Combining cone calorimeter and PCFC to determine the mode of action of flame-retardant additives

The flammability of various flame-retarded formulations containing different hydrated mineral fillers and/or phosphorous compounds and/or carbon nanotubes has been investigated using both a cone calorimeter and a pyrolysis combustion flow calorimeter (PCFC). A method was proposed to evaluate the barrier effect of the flame-retardant additives. This method is based on the fact that the PCFC is non-sensitive to physical flame-retardant effects whereas both chemical and physical phenomena have a great effect on cone calorimeter results. Therefore, normalized peak of heat release rate (pHRR) values obtained with both techniques do not always show a good correlation. It was highlighted that the mismatch between both pHRR results was related to the formation of a protective layer during combustion. Protective layers have been evidenced independently by visual observations. Thus, it is proposed that the magnitude of the deviation from a perfect correlation between cone calorimeter and PCFC pHRRs could be used to quantify the magnitude of barrier effect. Although the results obtained from different fire tests are generally not correlated, such an approach based on the complementarity of different techniques appears more relevant despite of its empirical nature. Copyright (C) 2011 John Wiley & Sons, Ltd.