Thermal degradation kinetics of flame-retardant glass-fiber-reinforced polyamide 6T composites based on bridged DOPO derivatives

Abstract

A novel phosphaphenanthrene oxide, based on bridged 9,10-dihrdro-9-oxa-10-phosphaphenamhrene-10-oxide (DOPO) derivatives (PN-DOPO), was synthesized and incorporated into glass-fiber-reinforced polyamide 6T (GFPA6T) composites. Moreover, a commercial product of aluminum diethyl-phosphinate (OP1230) was introduced as a comparison to examine the effects on the flame-retardant properties and thermal stabilities of GFPA6T. UL-94 test and cone calorimetry results displayed that PN-DOPO showed better flame retardancy of GFPA6T than OP1230. Scanning electronic microscopy results of the char residues after UL-94 test indicated that PN-DOPO promoted a compact char formation. More importantly, the activation energies and the kinetic parameters of the decomposition process were calculated through the Kissinger–Akahira–Sunose (K–A–S) and Flynn–Wall–Ozawa (F–W–O) methods, and the thermal degradation mechanism was studied with the Coats–Redfern method based on thermogravimetric analysis at multiple heating rates. The results demonstrated that the E values of GFPA6T/PN-DOPO at the early decomposition and the late decomposition are higher than those of GFPA6T and GFPA6T/OP1230, especially in the late decomposition stage. The fact indicates that the higher E value and more dense carbonization protection layer contribute to the superior flame retardancy of PN-DOPO for GFPA6T.