Polyolefins, and in particular polypropylene, are increasingly used in building, transport and electrical applications due to their low cost, properties and easy process. Across the good properties of polyolefins such as chemical and electrical properties, their flammability is poor. They burn with a hot and clean flame, accompanied by melting and subsequent dripping or flowing of the molten polymer, limiting the widening of their application domains. To flame retard polymer in general and polyolefins in particular, fire retardant additives can be added to the matrix using an extrusion process. This methodology is widely used in the case of polyolefins because it is a low cost and well known technology. However, in a number of applications, the required level of fire retardant properties is more and more difficult to reach. As an example, in electrical applications [1], whereas UL94 classification was desired by the companies for a thickness of sample of 3.2mm a few years ago, a UL94 classification for 1.6mm (and even 0.8mm) thick sample is now required. At such thickness, when the FR additives are added in the matrix at a level of 20-30% (typical loading for phosphorus based compound), the quantity of available additives in case of fire is very low and the FR properties of materials are not high enough. When increasing the FR content, the mechanical performances of the materials rapidly degrade. As a consequence, two approaches can be followed to achieve acceptable performance: (i) the development of higher effective FR systems and/or the development of synergistic systems and (ii) the use of fire retardant coatings. The second approach has been followed in this study.
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