Magnesium hydroxides polypropylene composites

Polypropylene compositions containing magnesium hydroxide, with and without magnesium stearate surface treatment, were characterised at low and high shear rates using dynamic and capillary measurement techniques [36]. A significant reduction in viscosity was observed when surface treatment was present, particularly at low shear rates. In addition, with this system, the yield stress for the onset of flow was markedly reduced (Compare magnesium hydroxide variants A and E in Fig. 9). 

Hornsby, P.R. and Mthupha, A., Analysis of fire retardancy in magnesium hydroxide-filled polypropylene composites, Plast., Rubber Composites Process. Appl., 25, 347-355, 1996. 

Hornsby, PR. and Watson, C.L., Interfacial modification of polypropylene composites filled with magnesium hydroxide, J. Mater. Sci., 30, 5347-5355, 1995. 

Attempts to improve flexural strength by surface treatment of fillers have not, to date, been successful. A variety of silanes, titanates, and fatty acids and their derivatives have been used to coat magnesium hydroxide for use as a filler in polypropylene. " Almost all composites had inferior flexural properties. In the few cases where some improvement was seen, it was 10% more then the unfilled material. 

Decomposition of PA-6 and PA-66 produces NH3, H2O, CO, CO2, and hydrocarbons. The addition of magnesium hydroxide decreases the amounts of volatiles produced but the chemical components and their proportions are very similar to unfilled polymers. The addition of zeolites to polypropylene changes the mechanism of degradation depending on the zeolite type, its morphology, and dispersion but, in the investigation, the composition of the decomposition products was not determined. ... 

Surface modifiers are used for a number of reasons, and these include reduction of dustiness and moisture content, improved processing, and enhanced composite properties. Table 11.1 shows that filling polypropylene with uncoated magnesium hydroxide results in a significant decrease in impact and flexural strength. However, surface treatment of the filler can counteract these effects to some degree. 

Natural fiber-reinforced polyolefins are commonly apphed to automotive and constmction applications. The most abundantly used additive is fire retardant. Flammability is an important factor that often limits the application of composites to a specified field. Magnesium hydroxide is the most common flame retardant material used in the constmction industry. This filler responds well to surface modifiers and decomposes by an endofliermic reaction that releases water at temperatures close to the polymer degradation temperature as show in Eq. 6.1. Rothon et al. [78] studied the effects of magnesium hydroxide on polypropylene as a flame retarder of 60 % by weight. The smdy found less heat emission at 100 kWm after 6 min of fire exposure compared to filled PP without Mg(OH)2 at 500 kWm. ... 

Oyama HT, Sekikawa M, Shida S. Effect of the interface structure on the morphology and the mechanical, thermal, and flammability properties of polypropylene/poly(phenylene ether)/magnesium hydroxide composites. Polym Degrad Stabil 2012 97(5) 755-65. 

Lomakin, S. Zaikov, G.E. Koverzanova, E.V. Thermal degradation and combnstibil-ity of polypropylene filled with magnesium hydroxide micro-filler and polypropylene nano-filled aluminosilicate composites, in M. Le Bras, C.A. Wilkie, S. Bonrbigot, S. Duquesne, and C. Jama, Eds., Fire Retardancy of Polymers New Applications of Mineral Fillers. Royal Society of Chemistry, London, 2005, pp. 100-113. 

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