Testing AlPi in epoxy

AlPi showed effective fire performance in epoxy resin, achieving UL 94 V-0 (3 mm), including with glass fibre. Aluminium diethyl phosphinate is a recognised and widely used PIN flame retardant in polyamides and polyesters. Here it was tested at 30% loading in DGEBA – DER-331 epoxy, with two different AlPi particle sizes, with and without 70% glass fibres and with zinc hydroxy stannate and inorganic silicate as possible synergists. Vertical UL 94 V-0 was achieved both with and without glass fibre with AlPi (30% loading) with LOI (limiting oxygen index increased by nearly +50% and heat transmission through the epoxy considerably reduced. AlPi particle size made little difference to fire performance. The synergists reduced heat release rate but in some cases caused failure of UL 94 V-0. The authors conclude that AlPi acts mainly in the gas phase without glass fibres, but also by char formation with glass fibres in the resin.
“Unveiling aluminum diethyl phosphinate dual identity: Transfer from epoxy resins to glass fiber-reinforced composites”, M. Jauregui Rozo et al., Polymer Composites. 2025;1–19 https://doi.org/10.1002/pc.29911 Illustration: Wikipedia - author Ed (Edgar181).