Flame retardancy and mechanical properties of ethylene-vinyl acetate rubber with expandable graphite/ammonium polyphosphate/dipentaerythritol system

摘要

Ethylene-vinyl acetate thermoset rubber (EVM) with high vinyl acetate content has been widely used in wires and cables for many years. However, the problem of melting drip and efficient flame retardance has not been effectively solved. The combination of expandable graphite (EG), ammonium polyphosphate (APP), and dipentaerythritol (DPER) as a flame retardant system for EVM rubber has been proven to be effective in preventing melting drip and improving flame retardance in this study. This is shown by limiting oxygen index (LOI) and vertical flammability (UL-94) tests. The thermal behavior of EVM treated with this instumescent-flame retardant (IFR) system was investigated by thermogravimetric analysis (TGA) experiments. The results indicated that the char residue of treated samples could reach up to 27.1% at 600°C, which is much higher than that of the untreated EVM. Scanning electron microscopy (SEM) micrographs of residue of treated and untreated EVM showed that the IFR system could promote formation of residual char which imparts the antidripping property to EVM. However, the mechanical properties, such as tensile strength (TS) and elongation at break (EB), decreased gradually with the increase of EG content. Compared to the EVM/APP/DPER system without EG, the TS decreased from 6.55 MPa to 6.13 MPa, while the EB decreased slightly from 570% to 558% when the EG content was 15 wt%.