Reaction of P-esters into epoxy generates a thermally recyclable polymer with fire performance and low smoke. The phosphorus ester TDPSD* was synthesised from diphenylphosphite, then reacted with epoxy DGEBA in a one-pot, two-step process without using solvents. This resulted in P-C reactive bonding of the PIN flame retardant into the final polymer, and also P-O bonds in the final polymer which enable thermal recyclability (reprocessability). Inclusion of TDPSD to 2.5% phosphorus loading enabled improved fire performance (-25% peak heat release rate compared to neat epoxy) and inhibition of smoke release (-27.5%) but 6% phosphorus load was necessary to ensure recyclability. The material could be recycled by grinding then by heat pressing at 150-160°C (6MPa, 5 mins).
* = 2, 4, 8, 10-tetraoxa-3, 9-diphosphaspiro[5.5] undecane, 3, 9-dioxide
“Recyclable flame retardant phosphonated epoxy based thermosets enabled via a reactive approach”, W.W. Klingler et al., Chem. Eng. J. 466 (2023) 143051 https://doi.org/10.1016/j.cej.2023.143051