Containing Flame Retardants

Chlorine-containing flame retardants can be divided into three groups aliphatic, alicyclic (cycloaliphatic), and aromatic. Their thermostability is increased in this order, bnt flame retardant efficiency is decreased in the same order. This reciprocal tendency is common among flame retardants. Clearly, the higher the thermal stability, the higher the temperatnre at which the flame retardant becomes chemically active and fnnctional as a flame retardant. 

A common disadvantage of chlorine-containing flame retardants is that they have to be added in quantities, which in turn decrease mechanical properties of the polymer materials. The same sitnation in terms of large amount that should be added into the base material holds for mineral flame retardants as well (ATH, Mg(OH)2) however, minerals typically improve both flexural modulus (stiffness) and flexural strength of composites. 

Aliphatic chlorine flame retardants are represented by chloroparaffins, with chlorine content between 40 and 70%. They typically have a poor thermal resistance, as their dechlorination often starts at 180°C (356°F) hence, their application is restricted by polyethylenes and PVC. 

Dover Chemical Corporation produces resinous chlorinated paraffins under a name Chlorez and advocates their usage as flame-retardant additives in plastics. All Chlorez grades have a physical form of white powder (particles smaller than 50 mesh) with chlorine content around 70%. Chlorez is not recommended to be processed above 180°C (356°F)- Indeed, an attempt to compound one of these materials with a WPC at 190°C (374°F) has resulted in a rather violent decomposition of the material. The melt turned dark, and some foaming occurred with an accompanying strong smell. 

On the contrary, chloroaromatic compounds, such as decachlorodiphenyl, are too stable thermally to be widely used as flame retardants. 

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The amount and physical character of the char from rigid urethane foams is found to be affected by the retardant (20—23) (see Foams Urethane polymers). The presence of a phosphoms-containing flame retardant causes a rigid urethane foam to form a more coherent char, possibly serving as a physical barrier to the combustion process. There is evidence that a substantial fraction of the phosphoms may be retained in the char. Chars from phenohc resins (qv) were shown to be much better barriers to pyrolysate vapors and air when ammonium phosphate was present in the original resin (24). This barrier action may at least partly explain the inhibition of glowing combustion of char by phosphoms compounds. 

Numerous variations in composition, appHcation method and surface treatment, and properties of Mg(OH)2-containing flame-retardant fillers are disclosed in the patent Hterature (92—95). Smoke-suppressant foams incorporating Mg(OH)2 are useful as roof insulation slabs (96). Mg(OH)2 is contained... 

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). 

Study of the Thermal Behaviour of Bromine Containing Flame Retardants during Incineration... 

As many bromine-containing flame retardants do not dissolve in common NMR solvents (typically CDCI3 and tetrachloroethane), ll 1-NMR can not generally be applied and 13C s-NMR may then be called in. However, in favourable circumstances, e.g. for FR 1025 (poly-pentabromobenzylacrylate, Ameribrom) in PBT (Tribit 1500 GN 30), direct H 1-NMR in C2D2Cl4 of the fraction insoluble in HFIP can be used, in view of the unique resonance position of the benzylacrylate fragment in FR-1025. 

T. Handa, T. Nagashima and N. Ebihara, Synergistic Action of Sb2(>3 with Bromine-Containing Flame Retardants in Polyolefins. II. Structure-Effect Relationships in Flame Retardant Systems," J. of Fire Retardant Chemistry,, 37 (1981). ... 

Three flame retardants were compared in this study, namely, a brominated polycarbonate oligomer (58% bromine), a brominated polystyrene (68% bromine), and a brominated triaryl phosphate ester (60% bromine plus 4% phosphorus). These are described in Table I. Figures 1 and 2 compare the thermal stability of the brominated phosphate with commercial bromine-containing flame retardants by thermogravimetric analysis (TGA) and by differential scanning calorimetry (DSC). The brominated phosphate melts at 110°C and shows a 1% weight loss at 300°C. Brominated polycarbonate and brominated polystyrene are polymeric and are not as volatile at elevated temperatures as the monomeric flame retardants. 

Brominated phosphate heated in a glass tube in air at 300°C for 30 minutes remains a water-white liquid. This was compared with commercial bromine-containing flame retardants which melt they all turn color. The excellent color stability of this brominated phosphate ester makes it suitable for the high temperature processing of engineering plastics. 

PBDEs are release to land as municipal wastes with the disposal of consumer products containing PBDEs. The disposal of consumer products containing PBDEs is likely to increase worldwide due to rapid obsolescence of plastic products. For example, between 1997 and 2004, the number of obsolete computers containing flame retardants is projected to be 315 million (NSC 1999). Based on a monitor weight of 30 pounds, an estimated 350 million pounds of brominated flame retardants will be released to landfills (NSC 1999). Although PBDEs will only be a fraction of this total, the amount of PBDEs released to the environment by disposal will still be significant. 

Dumler R, Lenoir HTD, Hutzinger O. 1989a. OBDF and PBDD from the combustion of bromine containing flame retarded polymers A survey. Chemosphere 19(12) 2023-2031. 

Dumler R, Thoma H, Lenoir D, et al. 1989b. Thennal formation of polybrominated dibenzodioxins (PBDD) and dibenzofurans (PBDF) from bromine containing flame retardants. Chemosphere 19(l-6) 305-308. 

A series of flame retardant additives for ABS have been discussed, including halogen containing flame retardants, as well as halogen free flame retardants. The latter are being preferred for environmental reasons, however, only a few are as effective as halogen containing flame retardants. For ABS blends, some flame retardants (20) have been described that are summarized in Table 8.9. 

In an analogous way as described above, in the case of ABS polymers that are equipped with bromine containing flame retardants, pyrolysis oils with low bromine content can be obtained (133). This issue is important for processing scrap plastics from waste of elec-... 

D. Hoang, J. Kim, and B.N. Jang, Synthesis and performance of cyclic phosphorus-containing flame retardants, Polym. Degrad. Stab., 93(11) 2042-2047, November 2008. 

Cross-linked polyethylene-based compounds that contain flame-retardant components and compounds based on PVC cross-linked by radiation have also received high temperature rating. They find use not only in appliance wires but also in manufacturing under-the-hood automotive wires. 

Because of the ease of formation of these flammable pyrolysis products, polyesters have LOI values of 20-22 vol% (see Table 2.4), and hence, burn readily and because of the styrene content, give heavy soot formation. As these resins are cured at room temperature, bromine-containing flame retardants, which would decompose in melt-processed, thermoplastic polymers, may be effectively used. 

There is only perhaps one significant case where low concentrations of an antioxidant shows flame-retardant behavior, in the case of certain hindered amine stabilizers (HAS) that at the normally used concentrations (<1 wt%), offer low levels of flame retardancy in polypropylene and show synergy with bromine-containing flame retardants.78 80... 

R.E. Lyon, R.N. Walters, M. Beach, and F.R Schall, Flammability screening of plastics containing flame retardant additives, ADDITIVES 2007, 16th International Conference, San Antonio, TX, 2007. 

The evidence for the action of halogen and halogen antimony compounds in the gaseous phase is well established however halogen-containing flame-retardant systems are often twofold systems providing radical action inhibition in the gaseous phase and, at the same time inhibition in the condensed phase as will be seen in the next section. 

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