Enhanced Flame Retardancy of Polypropylene with Magnesium Hydroxide, Melamine and Novolac

Abstract

It has been found that, even at levels of magnesium hydroxide too low to impart flame retardancy to polypropylene, the addition of melamine makes it possible 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 can not be obtained. It was then found that by the further addition of a novolac at lev els as low as 1%, together with melamine, a UL 94 V-0 rating could be reached. Levels of magnesium hydroxide could be as low as 30-50%, allowing the formula tion to be flexible. The novolac caused a useful dimension-stabilizing effect above the melting point of polypropylene. Some thermal evidence suggested that a novolac-magnesia gel may be formed.