Posted on 13/03/2019 in 2019
Smoke emission / heat release ratio with / without FRs

A detailed scientific paper is published by R. Sonnier, H. Vahabi and C. Chivas-Joly, comparing smoke emission and heat release rate for 22 neat polymers (commercially available). and 9 polymer-FR combinations The FR-polymers tested were (1) EVA (ethylene-vinyl acetate copolymer) with 0 – 60% ATH (aluminium trihydroxide) or MDH (magnesium hydroxide), and (2) polyethylene (LDPE) and polypropylene (PP) with zero or 10% of the phosphorus PIN flame retardant DOPO or the brominated flame retardant TBBPA. Each sample was tested duplicate or triplicate, using 2 mm or 4 mm thick 100 x 100 mm surface of material in cone calorimeter. The ratio A [smoke released per energy released] was calculated as the measured smoke release rate / measured heat release rate. Detailed results show that, for each material, this smoke/energy ratio changes over time with the development of the fire. A second parameter was also identified HRRth (or MLRth), that is the “smoke point” or minimum heat release rate below which smoke is not produced, around 100 kW/m2 for polyolefins, lower for aromatic polymers (can be different between the initial development of the fire and the final dying down). For pure polymers, aromatic polymers emit more smoke and there is a wide variation of A ratios, from below 0.01 (m2/kJ) for polyamides and PMMA poly(methyl methacrylate) to 0.03-0.05 for SBS, epoxies and polycarbonate. Inclusion of ATH or MDH very considerably reduces smoke emission rate and total smoke emission in EVA (to 1/3rd – 1/5th, taking into account the ‘dilution’ of the polymer by the filler), but the ratio A suggests that this is due mainly to the reduction in the heat release rate (not to specific smoke suppression). In polyolefins, the flame retardants (TBBPA and DOPO) did not increase significantly the A ratio [smoke release per energy released]. Both FRs decreased the ‘smoke point’ heat release threshold HRRth significantly. The authors remind that ventilation conditions are a primary factor influencing smoke emissions in fires, underline that assessment of flame retardants should consider both reduction of heat release and smoke emission, and conclude that the parameters developed in this study provide a useful tool to do this.

“New Insights into the Investigation of Smoke Production Using a Cone Calorimeter”, R. Sonnier (ITM Mines Alès), H. Vahabi (Université de Lorraine, Metz) and C. Chivas-Joly (LNE), Fire Technology 2019
A summary of this study was already presented at AMI Flame Resistance in Plastics Conference 2018, see pinfa Newsletter n°98.

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