Article pubs.acs.org/IECR
The Impact of Metal Oxides on the Combustion Behavior of Ethylene−Vinyl Acetate Coploymers Containing an Intumenscent Flame Retardant Lei Wang,†,‡,§ Wei Yang,†,‡,§ Bibo Wang,† Yu Wu,† Yuan Hu,†,§,* Lei Song,†,* and Richard K. K. Yuen‡ †
State Key Laboratory of Fire Science, University of Science and Technology of China, 96 Jinzhai Road, Hefei, Anhui 230026, People's Republic of China ‡ Department of Building and Construction, City University of Hong Kong and USTC-CityU Joint Advanced Research Centre, Suzhou, People's Republic of China § Suzhou Key Laboratory of Urban Public Safety, Suzhou Institute of University of Science and Technology of China, Suzhou, People's Republic of China ABSTRACT: The objective of this work was to compare the flame retardancy of intumescent flame retardant ethylene−vinyl acetate (EVA/IFR) composites containing different metal oxides including lanthanide oxide, iron oxide, the mixture of iron oxide and lanthanide oxide, and lanthanum ferrite nanocrystalline (LaFeO3). A novel compound containing iron and lanthanum, LaFeO3 was successfully prepared. The EVA/IFR composites with these different coadditives were then fabricated through a melt blending process. Thermogravimetric analysis data showed that these different coadditives could increase the char residue formation. Cone calorimeter results revealed that these different coadditives and IFR could clearly change the decomposition behavior of EVA and form a char layer on the surface of the composites, consequently resulting in efficient reduction of the flammability parameters, such as heat release rate, total heat release, average mass loss rate, average smoke extinction area, and so on. Moreover, significant improvements were obtained in limited oxygen index and Underwriters Laboratories 94 ratings. Among all of the samples, the fire risk of EVA/IFR/LaFeO3 system was the lowest. The residue characterization demonstrated that LaFeO3 could promote the formation of the homogeneous and compact intumescent char layer.
1. INTRODUCTION Ethylene−vinyl acetate copolymer (EVA) is widely used as insulating materials in the wire and cable industry due to its good mechanical and physical properties.1 However, the development and application are greatly limited by its high flammability. In past decades, the halogenated compounds were commonly used as fillers to improve the fire retardancy of EVA.2 Unfortunately, their fire retardant action is accompanied by negative effects, such as the generation of corrosive, obscuring, toxic smoke. In addition, the manufacture and application of some halogen-containing flame retardants are restricted by new regulations, such as the European Directives on WEEE (Waste of Electric and Electronic Equipment, became European Law in February 2003), RHS (Restrictions of Hazardous Substances, became European Law in February 2003), and REACH (Registration, Evaluation, Authorization, and Restriction of Chemicals, entered into force on 1 June 2007). Therefore, there is a growing demand for new, halogenfree flame retardants.3−5 In recent years, intumescent flameretardant (IFR) additives have been widely utilized in the flame retardation of flammable polymers,6−11 because of their low toxicity and low propensity for smoke generation. A typical and widely studied IFR system is composed of ammonium polyphosphate, pentaerythritol, and melamine (APP/PER/ MEL). But adding only IFRs usually requires high content to achieve a good flame retardant rating. A small amount of coadditives often brings significant improvements in thermal stability and flame retardant properties, implying that they can © 2012 American Chemical Society
enhance the efficiency of IFRs. Many compounds have been used as coadditives, such as fumed silica, zeolite, lanthanum oxide, iron compounds, α-zirconium phosphate, and so on. It has been reported that Fe2O3 and La2O3 can improve the efficiency of intumescent systems.14−16 The promotive effect of lanthanum oxide on intumescent flame-retardant polypropylene-based formulations has been investigated. The results demonstrated that La2O3 could significantly improve the thermal stability and flame retardancy of intumescent flameretardant polypropylene.14 Polypropylene/novel intumescent flame retardant in combination with lanthanum oxide was fabricated. It was found that a suitable amount of La2O3 played a promotive effect in the flame retardancy and smoke suppression of IFR composites.15 It has been also reported that Fe2O3 was an effective modifier to improve the thermal stability of the APP-PER-MEL coating.16 Inspired by the effectiveness of Fe2O3 and La2O3, a novel compound containing iron and lanthanum (LaFeO3) was prepared and used as a coadditive to improve the flame retardancy of an EVA/IFR composite. First, LaFeO3 was synthesized and characterized. In order to understand the impact of LaFeO3 on the combustion chacteristics of the EVA/ IFR composite, the effect of lanthanide oxide, iron oxide, the Received: Revised: Accepted: Published: 7884
November 1, 2011 April 26, 2012 May 23, 2012 May 23, 2012 dx.doi.org/10.1021/ie202502s | Ind. Eng. Chem. Res. 2012, 51, 7884−7890
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Article
X-ray diffractometer equipped with a Cu−Ka tube and Ni filter (l1/40.1542 nm). Transmission Electron Microscopy (TEM). Transmission electron microscopy (TEM) images were obtained using a Jeol JEM-100SX transmission electron microscope with an acceleration voltage of 100 kV. Specimens for the TEM measurements were obtained by placing a drop of sample suspension prepared by ultrasonic dispersion on a carbon-coated copper grid, and dried at room temperature. Thermogravimetric Analysis (TGA). Each sample was examined in air flowing at 150 mL/min using a Q5000 (TA, U.S.) thermogravimetric analyzer at a heating rate of 20 °C/ min. The weight of all samples was kept within 3−10 mg in an open Pt pan and heated from room temperature to 700 °C. The temperature reproducibility of the instrument is ±1 °C, while the mass reproducibility is ±0.2%. Limiting Oxygen Index (LOI). LOI was measured using a HC-2 oxygen index meter (Jiang Ning Analysis Instrument Company, China) on sheets 100 × 6.7 × 3 mm3 according to the standard oxygen index test ASTM D2863−77. UL-94 Vertical Burning Test. The vertical burning test was conducted by a CZF-II horizontal and vertical burning tester (Jiang Ning Analysis Instrument Company, China). The specimens which used were 127 × 12.7 × 3 mm3 according to UL94 test ASTM D3801−1996 standard). Cone Calorimeter Test (CCT). The cone calorimeter tests (CCTs) were carried out using the cone calorimeter (FTT), following the procedures in ISO5660. Square specimens (100 × 100 × 3 mm3) were irradiated at a heat flux of 35 kw/m2, corresponding to a mild fire scenario. Scanning Electron Microscopy (SEM). The scanning electron microscopy (SEM) image of the residue after the cone calorimetry experiment was taken using a DXS-10 scanning electron microscope produced by Shanghai Electron Optical Technology Institute. The char was adhibitted on the copper plate, and then coated with gold/palladium alloy ready for imaging. X-ray Photoelectron Spectroscopy (XPS). X-ray photoelectron spectroscopy (XPS) measurement was carried out with a VG ESCALB MK-II electron spectrometer. The excitation source was an AIKa line at 1486.6 eV. Elemental analysis was carried out with Inductively Coupled Plasma, Mass Spectrometer, Plasma Quad 3.
mixture of iron oxide and lanthanum oxide on the combustion of the EVA/IFR composite was also studied in this work. The thermal stability of EVA/IFR/metal oxide systems was characterized by thermogravimetric analysis (TGA). The combustion behavior of the various formulations was investigated by limiting oxygen index (LOI), underwriters laboratories 94 (UL-94), and cone calorimeter tests. Digital photographs and scanning electron microscope images (SEM) of the residue char of EVA/IFR and EVA/IFR/metal oxide systems were obtained to gain some inference about the mode of action of the flame retardants. The chemical components of the char residue were explored by X-ray photoelectron spectroscopy (XPS).
2. EXPERIMENTAL SECTION 2.1. Materials. Ferric nitrate nine hydrate (Fe(NO) 3 ·9H 2 O), lanthanum nitrate six hydration (La(NO)3·6H2O), citric acid (C6H8O7), iron oxide (Fe2O3), and lanthanide oxide (La2O3) were bought from Sinopharm Chemical Reagent Co., Ltd. Ammonium polyphosphate (APP) and pentaecrythritol (PER) were kindly provided by KeYan Co. (Hefei, P.R. China). EVA copolymer containing 28 wt % vinyl acetate was supplied by Hanwha CO., Ltd (Korea). 2.2. Preparation of Lanthanum Ferrite. Nanocrystalline lanthanum ferrite was prepared by the citrate method.12 In a typical synthesis of nanocrystalline LaFeO3, 0.025 g La2O3 and 0.05 g Fe(NO3)3·9H2O were dissolved in 5 mol/L HNO3 and ion-free water, respectively. The two solutions were then mixed homogeneously. About 30 g citric acid was added into the mixed solution. After 15 min of magnetic stirring, this citric acid was well dissolved. The sol was obtained by evaporating the solution at 80 ◦C, and a raw powder was obtained by drying the sol. The raw powder was preheated at 300 °C for 30 min in the air and ground for 20 min. Finally, the nanocrystalline LaFeO3 was obtained after calcining the powder at 450 ◦C for 1 h in the air. 2.3. Preparation of Samples. EVA, APP, PER, Fe2O3, La2O3, and LaFeO3 were dried overnight in an oven at 80 °C before use. They were melt-mixed in a twin-roller mill (KX-160, Jiangsu, China) for 10 min at the same time. The temperature of the mill was maintained at 130 °C, and the roller speed was 100 rpm for the preparation of all of the samples listed in Table 1. The resulting systems were hot-pressed into sheets of suitable thickness and size for LOI and UL-94 tests. 2.4. Characterization. X-ray Diffraction (XRD) Analysis. X-ray diffraction (XRD) patterns were performed using the 1 mm thick films with a Japan Rigaku D/Max-Ra rotating anode
3. RESULTS AND DISCUSSION 3.1. Characterization of LaFeO3. The TEM image of LaFeO3 is shown in Figure 1. It is found that the size of the particle is about 200 nm. The XRD pattern (Figure 2) of LaFeO3 is in agreement with that previously reported.12 The TGA curve of LaFeO3 is shown in Figure 3. It can be observed that the decomposition of LaFeO3 contains three weight loss steps. From room temperature to 200 °C, the weight loss mainly corresponds to desorption physically adsorbed water. The second weight loss is from 300 to 500 °C, which is attributed to vaporization of bit residual inner water and combustion of residual citric acid. The last loss process is above 500 °C, which is mainly caused by desorption of residual hydroxyl (OH) group.13 3.2. Thermal Stability of EVA/IFR and EVA/IFR/Metal Oxide Formulations. The thermal stability of synthesized samples was examined by thermogravimetry. The thermogravimetric analysis (TGA) and differential thermogravimetric (DTG) curves for these systems in a nitrogen atmosphere
Table 1. Thermogravimetric Analysis for EVA, EVA/IFR, and EVA/IFR/Metal Oxide Formulations in a Nitrogen Atmosphere (IFR: APP/PER = 2/1, by Weight) sample
compositions
T-10
T-50
residue at 700 °C (%)
EVA1 EVA2 EVA3 EVA4
EVA EVA+30% IFR EVA+29.5% IFR+0.5% Fe2O3 EVA+29.5% IFR+0.5% LaFeO3 EVA+29.5% IFR+0.5% La2O3 EVA+29.5% IFR+0.25% Fe2O3+0.25% La2O3
347.9 224.6 228.4 236.4
459.7 480.6 481.5 483.2
0.2 10.4 11.6 12.1
234.6 226.4
480.2 481.9
11.2 11.6
EVA5 EVA6
7885
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tems, respectively. The initial decomposition temperature for the EVA/IFR/LaFeO3 system is greater than that for the EVA/ IFR composite by 12 °C. Although the temperature at 50% weight loss is not greatly increased in the presence of added metal oxides, the change in temperature suggests that the thermal stability of EVA/IFR compositions is improved by the addition of the coadditives. Moreover, 10.4 wt % of the initial sample mass remains as char residue at 700 °C. With the addition of coadditives, the residual chars are improved. For example, about 12.1 wt % of char residue is retained at 700 °C for the EVA/IFR/LaFeO3 system. More residual char is formed by the addition of LaFeO3 in comparison with the other coadditives. The DTG curves show that the temperature at the maximum mass loss rate is not obviously influenced by the introduction of the coadditives. The improvement of the thermal stability of EVA/IFR compositions after adding LaFeO3 may arise from LaFeO3 promotion of cross-linking which leads to the formation of a robust char layer which prevents EVA pyrolysis. 3.3. LOI and UL-94 Testing of EVA/IFR and EVA/IFR/ Metal Oxide Formulations. LOI and UL-94 testing were performed to investigate the flame retardancy of EVA/IFR composites. The results are listed in Table 2. The LOI value of EVA/IFR composites is 28.5%. With the addition of La2O3, Fe2O3, and LaFeO3, all the LOI value and rating of UL-94 test are improved. The highest LOI value is 31.5%, with only 0.5 wt % LaFeO3 and 29.5 wt % IFR. The addition of LaFeO3 also influences the combustion kinetics, as perceived by measuring the time of burning after the first flame application (t1); indeed, t1 decreases (9 and 5.5 s vs 1 and 0.5 s) because a carbonaceous residue is quickly formed.17 The relative time (t2) decreases, and there is no dripping during the second phase of ignition. The UL-94 test shows that EVA with 30% IFR burns to the dripping point during the second phase of ignition and reaches V-2 rating. But with the addition of 0.5 wt % coadditives and 29.5 wt % of IFR, a V-0 rating may be obtained for all EVA compositions. Compared with La2O3, Fe2O3, the mixture of Fe2O3 and La2O3, LaFeO3, at equivalent loading, is more effective at reducing flammability of EVA. Therefore, it can be concluded that the addition of LaFeO3 to the EVA/IFR composite may be used to achieve high flame retardancy. 3.4. Cone Calorimeter Tests (CCTs) Date of EVA/IFR and EVA/IFR/Metal Oxide Formulations. Cone calorimeter tests (CCTs), first announced in 1982, has been developed to predict the flammability behavior of materials in real fire scenarios due to its good correlation with real fire disasters. Several key parameters like heat release rate (HRR), total heat release (THR), peak HRR (PHRR), time to ignition (TTI), time to peak HRR, average mass loss rate (AMLR), and average smoke extinction area (ASEA) which could be employed to evaluate the developing, spreading, and intensity of fires can be obtained from cone calorimeter. Figures 5 and 6 contain HRR and THR curves of the systems. The corresponding data are displayed in Table 3. For the EVA/IFR composite, the sample begins to catch fire when exposed to fire after 22 s. Its heat release rate increases just slightly in the following 260 s, soars to 536 KW/m2, then subsequently drops sharply to approximately zero. When 0.5 wt % La2O3, Fe2O3, the mixture of Fe2O3 and La2O3, and LaFeO3 are added to EVA/IFR composites, respectively, all of the PHRR values decrease. For the EVA/ IFR/LaFeO3 system, its PHRR value sharply decreases with a reduction of 59% compared with the result of the EVA/IFR
Figure 1. The TEM pattern of LaFeO3.
Figure 2. The XRD pattern of LaFeO3.
Figure 3. The TGA and DTG of LaFeO3 in the nitrogen.
are shown in Figure 4, and the data are summarized in Table 1. The temperature of initial decomposition, T−10, was taken as the temperature at which 10% mass loss had occurred and T−50 as the temperature at which 50% of the initial sample mass had been lost. When 10% weight loss is chosen as a point of comparison, the decomposition temperatures are 224, 228, 236, 234, and 226 °C for EVA/IFR, EVA/IFR/La2O3, EVA/IFR/ Fe2O3, EVA/IFR/La2O3/Fe2O3, and EVA/IFR/LaFeO3 sys7886
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Figure 4. The TGA (a) and DTG (b) curves obtained for samples in a nitrogen atmosphere.
Table 2. Results of UL-94 and LOI Testing for EVA, EVA/ IFR, and EVA/IFR/Metal o\Oxide Formulations UL-94, 3.2 mm bar sample EVA1 EVA2 EVA3 EVA4 EVA5 EVA6
LOI 17 28.5 29 31.5 29 30
± ± ± ± ± ±
t1/t2 (s) 0.5 0.5 0.5 0.5 0.5 0.5
a
9/5.5 3/3.5 1/0.5 2/2 1.5/1.4
dripping
rating
yes yes no no no no
NRb V-2 V-0 V-0 V-0 V-0
a
Means that the specimen burns completely and therefore t1,t2 is not detectable. bNR represents no rating.
Figure 6. The THR curves of EVA/30%IFR, EVA/29.5%IFR/0.5% La 2 O 3 , EVA/29.5% IFR/0.5%Fe 2 O 3 , EVA/29.5% IFR/0.25% Fe2O3+0.25% La2O3, and EVA/29.5% IFR/0.5% LaFeO3.
is reduced by 56% when the additive is LaFeO3. It is attributed to the presence of the additives, which may increase the amount of residual char and lead to the decrease of total smoke production. In order to understand the fire hazard of several studied materials more clearly, the fire performance index (FPI) and the fire growth index (FGI) are selected. FPI is defined as the proportion of TTI and PHRR. It has been reported that there is a certain correlation between the FPI value of material and the time to flashover. When the value of FPI reduces, the time to flashover will be advanced. Therefore, it can be accepted that when the FPI value of a material is smaller, the fire risk is higher. FGI is defined as the proportion of PHRR and the time to peak HRR. According to the previous report, the larger the FGI value, the shorter time it takes to arrive at a high peak HRR, and the more fire hazard the materials have. The comparison between the values of FPI and FGI of four specimens has been shown in Table 3. The FPI value of the EVA/IFR/LaFeO3 system is highest and the FGI value of that is the lowest among five samples. These mean that fire risk of the EVA/IFR/LaFeO3 system is the smallest. The results show the significant improvement of flame retardancy of EVA/IFR composites containing coadditives, which may be explained by the appearance of the char formed during the combustion. The digital photos of char residues for EVA/IFR, EVA/IFR/La2O3, EVA/IFR/Fe2O3, EVA/IFR/ La2O3/Fe2O3, and EVA/IFR/LaFeO3 systems after cone calorimeter tests are shown in Figure 7. For EVA/IFR and EVA/IFR/La2O3 systems, there are both sparse residual chars.
Figure 5. The HRR curves of EVA/30%IFR, EVA/29.5%IFR/0.5% La 2 O 3 , EVA/29.5%IFR/0.5%Fe 2 O 3 , EVA/29.5% IFR/0.25% Fe2O3+0.25% La2O3, and EVA/29.5% IFR/0.5% LaFeO3.
composite. The THR value of the EVA/IFR/LaFeO3 system is also the lowest. The data contained in Table 3 clearly demonstrate that adding La2O3, Fe2O3, the mixture of Fe2O3 and La2O3, LaFeO3 can decrease the average mass loss rate (AMLR) of the EVA/ IFR composite. It is also observed that all metal oxides improve the char yield from combustion of the EVA/IFR composite which is consistent with the results of TGA. The results of the average smoke extinction area (ASEA) are listed in Table 3. The average smoke extinction area reflects the smoke, which is produced per unit mass of volatiles. It can be noticed that ASEA of the EVA/IFR composite is 534 m2. kg−1. With adding La2O3, Fe2O3, the mixture of Fe2O3 and La2O3, and LaFeO3 to EVA/IFR composites, all of the ASEA decrease. Additionally, it 7887
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Table 3. Cone Calorimeter Data for EVA, EVA/IFR, and EVA/IFR/Metal Oxide Formulationsa sample
TTI (s)
tp (s)
PHRR (kW/ m2)
THR (MJ/ m2 )
FPI (10−2)
FGI (10−1)
AMLR (10−2g/s/ m2)
ASEA (m2/ kg)
ACOY (10−3)
ACO2Y (10−1)
CY (%)
EVA1 EVA2 EVA3 EVA4 EVA5 EVA6
18 22 27 31 25 25
200 260 285 335 260 315
1288 536 367 318 548 353
97.5 96.2 85.5 82.3 95.5 89.3
1.4 4.1 7.3 25.5 4.5 7.1
64.7 20.6 12.9 8.2 21.1 11.2
4.5 3.6 3.4 2.3 3.2 3.5
632 534 391 236 321 282
58.3 52.9 51.1 46.6 45.7 53.3
26.3 21.4 18.5 19.1 20.6 19.4
9.3 18 24 0.26 22 25
(TTI: time to ignition, ± 2 s; tp: time to reach the peak HRR, ± 2 s; PHRR: peak heat release rate, ± 15 kW/m2; THR: total heat release, ± 0.5 MJ/m2; AMLR: average mass loss rate, ± 0.1 g/s/m2; ASEA: average specific extinction area, ± 20 m2/kg; ACOY: average CO yield, ± 0.005 kg/kg; ACO2Y: average CO2 yield, ± 0.008 kg/kg; CY: char yield, ± 0.5%). a
Figure 7. The digital photographs of the residue char after cone calorimeter test, (a) EVA/30%IFR, (b) EVA/29.5%IFR/0.5%La2O3, (c) EVA/ 29.5%IFR/0.5%Fe2O3, (d) EVA/29.5% IFR/0.25% Fe2O3+0.25% La2O3, (e) EVA/29.5% IFR/0.5% LaFeO3.
The char of the EVA/IFR/Fe2O3 system is compact and strong but not integrated. The char is integrated but not compact and strong for the EVA/IFR/La2O3/Fe2O3 system. The char of the EVA/IFR composite with 0.5 wt % LaFeO3 is quite compact and strong, which is effective in reducing heat transfer. 3.5. Study of the Residual Char about EVA/IFR and EVA/IFR/Metal Oxide Formulations. To further investigate mode of action of the catalyzed carbonization of LaFeO3 on the char formation of EVA/IFR during combustion, the morphologies of the chars of the samples after cone calorimeter testing were studied by SEM. From Figure 8 (A1, A2), many flaws can be seen on the surface of the char residue of samples due to insufficient char formation or less condensed char during the burning process. This poor char quality cannot effectively prevent the underlying EVA from degradation during combustion which may be the primary reason for the low flame retardant properties. However, the char surface of the EVA/IFR/LaFeO3 system illustrated in Figure 8 (B1, B2) is compact and tight. The impact char serving as a barrier can prevent the penetration of oxygen and combustible gases. The char layer can also resist mass and heat transfer, and effectively retard the degradation of underlying material. As shown in Table 4, the chemical components of the chars of EVA/IFR and EVA/IFR/LaFeO3 systems after cone calorimeter testing were investigated by XPS. The peak at 284.61 eV is attributed to C−H and C−C in aliphatic and aromatic species. The peak at 285.81 eV is characteristic of C− O (ether and/or hydroxyl group). Moreover, the peak at 288.91 eV can be assigned to CO. For O1s spectra, the peak at
Figure 8. The SEM photographs of the chars: (a) EVA/30% IFR (inner ① and outer ②) and (b) EVA/ 29.5% IFR/0.5% LaFeO3 (inner ① and outer ②).
around 532.36 eV is assigned to −O− in C−O−C, C−O−P, and/or C−OH groups. For N1s spectra, the peak at around 401.56 eV may be assigned to the nitrogen functionality in melamine structures and pyrrolic group. As for the spectra of P2p, the peak at around 133.97 eV can be attributed to the pyrophosphate and/or polyphosphate. 7888
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Table 4. XPS Datum of Heat-Treated EVA/IFR and EVA/IFR/Metal Oxide Formulations EVA2 C1s C1s C1s O1s P2p N1s EVA5 C1s C1s C1s O1s P2p N1s
binding energy 284.61 285.87 288.91 532.36 133.97 401.56
atom%
64.73 12.69 4.32 15.86 1.02 1.38 binding energy 284.61 285.86 288.90 532.39 133.95 401.45
EVA3
binding energy
atom%
C1s C1s C1s O1s P2p N1s
284.60 285.85 288.90 532.38 133.96 401.50
66.62 12.19 4.16 15.02 1.01 1.00
EVA4
binding energy
atom%
EVA6
C1s C1s C1s O1s P2p N1s binding energy
65.80 12.39 4.19 15.33 0.98 1.31
C1s C1s C1s O1s P2p N1s
284.59 285.85 288.91 532.38 133.97 401.51
284.59 285.84 288.92 532.43 133.95 401.38
atom% 68.62 12.21 4.14 13.28 0.77 0.98 atom% 67.22 12.29 4.16 14.50 0.92 0.91
morphological structure of char residue caused by LaFeO3 had been observed by the digital photos and SEM. It proves that the addition of LaFeO3 is capable of initiating a compact and homogeneous char on the surface, which turns out to be of utmost importance for the flame retardant performance. XPS data indicate that LaFeO3 could delay the oxidation of the EVA/IFR composite.
To study the thermal oxidative resistance, Cox/Ca (Cox: oxidized carbons and Ca: aliphatic and aromatic carbons) values are calculated. The Cox/Ca value of the char for the EVA/IFR composite is 0.26. After adding different metal oxides, Cox/Ca values all reduced. They are 0.25, 0.23, 0.25, and 0.24 for EVA/ IFR/Fe2O3, EVA/IFR/LaFeO3, EVA/IFR/La2O3, and EVA/ IFR/Fe2O3+La2O3 systems, respectively. In this text, it is found that the Cox/Ca ratios for these systems are all lower than that for the EVA/IFR system. The changes of atomic oxygen content in the system also support the above discussion. The oxygen contents in production of these systems are less than that in the EVA/IFR system, indicating the high oxidation of the EVA/IFR system during combustion. The Cox/Ca ratio and the oxygen content in production of the EVA/IFR/LaFeO3 system are all the lowest. It can be concluded that the presence of LaFeO3 reduces the oxidation of the materials. Experiments above demonstrate that the flame retardant property of the EVA/IFR composite is effectively improved by La2O3, Fe2O3, La2O3, and Fe2O3, LaFeO3. Among them, LaFeO3 plays the most significant effect. The morphologies of the chars of the samples effect flame retardant property. The char of the EVA/IFR/LaFeO3 system is very compact, homogeneous and strong, which provides an effective protection from thermal feedback from a fire to the undegraded polymer. It is supposed that the EVA/IFR/LaFeO3 system can lead to the formation of ceramic-like materials with a homogeneous surface, which would protect the material throughout combustion.
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AUTHOR INFORMATION
Corresponding Author
*Fax: t86-551-3601664. E-mail:
[email protected] (Y.H.). Fax: t86-551-3601664. E-mail:
[email protected] (L.S.) Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS This work was financially supported by the Program for National Natural Science Foundation of China (No.51036007) and Opening Project of National Synchrotron Radiation Laboratory of USTC.
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REFERENCES
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4. CONCLUSIONS LaFeO3 was successfully prepared. The EVA/IFR composites with different coadditives, including La2O3, Fe2O3, the mixture of La2O3 and Fe2O3, and LaFeO3, were then prepared through a melt-blending process. TGA results indicate that the addition of these coadditives into the EVA/IFR composite can improve the char yields and the thermal stability compared with EVA/ IFR composite. The flame retardancy of EVA/IFR composites with these different coadditives is compared. The incorporation of these coadditives into IFR leads to a remarkable influence on charring of EVA formulations, as revealed by TGA and cone data. Cone data give a measure of the size of the fire. It is confirmed that these coadditives act as effective additives functioning both as flame retardant coadditives and as smoke suppressants. Moreover, significant improvements are obtained in LOI and UL-94 ratings. Among all the samples, the fire risk of the EVA/IFR/LaFeO 3 system is the lowest. The 7889
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