Performance evaluation of various phosphorus compounds on the flammability properties of short carbon fiber-reinforced polyamide 6 composites

The properties including combustibility, rigidity, thermal conductivity, and the color of the fiber sample influence the flammability characteristics of composite materials. Although the influence of phosphorus-based fire retardants on the flammability characteristics of glass fiber-based composite materials has been well studied, there is a need to better understand the effects of these fire retardants on the flammability characteristics of carbon fiber-based composites. In the current study, four different commercially available phosphorus compounds (melamine polyphosphate (MPP), 9, 10-dihydro-9-oxa-10-phosphaphenanthrene10-oxide (DOPO), aluminum diethyl phosphinate (AlPi), and zinc diethyl phosphinate (ZnPi)) are used. The flammability test results indicate that UL-94 V rating maintains to burn to clamp with the addition of MPP, DOPO, and ZnPi in all concentrations. The highest UL94 V rating of V0 is obtained with the addition 10 wt% AlPi. An increase in LOI value is observed in samples containing MPP, AlPi, and DOPO. The highest LOI value of 41.5% is observed with the addition of 20 wt% AlPi. According to the MLC results, the lower peak heat release rate (pHRR) and total heat evolved (THE) values are obtained with the addition of all studied phosphorus compounds. The lowest pHRR (157 ± 10 kW/m²) and THE (44 ± 5 MJ/m²) values are obtained with the use of 20 wt% MPP and DOPO, respectively. The highest fire performance index (FPI) is achieved with the use of AlPi. Apart from DOPO which shows its effect predominantly in the gas phase, the studied phosphorus compounds exert flame retardant action both in the condensed and gas phases.