Flame retarding effect, nature

G. Guo, Y.H. Lee, Y.S. Kim, C.B. Park, and M. Sain, Flame retarding effects of nanoclay on wood-fiber composites. In The Global Outlook for Natural Fiber Wood Composites 2004, Intertech, Portland, ME, New Orleans, LA, December 8-10, 2004. 

Talc is a naturally occurring magnesium silicate which is finding broad application as a filler in polyolefins. Apparently, it provides a moderate flame retardant effect, but because talc is inexpensive, it is used as a partial substitute for more expensive flame retardants. Fumed silica is used as a filler in epoxy resins for the encapsulation of electronic devices at a relatively high loading, np to 80 to 90 wt%. Because of the relatively small amount of combnstible resin, this composition can be flame retarded by the addition of a very small amonnt of a conventional flame retardant. It is not clear if the silica contribnles to the flame retardancy by any mechanism other than heat dispersion. Nanodis-persed clay, which is one of the main topics of this book, is an alnminosiUcate. The mechanism of its flame retardant action is discnssed in other chapters of the book. 

Chemical pretreatments with amines, silanes, or addition of dispersants improve physical disaggregation of CNTs and help in better dispersion of the same in rubber matrices. Natural rubber (NR), ethylene-propylene-diene-methylene rubber, butyl rubber, EVA, etc. have been used as the rubber matrices so far. The resultant nanocomposites exhibit superiority in mechanical, thermal, flame retardancy, and processibility. George et al. [26] studied the effect of functionalized and unfunctionalized MWNT on various properties of high vinyl acetate (50 wt%) containing EVA-MWNT composites. Figure 4.5 displays the TEM image of functionalized nanombe-reinforced EVA nanocomposite. 

Houben [256] has compared the determination of flame-retardant elements Br, P, S, K, Cl and F in polycarbonate using commercial (X40 and UniQuant ) software. For the X40 method, a calibration line for each element in PC or PC/ABS blends was mapped for the conversion of intensities to concentrations. With the universal UniQuant method, sensitivity factors (ks) were calibrated with pure standards. The X40 method turned out to be more reliable than UniQuant for the determination of FRs in PC and PC/ABS blends, even in the case of calibration of k values with PC standards. Standard errors of 5 % were achieved for Br, P, S and K, and 20% for Cl and F the latter element could not be determined by means of UniQuant (Table 8.44). GFR PC cannot be quantified with these two methods, because of the heterogeneous nature of the composites. Other difficult matrices for XRF analysis are PBT, PS and PP compounds containing both BFRs and Sb203 (10-30wt %) due to self-absorption of Sb and interelement effects. 

Magnesium hydroxide occurs in nature as the mineral brucite. It has a Moh hardness of about 3 and a specific gravity of 2.4. It starts to decompose endothermically with the release of water at about 300 °C and the principal interest in it is as a flame retardant filler for thermoplastics such as polyolefins and polyamides, where the processing temperature is too high for aluminium hydroxide to be utilised effectively. For thermoplastic appHcations low aspect ratio particles are favoured with a particle size of about 1 micron and a specific surface area in the range 4-10 m2 g ... 

The reactive approach has been employed recently to prepare various polymeric systems.34 35 Silicon-containing polystyrenes and poly(methyl methacrylate)s (PMMAs) copolymers have been prepared by free radical polymerization. The LOI data indicated that a marginal improvement in flame retardancy has been observed compared to the parent homopolymers. The authors speculated that the nature of the silicon-containing group has an effect on the flame-retardant mechanism.34... 

Wang, J. and Chen, Y., Effect of microencapsulation and 4A zeolite on the properties of intumescent flame-retardant natural rubber composites, J. Fire Sci. 2008, 26, 153. 

Fillers. Inert inorganic substances such as calcium carbonate, clay, silicates, and asbestos are often utilized in vinyl compositions where clarity is not a requirement. While the carbonates and clay are used ostensibly to reduce cost, beneficial results are forthcoming. The carbonates produce a dry, matte surface and are claimed, because of their alkaline nature, to benefit heat and light stability. Clay improves electrical insulation. Silicates enhance surface dryness. Asbestos fibers provide the reinforcement necessary for dimensional stability in floor tile. Antimony oxide, per se or as a surface coating on an inert carrier, provides flame retard-ance. Their only major adverse effects are to reduce tensile strength and elongation and require an increase in plasticizer level to compensate... 

Ethylenebis[tris(2-cyanoethyl)phosphonium bromide] was effective at 1% in natural crystal polystyrene. As soon as the burner in the D635 Flame Test was removed, the sample containing the flame retardant extinguished. Ethylenebis [tris (2-cyanoethyl) phosphoium bromide] at 2% in pigmented crystal polystyrene gave a self-extinguishing polymer, and at 4% in natural impact polystyrene such samples were self-extinguishing. 

Moreover, the sensitivity of the effect of a flame retardant to the ambient pressure should also be taken into account. Flame retardants that are active only in the gas phase usually fail to affect the composition of the volatile pyrolysis products and the coke yield. In this case whatever the nature of the polymer, the flame retarding element is released into the gas phase during combustion the type of oxidant (O /Nj, N O/N ) strongly affects the flammability. On the other hand the effect of flame retardants active in the solid phase depends on the polymer nature, but is independent of the nature of the oxidant. Variations of the pressure of the oxidative environment affect the rates of gas-phase as well as heterogeneous (interfacial solid-gas) reactions. 

The retarding effect of HX, X, RX introduced into the flame may be of either physical or chemical nature (in either case, the residue R in RX is an extra fuel source). In the first case, the flame retardant reduces the oxygen concentration in the combustible mixture in the flame reaction zone by mere dilution, in the same way as added carbon dioxide or nitrogen. The heat capacity of the resultant mixture determines the amount of heat drained off for its heating. In the second case, the flame retardant directly participates in the flame reactions and affects the complex combustion process kinetics. The HX molecule is the main inhibiting particle. When RX is released into the gas phase of fuel-rich flames, HX is formed predominantly via RX -b H HX + RX, when Xj is released, HX is formed via X + H HX + X. 

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