Ageing of FR HDPE and fire performance

Thermal ageing of PIN FR polyethylene for railway applications shows required fire performance lost after 59 days @ 120°C.The tested fibre-filled bio-based (>94% of carbon content) high density polyethylene (HDPE copolymer-1- butene) used a PIN FR package (intumescent, smoke suppressor, synergists) to achieve HL2-R1 under the EU railway fire standard. Until 59 days of thermal aging, the char structure generated by the material in fire tests was not significantly modified, but from 59 days the char showed larger pores, then progressively also showed cracks and became hollow. The material showed significantly deteriorated mass loss calorimeter (MLC) and peak heat release results from 59 days of thermal aging, resulting in failure of HL2-R1, a slight increase in smoke density, but no significant change in lateral flame spread nor smoke toxicity. The authors suggest that this failure of fire performance after nearly two months of high-temperature aging is probably related to oxidation of the polymer matrix which starts to occur at 43 days.

“Thermal ageing of flame-retardant high-density polyethylene designed for railway application”, R. Baron et al., Polymer Degradation and Stability 234 (2025) 111202 https://doi.org/10.1016/j.polymdegradstab.2025.111202