A preliminary study on the thermal degradation behavior and flame retardancy of high impact polystyrene/magnesium hydroxide/microencapsulated red phosphorus composite with a gradient structure

High impact polystyrene (HIPS) based composite filled by magnesium hydroxide (MH) and microencapsulated red phosphorus (MRP) with a gradient dispersion of the flame retardant was successfully prepared through layer-on-layer laminating. The gradient variations of structure and composition of the flame retardant along the thickness direction of the composite were characterized by scanning electron microscopy and energy dispersive spectroscopy. Fire performance of the gradient composite was determined by cone calorimeter test. It has been shown that the flame retardant displays a symmetric gradient dispersion along the thickness direction of the HIPS/MH/MRP composite. Thermo-oxidative degradation of the HIPS/MH/MRP gradient composite is retarded notably. This gradient composite can not only produce more charred residue upon thermal degradation, the residue is also more continuous and compact than its homogeneous counterpart with the same loadings of flame retardant. The time to ignition of the gradient composite is prolonged and the times to peak heat release rate, peak mass loss rate, peak smoke production rate and peak CO yield of the gradient composite are all delayed remarkably. Overall, the gradient composite exhibits significantly improved thermal stability, flame retardancy, smoke suppression and decreased toxic release in comparison with its homogeneous counterpart.