Thermal Degradation and Fire Behaviors of Glass Fiber Reinforced PA6 Flame Retarded by Combination of Aluminum Hypophosphite with Melamine Derivatives

Low-cost aluminum hypophosphite (AP) was used as the flame retardant for glass fiber reinforced polyamide 6 (GFPA6) together with melamine pyrophosphate (MPyP) or melamine cyanurate (MCA) to prepare halogen-free flame-retardant GFPA6 composites. The thermal degradation behavior and fire behavior of the resulting GFPA6 composites were investigated via thermogravimetric analysis (TGA) together with evolved gas analysis (TG-FTIR) and via limiting oxygen index (LOI) test, vertical burning test (UL-94) and cone calorimetry, respectively. Both AP/MPyP and AP/MCA flame retardant systems could endow GFPA6 composites V-0 rating in UL 94 test and increase the LOI values to 29.0% at 20wt% of total loading. Cone calorimeter results showed that AP combined with melamine derivatives could efficiently reduce the smoke production of the flame-retardant composites, particularly the production of CO. Thermal analysis indicated that some reactions occurred among AP, melamine derivatives and PA6 matrix during heating. The phosphorus-and nitrogen-containing volatile products were detected in the TG-FTIR. The burning residues showed compact, continuous and bladder-like char layers from the observation of morphologies by scanning electronic microscopy (SEM). All the results indicated that both condensed phase and vapor phase flame retardant mechanisms occur in these composites.