Abstract:

A hypophosphite/siloxane bi?functional compound （MVC?AlPi） and a diethyl aluminum hypophosphite compound （AlPi） were combined as a complex flame retardant to enhance the flame retardancy of polyamide 6 （PA6）. The effect of the aluminum hypophosphite/ siloxane weight ratio in the aluminum phosphate?rich compound on the flame?retardant efficiency of PA6 was investigated. The results indicated that there was a synergistic barrier and protective effect on the PA6 composite at a MVC?AlPi/AlPi weight ratio of 2.2/8.8. This made the PA6 composite obtain an improved limiting oxygen index of 31.5 vol% and reach a flammability rating of UL 94 V?0 in the vertical burning experiment. The composite exhibited a decrease in peak heat release rate by approximately 50 % compared to pure PA6， and meanwhile the total heat release decreased by 15 %. The PA6 composite with 2.2 wt% MVC?AlPi and 8.8 wt% AlPi showed a lower char yield than that the composite with 11 wt% MVC?AlPi. A two?layer carbon structure with a hard inner layer and a ceramic?like outer layer was observed from the residual char of the composite after combustion. The interaction of MVC?AlPi， AlPi， and PA6 could lock more P and C fragments， promoting the formation of a barrier protective carbon layer based on the silicon?containing phosphorus?rich residue. A better synergistic flame retardant effect could be achieved through adjusting the ratio of each component at the fixed total amount of flame retardants.

Key words: hypophosphite/siloxane bi?group compound, synergistic barrier and protective effect, polyamide 6, flame retardant