Study of using aluminum hypophosphite as a flame retardant for low-density polyethylene

Aluminum hypophosphite (AHP) was first used to improve the flame retardance of low-density polyethylene (LDPE). The flame-retardant properties of LDPE composites were investigated by the limiting oxygen index, vertical burning test (UL-94), microscale combustion calorimetry, and cone calorimeter tests. The results showed that the incorporation of AHP could improve the flame retardancy of LDPE dramatically, the limiting oxygen index of LDPE containing 50 phr AHP reached 27.5%, and the UL-94 could pass V-0 rating. The cone calorimeter test results indicated that PP/AHP composite exhibited superior performance, and the heat release rate and the total heat release of composites were significantly reduced. In addition, the strength of the char was improved with the load of AHP increased. The structure of the char was researched by Fourier transform infrared spectrometry (FTIR) and scanning electron microscope-energy dispersive spectrometer, and the results revealed that AHP promoted the formation of compact char layer. The TG-FTIR analyses proved that AHP could react with LDPE to reduce the production of olefin in gas phase. Moreover, the structure of P-O-C was found, and the effective mechanism of AHP in LDPE composites was also hypothesized in this work.