Silicon Containing Flame Retardants

Connell and co-workers [87] investigated silicate siloxane fire retardant composites derived from vermiculite by reaction with hydroxyl-terminated polydimethylsiloxanes. Cone calorimetry was used to obtain HRR measurements. The results show that even at the highest irradiance levels the samples have very long ignition times. Ignition resistance deceases as the hydrocarbon content of the composite increases. The results from the cone calorimeter were obtained by Py-GC-MS, which show that small, volatile, silicone-containing molecules are formed during pyrolysis. 

Harada and co-workers [88] investigated the flame retardancy of polyglycidyloxypropyl silsesquioxane layered titanate nanocomposites. The UL 94 test method [13] was used to investigate the burning properties of the nanocomposites. It was found that the spherical titanate-filled nanocomposite sample burned from one end to the other, whereas a fire extinguishing property was observed in the sheet-like titanate-filled nanocomposites. The latter nanocomposites were classified as UL 94 VO, even with a 5 wt% layered titanate content. 

Sample Epoxy monomer Curing agent Curing agent Post-curing T rc)  

DDM = Diamino diphenyl methane For the mixtures of epoxy monomers, 1 1 mol ratio was used. Stoichiometric amounts were used in all cases. From differential scanning calorimetry method measurements (10 °C/min). Maximum of the loss modulus from dynamic mechanical thermal analysis measurements. a relaxation peak of the loss factor. Reproduced with permission from M. Sponton, L.A. Mercado, J.C. Ronda, M. Galia and V. Cadiz, Polymer Degradation and Stability, 2008, 93, 2025. 2008, Elsevier [22]  

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Gao Ming, Wu Weihong, and Xu Zhi-Qiang. Thermal degradation behaviors and flame retar-dancy of epoxy resins with novel silicon-containing flame retardant. J. Appl. Polym. 

DPPES was grafted onto the surface of GNO by condensation to form a synergistic phosphorus/silicon-containing GNO flame retardant (DPPES-GNO). A series of nanocomposites that contained 0,1,5, and 10 wt% DPPES-GNO was prepared. XPS, FTIR, Raman spectroscopy, and TEM verified that DPPES covalently bonded to GNO. Furthermore, the addition of DPPES-GNO (up to 10 wt%) to neat epoxy significantly increased its thermal stability and improved the char yield and LOI by 42% and 80%, respectively. The phosphorus, silicon, and GNO layer stmctures of DPPES-GNO caused the continuous and insulating char layer to protect the inner polymer matrix. The approach that is described herein has great potential for the development of a novel synergistic phosphorus/silicon—GNO flame retardant with polymer nanocomposite applications. 

Although silicone rubber because of its basic inorganic nature burns less readily than most halogen-free organic rubbers, its burning characteristics are readily modified. The traditional halogen-containing flame retardant... 

Formulations for one-shot polyether systems are similar to those used for flexible foams and contain polyether, isocyanate, catalyst, surfactant and water. Trichloroethyl phosphate is also often used as a flame retardant. As with polyesters, diphenylmethane di-isocyanate is usually preferred to TDI because of its lower volatility. Tertiary amines and organo-tin catalysts are used as with the flexible foams but not necessarily in combination. Silicone oil surfactants are again found to be good foam stabilisers. Volatile liquids such as trichlorofluoro-methane have been widely used as supplementary blowing agents and give products of low density and of very low thermal conductivity. 

J.R. Ebdon, B.J. Hunt, M.S. Jones, and F.G. Thorpe, Chemical modification of polymers to improve flame retardance. II. The influence of silicon-containing groups, Polym. Degrad. Stab., 54, 395M-00 (1996). 

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. 

FIGURE 8.1 HRR for polycarbonate and polycarbonate-containing silicone (two repeated tests for each sample). (From Kashiwagi, T. et al., A nonhalogenated, flame retarded polycarbonate, in Conference of Advanced Fire Resistant Aircraft Interior Materials, Atlantic City, NJ, February 9-11, 1993, 175.)... 

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... 

Flame-retardant epoxy resins with different silicon contents were prepared using silicon-containing epoxides or silicon-containing prepolymers. The thermal stability and flame-retardant properties of the produced epoxide systems were evaluated and related to the silicon content. The char yields under nitrogen and air atmospheres increased with increase in silicon content. The authors pointed out that the silicon-containing resin has improved flame retardancy over the silicon-free resin as evidenced by the LOI. LOI values increased from 24 for a standard commercial resin to 36 for silicon-containing resins.35... 

Marosi, G., Bertalan, G., Balogh, I., Tohl, A., Anna, P., and Szentirmay, K. 1996. Silicone containing intumescent flame retardant systems for polyolefins. In Flame Retardants, ed. Grayson, S. London, U.K. Interscience Commun. Ltd. Publ., p. 115. 

NEC has a target to phase out the use of all halogenated flame retardants by 2011. In 1999 the company launched a polycarbonate containing a silicone flame retardant that it claims to be far superior to conventional flame retardants and is neither phosphorus nor halogen based and can be recycled up to five times for the same purpose. 

Polycarbonate exhibits a relatively high oxygen index of 26. It may be further flame retarded by the addition of flame-retardant additives, including tetrabromo-BPA polymer, oligomer, or other bromi-nated additives, alkali metal salts,polytetra-fluoroethylene, phosphorus-containing additives, or silicones.Glass fillers or other inert fillers may also provide improved performance in Underwriters Laboratories (UL) flame testing. 

Elastomers. Many applications of rubbers such as tires, gaskets, and washers normally do not require flame resistance. When improvement in flammability is required, it can be achieved by the addition of halogen-containing materials, phosphorus compounds, oxides of antimony, and combinations of these materials. Rubbers containing chlorine and silicon atoms, for example. Neoprene and Silicone, have self-extinguishing properties. Rogers and Fruzzetti (10) described the flame retardance of elastomers. 

Liquid immersed types use various forms of oil and special synthetic liquids. The chlorinated liquids, e.g. polychlorinated-biphenyl, have been banned in most countries because they are very strong pollutants and are almost impossible to destroy, except by intensive burning in a special furnace. Modern liquids are synthetic compounds typically silicone based, and are usually specified to be flame retardant. 1EC60296, 60836, and 60944 describe suitable liquids. These transformers are the type normally used in oil and gas plants. Resin insulated transformers are very suitable for indoor locations and off-shore plants because they contain no flammable liquid, produce no spillage and require minimal maintenance. They are usually more expensive than conventional liquid immersed transformers. 

Flame-retardant mechanisms of PC-containing sihcone additives (FR-PC) were also elucidated by Py-GC in the presence of TMAH using a similar approach. Recently, much attention has been paid to silicone additives as flame retardants because they generate particularly smaller amounts of toxic substances even in the case of extreme fire. In order to elucidate the structure change induced in the FR-PC system during thermal degradation, the FR-PC and its control PC samples before and after thermal treatment at 380°C (for 2 h) were comparatively subjected to the Py-GC measurement using TMAH at 400°C. 

These foams can then be extended into the area of flame-retardant materials, where methyl oleate-polyesters were used as polyols in the synthesis of silicon-containing polyurethanes [89]. Despite not strictly being foams, methyl oleate, soybean and sunflower oils have also been investigated to produce semi-rigid flame retardant materials [90]. In this instance, they were brominated, acrylated and then radically copolymerized with styrene to form the polymeric material. 

Phosphorus and silicon containing epoxy resins Nil Flame retardant properties evaluated high LOI values indicated that epoxy resins containing hetero atoms are effective flame retardants [22]... 

Antimony trioxide-brominated PC [30], silicones [46, 47] and hydroxyapatite [48] have all been studied as flame-retardants for PC. Figure 6.1 shows the perceived flame retardancy mechanism occurring during the thermal decomposition of PC containing trifunctional phenyl silicone based additives [47]. This process involves the formation of a p-cumylphenoxy end-structure. 

Phosphorus compounds are often combined with silicon rather than nitrogen, as in European Patent 899301 from General Electric, in which a polyester moulding compound is flame retarded with an organoclay, a polymeric siloxane composition and a boron and phosphorus containing material. 

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