Magnesium hydroxide nanodispersion for polypropylene nanocomposites with high transparency and excellent fire-retardant properties

Cooperation of the inorganic nanoparticles to optical polymer matrices can combine the advantages of inorganic and organic optical materials. However, because the nanoparticles are apt to aggregate, it is difficult to maintain the transparency of optical polymer. In this paper, we successfully prepare the transparent polypropylene/magnesium hydroxide (PP/MH) nanocomposites with excellent fire-retardant properties by the melt extrusion process. The MH nanosheets are homogenously dispersed in the PP matrix, which avoids the nanocomposites becoming opaque due to Rayleigh scattering caused by the aggregation of nanoparticles. The PP/MH nanocomposite samples with thickness of 4 mm can keep good transparency even at high MH contents and the flame-retardant performance of nanocomposites is improved obviously by MH. The limiting oxygen index (LOI) of PP/MH nanocomposite with 100 phr MH increases from 19.3 for pure PP to 29.1. In the cone calorimeter test, the peak of heat release rate (PHRR) is obviously decreased by 72% compared to pure PP. A uniform and continuous residue layer for the PP/MH nanocomposite is formed during burning, which acts as a shield for the transfer of flame gases and heat. These results indicate that the nanoparticles can be dispersed well in thermoplastic matrices to obtain high performance nanocomposites, which provides a good foundation to manufacture functional transparent polymer-based nanocomposites by the melt-extrusion process.