Nano-Al (OH)3 and Mg (OH)2 as flame retardants for polypropylene used on wires and cables

Abstract

While materials sustainability is mostly considered in terms of their long-time aging, fires are more important—while polymers are flammable. We have developed flame retardants (FRs) for polypropylene (PP) with varied FR concentrations since PP is a very widely used polymer. Stearic acid (SA) has been added to increase filler–matrix interactions and filler dispersion in the matrix. Effects of filler types, particle size, and their concentrations on fire resistibility of different composite samples have been determined via limiting oxygen index tests and burning times. As expected, the oxygen index increases with increasing concentration of either FR. The highest value of the index is seen for 10 wt% 50 nm Al (OH)3 sample. Mixing the two hydroxides does not provide a synergy effect. The longest burning time is seen for 5 wt% 50 nm Al (OH)3 + 7 wt% SA, longer than the time for pure PP sample by 137%. Neat PP has a relatively high dynamic friction value, while addition of 5% SA results in the lowest friction value of all. The highest tensile modulus is seen for PP with 7.5 wt% 15 nm Al (OH)3 particle addition. Thermogravimetric analysis shows high thermal stability for PP with 5% each of Al (OH)3 and Mg (OH)2. Scanning electron microscopy shows that the surfaces of Al (OH)3-containing samples are slightly rougher than those with Mg (OH)2. Energy dispersive X-ray spectroscopy shows uniform distribution of both Al and Mg atoms in the composites.