Lijuan Long

Structure and Properties Study of PA6 Nanocomposites Flame Retarded by Aluminium Salt of Diisobutylphosphinic Acid and Different Organic Montmorillonites

Two different types of organic montmorillonite, namely quaternary ammonium salt intercalated MMT (CMMT) and quaternary phosphonium salt intercalated MMT (PMMT) were used as fillers in the flame-retardant polyamide (PA6) based on aluminium salts of diisobutylphosphinic acid (ABPA). The influence of different types of organic montmorillonite (OMMT) on the structure and properties of flame-retardant PA6 nanocomposites were systematically investigated. The X-ray diffraction and transmission electron microscopy results suggested that the introduction of OMMT improved the dispersion of the flame retardant particles independently of the type of OMMT. The derivative thermogravimetry (DTG) curve transformed to one peak from two peaks (representing the degradation of ABPA and PA6, respectively) after incorporation of the OMMT, which further confirmed better ABPA dispersion. Viscoelastic measurements demonstrated that a mechanically stable network structure was formed with the introduction of OMMT or ABPA and OMMT, while PA6/ABPA/PMMT presented the highest storage modulus and viscosity, suggesting a more efficient network structure. From UL-94 and limited oxygen index (LOI) tests, PA6/ABPA/PMMT presented the best flame performance, with a UL-94 of V-0 and a LOI of 33%. In addition, the PA6/ABPA/PMMT presented the lowest peak heat release rate (pHRR) among the investigated samples. Combined with the char layer analysis, it can be deduced that the introduction of PMMT improved the dispersion of ABPA, and promoted the formation of more efficient network structure, before promoting more compact char structures, which finally resulted in improved flame retardancy.

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

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.