Effect of tea saponin-based intumescent flame retardant on thermal stability, mechanical property and flame retardancy of natural rubber composites

An efficient flame retardant (TS-IFR) was designed by combining phosphoric acid, tea saponin (TS) and melamine structures into a single structure to improve both the mechanical properties and flame retardant performance of natural rubber (NR) composites. A char-forming agent, TS, was successfully modified through chemical method to prepare tea saponin-based intumescent flame retardant (TS-IFR). The structure of the TS-IFR was characterized by Fourier transform infrared spectroscopy and H-1-NMR. A series of flame retardant natural rubber (FRNR) composites were prepared by mixing TS-IFR with NR using a two-roll mill. The thermal stability and fire behaviors of these FRNR composites were investigated by thermogravimetric analysis, limiting oxygen index, vertical burning test (UL-94), cone calorimeter test and scanning electron microscopy. The results revealed that the mechanical properties and flame retardant behavior of NR/TS-IFR were significantly improved for both the high interfacial interaction of TS-IFR with NR matrix and effective dispersion of TS-IFR into NR matrix. As a result, TS-IFR can act as an efficient flame retardant in improving the fire properties of NR.