Compounding for Flame Retardancy

Antimony trioxide (Sb203) and pentoxide (Sb205) are both used in combination with halogen compounds for flame retarding polymers. Their manufacture properties and use have been described by Touval [109]. The trioxide is the predominate form for use in thermoplastics. 

Herman was one of the first to demonstrate the versatility of polymers by developing application for acrylic polymers as oil additives, antioxidants, plasticizers, fibers, coatings and surfacants, as well as related compounds for flame retardants, foams, bactericides and pesticides. 

Molybdenum Oxide. Molybdenum compounds incorporated into flexible PVC not only increase flame resistance, but also decrease smoke evolution. In Table 10 the effect of molybdenum oxide on the oxygen index of a flexible PVC containing 50 parts of a plasticizer is compared with antimony oxide. Antimony oxide is the superior synergist for flame retardancy but has Httle or no effect on smoke evolution. However, combinations of molybdenum oxide and antimony oxide may be used to reduce the total inorganic flame-retardant additive package, and obtain improved flame resistance and reduced smoke. 

Organophosphorus Derivatives. Neopentyl glycol treated with pyridine and phosphorus trichloride in anhydrous dioxane yields the cycHc hydrogen phosphite, 5,5-dimethyl-l,3-dioxaphosphorinane 2-oxide (2) (32,33). Compounds of this type maybe useful as flameproofing plasticizers, stabilizers, synthetic lubricants, oil additives, pesticides, or intermediates for the preparation of other organophosphoms compounds (see Flame retardants Phosphorus compounds). 

Flame Retardants. Bromine compounds make up an important segment of the market for flame retardants used in polymers. Additive flame retardants are added to polymers during processing reactive flame retardants react chemically to become part of the polymer chain itself. In addition to the compounds Hsted in Table 3, a number of proprietary mixtures and phosphoms—bromine-containing flame retardants are also sold (see Elame RETARDANTS, HALOGENATED, FLAAffi RETARDANTS). 

In 1826 J. J. Berzelius found that acidification of solutions containing both molybdate and phosphate produced a yellow crystalline precipitate. This was the first example of a heteropolyanion and it actually contains the phos-phomolybdate ion, [PMoi204o] , which can be used in the quantitative estimation of phosphate. Since its discovery a host of other heteropolyanions have been prepared, mostly with molybdenum and tungsten but with more than 50 different heteroatoms, which include many non-metals and most transition metals — often in more than one oxidation state. Unless the heteroatom contributes to the colour, the heteropoly-molybdates and -tungstates are generally of varying shades of yellow. The free acids and the salts of small cations are extremely soluble in water but the salts of large cations such as Cs, Ba" and Pb" are usually insoluble. The solid salts are noticeably more stable thermally than are the salts of isopolyanions. Heteropoly compounds have been applied extensively as catalysts in the petrochemicals industry, as precipitants for numerous dyes with which they form lakes and, in the case of the Mo compounds, as flame retardants. 

F.K. Antra, C.F. Cullis, and M.M. Hirschler, "Binary Mixtures of Metal Compounds as Flame Retardants for Organic Polymers," European Polymer J., lfl. 96 (1982). 

The function of halogen-containing compounds as flame retardants has been explained by the radical trap theory. Liberated halogen acid (HX) competes in the above reactions for those radical species that are critical for flame propagation. 

The use of phosphorus compounds as flame retardants has been reviewed by Lyons and others (1, 2, 3, 4 5). The mechanism of the action of this element is generally accepted to involve decomposition to produce acids which function as char promoters. Phosphorus compounds are particularly effective flame retardants for polyesters where they function to increase the char yields. 

Since combustion is subject to many variables, tests for flame retardancy may not correctly predict flame resistance under unusual conditions. Thus, a disclaimer stating that flame retardancy tests do not predict performance in an actual fire must accompany all flame-retardant products. Flame retardants, like many organic compounds, may be toxic or may produce toxic gases when burned. Hence, care must be exercised when using fabrics or other polymers treated with flame retardants. 

Among the emerging pollutants of industrial origin, Bisphenol A [2,2 bis(4-hydroxydiphenyl)pro-pane] (BPA) has special relevance since it was one of the first chemicals discovered to mimic estrogens as endocrine disrupters.147 This compound was first reported by Dianin in 1891.1411 BPA is produced in large quantities worldwide, mainly for the preparation of polycarbonates, epoxy resins, and unsaturated polyester-styrene resins.149 The final products are used in many ways, such as coatings on cans, powder paints, additives in thermal paper, in dental composite fillings, and even as antioxidants in plasticizers or polymerization inhibitors in polyvinyl chloride (PVC). To a minor extent, BPA is also used as precursor for flame retardants such as tetrabromobisphenol A or tetrabromobisphenol-S-bis(2,3-dibromopropyl) ether.150 This substance can enter the environment... 

FIGURE 26.5 Relationships between LOI and HRC for pure polymers and FR compounds. (From Lin, T.S. et al., Correlations between microscale combustion calorimetry and conventional flammability tests for flame retardant wire and cable compounds, in Proceedings of 56th International Wire and Cable Symposium, 2007, pp. 176-185.) The LOI-HRC relationship for pure polymers is obtained from the literature. (From Lyon, R.E. and Janssens, M.L., Polymer flammability, Final Report DOT/FAA/AR-05/14 May, 2005.)... 

Mono- and diphosphonium halides have been found to be flame retardants for plastic materials. Their effectiveness can be related to the formation of various active phosphorus compounds, as well as to many of the postulated mechanisms for flame retardant action. The compounds are postulated to be effective because they decompose on ignition to thermally stable phosphine oxides or phosphonic acids which, in turn, are decomposed to continuous films of phosphate glass. In addition, the phosphonium halides form alkyl halides which cool the flame and/or form halogen acids which are fame retardants. 

Early in our studies, we found that ethylene-bis[tris(2-cyanoethyl)-phosphonium bromide] (6) is an effective fire retardant for polyethylene. When this compound showed flame retardant activity, a wide variety of other related compounds were synthesized and evaluated. 

Flexible PVC (Table 15.6) is made by polymerizing at 40-55°C and then compounding with 20-80 PHR (parts per hundred of resin) of dioctyl phthalate and/or other monomeric liquid plasticizers (e.g., dioctyl adipate for low-temperature flexibility, oligomeric polyesters for permanence, organic phosphates for flame-retardance), plus a synergistic stabilizer system usually composed of barium or calcium soap, zinc soap, epoxidized fatty ester, and organic phosphite. 

Several Co, Sn, Pr, Cu, Cu ", and Fe compounds were used for flame retardation of epoxy-based polymers Zarkhina et al. have shown that Mn ",... 

Compared with data of the worldwide use in 1992, the demand for flame retardants in the USA in 1993 was extremely high. However, only a small fraction of this consisted of brominated compounds. The use of brominated compounds as flame retardants in Japan in 1993 was higher, both relatively and in absolute amounts. The 1998 USA consumption of brominated compounds (in absolute amounts) was expected to reach the same level as Japan in 1994. Unfortunately more accurate data on flame retardants demands in Europe are not available. The European consumption of brominated compounds is estimated to be at a similar level as in Japan and the USA. 

Common flame retardants are aluminum trihydrate, brominated compounds, phosphorous compounds, antimony oxide, chlorinated compounds, and boron compounds. Brominated flame retardants are preferred for thermoplastic resins such as polystyrene, polyesters, polyolefins and polyamides but are also used in epoxies, ABS and polycarbonates. Decabromodiphenyl oxide is the most common brominated flame retardant used. 

These results give further impetus to our belief that a variety of additives may be more effectively delivered to polymer films and fibers as high melting inclusion compounds formed with CDs. In this connection for flame retardants, which can be toxic and mutagenic on contact, their confinement in CD-ICs not only protects them from the environment, but protects the wearer of fabrics containing embedded FR-CD-ICs from direct contact with the FR. Thus, one can envision the use of the most effective FRs with little regard to issues of FR toxicity, if they are delivered in the form of their CD-ICs. 

Bromine and chlorine are two reactive halogens that have worked well for flame retardant purposes. Organo-fluorine compounds have not been as effective as flame retardant additives because the carbon-fluorine bond energy is so high that other events dominate at temperatures where halogenated flame retardants operate. ... 

Morgan, A.B. Tour, J.M. Synthesis and Use of Non-Halogenated Aromatic Compounds as Flame Retardants for Polymer-Containing Materials. U.S. Patent 6,566,429 B2, 20 May, 2003. 

In the course of preparing organophosphorus compounds as flame retardant additives for plastics, a number of requirements were estab1ished. 

Fire resistant PU are obtained by the addition or by introduction into the PU structure of special compounds, called flame retardants. The flame retardants are organic compounds containing halogens (chlorine, bromine) and phosphorus. Compounds of antimony (Sb) or boron [1-13] are rarely used. Sometimes inorganic compounds are used as flame retardants for PU, such as, hydrated alumina (Al203 nH20), Sb203 or ammonium polyphosphate [1-3, 14]. 

Retardation of the combustion of nylon fibers has been reviewed by Pearce et al. (10). Several bromine and phosphorus compounds have been suggested to be effective for flame retarding nylon 6, but none of them is used in practice on a reasonable scale (12). 

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