Phosphorus Flame Retardants
Phosphorus chemicals are known as flame retardants. The phosphorous content of different chemicals vary from as low as 9.5% to as high as red phosphorus. Besides, the phosphorus atom is found in oxidation states ranging from 0 to 5. Typically, phosphorus based flame retardant is designed to develop its activity in combination with the starting decomposition of basic polymer. It can offer a partial gas phase contribution to the flame extinguishing effect which is comparable to brominated flame retardants. However, the main feature is char forming activity sometimes combined with foaming or intumescences, which forms a protective top layer on the surface. This type of solid phase mechanism provides an advantage of less release of smoke and gases in case of fire situation.
“Among all different types of phosphorus flame retardants, organic phosphinates are quite efficient and can be used to develop polymer products with V0 fire resistant properties despite their lower phosphorus contents. Phosphinates also have excellent thermal stability. This type of flame retardant has a very low solubility in water and can be effectively used in polyamides without them losing their inherent properties. This type of phosphorus flame retardant provides synergetic effect with melamine flame retardants.”
“Polyester thermoplastic products can be very effectively developed to achieve V0 rating with phosphinate. However it has different synergy system & does not require melamine flame retardant for synergy. Polyolefins also can achieve V0 flame retardant property with phosphinates.”
“Organic phosphinates are a newly developed class of flame retardants for engineering thermoplastics, and are especially effective for polyamides and polyesters. Different polyamides, especially glass fibre reinforced grades, can be effectively fire retarded with these new halogen-free products based on the phosphinates. The required dosage for a UL 94 V-0 performance is lower than for other flame retardant formulations apart from red phosphorus.”
Review Articles
Reactive modifications of some chain- and step-growth polymers with phosphorus-containing compounds: effects on flame retardance—a review
(395–406) Polymers for Advanced Technologies 22 #4 (2011)
Joseph and Tretsiakova-Mcnall of the University of Ulster, United Kingdom, reviews the synthetic strategies to chemically modify several chain-growth polymers for flame retardance including step-growth thermoplastics and thermoset materials. For chain-growth polymers, this involves primarily copolymerization reactions, under radical initiation, of acrylic or styrenic monomers with phosphorus-containing comonomers, or optionally, by post-modification reactions on preformed olefinic polymeric substrates with appropriate phosphorus-containing reagents. In the case of step-growth polymers, generally, an appropriate phosphorus-bearing moiety is employed, as one of the reactive components, during the step-growth synthetic process. Incorporating phosphorus, through chemical modification reactions, on to the various thermoplastics resulted in substantial increases in the flame retardation. (RDC 3/25/2011).