The effect of DOPO concentration and epoxy amine stoichiometry on the rheological, thermal, mechanical and fire‐retardant properties of crosslinked networks

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Abstract Presented here is an investigation into the effect of a phosphorus‐based fire retardant on the thermal, rheological and mechanical properties and flammability of an epoxyamine network prepared using stoichiometric and off‐stoichiometric epoxyamine compositions. The flame retardant 9,10‐dihydro‐9‐oxa‐10‐phosphaphenanthrene‐10‐oxide (DOPO) was reactively incorporated into a blend of a bisphenol‐F diglycidyl ether epoxy resin and a polyfunctional epoxidized phenol Novolac resin, then cured with diethyltoluenediamine and accelerated using imidazole. Increased DOPO concentration improved fire retardancy, but reduced reactivity and thermal and mechanical properties. An increasing amino excess stoichiometry, however, comparatively increased reactivity and improved thermal and mechanical properties. Despite evidence of an earlier onset of degradation and higher char yield, enhanced graphitisation and reduced volatile emissions for the off‐stoichiometric networks, no significant improvements in fire resistance as a function of stoichiometry were observed using UL‐94 and limiting oxygen index measurements. © 2022 The Authors. Polymer International published by John Wiley & Sons Ltd on behalf of Society of Industrial Chemistry.

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