Research on Low Heat Release Low-Smoke Halogen-Free Flame Retardant Polyolefin Composite Materials

Using polyolefin resin as matrix, metal hydroxides magnesium hydroxide and aluminum hydroxide as flame retardants, low-smoke halogen-free flame retardant polyolefin composite materials were prepared by compounding granulation process. Effects of resin, flame retardant, silicate flame retardant synergist, and phosphorus nitrogen flame retardant on peak heat release rate(PHRR) and total heat release(THR) of low-smoke halogen-free flame retardant polyolefin composite materials were studied. Results showed that effects of three resins including ethylene-vinyl acetate copolymer(EVA), polyolefin elastomer(POE), and linear low-density polyethylene(LLDPE) on PHRR and THR were POE, LLDPE, and EVA in descending order. Therefore, the use of POE should be minimized in low heat release materials. Compared with the use of aluminum hydroxide or magnesium hydroxide alone, PHRR and THR of magnesium hydroxide and aluminum hydroxide were lower. When the ratio of magnesium hydroxide to aluminum hydroxide was 1∶5, heat release of composite materials was the smallest. Although some silicate flame retardant synergists had good carbon layer integrity after combustion, heat release after combustion was larger, which might be due to different types of organic modifiers used or high content of organic modifiers, making composite materials easier to ignite in the early stages of combustion. Phosphorus nitrogen flame retardants could be used in combination with aluminum hydroxide to not only reduce heat release of composite materials, but also further enhance strength of carbon layer, while combination of phosphorus flame retardants with magnesium hydroxide could actually cause a decrease in flame retardancy of composite materials.