Aluminum Hypophosphite versus Alkyl-Substituted Phosphinate in Polyamide 6: Flame Retardance, Thermal Degradation, and Pyrolysis Behavior

Abstract

Aluminum hypophosphite (AP) and aluminum isobutylphosphinate (APBu) were used to flame retard polyamide 6 (PA6). Addition of either AP or APBu resulted in an increased LOI value, UL-94 V-0 rating, and decreased heat release in cone calorimetric tests. However, different chemical structures of two flame retardants caused different flame-retardant effects: APBu endowed PA6 a higher LOI value and better UL-94 result than did AP. Decomposition pathways of AP, APBu, and the corresponding composites were investigated using TGA, TG-IR, Py-GC/MS, and FTIR characterization of the residues. The introduction of AP changed the thermal stability and decomposition behavior of the composites due to the cross-linking reactions occurred, which were proved by rheological analysis and TG-DSC. APBu could not essentially affect the composition of pyrolysis products and decomposition behaviors, but mainly produced phosphorus-containing free radical scavengers in the gaseous phase, which were positive to flame retardation. Finally, the proposed flame-retardant mechanisms of such systems were summarized.