Flame-retardant efficiency

Powdered antimony pentoxide is used primarily in plastics. Stabilizers used to prevent the particles from growing are caustic, and can react with the halogen in the formulation. This can result in color formation and a lower flame-retarding efficiency of the system. 

Tetrachlorphthalic Anhydride and Tetrachlorphthalic Acid. Tetrachlorphthalic anhydride [117-08-8] (TCPA) is manufactured by the ferric chloride catalyzed chlorination of phthalic anhydride. The relatively low chlorine content and the lower flame retardant efficiency of the aromatic chlorides limit use to unsaturated polyester resin formulations that do not requite a high degree of flame retardancy. 

Convincing evidence for phosphorus/bromine synergy has now been found in a 2/1 polycarbonate/polyethylene terephthalate blend. Phosphorus and bromine blends were studied as well as compounds which have both elements in the same compound. The relative flame retardant efficiencies of phosphorus and bromine are also reported. 

The results obtained by Kuila et al. and Acharya et al. [63,64] from the EVA elastomer blended with lamellar-like Mg-Al layered double hydroxide (LDH) nanoparticles demonstrate that MH nanocrystals possess higher flame-retardant efficiency and mechanical reinforcing effect by comparison with common micrometer grade MH particles. Kar and Bhowmick [65] have developed MgO nanoparticles and have investigated their effect as cure activator for halogenated mbber. The results as shown in Table 4.2 are promising. 

A further improvement in flame-retardant efficiency is observed when a colloidal dispersion of tin(IV) oxide is incorporated into the polyester. At a 1.5% addition level, colloidal SnO gives an 01 value (49.0) which is markedly higher than that obtained with 5% loadings of either anhydrous SnO, (47.7) or 8-stannic acid (47.9), as powdered additives (Figure 2). In addition to its increased flame-retardant ability, colloidal Sn02 offers the further advantages of translucency in the cured plastic, ease of incorporation and nonsettling in the resin prior to cure. 

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. 

Methyl methacrylate is often used in combination with styrene to improve light transmission and uv stability in flame-retardant glazing applications. Phosphate ester (triethyl phosphate) additives are also included to supplement flame-retardant efficiency benzophenone uv stabilizers are required to prevent yellowing of these uv-sensitive resins. 

Bagdanova, V. V. Fedeev, S. S. Lesnikovic, A. I. Klimovtsova, I. A. Sviridov, V. V. The formation of antimony oxychloride in flame retardant mixtures and its influence on flame retardant efficiency, Polymer Degradation and Stability, 1985, 11, 205-210. 

Both REZ-O-SPERSE A-1 and REZ-O-SPERSE 3 typically contain 45% available chlorine for maximum flame retardant efficiency. 

The chain reactions from the flame are stopped and a phenomenon called self-extinguishing occurs which is characterised by the self-extinguishing time, a measure of flame retardant efficiency. 

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. 

The applications potential of cyclophosphazenes is apparent from the large number of patents and applications oriented studies which have appeared this year. The use of phosphazenes as flame retardants continues to represent the area of greatest activity. A comprehensive structure-activity study of the oxygen index, and thermogravimetric characteristics of several cyclo- and cyclolinear phosphazenes shows that flame retarding efficiency is in the following order NPCl2>NP(ORp) Cl>NP(0Rp)2>NP(0Rp) (OR) >NP(OPh) Cl>NP(OR) 2 (Rp=CH2(CF2) H, n=2,4,6 R=alkyl) Similar studies on... 

Figure 3.18. Flame retardant efficiency in PVC containing variable concentrations of antimony dioxide. [Data from Wang, H. Wang, H. Guo, Z. Qi, S. Tian, C., J. FimSci., 24, 3, 195-210, 2006.]...

The flame-retardant efficiency of halogens decreases along the following sequence ... 

F-2016 is a brominated epoxy oligomer with around 50% bromine and a molecular weight of 1600 designed to ensure optimal properties in styrenic copolymers. Brominated epoxy oligomers offer a combination of high flame retardant efficiency, UV stability, good mechanical properties and thermal stability. They are non-blooming due to their physicochemical properties and polymeric... 

Exolit OP 550 is a low-fogging additive that is recommended for moulded and high-density slabstock foams where flame retardant efficiency is uppermost. OP 551 (TP) is a low-fogging liquid flame retardant for slabstock where a lack of discoloration is critical. 

The lack of adequate TIP data on alternatives to BFRs should give pause for thought, not to speak of the relative flame-retardant efficiency and design adequacy of the candidate substitutes. 

Resin formulators and compoimders must select a flame retardant that is both physically and economically suitable for specific resin systems and the intended applications. It is common to formulate resins with multiple flame-retardant types, typically a primary flame retardant plus a synergist such as antimony oxide, to enhance overall flame-retardant efficiency at the lowest cost. Several hundred different flame-retardant systems are used by the plastics industry because of these formulation practices. 

Processing conditions also strongly influence the flame-retardant behavior. For example, in the case of PS-based nanocomposites, extrusion above 180°C imder partially oxidative conditions yields an intercalated nanocomposite but with no flammability improvement, whereas the melt-extruded system at 170°C imder nitrogen or vacuum exhibits flame-retardant efficiency (41). The way thermal degradation of the organic modifier alters the flammability reduction mechanism has yet to be imderstood. 

Most announcements of the systems proposed as flame retardants appear in the patent literature A non-inclusive survey of recent reports is presented in Table 3.2.1 [93]. In this Table it should be noted that in addition to inert additives, substituents with reactive exocyclic substituents are available and, consequently, reactions between the additive and host are possible, e.g. polyurethanes are prepared in the presence of the phosphazene, The supposed inert additives may undergo host reactions on combustion as shown by formation of P-O-C bond in combustion residues of wood treated with methoxy and phenoxy phosphazenes [94], Gases involved in pyrolysis of the treated samples show a decreased amount of combustible CH4 and CO [94]. The flame retardant efficiency of phosphazene derivatives has been shown to exhibit the following order ... 

Figure 1.1 compares the flame retardant efficiency of aliphatic brominated flame retardant and aromatic brominated flame retardant. Because the thermal decomposition of the aliphatic flame retardant starts at temperatures below the thermal decomposition of pol5T)ropylene, it shows very good performance in polypropylene. In contrast, because the aromatic brominated fire retardant is significantly more stable, optimum debromination is not achieved at the temperature of decomposition of polypropylene, and this flame retardant shows inferior performance. 

Therefore, it appears that a combination of organoclays and conventional flame retardants possesses significant potential to be useful flame retardant systems. A more detailed understanding of the flame retardant mechanism by which such an additive combination exerts its positive effects may further improve its performance and safety and reduce overall additive loading and cost. Moreover, the development of feasible and relevant manufacturing methods based on the intercalated flame retardant clays described here which facilitate the dispersion of flame retardant additives and increase flame retardant efficiency foretells of a promising future for flame retardant polymer nanocomposite materials in everyday applications. 

Instead, these type of flame retardants exhibit some drawbacks compared with bromine-containing flame retardants, such as low flame retardant efficiency and low thermal stability. Improved intumescent flame retardant systems have been found by formulating with zeolites and organoboron siloxanes (9). 

Improved flame retardant efficiency due to bromine/cblorine synergy... 

High flame retardant efficiency for minimal added weight or change in hand. 

The high flame-retardation efficiency of siliconized epoxy resin cured with phosphorus diamine curative was observed mainly because of the char enrichment of phosphorus and the char protecting effect of silicone to exhibit their synergistic effect on LOI enhancement. Hence, we suggest the suitability of these matrices in the field of advanced electronics, adhesives and coatings for better performance and longevity. 

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