Ceramifiable polyolefin materials have an excellent application prospect in high-temperature-resistant wires and cables because of their excellent fire safety performance via a ceramization process under fire conditions. During the ceramization process, the control of the crystalline phase plays a vital role in determining the final fire resistance and ceramifiable properties. In this work, ammonium polyphosphate/zinc borate (APP/ZB) was developed to achieve the highly efficient flame retardance and ceramization of the ethylene-vinyl acetate/mica powder/organo-modified montmorillonite (EVA/MP/OMMT) composite. In the combustion test, the EVA/MP/OMMT/APP/ZB system displayed obvious flame retardance feature, showing much lower total heat release and total smoke production than neat EVA. After treating at high temperatures, rigid ceramic products were formed for EVA/MP/OMMT/APP/ZB. The ceramic that was formed at 900 °C had a flexural strength of 10.3 MPa for EVA/MP/OMMT/APP/ZB containing 23 wt % of APP/ZB (9.9:13.1), increased by 2475.0, 635.7, and 586.7% compared to the corresponding values of EVA/MP/OMMT, EVA/MP/OMMT/ZB, and EVA/MP/OMMT/APP. For the latter two systems, the content of ZB or APP was 23 wt %. APP/ZB showed a remarkable fluxing effect on the ceramization of the MP-based EVA composite. The fluxing mechanism of APP/ZB was revealed by different measurements. Both APP and ZB led to the formation of a glass melt containing α-Zn3(PO4)2 and orthophosphate by increasing the temperature. Successively, the melt crystalline structure cohered the OMMT and MP together, accompanied by the gradual disappearance of the mica phase and the generation of eutectic phenomenon. Finally, a ceramic with high flexural strength was formed, leading to the improved flame retardance and ceramifiable properties of EVA-based composites.
Keywords: ammonium polyphosphate; ceramic; ethylene-vinyl acetate; flame retardance; fluxing agent; zinc borate.