Flame retarders in nylon

Lead dichloride occurs in nature as the mineral cotunnite. The compound is used in making many basic chlorides, such as Pattison s lead white. Turner s Patent Yellow, and Verona Yellow, used as pigments. Also, it is used as a flux for galvanizing steel as a flame retardant in nylon wire coatings as a cathode for seawater batteries to remove H2S and ozone from effluent gases as a sterilization indicator as a polymerization catalyst for alpha-olefins and as a co-catalyst in manufacturing acrylonitrile. 

Markezich, R. L. Use of alternate synergists with a chlorinated flame retardant in nylon. In FRCA Meeting, Lancaster, PA Fire retardant chemical association, 1987. 

Levchik, S.V., Camino, G., Costa, L., and Levchik, G.F. 1995. Mechanism of action of phosphorus-based flame retardants in nylon 6.1. Ammonium polyphosphate. Fire Mater. 19 1-10. 

Zinc Sulfide [1314-98-3]. This stable white pigment shows synergistic flame-retardant action in PVC and can be partially substituted for antimony oxide. It can enhance other flame retardants in nylons and nylon blends (18). 

Uses. As a flame retardant on Nylon 6 fibers intermediate in the production of pesticides and herbicides as a stabilizer in oil and plaster an additive to lubricants... 

Dimethyl hydrogen phosphite is used as a flame retardant on nylon 6 fibres, as a chemical intermediate in the production of pesticides and in lubricant additives and adhesives. No data on occupational exposure levels were available. A potential source of exposure to this chemical is from its occurrence as a degradation product of the chemical intermediate trimethyl phosphite and of pesticides such as trichlorphon and malathion (lARC, 1990). 

There have been substantial efforts to improve the flame resistance of nylons. Various halogen compounds (synergized by zinc oxide or zinc borate) and phosphorus compounds have been used (see the section on Flame Retardation in Chapter 1). They are, however, dark in color. 

Additives encompass a wide range of substances that aid processing or add value to the final product [6,7]. Found in virtually all plastics, most additives are incorporated into a resin family by the supplier as part of a proprietary package. For example, you can choose standard PC resin grades with additives for improved internal mold release, UV stabilization, and flame retardance, or nylon grades with additives to improve impact performance. 

Inorganic phosphates. Inorganic phosphates consist of ammonium polyphosphate and red phosphorus. The ammonium polyphosphate product is primarily used in intumescent coatings and rubber as well as plastics. Red phosphorus is used as a flame retardant in coatings and nylon. 

Condensed phosphoramides with linear, cyclic, or cross-linked structures are produced by the reaction of POCI3 with ammonia. The higher molecular weight products are insoluble in water and on fnrther heating are converted to a cross-linked insoluble polymer, phosphorus oxynitride (PON)j (25). Phosphorus oxynitride can be made by prolonged heating of melamine phosphates (26), urea phosphate (26), or ammonium phosphate imder conditions where ammonia is retained (27). Phosphorus oxynitride is an effective flame retardant in those polymers, such as nylon 6, which can be flame retarded by exclusively char-forming condensed-phase means. However, phosphorus oxynitride is ineffective (at least by itself) in those... 

Starflam is a member of a family of flame retarded vmreinforced Nylon 66 materials. They are rated V-0A7-0 at 3 mm and 1.6 mm in the UL-94 test. 

Nylons are often used in electrical products, such as electrical connectors, terminal blocks, smah electrical housings, switch components, wire ties, and other industrial parts, where thermal stability and fire resistance are priorities. Because of this practical interest, the thermal stability and flame retardancy of nylons have been studied extensively. Halogen compounds are effective flame retardants for polyamides [14-17], but they have limited utility because their combustion products are toxic. Alternative flame retardants are used with polyamides, such as phosphorus- and nitrogen-containing substances. The most important organic nitrogen-containing flame retardants are melamine and its derivates [14, 18-20]. However, these traditional flame retardants are outside the scope of this chapter. 

Levchik, G.F. Levchik, S.V. Lesnikovich, A.I. Mechanisms of action in flame retardant reinforced nylon 6. Polym. Degrad. Stab. 1996, 54, 361-363. 

Red Phosphorus. This aHotropic form of phosphoms is relatively nontoxic and, unlike white phosphoms, is not spontaneously flammable. Red phosphoms is, however, easily ignited. It is a polymeric form of phosphoms having thermal stabiUty up to ca 450°C. In finely divided form it has been found to be a powerful flame-retardant additive (26,45—47). In Europe, it has found commercial use ia molded nylon electrical parts ia a coated and stabilized form. Handling hazards and color have deterred broad usage. The development of a series of masterbatches by Albright Wilson should facihtate further use. 

Usage of phosphoms-based flame retardants for 1994 in the United States has been projected to be 150 million (168). The largest volume use maybe in plasticized vinyl. Other use areas for phosphoms flame retardants are flexible urethane foams, polyester resins and other thermoset resins, adhesives, textiles, polycarbonate—ABS blends, and some other thermoplastics. Development efforts are well advanced to find appHcations for phosphoms flame retardants, especially ammonium polyphosphate combinations, in polyolefins, and red phosphoms in nylons. Interest is strong in finding phosphoms-based alternatives to those halogen-containing systems which have encountered environmental opposition, especially in Europe. 

Flame retardants designated for nylon include halogenated organic compounds, phosphorous derivatives, and melamine cyanurate (160—163). Generally, flame retardants are difficult to spin in nylon because of the high loading required for effectiveness and their adverse effects on melt viscosity and fiber physical properties. 

Flame Retardants. Flame retardants are added to nylon to eliminate burning drips and to obtain short self-extinguishing times. Halogenated organics, together with catalysts such as antimony trioxide, are commonly used to give free-radical suppression in the vapor phase, thus inhibiting the combustion process. Some common additives are decabromodiphenyl oxide, brominated polystyrene, and chlorinated... 

Noryl. Noryl engineering thermoplastics are polymer blends formed by melt-blending DMPPO and HIPS or other polymers such as nylon with proprietary stabilizers, flame retardants, impact modifiers, and other additives (69). Because the mbber characteristics that are required for optimum performance in DMPPO—polystyrene blends are not the same as for polystyrene alone, most of the HIPS that is used in DMPPO blends is designed specifically for this use (70). Noryl is produced as sheet and for vacuum forming, but by far the greatest use is in pellets for injection mol ding. 

---