Study On Halogen-free Flame-retardant High Impact Polystyrene/magnesium Hydroxide/microencapsulated Red Phosphorus Composite With A Special Structure

Halogen-free flame retardation is an important developing trend in the field of polymer materials. Generally, the introduction of flame retardant into polymer matrix often decreases the processing and mechanical performances of the material. Therefore, it is vital to study the synergistic effect between different flame retardants and improve the efficiency of flame retardant. In this paper, magnesium hydroxide(MH) and microencapsulated red phosphorus(MRP) were chosen as halogen-free flame retardant(HFFR) and high impact polystyrene(HIPS) was used as polymer matrix. First of all, a series of HIPS/MH/MRP homogeneous composite were prepared, which were used to investigate the synergistic flame retardant effect between MH and MRP in HIPS matrix. Moreover, the effect of MRP concentration on the thermo-oxidative degradation(TOD) behavior and fire performance was also studied. Secondly, a series of HIPS/MH/MRP inhomogeneous composites with the flame retardant dispersed unevenly in HIPS matrix were prepared and investigated in terms of their thermal degradation and fire performance by various means. The main content of this paper is as follows:1. A series of HIPS/MH/MRP homogeneous composites with different compositions were prepared by melt compounding. Thermal degradation behavior and fire performance of the as-prepared composites were investigated by thermal analysis(TA), scanning electron microscopy(SEM), limiting oxygen index(LOI), horizontal and vertical burning test(UL-94), cone calorimetry test(CCT), Fourier transform infrared(FTIR), X-ray diffraction(XRD), et al. It is shown that the thermo-oxidative reaction of MRP has an important effect on the thermal degradation behavior of the composite. The HIPS/MH/MRP composite can generate a smooth, compact and continuous residue layer upon thermal degradation and burning in air. There is remarkable synergy between MH and MRP in the flame retardation of HIPS. The combination of MH and MRP in a proper mass ratio can improve the flame retardancy of the composite and reduce the loading of flame retardant considerably. The flame retardancy of the HIPS/MH/MRP composite increases first, then reaches a peak and subsequently decreases with the rise of MRP content. Overmuch loading of MRP not only leads to decrease of fire retardancy, it also increases the smoke release upon burning.2. First of all, a series of HIPS/MH/MRP homogeneous thin sheets with different compositions were prepared by melt compounding. Then, three different types of HIPS/MH/MRP inhomogeneous composites were obtained by laminate hot-pressing method. The three different inhomogeneous composites are as follows:(1) the flame retardants were dispersed in symmetric gradient mode from surface layer to the central layer and the obtained composite was named as a gradient composite;(2) the flame retardants were dispersed on both surface layers of the composite and there was no flame retardant except the surface layer. In this mode, the obtained composite is called a sandwich composite;(3) the flame retardant was dispersed alternately along the thickness direction of the composite. In this manner, the obtained composite was denoted as an alternating composite. The structure and property of these inhomogeneous composites were investigated by various means. It is shown that the aforementioned inhomogeneous composites with special structures can be successfully prepared by the laminate hot-pressing method. In comparison with the corresponding homogeneous composite containing identical loading of flame retardant, the efficiency of flame retardant is much higher and a smooth, compact and continuous residue layer cam be generated on the surface of these inhomogeneous composites in case of TOD and combustion. The compact residue layer can act as a fire-proof barrier preventing combustion heat in flame area from transmitting into the interior of the material and hinders the escape of volatile gases produced by degradation of polymers. In particular, these composites with special structures exhibit much decreased heat release rate(HRR), total heat release(THR), smoke production rate(SPR) and total smoke release(TSR). This is very important to evacuation, escape and rescue in real fires.