Effects Of Thermal-oxidative Aging On The Service Life And Flame Retardancy Of Flame Retardant PA6/LGF Composites

In the experiments, the PA6/LGF samples stabilized with a synchronized antioxidantsystem of copper salt antioxidant and phosphorous acid antioxidant, brominated epoxy resins(BER)/antimony trioxide (Sb2O3) and tris (tribromophenyl) cyanurate (BrN)/Sb2O3whichacted as synchronized flame retardant systems to flame retardant PA6/LGF compositesrespectively were prepared via melting impregnation with self-designed pre-dispersionequipment and impregnation groove. Then these samples were subjected to oven aging fordifferent lengths of time, the change patterns in static and dynamic mechanical properties andtheoretical analysis by different degradation kinetics were considered, also the most suitabledegradation kinetics model was confirmed. In addition, the service life and flame retardancy ofthose BER/PA6/LGF、BrN/PA6/LGF flame retardant systems were compared.The results indicated that the crystallinity and thermal stability of PA6/LGF compositesafter thermal-oxidative aging treatment decreased, numerous sharp microcracks and yellowingphenomenon appeared on the surface of composites, and interfacial debonding would easilyhappened under outer loading whether samples aged or not, thus both composites’ staticmechanical behaviors had being reduced. The glass transition temperatures (Tg) moved to ahigher temperature because of crosslinking of PA6chains in the dynamic mechanical propertytests. However, all of the above properties of stabilized composites performed well than thoseof pure samples.The tensile strength, flexual strength and crystallinity of BER/PA6/LGF andBrN/PA6/LGF composites peaked after10d under160oC. However, both static mechanicalproperties and crystallinity decreased with the aging time prolonged, also numerous pits, holesand defects appeared on the composites’ surfaces accompanied by debonding of matrix andglass fibers, furthermore, certain amount of flame retardants migrated to the surface. Themolecular chain and damping property of these flame retardant systems were subjected tolimitations. The residue char barriers of those aged flame retardant systems reflected a moreprotective, dense, continuous and well-distributed char layer structure with advanced LOIvalues and constantUL-94rating as V-0. For aged BER/PA6/LGF composites, this kind ofaging reduced the effect of flame-retardant efficiency on gaseous phase and slightly enhanced the flame-retardant efficiency on solid phase. As to the aged BrN/PA6/LGF composites, thethermal-oxidative aging had positive effect on the flame-retardant efficiency on both ofgaseous and solid phase, to some extent. The integral method of Ozawa was capable ofproviding more reliable information when evaluating the thermal-oxidative degradationkinetics of fiber reinforced composites exposed to a thermal-oxidative aging condition than theKissinger method. The thermal-oxidative degradation of both unaged and aged composites ofBER/PA6/LGF and BrN/PA6/LGF revealed two stages, whose cause in changes correspondedto the changes in HRR curves of relevant flame retardant system. The results indicated thatBrN/PA6/LGF not only showed an more excellent anti-aging property than that ofBER/PA6/LGF in the long term service behavior, but also behaved more stable in combustionproperties which included the flaming degree, flame retardant efficiency and release of harmfulvolatile products.