Study on flame retardant unsaturated polyester resins - an overview of past and new developments

A review over 1961-1998 with 34 refs. covering directions and results of studies on synthesis, crosslinking and modifications intended to impart flame retardancy to; unsaturated polyester resins (UPR). Non-halogenated and halogenated UPR are described, characterized by medium-suppressed flammability, which continue to be marketable despite some environmental demerits. This is true of the resins retarded with tetrahalophthalate compounds and brominated dials; studies are conducted on addition of elemental bromine to double bonds in polyester resins. In addition to flame-retardant, highly lightfast resins are prepared with the aliphatic C-Br bond which, in contrast to the aromatic C-Br, is not dissociated by light rays. No-waste copolymerization of epichlorohydrin with dicarboxylic acid anhydrides is ecologically still essential. Flame retardants and smoke suppressants are grouped into groups comprising hydrated mineral fillers, phosphorus compounds, and inorganics [Sb2O3, Mg(OH)(2), MoO3, SnO2, ATH, CaCO3, etc.). Mechanisms operative in flame retardancy and smoke suppression are reviewed, with particular reference to the synergistic action of Sb-Cl. 'Flame retardants additives' continue to be the most potent flame retardants and smoke suppressants. Aluminum trihydrate (ATH) is mass used, but is effective only at high concentrations and is now recommended for use when prepared with the bimodal particle size distribution. Mg(OH), is another endothermic additive, yet Ca sulfate and Zn berate are cheaper. Low-viscosity phosphoric acid esters, e.g., tris(2-chloroethyl) phosphate, tri(2,3-dibromopropyl) tricresol phosphate, etc. fail to bond with the resin and act also as plasticizers; unsaturated additives, e.g., di(2-chloroethyl) vinyl phosphonate (Stouffer's Fyrol bis-beta), can also be used as crosslinkers. A novel retardant, Great Lakes Chemical's NH-1197 (CN-1197), a bicyclic structure synthesized from pentaerithritol and a phosphorylant, is a char-forming low-smoke fire retardant. Melamine alone or melamine phosphate and/or superphosphoric acid give satisfactory formulations. Sb2O3 can be replaced by zinc berate, 2ZnO . 3B(2)O(3)3.5H(2)O. Zinc oxide and boron oxide alone are char promoter and char stabilizer, respectively. Zinc hydroxystannate and zinc stannate are navel flame retardants and smoke suppressants, especially for halogenated polyester resins.