Cables with mineral PIN flame retardants showed durable fire performance after prolonged harsh weathering. Simple test cables (copper core plus mono-material sheath) were formulated by Leoni Kabel, using EVA and EVA-LLDPE (ethylene vinyl acetate and linear low density polyethylene) and the well-recognised mineral PIN flame retardants ATH and MDH (aluminium tri hydroxide at 35-40% loading and magnesium di hydrate at 60% loading, both supplied by Nabaltec), plus 0.25% antioxidant. The cables were exposed to cycles of temperature (-10°C to +70°C), UV and humidity in a weathering chamber for up to 12 weeks (continuous cycles). Fire performance of the cables was little changed after weathering (e.g. peak heat release rate decreased slightly). After 12 weeks weathering, serious structural problems showed with all cables, with visible cracks and degradation of sheaths. The authors conclude that there will be no problem with flame retardancy performance for such materials subjected to natural weather exposure for several years, but that durability of fire retardancy for longer periods requires further investigation.
“Degradation of flame retardance: A comparison of ethylene-vinyl acetate and low-density polyethylene cables with two different metal hydroxides”, Y. Tan et al., J Appl Polym Sci. 2021, https://doi.org/10.1002/app.50149