Improving fire retardancy of ceramifiable polyolefin system via a hybrid of zinc borate@melamine cyanurate

To achieve a high flame retardancy of ethylene-vinyl acetate copolymer (EVA)-based ceramifiable composites, we prepared a hybrid of zinc borate@melamine cyanurate (ZB@MCA) by depositing zinc borate (ZB) at the surface of melamine cyanurate (MCA) on the basis of their hydrogen bonding, and incorporated the ZB@MCA into the EVA/glass powder/mica powder/organo-modified montmorillonite (EVA/GP/MP/OMMT) system to form a novel flame-retardant and ceramifiable EVA composite (EVA/GP/MP/OMMT/ZB@MCA). For EVA/GP/MP/OMMT/ZB@MCA composite with a weight ratio of 35/23/17/5/20, its ceramic formed at 800 °C has the flexural strength of 13.9 MPa, keeping at a high level. The burning tests confirmed that the limiting oxygen index (LOI) value of the composite reached 27.5%, and the UL-94 V-0 rating was achieved. The peak of heat release rate (PHRR) and the peak of smoke production rate (SPR) decreased remarkably compared with the corresponding value of neat EVA in cone calorimeter test. Thermogravimeter-Fourier transform infrared spectroscopy (TG-FTIR) and X-ray photoelectron spectroscopy (XPS) spectra were used to illustrate the flame-retardant mechanism of ZB@MCA in ceramifiable EVA system, and the result illustrated that the gas-phase flame-retardant mechanism was dominant, meanwhile, the ZB facilitated the formation of ceramic layer as a physical barrier in condensed phase, further leading to the enhancement of flame retardancy of EVA composite.