. The development of pyrolysis models for composites and engineered materials can improve the understanding of the flammability characteristics of these new materials and inform the design of the built environment to mitigate the effects of fires.

As computational fire models have become more frequently relied upon and increasingly complicated, it has become evident that more sophisticated pyrolysis submodels are required to accurately predict fire behavior. Pyrolysis submodels have been developed to calculate heat transfer, thermal degradation, heterogeneous reactions, and mass transport, and have been coupled to gas-phase solvers in fire models. Concurrent with the increase in sophistication of pyrolysis models is the growing prevalence of engineered polymers and composite materials in the built environment. The motivation behind this project is to develop a standard methodology to measure the thermo-physical properties and determine the thermal degradation reaction parameters for composite materials that are common in industrial and commercial applications for the purpose of parameterizing fire models to improve predictive capabilities.

The standard methodology resulting from this project was developed while studying corrugated cardboard [1], and current work is focused on demonstrating the procedure on low-pile carpet and fiberglass. Each of these composites feature a layered structure in which each layer can be investigated separately. A battery of milligram-scale experiments (thermogravimetric analysis, differential scanning calorimetry, and pyrolysis-combustion flow calorimetry) is conducted on each layer. The ThermaKin modeling environment [2] is employed to analyze the data to extract the thermal degradation reaction parameters and energetics of the material in each layer.

Bench-scale gasification tests are conducted in a low oxygen environment on 80 mm x 80 mm samples of the composite material subject to radiant heat fluxes in the range of heat fluxes observed in a fully-involved room fire (20-80 kW m-2).  These experiments are conducted in a modified cone calorimeter apparatus developed in our laboratory (Controlled-Atmosphere Pyrolysis Apparatus) [3]. Mass loss data and sample back temperature data are collected simultaneously with the cone calorimeter mass balance and an infrared camera, respectively. These data are analyzed using the ThermaKin modeling environment to extract the thermal transport properties of the each layer of the sample. The thermo-physical properties extracted from the experimental data are used to define the composite materials in the ThermaKin modeling environment, which solves discretized mass and energy conservation expressions to accurately predict the burning rate and heat release rate of the sample material as a function of both incident heat flux and time.

figure 2-4

[1]    McKinnon, M.B., Stoliarov, S.I., and Witkowski, A., (2013) Development of a Pyrolysis Model for Corrugated Cardboard, Combustion and Flame 160: 2595-2607
[2]    Stoliarov, S.I., and Lyon, R.E., (2008) Thermo-Kinetic Model of Burning, Federal Aviation Administration Technical Note DOT/FAA/AR-TN08/17.
[3]    Semmes, M.R., Liu, X., McKinnon, M.B., Stoliarov, S.I., and Witkowski, A., (2014) A Model for Oxidative Pyrolysis of Corrugated Cardboard, IAFSS Symposium 2014.

Mark McKinnon

Mark McKinnon is a Doctorate Student of the A. James Clark School of Engineering. He received his Master of Science degree from the Department of Fire Protection Engineering at the University of Maryland in 2012 and received a Bachelor of Engineering degree from Cooper Union in Mechanical Engineering in 2010. His research is in the area of material degradation and pyrolysis, with a focus on composite materials. For more information about his work, he can be reached at:

Student Phone: 
484-894-3876