Development of halogen‐free flame‐retardant thermoplastic elastomer polymer blend

Ethylene‐propylene diene rubber (EPDM) and isotactic polypropylene (iPP) blends have widest industrial applications that require a degree of flame retardancy. Halogen‐free intumescent technology based on phosphorous salt is a significantly advanced approach to make the polymer flame‐retardant. Both ammonium polyphosphate and ethylenediamine phosphate are important intumescent compounds. Their combination with carbonific and spumific agents were studied in binary blends of EPDM/PP. The polymer system was vulcanized online during melt mixing. Intumescent flame‐retardant polymer systems exhibit good flame‐retardancy with optimum comparable physiomechanical, electrical, and fluid resistance properties, including lower smoke emission, which is essential to protect people because the visibility remains unaffected in the event of fire. Pronounced charring and intumescent effect appear to enhance the flame‐retardancy of the polymers. Possible expected intumescent mechanism is proposed based on the nonpyrolysis mechanism for the flame‐retarded polymer and the intumescent components. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 407–415, 2004     

A macromolecular halogen‐free flame retardant and its effect on the properties of thermoplastic polyesters

A halogen‐free flame retardant with a macromolecular structure is presented. Its synthesis proceeds via polymerization of phosphorus‐containing acrylate monomers. The flame retardant was incorporated into poly(ethylene terephthalate) by extrusion. Samples with different concentrations (0.5, 2.5, and 5.0 wt%) as well as a 25 wt% masterbatch were prepared. All samples were transparent and colorless without any visible irregularities. Thermal investigations reveal an unchanged glass transition temperature. Tensile tests show the typical mechanical behavior of poly(ethylene terephthalate), but with an elevated Young's modulus. The burning behavior was investigated by several small‐flame tests in vertical and horizontal orientation, as well as by cone calorimetry. It is shown that samples with 2.5 wt% flame retardant pass the vertical UL94 test (V‐2, 20‐mm flame). The sample cannot be ignited in the horizontal fire test according to FMVSS 302. The oxygen index was measured to 28 vol%. Cone calorimetric measurements show that the effective heat of combustion as well as the total heat evolved is reduced.     

Effects of gamma radiation on properties of halogen‐free flame retardant EPDM‐PVMQ rubber blends

In this study, the effects of gamma radiation on properties of ethylene–propylene–diene monomer (EPDM) and its blends with phenyl vinyl methyl silicon rubber (PVMQ) were studied. The samples were irradiated with the dose rate of 171.7 Gy/min, and the total dose was up to 500 kGy. Mechanical properties, electrical insulation, limiting oxygen index (LOI), crosslink density, and ATR‐FTIR spectroscopy of the rubber were carried out to characterize the properties via irradiation. The results indicated that PVMQ acted as an irradiation degradation retarder for EPDM. After a postvulcanized period corresponding to 50 kGy dose, the elongation at break and electrical insulation decreased with LOI unaffected, while the crosslink density and tensile strength presented a complicated change with the increasing of radiation dose. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

A novel halogen‐free and formaldehyde‐free flame retardant for cotton fabrics

A novel halogen‐free and formaldehyde‐free flame retardant (FR), which contains phosphorus, nitrogen, and silicon, was synthesized for cotton fabrics considering the synergistic effect of phosphorus, nitrogen, and silicon. The structure of the new FR was characterized by Fourier‐trans‐form infrared spectroscopy, and the surface morphology of the treated fibre was observed using scanning electron microscope. The thermal property of the FR treated cotton fabric was studied through thermal gravimetric analysis. The TG results indicate that the FR can protect cotton fabric from fire to a certain degree. The vertical flammability test and limiting oxygen index results further indicate that the FR has excellent FR properties. Finally, the durability and other performance properties of the treated fabric were studied and the results show that the new materials can be used as a semi‐durable FR for cellulosic fibres. Copyright © 2011 John Wiley & Sons, Ltd.     

Reactive,intumescent, halogen‐free flame retardant for polypropylene

A reactive, intumescent, halogen‐free flame retardant, 2‐({9‐[(4,6‐diamino‐1,3,5‐triazin‐2‐yl)amino]‐3,9‐dioxido‐2,4,8,10‐tetraoxa‐3,9‐diphosphaspiro[5.5]undecan‐3‐yl}oxy)ethyl methacrylate (EADP), was synthesized through a simple three‐step reaction from phosphorus oxychloride, pentaerythritol, hydroxyethyl methacrylate, and melamine. EADP exhibited excellent thermal stability and char‐forming ability, as revealed by thermogravimetric analysis (TGA) and scanning electron microscopy (SEM). The TGA results show that the temperature at 5% weight loss was 297.8°C and the char yield at 700°C was 51.75%. SEM observation revealed that the char showed a continuous and compact surface and a cellular inner structure with different sizes. Composite of polypropylene (PP) with a 25 wt % addition of EADP (PP/EADP25) passed the UL‐94 V‐0 rating and showed a limiting oxygen index value of 31.5. Compared with those of neat PP, the flexural strength and modulus values of PP/EADP25 were somewhat improved, the tensile strength was basically unchanged, and the notched Izod impact strength was slightly decreased. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40054.     

Co‐microencapsulation of ammonium polyphosphate and aluminum hydroxide in halogen‐free and intumescent flame retarding polypropylene

In this article, co‐microencapsulated ammonium polyphosphate (APP) and aluminum hydroxide (ATH) [M(A&A)] was prepared by using 4,4'‐diphenylmethane diisocyanate (MDI) and melamine (MEL) via in situ surface polymerization method. The chemical composition of M(A&A) was confirmed by Fourier transform‐infrared spectra (FT‐IR). Thermal behavior and surface morphology of M(A&A) were systematically analyzed by thermogravimetric analysis (TGA) and scanning electron microscope (SEM), respectively. Water solubility tests indicate that water solubility of M(A&A) decreases greatly than un‐microencapsulated ones. Besides, flame retardant properties of polypropylene (PP) compositing with M(A&A) were investigated by limiting oxygen index (LOI), vertical burning tests (UL‐94) and cone calorimeter. The results demonstrate the LOI value of PP composites is improved after combining with co‐microencapsulated flame retardants. Compared with PP/A&A, the peak heat release rate of PP/M(A&A) decreases from 210 to 120 kW/m² at the same flame retardant loading level. Moreover, in order to investigate the flame retardant mechanism, the char residue of PP composites after combustion was studied by optical photos, X‐ray photoelectron spectroscopy (XPS) spectra and FT‐IR. POLYM. COMPOS., 35:715–729, 2014. © 2013 Society of Plastics Engineers     

Application of a novel halogen‐free intumescent flame retardant for acrylonitrile‐butadiene‐styrene

A novel intumescent flame retardant (IFR), containing ammonium polyphosphate (APP) and poly(tetramethylene terephthalamide) (PA4T), was prepared to flame‐retard acrylonitrile‐butadiene‐styrene (ABS). The flame retardation of the IFR/ABS composite was characterized by limiting oxygen index (LOI) and UL‐94 test. Thermogravimetric analysis (TGA) and TGA coupled with Fourier transform infrared spectroscopy (TG‐FTIR) were carried out to study the thermal degradation behavior of the composite and look for the mechanism of the flame‐retarded action. The morphology of the char obtained after combustion of the composite was studied by scanning electron microscopy (SEM). It has been found the intumescent flame retardant showed good flame retardancy, with the LOI value of the PA4T/APP/ABS (7.5/22.5/70) system increasing from 18.5 to 30% and passing UL‐94 V‐1 rating. Meanwhile, the TGA and TG‐FTIR work indicated that PA4T could be effective as a carbonization agent and there was some reaction between PA4T and APP, leading to some crosslinked and high temperature stable material formed, which probably effectively promoted the flame retardancy of ABS. Moreover, it was revealed that uniform and compact intumescent char layer was formed after combustion of the intumescent flame‐retarded ABS composite. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Decabromobiphenyl oxide–aluminum hydroxide system as a flame retardant for styrene–butadiene rubber

Styrene–butadiene rubber (SBR) was treated with decabromobiphenyl oxide (DBBO) and/or aluminum hydroxide [Al(OH)₃] as a flame retardant. The flammability of the resulting system was determined by the limiting oxygen index method. The effect of the added flame retardants on the maximum torque (MH), curing rate, and tensile properties was also evaluated. The results showed, particularly, that DBBO was a more effective flame retardant than was Al(OH)₃. On the other hand, this brominated compound reduced the modulus of elasticity while its effect on the maximum torque was insignificant. Moreover, the addition of DBBO was found to decrease the curing rate of SBR. In contrast, Al(OH)₃ significantly increased the maximum torque and also markedly reduced the modulus of elasticity. Moreover, the effect of the treatment with Al(OH)₃ on the curing rate was found to be insignificant. The flammability measurement of the SBR treated with different mixtures of the two flame retardants indicated that the two compounds reacted slightly antagonistically. The addition of Al(OH)₃ to DBBO in a mixture that was applied to SBR remedied some negative impacts on the mechanical properties when DBBO was added separately to the rubber. The value of the maximum torque of SBR increased and the curing rate slightly increased as well. Meanwhile, the values of the modulus of elasticity were not affected. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 2134–2139, 2000     

Effect of aluminum trihydrate as flame retardant on properties of a thermoplastic rubber nanocomposite

In this work, different concentrations, per hundred rubber (phr), of aluminum trihydrate (ATH) were added to thermoplastic rubber nanocomposite based on ethylene propylene diene monomer and linear low‐density polyethylene. The effect of the added compound on the flammability, rheological, mechanical properties, and electrical conductivity of the composite was studied. The results of the cone calorimeter showed a significantly reduction in the flammability of the composites occurred when the composite was treated with ATH. The peak heat release rate was reduced by about 66% when the composite was loaded with 180 phr of ATH. Moreover, the time to ignition prolonged up to 160%. The total smoke released decreased significantly as the concentrations of the ATH were increased. A reduction of about 69% in the total smoke released was observed when the composite was treated with 180 phr. The thermogravimetric analysis showed a reduction in the overall weight loss as the concentrations of ATH were increased. A reduction of about 50% of the original weight was observed when 180 phr of ATH was used. An appreciable decrease in tensile stress and strain with increasing ATH contents had been observed. The addition of ATH markedly reduced the conductivity of the thermoplastic rubber nanocomposite. Copyright © 2016 John Wiley & Sons, Ltd.     

Preparation and characterization of microcapsulated red phosphorus and its flame‐retardant mechanism in halogen‐free flame retardant polyolefins

Microcapsulated red phosphorus (MRP), with a melamine–formaldehyde resin coating layer, was prepared by two‐step coating processes. The physical and chemical properties of MRP were characterized by Fourier‐transform infrared spectroscopy (FTIR), X‐ray photoelectron spectroscopy (XPS), and transmission electron microscopy (TEM) and other measurements. The flame retardant action and mechanism of MRP in the halogen‐free flame retardant (HFFR) polyolefins (PO) blends have been studied using cone calorimeter, limiting oxygen index (LOI), thermogravimetric analysis (TGA) and dynamic FTIR spectroscopy. The results show that the MRP, which is coated with melamine–formaldehyde resin, has a higher ignition point, a considerably lower amount of phosphine evolution and of water absorption compared with red phosphorus (RP) itself. The data observed by cone calorimeter, LOI and TGA measurements from the PO/HFFR blends demonstrated that the MRP can decrease the heat release rate and effective heat of combustion, and increase the thermostability and LOI values of PO materials. The dynamic FTIR results revealed the flame‐retardant mechanism that RP can promote the formation of charred layers with the P–O and P–C complexes in the condensed phase during burning of polymer materials. Copyright © 2003 Society of Chemical Industry     

Preparation,thermal, and flammability of halogen‐free flame retarding thermoplastic poly(ether‐ester) elastomer/montmorillonite nanocomposites

In this article, the nanocomposites thermoplastic polyester‐ether elastomer (TPEE) with phosphorous–nitrogen (P–N) flame retardants and montmorillonite (MMT) was prepared by melt blending.The fire resistance of nanocomposites was analyzed by limiting oxygen index (LOI) and vertical burning (UL94) test. The result shows that the flame retardants containing P–N increased the LOI of the material from 17.3 to 27%. However, TPEE containing P–N flame retardants just got UL94 V‐2 ranking, which resulted in the flaming dripping phenomenon. On the other hand, TPEE containing P–N flame retardant and organic‐modified montmorillonite (o‐MMT) achieved UL94 V‐0 rating for the special microstructure. The XRD and TEM morphology has demonstrated that the formation of multi‐ordered structure regarding restricted segmental motions at the organic–inorganic interface and stronger interactions between the clay mineral layers and the polymer chains. The structure was supported by the results of rheological properties and DSC analysis. The thermal degradation and char residue characterization was studied by thermal gravimetric analysis (TGA) and SEM‐EDX measurements, respectively. The TGA and SEM‐EDX have demonstrated that o‐MMT results in the increase of char yield and the formation of the thermal stable carbonaceous char. POLYM. COMPOS., 37:700–708, 2016. © 2014 Society of Plastics Engineers     

Study of a novel halogen‐free flame retardant system through TGA and structure analysis of polymers

Butadiene‐rubber toughened styrene polymers, such as acrylonitrile‐butadiene‐styrene (ABS) copolymer and high impact polystyrene (HIPS), are noncharring polymers. They are generally blended with polycarbonate (PC) or polyphenyleneether (PPE), which are char forming polymers, to improve char forming ability for styrenic blends containing conventional phosphate flame retardants. To achieve cost effective flame retardant system, PET was selected as a potential char‐source for ABS blends through the thermogravimetric analysis (TGA) and chemical structure analysis of various polymers. PET may contribute to the enhancement of flame retardancy of ABS/PET blends, especially in the presence of small amounts of phenol novolac (PN). The effective flame retardancy of this system is believed to be accomplished through the enhancement of interchain reactions by PN. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Effect of zinc oxide on properties of phenolic foams/halogen‐free flame retardant system

A halogen‐free flame retardant system consisting of ammonium polyphosphate (APP) as an acid source, blowing agent, pentaerythritol (PER) as a carbonific agent and zinc oxide (ZnO) as a synergistic agent, was used in this work to enhance flame retardancy of phenolic foams. ZnO was incorporated into flame retardant formulation at different concentrations to investigate the flammability of flame retardant composite phenolic foams (FRCPFs). The synergistic effects of ZnO on FRCPFs were evaluated by limited oxygen index (LOI), thermogravimetric analysis (TGA), cone calorimeter tests, and images of residues. Results showed that the flame retardant significantly increased the LOI of FRCPFs. Compared with PF, heat release rate (HRR), total heat release (THR), effective heat of combustion (EHC), production or yield of carbon monoxide (COP or COY) and Oxygen consumption (O₂C) of FRCPFs all remarkably decreased. However specific extinction area (SEA) and total smoke release (TSR) significantly increased, which agreed with the gas‐phase flame retardancy mechanism of the flame retardant system. The results indicated that FRCPFs have excellent fire‐retardant performance and less smoke release. And the bending and compression strength were decreased gradually with the increase of ZnO. The comprehensive properties of FRCPFs were better when the amount of ZnO was 1～1.5%. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42730.     

Flame retardant and thermal decomposition properties of flexible polyurethane foams filled with several halogen‐free flame retardants

Expandable graphite (EG), dimethyl methylphosphonate (DMMP), melamine (MEL), zinc borate (ZB), or magnesium hydroxide (MH) was separately added to polyurethane to form flame retardant flexible polyurethane foam (FPUF) in one‐step. The cell morphologies of the FPUF composites before and after burning were observed by scanning electron microscopy (SEM), their flammability was evaluated by limiting oxygen index (LOI) tests, and their thermal stability and evolved gaseous products were examined by thermogravimetric analysis‐Fourier transform infrared spectroscopy (TGA‐FTIR). The results indicated that all the five flame retardants could improve the flame retardant performance of FPUF on the basis of their own mechanism. DMMP possessed the highest flame retardant efficiency, and one of the important reasons was that it could promote the formation of char. EG could inhibit molten drop of FPUF during burning effectively. All the five flame retardants could decrease the maximum decomposition velocity mainly because of their heat absorption effect. ZB displayed an excellent inhibition ability for the release of the evolved gaseous products because of its adsorption effect. All the flame retardants except DMMP were capable to decrease the CO yield at the temperature (400°C) of maximum decomposition velocity for their respective mechanisms, but all of them were not able to inhibit CO generation at higher temperature (600°C). POLYM. ENG. SCI., 54:2497–2507, 2014. © 2013 Society of Plastics Engineers     

Correlations between pyrolysis combustion flow calorimetry and conventional flammability tests with halogen‐free flame retardant polyolefin compounds

Seven halogen‐free flame retardant (FR) compounds were evaluated using pyrolysis combustion flow calorimetry (PCFC) and cone calorimetry. Performance of wires coated with the compounds was evaluated using industry standard flame tests. The results suggest that time to peak heat release rate (PHRR) and total heat released (THR) in cone calorimetry (and THR and temperature at PHRR in PCFC) be given more attention in FR compound evaluation. Results were analyzed using flame spread theory. As predicted, the lateral flame spread velocity was independent of PHRR and heat release capacity. However, no angular dependence of flame spread velocity was observed. Thus, the thermal theory of ignition and flame spread, which assumes that ignition at the flame front occurs at a particular flame and ignition temperature, provides little insight into the performance of the compounds. However, results are consistent with a heat release rate greater than about 66kW/m² during flame propagation for sustained ignition of insulated wires containing mineral fillers, in agreement with a critical heat release rate criterion for burning. Mineral fillers can reduce heat release rate below the threshold value by lowering the flaming combustion efficiency and fuel content. A rapid screening procedure using PCFC is suggested by logistic regression of the binary (burn/no‐burn) results. Copyright © 2008 John Wiley & Sons, Ltd.     

Preparation and investigation of flame‐retardant epoxy resin modified with a novel halogen‐free flame retardant containing phosphaphenanthrene,triazine‐trione,and organoboron units

In this article, a novel flame retardant (coded as BNP) was successfully synthesized through the addition reaction between triglycidyl isocyanurate, 9,10‐dihydro‐9‐oxa‐10‐phosphaphenanthrene‐10‐oxide and phenylboronic acid. BNP was blended with diglycidyl ether of bisphenol‐A to prepare flame‐retardant epoxy resin (EP). Thermal properties, flame retardancy, and combustion behavior of the cured EP were studied by thermogravimetric analysis, limited oxygen index (LOI) measurement, UL94 vertical burning test, and cone calorimeter test. The results indicated that the flame retardancy and smoke suppressing properties of EP/BNP thermosets were significantly enhanced. The LOI value of EP/BNP‐3 thermoset was increased to 32.5% and the sample achieved UL94 V‐0 rating. Compared with the neat EP sample, the peak of heat release rate, average of heat release rate, total heat release, and total smoke production of EP/BNP thermosets were decreased by 58.2%–66.9%, 27.1%–37.9%, 25.8%–41.8%, and 21.3%–41.7%, respectively. The char yields of EP/BNP thermosets were increased by 46.8%–88.4%. The BNP decomposed to produce free radicals with quenching effect and enhanced the charring ability of EP matrix. The multifunctional groups of BNP with flame retardant effects in both gaseous and condensed phases were responsible for the excellent flame retardancy of the EP/BNP thermosets. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45291.     

A novel halogen‐free intumescent flame retardant containing phosphorus and nitrogen and its application in polypropylene systems

A novel halogen‐free intumescent flame retardant, pentaerythritol spirobisphosphoryl‐dicyandiamide (SPDC), was synthesized and characterized by FTIR, ¹H NMR, and ³¹P NMR spectra. The new flame retardant was used in polypropylene (PP) to prepare flame‐retardant materials whose flammability and thermal behavior were studied by the limiting oxygen index (LOI) method, thermogravimetric analysis (TGA), and cone calorimetry (CONE). The mechanical properties were also investigated. The results indicated that when the addition of SPDC reached 30 wt%, the material showed both excellent flame retardancy and anti‐dripping abilities for PP. Moreover, the LOI value of the PP‐IFR(30%) was 32.5, and it passed the UL‐94 V‐0 rating test. The CONE results revealed that in PP, SPDC(30%) significantly decreased the peak heat release, total heat release, and smoke relative to their values for pure PP. The morphological structures observed by SEM demonstrated that SPDC could promote the formation of a homogeneous and compact intumescent char layer. The TGA data showed that SPDC could enhance the thermal stability of PP and effectively increase the char residue formation. J. VINYL ADDIT. TECHNOL., 2010. © 2010 Society of Plastics Engineers     

Synthesis of a magnesium/aluminum/iron layered double hydroxide and its flammability characteristics in halogen‐free,flame‐retardant ethylene/vinyl acetate copolymer composites

Mg–Al–Fe ternary hydrotalcites were synthesized by a coprecipitation method and characterized with powder X‐ray diffraction, Fourier transform infrared spectroscopy, and thermogravimetric analysis. The flame‐retardant effects of Mg/Al–CO₃ layered double hydroxides (LDHs) and Mg/Al/Fe–CO₃ LDHs in an ethylene/vinyl acetate copolymer (EVA) were studied with the limited oxygen index (LOI), the UL‐94 test, and the cone calorimeter test (CCT), and the thermal degradation behavior of the composites was examined by thermogravimetric analysis. The results showed that the LOI values of the EVA/(Mg/Al/Fe–CO₃ LDH) composites were basically higher than those of the EVA/(Mg/Al–CO₃ LDH) composites at the same additive level. In the UL‐94 test, there was no rating for the EVA/(Mg/Al–CO₃ LDH) composite at the 50% additive level, and a dripping phenomenon occurred. However, the EVA/(Mg/Al/Fe–CO₃ LDH) composites at the same loading level of LDHs containing a suitable amount of Fe³⁺ ion reached the V‐0 rating, the dripping phenomenon disappearing. The CCTs indicated that the heat release rate (HRR) of the EVA composites with Mg/Al/Fe–CO₃ LDHs containing a suitable amount of Fe³⁺ decreased greatly in comparison with that of the composites with Mg/Al–CO₃ LDHs. The introduction of a given amount of Fe³⁺ ion into Mg/Al–CO₃ LDHs resulted in an increase in the LOI, a decrease in the HRR, and the achievement of the UL‐94 V‐0 rating. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Synergistic flame retardant effect of cerium oxide in ethylene‐vinyl acetate/aluminum hydroxide blends

The flammability characterization and synergistic flame retardant effect of cerium oxide (CeO₂) in the ethylene‐vinyl acetate/aluminum hydroxide blends were studied using limiting oxygen index (LOI), UL‐94 test, and cone calorimeter test (CCT). The results showed that the addition of a given amount of CeO₂ apparently increased the LOI value and UL‐94 rating. The data obtained from the CCT indicated that the addition of CeO₂ greatly decreased the heat release rate and prolonged the combustion time. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Layer‐by‐layer assembly of halogen‐free polymeric materials on nylon/cotton blend for flame retardant applications

Thin films of environmentally safe, halogen free, anionic sodium phosphate and cationic polysiloxanes were deposited on a Nyco (1:1 nylon/cotton blend) fabric via layer‐by‐layer (LbL) assembly to reduce the inherent flammability of Nyco fabric. In the coating process, we used three different polysiloxane materials containing different amine groups including, 35–45% (trimethylammoniummethylphenythyl)‐methyl siloxane‐55‐65% dimethyl siloxane copolymer chloride salt (QMS‐435), aminoethylaminopropyl silsesquioxane‐methylsilsesquioxane copolymer oligomer (WSA‐7021) and aminopropyl silesquioxane oligomers (WSA‐991), as a positive polyelectrolyte. Thermo‐gravimetric analysis showed that coated fabric has char yield around 40% at 600 °C whereas control fabric was completely consumed. The vertical flame test (VFT) on the LbL‐coated Nyco fabric was passed with after flame time, 2 s, and the char length of 3.81 cm. Volatile and nontoxic degradation products of flame retardant‐coated fabric were analyzed by pyrolysis gas chromatography mass spectroscopy (Py‐GCMS). Surface morphology of coated fabrics and burned fabric residues were studied by scanning electron microscopy. Copyright © 2014 John Wiley & Sons, Ltd.