Flame retardant effect of aluminum hypophosphite in heteroatom-containing polymers

In the present study, the effect of the aluminum hypophosphite (AlHP) concentration on the flame retardant properties of the four different polymers [polyamide 6 (PA6), poly(lactic acid) PLA, thermoplastic polyurethane (TPU) and poly(methyl methacrylate) (PMMA)] was investigated through mass loss calorimeter tests (MLC), thermogravimetric analysis, limiting oxygen index (LOI) and vertical burning test (UL-94). Test results from UL-94 test revealed that 20 wt% AlHP was needed to reach V0 rating in the PA6, TPU and PMMA and 10 wt% was required for PLA. LOI values and the char yields of all composites were increased with increasing AlHP amount. However, peak heat release (pHRR) and total heat evolved values decreased as the added amount of AlHP increased. The highest LOI value (31) and the lowest pHRR value (134 kW/m2) were obtained in TPU/30 AlHP composites. In brief, the comprehensive test results showed that the incorporation of the AlHP improved the flame retardant properties of the PA6, PLA, TPU and PMMA via the formation of the char in the condensed phase and radical trapping and dilution effect in the gas phase.