Investigation of the modes of action for phosphorous flame retardants in a fully waterborne sugar-based epoxy resin

A fully waterborne epoxy system was prepared from waterborne sorbitol-based epoxy resin cured with an alkylated polyalkylene polyamine hardener. The flame-retardant property was accomplished by the application of different additive phosphorous flame retardants (FRs). Phosphonate polyol and ethyl ethylene glycol phosphate which are in the liquid phase, and two FRs in the form of fine-grained particles; aluminium diethyl phosphinate (AlPi), ammonium polyphosphate (APP). The flame-retardant epoxy resin blends were prepared at the same levels of phosphorus content. The results are very promising as the self-extinguishing behaviour was observed at 3%P for all the investigated FRs and at 1%P in the case of APP. Limiting oxygen index (LOI) values were practically good for all FRs and extremely improved in the case of APP. LOI was 48% for the APP sample at 3%P content. Furthermore, this blend showed the best results in the forced flaming conditions as the total heat release in cone calorimetry measurements (THR) decreased by 43% and the peak of heat release rate (pHRR) decreased by 65% with more elongated burning compared to the reference SPE matrix. The efficient solid-phase FR effect of APP was confirmed by scanning electron microscopic (SEM) and attenuated total reflection-infrared spectrometry (ATR-IR) analysis of the residual char after cone calorimetry measurements.