Enhanced flame retardancy of polypropylene with magnesium hydroxide, melamine and novolac

It has been found that, even at levels of magnesium hydroxide too low to im part flame retardancy to polypropylene, the addition of melamine makes it p ossible to reduce burning time under UL 94 conditions sufficiently to meet the V-2 rating. However, flaming drips still persist, so that a V-0 rating by UL 94 cannot be obtained. It was then found that by the further addition of a novolac at levels as low as 1%, together with melamine, a UL 94 V-0 r ating could be reached. Levels of magnesium hydroxide could be as low as :3 0-50%, allowing the formulation to be flexible. The novolac caused a useful dimension-stabilizing effect above the melting point of polypropylene. Som e thermal evidence suggested that a novolac-magnesia gel may be formed.