The natural mineral colemanite (hydrated calcium borate), quarried in Turkey, was tested in EVA and EMA (ethylene vinyl acetate and ethylene methyl acrylate, polymers used in particular in wires and cables), including in combination with the PIN flame retardants magnesium hydroxide (MDH) and aluminium trihydroxide (ATH). Various combinations of colemanite, MDH and ATH were tested at total 60% additive / 40% polymer, in 4 mm sheets, and compared to neat polymers EVA and EMA for heat release rate, peak heat release (pHRR), total heat release and time to ignition / self-extinguishment. Optimum reduction in peak heat release (pHRR) for EVA was achieved with 60% colemanite (-82%) and with 30%-MDH / 30%-colemanite in EMA (-69%). Analysis suggests that the colemanite is contributing to a surface barrier effect on polymer. The colemanite also improves ignition resistance and self-extinguishment properties and acts as a smoke suppressor, reducing total smoke release (TSR). The authors note that colemanite seems to act in synergy with MDH but not with ATH in these polymers.
“Influence of colemanite on the fire retardancy of ethylene-vinyl acetate and ethylene-methyl acrylate copolymers”, F. Cavodeau et al., Polymer Degradation and Stability, vol. 144, Oct. 2017, pp. 401-410 http://dx.doi.org/10.1016/j.polymdegradstab.2017.08.016