Synergistic effect of nano silicon and piperazine pyrophosphate/melamine polyphosphate on flame retardancy of polypropylene

To improve the flame retardant efficiency of intumescent flame retardants, some nano-scale additives as synergists were always added. In this work, nano silicon and piperazine pyrophosphate/melamine polyphosphate into polypropylene was investigated, which was obviously efficient to improve thermal stability and flame retardancy. The optimal synergistic ratio corresponded to 1 wt% SiO2, 10 wt% piperazine pyrophosphate, and 5 wt% melamine polyphosphate. The system passed the UL-94 V-1 classification and had a limiting oxygen index value of 34.5%. It exhibited a decrease on peak heat release rate and peak smoke production rate by 81% and 80%, respectively. Based on characterizations of scanning electron microscope, Fourier-transform infrared spectroscopy, and X-ray photoelectron spectroscopy, the synergistic mechanism was investigated. A reactive cross-linking network between SiO2 and piperazine pyrophosphate/melamine polyphosphate during burning was formed to enhance the structure of carbon protective layer. Nano silicon acted as a foaming nucleating agent to promote the formation of porous dense carbon layer in intumescent flame retardants during burning. The synergistic strategy of SiO2 and piperazine pyrophosphate/melamine polyphosphate provided new compounded system for the design of polymeric materials with excellent flame retardancy, great thermal stability, and low release of heat and smoke.

Automated summary

In this study, the addition of nano silicon and piperazine pyrophosphate/melamine polyphosphate into polypropylene was found to improve thermal stability and flame retardancy. The optimal synergistic ratio was determined as 1 wt% SiO2, 10 wt% piperazine pyrophosphate, and 5 wt% melamine polyphosphate. The synergistic mechanism involved the formation of a reactive cross-linking network and a foaming nucleating agent to enhance the carbon protective layer.