Journal Article Presents a Novel Approach to Measuring Thermal Conductivity of Materials for Pyrolysis Modeling

Fire safety engineers leverage fire models to predict the burning behavior of materials, which helps them design safer buildings and improve firefighting strategies. Accurate model predictions require an understanding of the thermal decomposition mechanism and a corresponding set of material properties, which may be measured using bench-scale tests. Of the required properties, the thermal conductivity of thermally reactive materials (e.g., wood and plastics) is notoriously difficult to measure at elevated temperatures using existing methodologies.  

A new peer-reviewed journal article from the Fire Safety Research Institute (FSRI), part of UL Research Institutes, was recently published in Fire and Materials to address this issue. This article presents and evaluates a method for measuring the thermal conductivity of thermally reactive materials in a manner that is compatible with contemporary pyrolysis models. The paper was authored by FSRI research engineers Matthew DiDomizio, Mark McKinnon, and Grayson Bellamy as part of the Thermal Decomposition of Materials research project. 

Measuring the thermal conductivity of thermally reactive materials

As a material is heated in an inert atmosphere, such as the conditions generated between a diffusion flame and a burning material in an open burning configuration, it will thermally decompose from its original species to a residual species (e.g., char). Intermediate species may also be produced during this process. In a contemporary pyrolysis model, the thermal conductivity must be defined for each distinct species. Thus, characterizing the thermal conductivity is essential for understanding the physics of decomposition. 

In light of this modeling paradigm, FSRI researchers developed a methodology for isolating and measuring the thermal conductivity of each distinct species. This involved a series of bench-scale tests, including:  

• thermogravimetric analysis to derive a reaction mechanism, identify distinct species of the decomposed material, and assess the thermal stability of those species;
• differential scanning calorimetry to derive heats of reaction and specific heat capacities;
• the production of gram-scale samples of each species using a controlled-atmosphere pyrolysis chamber; and
• laser flash analysis on gram-scale samples to measure the thermal conductivity of each species. 

The researchers selected eucalyptus hardboard, colloquially known as “masonite board” in some locales, to evaluate the effectiveness of this methodology. Using this method, the researchers successfully gathered all the necessary information about the material to accurately model how it burns. 

Evaluation of the measured material properties with a pyrolysis experiment and simulation

Next, researchers conducted experiments in which the mass and temperature of hardboard samples were measured as they were exposed to heat representative of a fire. They also developed a pyrolysis model of that experiment using the previously measured material properties. It was shown that the mass loss rate and temperature rise predicted with the model matched well with measurements in the experiments. These results demonstrated the suitability of the material properties, the pyrolysis model, and the overall utility of this approach. 

“We have demonstrated the value of a novel approach for measuring the thermal conductivity of materials in a way that aligns with an accompanying thermal decomposition process, ensuring that the measured data are compatible with contemporary pyrolysis models.” —Matt DiDomizio, research engineer, FSRI

By demonstrating the utility of this methodology, this study sets the foundation for measuring thermal conductivity of materials in future pyrolysis research. 

About Fire and Materials: 

Fire and Materials is the leading journal at the interface of fire safety and materials science. The publication covers all aspects of the fire properties of materials and their applications, including polymers, metals, ceramics, and natural products such as wood and cellulosics. Papers on all areas of fire safety science and engineering are welcomed, including those on passive and active fire prevention, modeling, fire retardant chemicals, human behaviour and wildland and large fires.