The PIN FR DOPO is shown to achieve fire and mechanical performance, transparency and recyclability in epoxy. The commercial phosphorus PIN FR 9,10-dihydro-9-oxa-10-phosphaphenanthrene 10-oxide (DOPO) was pre-reacted into DGEBA epoxy before curing. AFD (4-Aminophenyl disulphide) was used as curing agent, resulting in epoxy resin with disulphide bonds. LOI was increased from 24% (neat epoxy) to nearly 30% and peak heat release rate was decreased by nearly 50% at 4% DOPO. UL 94 V-0 (2 mm) was achieved at 3% and 4% DOPO. Good mechanical properties and transparency were maintained. One-cycle mechanical recycling was tested (regrinding then hot pressing at 200°C, without ageing) resulting in limited loss of mechanical properties (90% of initial tensile strength). Fire performance after recycling was not tested.
“Recyclable flame-retardant epoxy composites based on disulfide bonds: Flammability and recyclability”, X. Li et al., Composites Communications 25 (2021) 100754, https://doi.org/10.1016/j.coco.2021.100754