Process for stabilizing by encapsulation red phosphorus to be used as flame retardant of polymeric materials and product so obtained

A process for stabilizing red phosphorus powder, in its various allotropic forms, by encapsulating the particles of said powder in a malamine resin for its safe use as a flame retardant of polymeric materials, which comprises the steps of:

• (a) preparing an aqueous solution of a melamine condensate cationized with a mineral acid by reacting in an aqueous medium melamine, formaldehyde, triethanolamine, and an aliphatic monohydroxyl alcohol having up to 5 carbon atoms, in the respective percent by weight ratios:
• 25.27% to 21.62%, 36.04% to 30.85%, 29.87% to 25.57% and 8.82% to 21,96%, and adjusting the pH thereof with the mineral acid;
• (b) forming a hydrodispersion of the solution formed in step (a) by dispersing red phosphorus powder directly therein;
• (c) heating said hydrodispersion, under stirring, at 80.degree. to 100.degree. C. to encapsulate individual particles of the red phosphorus powder by precipitating onto said individual particles of red phosphorus powder, said melamine condensate to form a continuous and compact layer of an insoluble, partially cross-linked melamine resin;
• and
• (d) subsequently drying the insoluble, partially cross-linked layer of melamine resin in an inert gas stream at 80.degree. to 130.degree. C. to obtain a cross-linked melamine resin-encapsulated red phosphorus powder suitable for easy and safe dispersion in polymeric materials, said layer of melamine resin which encapsulates said red phosphorus powder amounting to 0.1 to 30% by weight of the red phosphorus powder.