Combinations of Flame Retardants

Some industrial minerals have flame-retardant properties and can be used in systems to replace synthetic retardants. A number of minerals have equal synergistic action with organic halogenated and phosphorated FRs and synergistic processes have also been observed in thermosets, between borates, and other hydrated minerals. Incorporation of minerals in intumescent formulations makes it possible to manage better the morphology of the expanded structure that develops on exposure to flame. 

With brominated FRs, a partial substitution with minerals makes it possible to improve certain of the mechanical properties and reduce the opacity and corrosivity of the fumes generated. This in turn makes it possible to reduce the environmental hazards arising from the incineration of fumes. 

The use of pure talcs of tine particle and high lamellarity index, in combination with a new generation bromohalogenated compound, makes it possible to obtain optimum mechanical properties and fire resistance as well as limitation of emission of corrosive products, compared with traditional and more costly solutions. Among the minerals studied, special Luzenac talcs show a high resistance to flame in polyolefins in synergy with bromine compounds, and are recommended for various applications, such as connectors, and in electrical appliances. 

Used with other retardants, addition of melamine to mineral filler fire retardants for PP generally improves the UL 94 behaviour, eliminating at the same time the afterglow phenomenon which is typical of mineral fillers used alone. Unfortunately, this additive is not sufficiently thermally stable and requires special precautions in processing, which still have to be improved. Melamine also reduces the specific weight of fire-retarded PP. which results in an 

Melamine is the most effective fire retardant in terms of UL 94 leading to a V-0 rank at 45% of loading 60% of Al(OH)3 leads to a V-0 rank and 60% of Mg(OH)2 to a V-1 rank. It is necessary to increase the loading at 65% in order to get a V-1 behaviour using MgCO. Talc and kaolin are ineffective up to 7 5% of loading. 

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Recent developments in the field of flame retardants have been reviewed (27). A combination of flame retardants with other properties, such as antioxidants have been developed. An example of such a compound is shown in Figure 9.4. 

Figure 9.4 Combination of Flame Retardancy with Antioxidant Functionality (27)...

Using factorial analysis, samples of the mohair/silk (MS) fabric were variously treated with a selection of flame retardants, back-coating formulations and adhesive, mounted on a typical aramid honeycomb board specimen, and each composite was tested using cone calorimetry at the preferred heat flux of 50 kW (shown to be equivalent to the 35 kW m flux used in the OSU calorimeter). 1 An optimum combination of flame retardant, back-coating and adhesive at specific application levels was found to yield the lowest heat release values, and this system was applied to each of the above six fabrics. Testing in both the OSU at 35 kW m heat flux and at 50 kW m" in the cone calorimeter gave the results for peak heat release in Table 4.5 below. From this it is seen that all fabrics have PHRR values < 65 kW m" and that OSU and cone calorimeter results are equivalent. 

ADVANTAGES AND DISADVANTAGES OF THE BLEND Combination of flame retardancy, toughness, weather resistance, low temperature ductility, excellent flow properties and processability. The material offers economical solution for parts having properties associated with ABS, flame retarded ABS, PPO, and PC/ABS blends. Benefits are not only associated with the cost of materials but also economy of processing. 

There also were many studies reported on the flame retardation of PET by incorporation of halogen or phosphorus . Similarly, we have studied a combination of flame retardants, hexabromobenzene and triphenyl phosphate, in PET. The luster and color of the spun PET fiber was preserved and had a fabric oxygen index of 28 vs. 21 for unmodified PET. The retention of luster was unusual since most flame retardants were incompatible and thus opacify the system. 

The practical development of halogen-free systems will continue to exploit the potential of additive blends, particularly where synergistic effects can be seen. Such blends offer the best opportunity of tailoring a combination of flame retardant mechanisms to achieve an efficient, cost-effective performance in each plastics application. 

Combination Flame Retardant—Durable Press Performance. Systems using THPC, urea, and TMM can be formulated to give fabrics which combine both flame-retardant performance and increased wrinkle recovery values (80). Another system employs dimethylol cyanoguanidine with THPC under acidic conditions (115). Both of these systems lead to substantial losses in fabric tensile and tearing strength. 

The polymers combine a high level of flame retardancy with good thermal insulation and sound absorption characteristics. Densities are somewhat high (16-20 kg/m ). 

The quantitative relationship of flammability of a polymer with respect to the concentration of flame retardant is usually not linear, and there is no logical reason to expect combinations of different flame retardants to show a linearly additive result either (43). The actual result is often found to be "synergistic" or "antagonistic", or in regression analysis terminology, the interaction term is often found to be statistically significant. 

Air Products, a manufacture of latex binders, has completed a comprehensive study of flame retardants for latex binder systems. This study evaluates the inherent flammability of the major polymer types used as nonwovens binders. In addition, 18 of the most common flame retardants from several classes of materials were evaluated on polyester and rayon substrates. Two of the most widely recognized and stringent small scale tests, the NFPA 701 vertical burn test and the MVSS-302 horizontal burn test, are employed to measure flame retardancy of a latex binder-flame retardant system. Quantitative results of the study indicate clear-cut choices of latex binders for flame retardant nonwoven substrates, as well as the most effective binder-flame retardant combinations available. 

Cold cure" or high resilience PU foams tended to liquify before igniting were developed and gave good results in standard tests such as BS 4735(25) (similar to the discontinued ASTM D1692) but could still burn when used with flammable fabrics in furniture (Table IV). However they have been used most successfully in the UK in combination with flame retarded cotton interliners and fabrics of low flammability e.g. wool, nylon, FR cotton etc. and formed the basis of public area furniture used in the UK since the early 1970 s (Table V). 

In their further work, Xu et al. combined the effects of the two different groups of flame retardants, halogens and phosphates, into one molecule in the hope that the integration would result in the improvement of flame retarding efficiency.For this purpose, they synthesized a series of organo-phosphates with partially fluorinated alkyls, which included TEP, BMP, and TDP. 

The use of phosphorus-based flame retardants in combination with other, better established, flame retardants is most effective in situations in which the combination proves synergistic. However, as yet our understanding of such synergistic effects is far from complete and more fundamental work is required in this area Work in which the gaseous and solid products of combustion, with and without the presence of flame retardants, are carefully analyzed. Such analyses can now be undertaken more readily than in the past, owing to the relatively recent development of techniques such as gas-phase FT-infrared spectroscopy and laser-pyrolysis time-of-flight mass spectrometry for the identification of volatiles, and solid-state NMR spectroscopy and x-ray photoelectron spectroscopy for the analysis of chars. 

In this chapter, we have discussed recent developments of intumescent flame-retarded materials in terms of reaction and resistance to fire. Research work in intumescence is very active. New molecules (commercial molecules and new concepts) have appeared. Nanocomposites are a relatively new technology in the held of flame retardancy. This technology gives the best results combined with conventional FRs and leads to synergistic effects with intumescent systems. Very promising developments in the synergy aspects are then expected and efforts should be continued in this way. 

Metal hydroxides in combination with various silicon-containing compounds have been used to reduce the amount of additive required to achieve a required level of flame retardancy in a variety of polymeric materials, including polyolefins.62-63 Systems that have been used contain a combination of reactive silicone polymers, a linear silicone fluid or gum, and a silicone resin, which is soluble in the fluid, in addition to a metal soap, in particular magnesium stearate. However, there is little insight given into how these formulations work. 

To take advantage of both modified layered silicate and the substantial presence of phosphorus, the combined use of phosphorus-modified silicates and phosphorus compounds may represent an innovative solution to achieve high levels of flame retardancy. Phosphonium-modified layered silicates in epoxy resins were associated with organo-phosphorus FRs by Schartel et al.59 Ion exchange of Na-montmorillonite was carried out using tetraphenyl phosphonium bromide. Triphenyl phosphate and a reactive phosphorus compound were used as FR incorporated in the epoxy resin. 

Combining data obtained by the cone calorimeter with pyrolysis combustion flow calorimeter (PCFC sometimes called microscale combustion calorimeter, MCC) results was also proposed to increase the understanding of flame retardancy and flame retardancy mechanisms.104 Dividing the fraction of the effective heat of combustion of the volatiles (THE/ML) obtained from the cone calorimeter by the heat of complete combustion of the volatiles obtained from PCFC yields the combustion efficiency %. Thus the combination of fire test and PCFC enables a quantitative... 

FIGURE 15.21 Using the Petrella plot for comprehensive and reasonable scientiflc assessment of flame retardancy by comparing different approaches, or by comparing the effects for different irradiations. THE stands for the Are load and PHRR/tig for the fire growth rate hence, the two most important fire risks are monitored at the same time. An ideal flame retardancy would decrease both hazards significantly as is the case for the combination of both flame retardants on the left (comparison of HIPS), HIPS/Pmd, HIPS/Mg(OH)2, and HIPS/Pmd/Mg(OH)2) and for low external heat flux on the right (comparison of PA 66-GF and PA 66-GF/Pred for different irradiations). 

PVC-U formulations have low flammability due to the chlorine content. The addition of plasticiser in PVC-P formulations necessitates the use of flame retardant and smoke suppressant additives. These additives are known as functional fillers and a correct balance is necessary to achieve all the end-use specification requirements. They are predominately used in cable, conveyer belting and roofing membrane formulations to give resistance to fire initiation and propagation. It is also important to reduce dripping in a fire situation and that as little smoke as possible is generated. Antimony trioxide has been used extensively, usually in combination with phosphate ester plasticisers, giving excellent fire performance and mechanical properties. 

Details are given of the addition of flame retardant and smoke suppressant additives to PVC to meet specifications such as oxygen index, heat release, smoke evolution or extent of burning in cable tests. Data are presented for synergistic combinations of additives in PVC formulations. 31 refs. 

Ion-pair extraction and IPC were combined to analyze phosphoric acid mono- and diesters originating from the microbial hydrolysis of flame retardants. Even tertiary treatment did not ensure complete removal of the studied compounds detected in municipal wastewater [107], Chlorophenols extracted from water samples as anionic chlorophenolates were studied by IPC because the anionic forms of these analytes provide better UV ultraviolet absorption than uncharged chlorophenol based on their auxochromic effects. IPC conditions yielded adequate retention of the charged analytes and good sensitivity [108]. 

Fortunately true antagonistic effects are rare, but true synergistic effects are also rare, where the resnlting effect of a combination is greater than the sum of the single effects of the combined products. Examples of both cases are different types of flame retardants. 

The so-called intumescents form another class of flame retardants. These are low smoke release flame retardants which combine nitrogen and phosphorus. They are more costly than many halogenated compounds but are used in a.o. wire-and-cable and electronic housing uses where toxic smoke poses an immediate threat [7]. 

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