Effect of water erosion on flame retardancy of high‐impact polystyrene/magnesium hydroxide composite and its mode of action

Abstract

High-impact polystyrene (HIPS) flame retarded by magnesium hydroxide (MH) was treated in water at different conditions. The effect of water erosion on flame retardancy of the HIPS/MH composite and its mode of action was investigated by various means. The results indicate that both limiting oxygen index value and UL-94 rating of the HIPS/MH composite decrease observably after water erosion. The average heat release rate, average mass loss rate, total heat release, and total smoke release of the composite all increase remarkably after water erosion. The MH content in the surface layer of the HIPS/MH composite reduces, and the surface of this composite becomes rough and porous after erosion. The water-eroded composite shows a loose and discrete surface morphology after subjected to fire, which favors heat transfer and mass exchange between flame area and the underlying polymers. Consequently, both flame retardancy and smoke suppression of the polymer composite decrease significantly. The decrease in flame retardancy occurs in condensed phase. The result of this work has provided a basis for further investigations to prevent this detrimental effect induced by water erosion. K E Y W O R D S flame retardancy, high-impact polystyrene, magnesium hydroxide, thermal degradation, water erosion 1 | INTRODUCTION In recent years, developing halogen-free flame retardant (HFFR) polymer materials with low emission of smoke and poisonous gases has become a popular tendency worldwide. 1-4 Many investigations have indicated that inorganic metal hydroxide fillers, such as magnesium hydroxide (MH), aluminum trihydrate (ATH), and layered double hydroxide (LDH), are excellent nontoxic and smokesuppressing HFFR additives. Besides their environmental friendliness, their prices are low. These inorganic metal hydroxides play a flame retardant role in both the condensed and gaseous phases. 5-8 Their decomposition is an endothermic reaction, which reduces temperature of polymer, inhibits thermal degradation of polymer, and lowers supply of volatile gases for the burning flame. Meanwhile, the water released upon thermal degradation of these fillers can dilute the concentration of combustible gases and retards combustion. Furthermore, the metal oxides produced by degradation of metal hydroxides, such as MgO and Al 2 O 3 , are very stable at high temperature. Their deposition on the surface of polymer composite can act as a barrier and protect the underlying polymer from

A Study of Thermal Degradation and Fire Behaviour of Polymer Composites and Their Gaseous Emission Assessment

“…In addition, the most important fire reaction property that evaluates the fire hazard potential of a composite is the heat release rate [46,47]. The fire property of heat release ranges from low-intensity fires (where the radiant heat flux is under 20 kW/m 2 ) to intense fires (with the heat flux exceeding 150 kW/m 2 ) [48][49][50].…”