Flame retardant polypropylene moulding materials are comprised of polypropylene, a flame retardant organic bromine cpd. and a trityl synergist. Typical trityl cpds. are trityl alcohol, tritylthiol, tritylamine, a trityl halide, a trityl ether, trityl ester, etc. It is generally used at 0.1-10 wt. % on the final material. The Br-contg. fire retardants are known cpds. e.g., tetrabromophthalic anhydride, etc. The trityl cpds. have a synergistic effect on the flame retardant action of the bromine cpd., and allow the prodn. of polypropylene compsns. with good flame retardancy but using smaller amts. of flame retardant additives than previously, so that there is less adverse effect on the physical properties of the polypropylene than when using known flame retardant additives.
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