MacromolecularChemistry and Physics Talents & Trends Trends in Polymer Science Combinations of Elements: a New Paradigm for Fire Retardancy Thirumal Mariappan, Charles A. Wilkie* This trend article describes some recent work related to the development of flame retardancy of six common plastic materials, polypropylene, polystyrene, poly(methyl methacrylate), unsaturated polyester, polyurethane, and epoxy resin. Conventionally, a single fire retardant element is used to achieve fire retardancy but in this paper, there is a description of combinations of fire retardant elements, including a nano-sized material. Introduction In modern society, there is an increasing use of plastic materials to replace metals due to the lighter weight and high specific strength of plastic materials. However, the utilization of plastics carries a fire risk that is not seen with metals and this brings about the need for fire retardancy. Plastic materials, when exposed to high temperatures, decompose with the release of heat, smoke, soot, and toxic volatiles with smoke considered as the primary cause of death in most fires rather than heat.[1] There are two ways to render a plastic flame retardant (FR): 1) the plastic can be blended with FRs (additive approach) and 2) an FR element can be introduced into the plastic via a chemical reaction (reactive approach). Both T. Mariappan, C. A. Wilkie Department of Chemistry and Fire Retardant Research Facility, Marquette University, PO Box 1881, Milwaukee, WI 53201, USA E-mail:
[email protected] classes of FRs have advantages in different applications.[2,3] The additive approach has been most often followed. High loadings are sometimes necessary, which can have a negative impact on the mechanical properties and impair the processing ability of plastic materials. With the reactive approach, only a little amount of the FR may be necessary but it may be very expensive.[4,5] There are a variety of elements that are considered the backbones of the FRs, these include halogens, phosphorus, nitrogen, silicon, minerals [typically aluminum trihdroxide (ATH) and magnesium hydroxide (MDH), boron, iron, tin, and antimony]. The last three are typically not used alone but rather are synergists that can make other elements, usually halogens, more effective. It should be noted that the well-used monomeric halogen-based fire retardants have been at least partially banned world-wide; it may be expected that only polymeric halogen-based FRs will be used in the future.[1] Macromol. Chem. Phys. 2012, 213, 1987−1995 © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim wileyonlinelibrary.com Fire retardancy may occur in the vapor phase, by trapping the hydrogen and hydroxyl radicals that make up the flame, or in the condensed phase, changing the course of the thermal degradation of the polymer from one that produces volatile to one that produces char. The minerals ATH and MDH decompose endothermically with the elimination of water so the heat goes to decompose the mineral and not to decompose the polymer. There are several laboratory tests that are used to evaluate fire retardancy; those must often used are the limiting oxygen index (LOI), the UL-94 protocol and the cone calorimeter. LOI measures the minimum concentration of oxygen required for a material to burn; the higher one can drive up this minimum concentration, the more fire safe a material may become. The UL-94 protocol evaluates the ease of extinction of a polymer, the shorter the time for which a material burns the safer it may be. The cone calorimeter measures the heat release rate (HRR), that is, how DOI: 10.1002/macp.201200363 1987 unsaturated polyester/vinyl ester resin. He et al.D. A minimum of 30 wt% of IFR loading is necessary for Macromol. polypropylene. and epoxy resin. C5. For more than 10 years. Thirumal Mariappan obtained his M. The utilization of a nanodimensional material also offers enhanced mechanical performance so that if it is combined with another fire retardant. Wilkie retired from Marquette University in 2009 and is now professor emeritus. The classical intumescent (IFR) composition contains three basic components.[6–9] Polymers containing MMT.[11] Many commercially available FRs are not completely compatible and tend to bleed out. which acts as an effective barrier for heat and oxygen. poly(methyl methacrylate). Addition of clay could improve both thermal stability and fire retardant properties of PP filled with FRs. The addition of clay imparts good fire retardant properties with lower amounts of metal hydroxide. which can limit the flow of heat to the polymer.[6] This trend article addresses the combination of conventional fire retardants together with nanodimensional materials for six different common plastic materials. He is currently a postdoctoral fellow at Marquette University. It is unfortunate that each of these evaluations measures a different property of a fire and one cannot correlate the results from one evaluation with those of a different technique. DRDO.Macromolecular Chemistry and Physics T. Mariappan and C. One obvious example that has not been often exploited is the combination of an FR that functions in the vapor phase with one that is condensed phase active. polyurethane.[14] A synergistic effect was observed from the combination of clay and decabromondiphenyl ether (Deca) plus Sb2O3 in PPg-MA system.Tech.com . The premise of this work is that.mcp-journal. in fire retardancy of polyurethane foam from Indian Institute of Technology.D. Wilkie www. as well as an increasing the LOI value.de big is the fire. thus improving the flame retardancy of intumescent flame-retarded PP samples. A. The FR requirements for PP are generally similar to those for other polyolefins. or other nanodimensional materials.[18] www. via a random scission mechanism with a complex mixture of gaseous pyrolysis products of C4. In this case. Intumescent compositions swell when heat is applied and thus form a thick layer of insulating material. and an Engineering College. acid [ammonium polyphosphate (APP). the loss of properties due to this material may be at least partially offset by the presence of the nanodimensional material. char-former (pentaerythritol). Various nanodimensional materials have been incorporated into IFR PP formulations.MaterialsViews. polystyrene (PS). 1988 Charles A. and C6 hydrocarbon fragments with only small amounts of propylene monomer present. degree (after bachelor and master in Chemistry) in Polymer Technology from Cochin University of Science and Technology. has been used.[10] The fire retardancy of PP usually relies on the use of endothermic additives. 1987−1995 © 2012 WILEY-VCH Verlag GmbH & Co. he received his Ph. and it has been found that this reduces the peak HRR as evaluated by the cone calorimeter.[15] Hu et al. In 2010. The addition of organobentonite can improve the FR properties of IFR–PP due to an increase of the char residue. perhaps with a synergist. His research group has been studying fire retardancy for more than 30 years and polymer nanocomposites for more than 10 years. Weinheim effective flame retardancy (UL-94 V-0 rating) in PP. This is not to suggest that the typical FR package does not contain several different materials but usually only one of these is the fire retardant. The group currently is focused on the utilization of nanocomposites to enhance the fire retardancy of polymers. typically show no improvement when evaluated by other fire retardancy evaluative protocols. Zhang and Wilkie[17] have studied the fire retardancy of PP using metal hydroxides (ATH and MDH) and clay combinations. The situation in the past has been that most often a single FR element. Microencapsulated APP has a lower water solubility and thus may show some improvement. vapor-phase additives. Chem. in the future. 2012. which requires about 60% additive and thus the mechanical properties are severely impacted. we will see combinations of fire retardant elements used together. Flame Retardancy of Polypropylene Polypropylene (PP) burns readily in air (LOI = 17%) with melting and dripping and produces virtually no soot nor leaves any residual char. 213. he worked for 6 years in some of the research projects from various Indian Government R&D Institute like CSIR. work. or intumescent compositions. Kharagpur.[12] A potential problem for IFR compositions is the water solubility of both APP and pentaerythritol.[13] showed a V-0 rating with 25% of IFR loading with addition of organoclays. typically montmorillonite (MMT) and related clays. PP starts to degrade thermally above 290 °C. Before his Ph. FRs for PP have to be thermally stable at the processing temperature of about 250 °C.[16] studied the flammability of PP/clay and PP/ clay/nano-CaCO3 nanocomposites and showed a synergistic FR effect of nanocomposites with IFR additives. and blowing agent (melamine)]. Phys. one might expect that the amount of volatiles will be reduced and that the halogen or phosphorus can then trap what is produced. many groups have been studying nanodimensional materials. KGaA. 6 No rating Yes PP . and nickel catalyst have been reported. Moreover. but showed a severe deterioration of flame retardancy.com In this case. However. higher loadings of sepiolite decrease the FR properties. deteriorates the FR activity of IFR filled PP. Sepiolite showed synergistic FR effect with IFR filled PP and a V-0 rating was observed with 24% of IFR and 1% sepiolite clay (Table 1).8 V-1 No PP . EG shows better flame resistance than natural Macromol. and manganese dioxide) on the fire retardancy of PP filled with IFR.4 V-1 No PP . zeolite 4A.5 wt% IFR (APP + PER) provides a UL-94 V-0 rating with an LOI of 37%. The amount of fumed silica is critical.[34] Nyambo et al. it is able to condense to large polycyclic structures. The results showed that ZrO2 and Cr2O3 exhibit better flame resistance (V-0 rating in UL-94) than do the other oxides. Physical and chemical interactions between MgAl–LDH and APP are responsible for the observed synergy in thermal stability and fire 1989 . which leads to composites with different flammability performance. nano ZnO. Sample [wt%] IFR [%] Sepiolite [wt%] LOI [%] UL 94 test Dripping PP . less than 1% fumed silica loading increases both thermal stability and fire retardant properties of IFR filled PP.3 V-2 No Sepiolite is part of a family of fibrous hydrated magnesium silicate with the theoretical formula Si12O30Mg8(OH)4·8H2O characterized by a needle-like morphology. OZrP modified with different salts had various effects.[25] studied the effect of different metallic oxides (titanium dioxide.32].5 wt%) of organically modified α-ZrP with 22. water. including clay.0 V-0 No PP .[33] A synergistic effect of CNT with Deca/Sb2O3 was observed in PS system. the introduction of CNTs enhances the thermal stability of PP.[35] showed synergistic effects in both TGA and cone calorimetry for PS formulations containing both MgAl-LDH and APP. [19] with permission).75 23 2 35. lanthanum trioxide.[22] Another study showed that nanoZrO2 is also synergistic in IFR filled PP. Since the fuel is aromatic. Phys. which effectively protects the underlying polymer from burning.75 22 3 35. (Reproduced from ref. KGaA. The presence of these additives changes the structure. resulting in a very smoky or sooty flame. yield. on the FR efficiency of IFR system. Du and Fang[26] investigated the effects of carbon nanotubes (CNTs) on the flammability of PP–IFR system. because the fumed silica promotes the formation of a compact intumescent char layer and prevents the cracking of the char layer.75 25 0 34. 213. Weinheim graphite at the same loading in PP filled with IFR. H2O] is used in intumescent fire retardant PP systems as a synergistic agent. CNT.[27] studied the flame retardancy of calcium carbonate nanoparticles combined with APP in PP and showed that better burning rates are caused by the formation of calcium metaphosphate with the evolution of ammonia. the addition of clay can ameliorate this. depending on the cations.[21] The layered phosphate.Macromolecular Chemistry and Physics Combinations of Elements: a New Paradigm for Fire Retardancy www. Beach et al. Synergy was observed between phosphate and bromine fire retardants and clay[31. and the volatile products. www.[24] also found a synergistic effect of fillers. Wang et al. such as ZnO. and aluminum hypophosphite. Improvements in fire performance of PS/IFR composites by the partial substitution of nanofillers. α-ZrP acts as a “solid acid” that can catalyze dehydrogenation of the polymer.de Table 1.75 21 4 32. which deteriorates the FR and thermal properties of the PP/ IFR blends.100 0 0 17. dimer. molybdenum trioxide. Fe2O3. OZrP. α-zirconium phosphate [α-Zr(HPO4)2. A low loading (2 phr) of expandable graphite (EG) gives higher LOI values for PP filled with IFR and increasing the loading of EG.[19. significant deterioration of mechanical properties is observed upon the addition of conventional FR but.20] A synergistic FR effect was observed for the combination of fumed silica and IFR in PP.[30] found that a low loading of sulfur could improve the LOI values of PS filled with triphenylphosphate.mcp-journal. 2012. PP with low loading (2. 1987−1995 © 2012 WILEY-VCH Verlag GmbH & Co. LOI and UL94 data of FR filled PP with different loading of sepiolite.8 V-0 No PP .[28] Flame Retardancy of Polystyrene Polystyrene (PS) is intrinsically highly flammable (LOI = 18%) and has a tendency to depolymerize when exposed to high temperatures.MaterialsViews. The claycontaining sample showed the lowest flammability. zirconium dioxide. and carbon dioxide.[26] Deodhar et al. have high fuel value. with IFR filled PP.75 24 1 36. acting as an effective crosslinking agent.[29] showed that nanosilica could effectively improve the flame retardancy of brominated PS. a high loading of fumed silica restricts the formation of charred layers with P-O-P and P-O-C complexes formed from burning of polymeric materials and destroys the swelling behavior of intumescent charred layers.[23] Yi et al. Chem. and benzene and lower alkyl benzenes. styrene monomer. Yang et al. and thermal stability of the char. which promotes charring and an efficient insulating layer.[37] Flame Retardancy of Poly(methyl methacrylate) Poly(methyl methacrylate) (PMMA) ignites readily (LOI = 17%) and softens as it burns. Phys. an unsaturated acid. excellent transparency and aging characteristics are critical properties in most applications for PMMA. high-molecular-weight products. KGaA. if any. The FR properties of PMMA modified with a zinc aluminum undecenoate LDH and/or melamine were studied. the pyrolysate contains much monomer and little. The effect of the two additives on the fire behavior of the PMMA samples was dictated by the additive. Addition of nanoparticles. giving great importance to fire hazards. and buildings. but less effort has been devoted to the fire retardation of PMMA than to that of other polymers. It is noteworthy that the decrease of peak HRR and smoke as well as an increase of LOI were noticed with hydrophobic silica combined with APP both in PMMA and PS. and RDP). which are prepared by the condensation of a glycol. ATH. 213. decrease the time to ignition. The combination of either phosphinate or APP with metal oxide nanoparticles can enhance the thermal stability as well as fire retardancy of PMMA.[43] Macromol. The combination of MWCNT and clay significantly reduced the HRR and mass loss rate relative to compounds with only one type of nanoparticles.de performance. Styrene or methyl methacrylate is most commonly employed as the cross linking agents for the polyester resin. Higher loadings of melamine are required to obtain enhancement in fire properties. whereas LDH seems to give similar reductions in PHRR at lower loading (10%). This behavior was ascribed mainly to the formation of a specific silicon metaphosphate (SiP2O7) crystalline phase.com . Pack et al. The nanoparticles aid the catalytic effect and the reinforcement for the carbonaceous layer promoted by the FR additives. Both attapulgite and silica nanocomposites improve the vertical burning flame retardancy of FR filled PS by reducing dripping. nanoclays were better than CNT in improving the fire properties of FR filled PMMA samples assessed by cone calorimetry. The observed behavior was explained as due to the restriction of intumescence by strong CNT networks formed on the flaming surfaces during combustion but enhanced intumescent chars by nanoclays.Macromolecular Chemistry and Physics T. char formation is promoted and the total heat released during burning is reduced. In contrast.mcp-journal. Laachachi et al. and a saturated aromatic acid. they showed a V-0 rating with the addition of a small amount of MWCNT to the Deca/Sb2O3 filled PMMA sample. Mariappan and C. probably accounts for the lower smoke formation per unit weight in comparison with that of hydrocarbon polymers under most burning conditions. with melamine increasing the time to PHRR and lowering the amount of smoke produced relative to the LDH-rich PMMA composites. Depolymerization. Moreover.[42] A synergistic effect was observed between EG and silica in PMMA in terms of LOI. Tutunea and Wilkie[36] studied the effect of nanosized fillers such as layered silicate and MWCNT on the fire properties of PS filled with different FR additives (Deca/Sb2O3. FIGRA.46] studied the effect of oxide nanoparticles (TiO2. However. surface coatings. Depolymerization together with the presence of oxygen in the ester group. Flame Retardancy of Unsaturated Polyester Unsaturated polyester resins are lowmolecular-weight prepolymers or precursors. The combination of MWCNT with either ATH or RDP did not improve FR properties of PS compared with the sample containing FR alone. Both melamine (10%) and LDH (5%) showed better performance when considering the reduction in PHRR. Al2O3) on the flammability of PMMA filled with organophosphinates and APP. When low smoke www. fires may arise in these uses at any time. This lack of effort is due partly to the realization that it is difficult to inhibit the unzipping depolymerization mechanism characteristic of this polymer. A synergistic effect of nano-ZrO2 with TPP in PMMA was observed by cone calorimetry. there is a synergistic interaction between MWCNT and Deca and a greater reduction of peak HRR was observed. causes PMMA to drip less during burning than most other polymers. The effect of nanosilica and attapulgite clay as nanofillers on the flame retardancy of PS has been investigated. 2012.[44] found synergistic fire properties in PMMA and PS between nano-sized oxides (alumina and silica) and APP. including the standard FR formulations. fire 1990 retarding additives usually detract from one or both of these properties. transportation. large amounts of smoke can be released. They are employed in a wide range of applications such as flooring. Chem.[38] Halogenated compounds have been used to reduce burning rates and ease of ignition of PMMA. boats. rather than chain scission.[39] showed that a mixture of MWCNT and clay nanosized materials can enhance flame retardancy of PMMA to a greater degree than the addition of either of the nanoparticles alone.[47] Because of the aromatic content (styrene) in polyester resins. Wilkie www. and FPI.[45. A. Cast and glass fiber reinforced resin constitute a large proportion of the high volume composite materials currently in use.MaterialsViews. In addition. TiO2 does not improve the fire behavior of the composites significantly as compared with Al2O3.[40] Isitman and Kaynak[41] investigated the effect of organophosphinate FR with nanofillers (nanoclay and MWCNT) in PMMA. Weinheim Cinausero et al. 1987−1995 © 2012 WILEY-VCH Verlag GmbH & Co. For example. Flame retardancy was observed for the resin filled with APP and ZB due to the cross-linking of APP in the presence of zinc borate. zinc stannate (ZS).com flammability. polyester.[53] studied the influence of inorganic tin oxide and stannate additives such as ZS and ZHS on the flammability of halogen-containing polyester resin. Cone calorimetry showed that the melamine filled sample had higher ignition time. Horrocks et al. The combination of expandable graphite (EG) and APP mixtures showed synergistic FR behavior with polyester resin. and smoke values of polyester resin containing DBNPG under 35 kW m−2. APP alone is a good smoke suppressant and in the presence of ZB and ZS there is further smoke suppression. 213.[55. Chem. catalyst. Cloisite 25A. copper hydroxy dodecyl sulfate modified LHS and Cloisite 15A. while greater reduction of both peak HRR and smoke was observed from the EG filled sample and synergistic behavior with the combination of melamine and EG was observed. Macromol. and isocyanate index.[59] showed the synergistic effect of conventional FR with polydimethylsiloxane in polyurethane elastomer. Both halogenated samples containing Sb2O3 and ZHS give lower smoke compared with the filled sample alone (Figure 1). Furthermore. Phys.[48] Nazare et al. Sb2O3. TEP acts predominantly in the gas phase and the improved results obtained for TEP/EG filled foams are due to the simultaneous FR action both Figure 1. they also showed that clay could improve the flame retardancy of polyester resin filled with APP rather than melamine phosphate. Weinheim 1991 . The flammability of PU strongly depends on the structure of the polyol. stannates are more effective than tin oxide.[49] studied the flame and smoke retardant properties of polyester resin filled with the combination of APP. the use of methyl methacrylate or dicyclopentadiene in place of styrene is advantageous. PHRR. (Reproduced from ref. density. and ATH. and zinc hydrostannate (ZHS)]. a mixture of particles led to a strong decrease of www.. Tibiletti et al.[58] Flame Retardancy of Polyurethane Polyurethanes or/polyureas (PU) represent a broad group of polymeric materials made by reacting diisocyanates with diols or/diamines.MaterialsViews.[57] studied the flammability of poly vinyl ester resin using RDP. various kinds of PU materials useful for the manufacture of foams (flexible or rigid).mcp-journal. and ATH on the flammability of polyester resin containing decabromodiphenyl ether and dibromoneopentyl glycol (DBNPG) was also studied. ABS. and epoxy resin. particularly the combination of fumed silica and ATH showed greater reduction of peak HRR as compared with the mixture of alumina with ATH and dehydrated ATH at the same loading. KGaA.de properties are required in a product. etc. coatings.Combinations of Elements: a New Paradigm for Fire Retardancy Macromolecular Chemistry and Physics www. 2012. IFR mixture. polyester resin filled with APP and Cloisite 10A show good flame resistance compared with Cloisite 15A and 25A.50] Another study showed that the improvement of flame resistance depends on the nature of the surfactant in the clay. [56] with permission). and fumed silica on the FR properties of polyester resin.[51. They found that the combination of RDP with nanofillers showed antagonistic FR effect. Depending on the ratio of reactants and their types. TSR.[49. elastomers. 1987−1995 © 2012 WILEY-VCH Verlag GmbH & Co. Kandare et al. degree of cross-linking. PA. however. Jayakody et al. reaction conditions. Bashirzadeh and Gharenhbaghi[60] studied the flammability of flexible PUF using melamine and EG. POSS and organoclay with conventional FRs showed a synergistic effect. ATH.56] reviewed the influence of stannate additives on the flammability of different polymers such as PVC. Polyurethanes are readily flammable (LOI = 16%–22%) with release of toxic smoke. and adhesives can be produced.52] Atkinson et al. This study shows that one particle alone has little influence on the fire behavior of polyester resin. The effect of ZHS. especially foams. and smoke suppressants [zinc borate (ZB). Addition of Cloisite 25A to the APP filled sample shows reductions in smoke formation in both well-ventilated and under-ventilated fire conditions. Triethylphosphate (TEP) and red phosphorus (RP) are useful coadditives in combination with EG.[54] studied the effect of different metallic oxides such as alumina. the addition of Sb2O3 to both brominated resins provides a V-0 rating with higher LOI values compared with either ZHS or ATH added alone or in combination with ZHS and Sb2O3. PP. the presence of TEP helps to decrease the heat conductivity of the foam and overcome the poorer physical properties because of plasticization. On the other hand. but zinc stannates do not promote cross-linking of APP and hence show no improvement in flame retardancy. the addition of nanofiller such as clay. while unmodified and ammonium modified clays do not.68] There is no change in flame resistance of PUF filled with hollow microsphere and whisker silicon oxide separately.[63] Fly ash. gives a slight improvement of flame retardancy of FR filled PU. The LOI of TPU/APP (30 vol%) is not improved 1992 Figure 2.MaterialsViews.2 mm (TPU/ APP exhibits a V-2 rating without MWCNT). their flammability can be reduced considerably by the use of a variety of phosphorus and halogen additives or monomers. Modesti et al.[62] For example.com . 1987−1995 © 2012 WILEY-VCH Verlag GmbH & Co. Al2O3. Butyl acrylate-modified clay improves the flame retardancy of the IFR filled PU sample. KGaA. respectively. It is important because it correlates to the “time to flashover” and indicates the time available to escape in a full-scale fire situation. it may be considered as a good individual indicator of the overall fire hazard.[71] Kozlowski et al. Epoxy resins are relatively low-molecular-weight prepolymers capable of being processed under a variety of conditions. [69] with permission). www.de in the solid and in the gas phases. Materials Fire performance index (FPI) TPU 0. Mariappan and C. and in molding and casting applications because of a unique combination of properties. MnO. while for RP/EG filled foams the FR action is effectively only in the solid phase. Although epoxy resins normally are flammable (LOI = 22%).5%. TiO2.5%. even though a higher quality char is formed. MgO. SO3. and P2O5. HRR as a function of time of TPU and TPU/APP-MWCNT (heat flux 35 kW m−2). Weinheim extender improves the thermal stability. and dextrin. (Reproduced from ref. containing SiO2. and also mechanical properties of segmented PU elastomer compared with commercial PU containing 1.199 Macromol. and layered silicates.4-butane diol as a chain extender. 2012. The FPI (ratio of the time to ignition and the peak HRR) is used to characterize the flame retardancy of materials. The influence of hollow microspheres and whisker silicon oxide on the properties of EG filled PUF was investigated by Bian et al. whisker silicon oxide performs better than the hollow microsphere in combination with EG. zinc stannate.071 TPU + phosphate ester + 5% organoclay 0. (Reproduced from ref. Hence. the better is the flame retardancy of a material. a by-product of coal-fired power stations. by the substitution of APP by MWNT but a V-0 rating at 3. Phys. MWCNT. could improve the flame retardancy of IFR filled rigid PUF. phosphorus polyol. Chem. whereas a high loading of EG with hollow microspheres improves the flame retardancy of PUF and moreover. expandable graphite. they believed that the nanocomposite approach gives the best results combined with conventional FRs and leads to synergistic effects. The optimal ratio of APP to EG in rigid PUF is 1:1 by weight (total loading is 15 wt%) and the LOI value was 30. flame retardancy.[72] studied the effect of butyl acrylate-modified clay on the flammability of polyurethane filled with melamine polyphosphate. Na2O. The addition of clay improves the flame retardancy of foam containing EG and ZS. POSS. CaO.[64] Zatorski et al.[70] The addition of nanoclay with 3-chloro-1. The higher the FPI value.[65] investigated the flammability of polyurethane-polyisocyanurate foam (PIR) containing different FRs such as brominated triol.[67. The addition of organoclay and phosphate ester FRs in TPU gave a better fire performance index (FPI) than organoclay and phosphate ester filled TPU (Table 2).073 TPU + 5% organoclay 0.Macromolecular Chemistry and Physics T. Wilkie www. K2O. Awad et al. Therefore.[61] Both APP and EG improve the flame retardancy of PU materials but EG was better than APP in terms of both fire and smoke retardancy. The diglycidyl ether of bisphenol A (DGEBA) is the most commonly used liquid diepoxide.[73] studied the flammability of polyurea nanocomposites containing APP and EG. 213.mcp-journal. The substitution of APP by MWCNT is not beneficial in terms of PHRR (Figure 2).[69] studied the flame retardancy of TPU using APP and MWCNT. Effect of organoclay on the fire performance index of TPU.130 TPU + phosphate ester 0. Flame Retardancy of Epoxy Resin Epoxy resin is a specialty thermosetting plastic that has developed a significant market as adhesives and coatings in reinforced laminates. starch. Fe2O3. [70] with permission). A. Bourbigot et al. 15 wt% of both EG and APP used alone in rigid PUF gave LOI values of 32% and 24. 2-propane diol as chain Table 2.[66] showed that phosphonium-modified clay improves the flame retardation of aluminum phosphinate filled rigid PUF. In the case of tetraethoxysilane. Nanosilica did not migrate to the surface of the epoxy during thermal degradation and showed antagonism with phosphorus. Liu and Chou[86] studied the effect of silicon additives such as nanosilica.4 9. the addition of silicon compounds enhances the thermal stability and char yields of epoxy resins.5 EP + 10 MB 24.3′.3 Many applications of epoxy resins require the system to be fire resistant.l aye r e d titanate system was superior to the poly(glycidyloxypropyl) silsesquioxane/organo-layered titanate system probably because the presence of phenyl promotes charring. Camino et al.0 EP + 10 APP 23. Sample LOI (%) UL 94 ±1 tig (S) ± 3 THE/ML Residue THE [MJ m−2] [MJ g m−2] [%] ± 2 ± 10 ± 0.0 EP + Clay 21. the combination of phosphonium-modified clay with ATH is a promising approach for flame retardancy.MaterialsViews.3.1′spirobiindane (SpiroP) and clay and found synergistic and additive effects from SpiroP and BisP with clay when evaluated in terms of peak HRR reduction.4 5.[[85] studied the effect of metallic oxides (TiO2.89] because phosphorus provides the char formation and silicon provides the enhancement on thermal stability of the char during combustion.[80] studied the combined fire retardant action of phosphonates 2. 2012. Addition of La2O3 causes the formation of a more compact char with smaller carbonaceous microstructure.[75] Schartel et al. barrier 1993 . La2O3) on the FR properties of APP filled epoxy resin. Clay alone gives better flame resistance in epoxy than CNT.3 12. Chem.9 HB 63 116 2.2 21.2-bis(3-diethyloxyphosphonyl-4hydroxyphenyl)propane (BisP) and 5.4 12.6′dihydroxy-3.1 EP + 15 APP 28. electrical laminates for PCB and certain structural composites.9 V0 66 84 2.3 9. Weinheim in epoxy resin filled with POSS and triglycidyl isocyanurate.mcp-journal. 213. [76] with permission). 1987−1995 © 2012 WILEY-VCH Verlag GmbH & Co. The combination of clay with MB or APP shows antagonism as result of inhibition of the intumescent behavior. Song et al. A common method of imparting this fire resistance is the incorporation of tetrabromobisphenol-A (TBBA) or the diglycidyl ether of TBBA into the resin formulation.com heat conductivity and lower mobility of clays due to the cross-linked structure. and diglycidylether-terminated polydimethylsiloxane on the flammability of epoxy resin filled with phosphorus.[90.[79] showed better flame retardation of epoxy filled with APP and clay than clay with RDP and TBP.[82] showed that the flame retardancy of epoxy filled with poly(glycidyloxypropyl) phenyl s i l s e s q u iox a n e / o r ga n o . However.[83] Wang et al.3 HB 60 142 2. No synergistic effect was observed Macromol.[84] studied the effects of metal compounds on the flame retardancy of epoxy resin filled with APP.8 HB 62 105 1.[87] In general.2 EP 20.5 HB 60 135 2.2 EP + 5 MB 23.6 EP + Clay + 10 APP 21.and phosphoruscontaining compounds[88. (Reproduced from ref.2 HB 90 130 2.9 15. However. whereas the combination of APP and CNT shows greater flame retardation than that of the APP– clay mixture. However.Macromolecular Chemistry and Physics Combinations of Elements: a New Paradigm for Fire Retardancy www.3′-tetramethyl-1. enhancing flame retardancy. there is no improvement when both clay and CNT are used with APP.[76] studied the FR properties of epoxy filled with phosphonium-modified clay with conventional FR additives (melamine borate and APP) and showed that the flame retardancy efficiency does not increase linearly with the MB and APP concentrations (Table 3). tetraethoxysilane.[81] found synergistic FR behavior epoxy resin filled with phosphonium-modified clay and lowmelting phenylsiloxane glass.de Table 3 Fire retardancy of epoxy filled with clay and conventional FRs.0 35. mainly because of environmental concerns and recycling issues. Harada et al. thermal stability and flame retardancy of epoxy resin are improved by the combination of silicon. there has been a growing interest in halogen-free FRs.1 HB 53 129 2. Phys. Wu et al.[78] Katsoulis et al.8 EP + Clay + 5 MB 23. The use of ATH and TPP in epoxy resin displays notable flame-retardant synergism[74]. APP alone in EP obtains a V-0 rating at a loading of 20%.5′-bis(diethyloxyphosphonyl)-6. for example.[77] Another study also showed that the incorporation of clays did not give the desired FR effect to epoxy resin probably due to the increased www. the diglycidylether-terminated polydimethylsiloxane filled sample showed significant silicon migration and could form a protective layer to prevent further degradation of the char. another study showed that synergistic efficiency of phosphorus and silicon was not observed in terms of LOI. the addition of APP and metal compounds improves the fire safety of epoxy resin significantly presumably because the metal compound show a catalytic effect.91] Summary Nanodimensional materials have three major areas of application.5 HB 102 140 2. Furthermore. the combination of APP and boric acid leads to the best IFR protective coating in epoxy resin compared with their use separately. KGaA. 27. (Eds: T. polypropylene. Sci. He. [30] M. [40] X. Kandola). 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