Flame-retardant expandable graphite

For the most rigorous specifications it may be necessary to use expanded graphite as a flame-retarder but its use can pose other difficulties. 

X-ray diffraction (XRD) has been poorly used to characterize the carbon phase of intumescent structure. Indeed, as shown previously, the carbon structure resulting from the development of the intumescent system is mainly disordered whereas XRD characterizes ordered structure. However, this technique may be of interest to study the carbonization process in the case of flame-retardant systems containing layered additives, such as expandable graphite,28,42 or even more in the case of lamellar nanocomposites, such as MMT-based nanocomposites. 

Qu, B. and Xie, R. 2003. Intumescent char structures and flame-retardant mechanism of expandable graphite-based halogen-free flame-retardant linear low density polyethylene blends. Polymer International 52(9) 1415-1422. 

Xie, R.C. and Qu, BJ. 2001. Synergistic effects of expandable graphite with some halogen-free flame retardants in polyolefin blends. Polymer Degradation and Stability 71(3) 375-380. 

Wang, Z., Han, E., and Ke, W. 2007. Influence of expandable graphite on fire resistance and water resistance of flame-retardant coatings. Corrosion Science 49(5) 2237-2253. 

Xie, R.C. and Qu, B.J. 2001. Expandable graphite systems for halogen-free flame-retarding of polyolefins. I. Flammability characterization and synergistic effect. Journal of Applied Polymer Science 80(8) 1181—1189. 

Modesti, M. Lorenzetti, A. Simioni, F. Camino G. Expandable graphite as an intumescent flame retardant in polyisocyanurate-polyurethane foams. Polym. Degrad. Stab. 2002, 77, 195-202. 

Shi, L Li, ZM Xie, BH. et al. Flame retardancy of different-sized expandable graphite particles for high-density rigid polyurethane foams. Polym. Int. 2006, 8, 862-871. 

Bian, XC Tang, JH Li, ZM. et al. Dependence of flame-retardant properties on density of expandable graphite filled rigid polyurethane foam. J. Appl. Polym. Sci. 2007, 104, 3347-3355. 

The next major class of flame retardant additives that are nonhalogenated is the phosphorus-based flame retardants, but even these materials have some regulatory environmental concerns.Other nonhalogenated flame retardants that are not phosphorus-based exist, including mineral fillers (i.e., Al(OH)3, Mg(OH)2), expandable graphite, mela-mine, and polymer nanocomposites combined with other flame retardants.Each of these materials has its own advantages and disadvantages, and effectiveness in one polymer system often does not translate into another system. 

Ou, K. Duan, H. Zhang, W. Tang, J. Li, Z. Synthesis of core-shell expandable graphite/melamine-formaldehyde particles and their flame retardant applications. Gaofenzi Cailiao Kexue Yu Gongcheng (2013), 29(1), 22-26. 

Expanded graphite [39,40] is the best-suited of all halogen-free flame retardants in terms of combustion rate (self-extinguishing, 0 s). This means the required mass percentages of expanded graphite are lower, resulting in improved mechanical properties [40]. 

In case of other fillers, the nanofillers can introduce new functionality into the polymer, e.g. electrical conductivity in case of carbon based nanoparticles, barrier properties in case of platelet like nanofillers (nanoclay, expanded graphite), enhancement of mechanical properties, enhanced flame retardancy, and many others. 

Chen and co-workers [2] carried out a study of the flammability characteristics and synergistic effects of different particle sizes of expanded graphite with modified magnesium hydroxide in flame retardant PP composites. They showed by LOI measurements that the particle size of the expanded graphite had a great effect on the flammability of PP - magnesium hydroxide - expanded graphite composites their similar particle sizes increased the LOI value. 

PMMA expandable graphite composites Silane grafted on polymer LOl and TGA used to calculate flame retardance and thermal stability [41]... 

Phosphorus containing unsaturated polyesters Expandable graphite ammonium polyphosphate, triphenyl phosphate Flammability and thermal properties investigated, by UL 94 [13] and LOL Polymers containing ethylene glycol and ammonium polyphosphate showed the best flame retardance [44]... 

A new type of intumescent additive is expandable graphite. This material has already found uses as a special effect pigment due to its metallic sheen and grey-black colour. Nord-Min has been developed by suppliers Nordmann Rassmann with flame retarding of plastics in mind. It is a halogen-free fire barrier additive from Chinese sources, based on natural graphite flakes with... 

Ucar Carbon Co of Cleveland, OH sells GRAFGuard expandable graphite flakes. Flame retardancy is promoted by inserting an expansion agent between the carbon layer planes, to form an insulating char layer when heated. The char layer provides a heat barrier, cuts off air and reduces the migration of decomposition products. 

Expandable graphite has potential as the flame retardant in polypropylene-flax composites under consideration for vehicle trim, along with other natural fibres, and also in building applications. 

Expandable graphite when used as flame retardant in polyisocyanurate-PU leads to a marked decrease in compression strength and a significant increase in thermal conductivity [48]. 

R. C. Xie, B. J. Qu, and K. L. Hu, Dynamic FTIR studies of thermo-oxidation of expandable graphite-based halogen-free flame retardant LLDPE blends. Polymer Degradation and Stability, 72 (2001), 313-21. 

Very effective flame retardant data were obtained with styrene-butyl acrylate copolymer/graphite oxide (St-BA/GO) nanocomposites. "- The GO was prepared by oxidation of expandable graphite, and the St-BA/GO nanocomposites (GO content of up to 4% mass fraction) were synthesized by exfoliation- adsorption of monomer followed by in situ emulsion polymerization. The distribution of the GO particles was examined by XRD, TEM, and electron diffraction exfoliated GO layers in crystalline structures were observed. The thermo-gravimetric analysis (TGA) data show a slight increase in thermal stability (up to 15°C with a 3% mass fraction of GO). Significant reduction in heat release rate by increasing GO content has been reported all nanocomposites reduced about 40% of total heat released compared with that of St-BA, as shown in Figures 10.14 and 10.15. 

Table 24 Flammability of non-halogenated unsaturated polyester resin with expandable graphite and other fire retardants. Reprinted from (2000) Flame Retardants 2000, Interscience Commun, London 2000, p 105 [113] with permission... 

Sample No. Expandable graphite [phr] Auxiliary fire retardant [phr] 1 11 After- flame time [s] Non- burnt length [mm] Limiting Oxygen Index (LOl) [%] Self- extingui- shing Sparkling... 

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