Research on Low Smoke Flame Retardant Natural Rubber Based on Aluminum Hypophosphate

The flame retardancy and smoke suppression of natural rubber are very important safety performances for its use as vibration damping materials for rail transit. In order to improve its fire safety, aluminum hypophosphate and aluminum hydroxide were used to prepare flame retardant natural rubber. Cone calorimetry test results show that 20 parts aluminum phosphate and 100 parts aluminum hydroxide is the optimum proportion, which could reduce the maximum heat release rate of natural rubber from 515 kW/m² to 169 kW/m², and the total smoke production from 43 m²/m² to 14 m²/m². Both peak heat release and total smoke production decreased by up to 67%. The test results of mechanical properties show that the addition of aluminum hypophosphate alone greatly deteriorated the mechanical properties of rubber materials, while the use of aluminum hypophosphate combined with aluminum hydroxide still keeps the mechanical properties of rubber materials at a high level: the tensile strength is more than 15 MPa, and the permanent compression deformation is less than 30%. Therefore, aluminum hypophosphite and aluminum hydroxide can not only play a synergistic role of flame retardant natural rubber, but also maintain its high mechanical properties. This work provides a new technical strategy for obtaining flame retardant and low smoke natural rubber.