Influence of Different Metal Oxides on the Thermal ... - ACS Publications

May 13, 2013 - Suzhou, P.R. China. §. Suzhou Key Laboratory of Urban Public Safety, Suzhou Institute of University of Science and Technology of China...
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Influence of Different Metal Oxides on the Thermal, Combustion Properties and Smoke Suppression in Ethylene−Vinyl Acetate Lei Wang,†,‡,§ Lei Song,*,† Yuan Hu,*,†,§ and Richard K. K. Yuen‡ †

State Key Laboratory of Fire Science, University of Science and Technology of China, 96 Jinzhai Road, Hefei, Anhui 230026, P.R. China ‡ Department of Building and Construction, City University of Hong Kong and USTC-CityU Joint Advanced Research Centre, Suzhou, P.R. China § Suzhou Key Laboratory of Urban Public Safety, Suzhou Institute of University of Science and Technology of China, Suzhou, P.R. China ABSTRACT: The composites based on ethylene−vinyl acetate copolymer (EVA) and β-FeOOH, MoO3, or Sb2O3 were prepared through a melt blending process. Apart from MoO3, the nanoparticles homogeneously disperse in the EVA matrix. In thermogravimetric analysis (TGA), EVA/5%MoO3 and EVA/5%Sb2O3 exhibit an enhanced thermal behavior at initial temperatures. However, β-FeOOH only can improve the thermal behavior of EVA at high temperatures. The glass transition temperature (Tg) and the storage modulus are all raised with the addition of β-FeOOH, MoO3, or Sb2O3. According to a cone calorimeter (CONE), the addition of these oxides brings an efficient reduction of the flammability parameters, such as peak heat release rate (PHRR), total heat release (THR), peak smoke production rate (PSPR), total smoke production (TSP), peak carbon monoxide production rate (PCOR), and so on. Laser Raman spectroscopy (LRS) and thermogravimetric analysis-Fourier transform infrared spectrometry (TGA-FTIR) reveal the cause of the retarding combustion and smoke suppression of β-FeOOH, MoO3, or Sb2O3 in EVA matrix.

1. INTRODUCTION Ethylene−vinyl acetate copolymer containing 28% vinyl acetate, fully developed flaming of both relatively high and low ventilation, could give much higher yields of carbon monoxide normally and the smoke. It is very well established now that the real killer in fires is, in most cases, not the heat of the fire itself but the smoke and volatiles produced. The smoke, smoke particulates, and some toxic compounds (especially carbon monoxide) produced during the course of a real fire are known to cause more than 70% of the fatalities. Hence reducing the amount of smoke formed during burning by changing the path of decomposition of the burning materials so that they retain polymer carbon and form char instead of smoke and volatiles is very important.1,2 It has been proved that most metal compounds, in particularly, transition metal compounds, such as iron, molybdenum, and antimony compounds, are most effective as smoke retardantss to some plastics, such as poly(vinyl chloride) and acrylonitrile-butadiene-styrene (ABS).3,4,1 The influence of CuO, MoO3, and FeOOH on thermal decomposition and smoke emission of poly(vinyl chloride) has been investigated. The experimental data indicated that these metal oxides presented important effects on the thermal decomposition, heat release, and smoke emission of PVC.3 The thermal decomposition and smoke suppression of poly(vinyl chloride) treated with Cu2O, CuO, MoO3, and Fe2O3 were studied. It has been found that the four transition metal oxides showed good flame retardancy and smoke suppression by effectively reducing peak and average heat release rate (pk-HRR and av-HRR), peak smoke production rate (pk-SPR), and total smoke production (TSP).4Acrylonitrile-butadiene-styrene (ABS)/chlorinated © XXXX American Chemical Society

poly(vinyl chloride) (CPVC) in combination with basic iron(III) oxide (FeOOH) was fabricated. The results clarified that FeOOH could promote the formation of char, which is associated with flammability properties and smoke suppression in these polymer blends.1 However, there have less studies about smoke suppression of transition metal compounds in EVA matrix. In the present work, the dispersion of β-FeOOH, MoO3, and Sb2O3 in EVA matrix was studied by scanning electron microscopy (SEM). The thermal stability of pure EVA, EVA/ β-FeOOH, EVA/MoO 3 , and EVA/Sb 2 O 3 systems was characterized by thermogravimetric analysis (TGA). The dynamic mechanical property of systems was studied by dynamic mechanical thermal analysis (DMTA). The effects of these metal oxides on the combustion and smoke in EVA were investigated by cone calorimeters (CCTs). The reasons for the retarding combustion and smoke suppression were found by the results of laser Raman spectroscopy (LRS) and thermogravimetric analysis-Fourier transform infrared spectrometry (TGA-FTIR).

2. EXPERIMENTAL SECTION 2.1. Materials. Iron(III) chloride hexahydrate (FeCl3·6H2O), molybdenum oxide (MoO3), and antimony oxide (Sb2O3) were bought from Sinopharm Chemical Reagent Co., Ltd. The reagents are of analytical grade and used without Received: February 25, 2013 Revised: May 4, 2013 Accepted: May 13, 2013

A

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Laser Raman Spectrometry (LRS). Laser Raman spectroscopy (LRS) measurements were carried out at room temperature with a SPEX-1403 laser Raman spectrometer (SPEX Co.) with excitation provided in backscattering geometry by a 514.5 nm argon laser line. Thermogravimetric Analysis-Fourier Transform Infrared Spectrometry (TGA-FTIR). TGA-FTIR of the samples was performed using the TGA Q5000 IR thermo-gravimetric analyzer that was interfaced to the Nicolet 6700 FTIR spectrophotometer. About 5.0 mg of the samples were put in an alumina crucible and heated from 30 to 500 °C. The heating rate was 20 °C/min (nitrogen atmosphere, flow rate of 45 mL/ min).

further purification. EVA copolymer containing 28 wt % vinyl acetate was supplied by Hanwha Co., Ltd. (Korea). 2.2. Preparation of β-FeOOH. In a typical synthesis,5ironiron(III) chloride hexahydrate (FeCl3·6H2O, 0.487g) was dissolved in distilled water (30 mL) under stirring. Then the mixture was transferred to a 40 mL Teflon lined autoclave. Hydrothermal synthesis was carried out in an oven at 110 °C for 2 h. The products were collected by filtration, washed with distilled water and ethanol several times, and then dried in an oven at 60 °C for 6 h. 2.3. Preparation of Samples. EVA, β-FeOOH, MoO3, and Sb2O3 were dried in an oven at 80 °C overnight 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 the samples listed in Table 1.

3. RESULTS AND DISCUSSION 3.1. Characterization. The XRD patterns of the pure EVA, EVA/β-FeOOH, EVA/MoO3, and EVA/Sb2O3 composite are shown in Figure 1. The XRD pattern of pure EVA from Aldrich

Table 1. TGA Data of EVA, EVA/5% β-FeOOH, EVA/5% MoO3, and EVA/5% Sb2O3 Formulations at Nitrogen Atmosphere sample

compositions

T−10

T−50

residue at 700 °C (%)

EVA1 EVA2 EVA3 EVA4

EVA EVA + 5% β-FeOOH EVA + 5% MoO3 EVA + 5% Sb2O3

361.2 342.0 363.4 365.2

469.8 471.1 472.7 474.4

0.1 6.3 6.3 4.2

2.4. Characterization. X-ray Diffraction (XRD) Analysis. X-ray diffraction (XRD) patterns were performed on the 1 mm thick films with a Japan Rigaku D/Max-Ra rotating anode X-ray diffractometer equipped with a Cu−Ka tube and Ni filter (l1/ 40.1542 nm). Scanning Electron Microscopy (SEM). The scanning electron microscopy (SEM) image of the residue after limited oxygen index (LOI) tests 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. Fourier Transform Infrared Spectroscopy. Fourier transform infrared spectroscopy (Nicolet 6700 FT-IR spectrophotometer, Thermo Fisher Scientific) was employed to characterize the DPHA using thin KBr disc. The transmission mode was used, and the wavenumber range was set from 4000 to 500 cm−1. Thermogravimetric Analysis (TGA). Each sample was examined in air flowing at 150 mL/min on a Q5000 (TA, USA) 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%. Dynamic Mechanical Thermal Analyses (DMTA). Dynamic mechanical thermal analyses (DMTA) were performed on a Perkin-Elmer Diamond DMA (Massachusetts) at a constant frequency of 10 Hz and a heating rate of 5 °C/min over the range of −40−20 °C. 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.

Figure 1. XRD patterns of (a) EVA, (b) EVA/β-FeOOH, (c) EVA/ MoO3, and (d) EVA/Sb2O3 composites.

is shown in Figure 1a. The XRD pattern of the EVA/β-FeOOH composite is presented in Figure 1b. The XRD peaks exactly matches 110, 200, 310, 211, and 521 crystal planes of βFeOOH with tetragonal crystal structure,6 in agreement with the literature value (JCPDS card no.77-0244), confirming the existence of β-FeOOH in the polymeric matrix. The XRD spectrum of MoO3 incorporated in EVA matrix is shown in Figure 1c. The appearance of 020, 110, 040, 021, and 060 crystal planes, in accordance with the literature value (ICDD PDF reference code 00-005-0508), verifies the existence of MoO3 in the polymeric.7 The XRD pattern of the EVA/Sb2O3 composite is displayed in Figure 1d. The XRD peaks which exactly corresponds to 111, 222, 400, 331, 422, 511, 440, 531, 622, 444, and 551 crystal planes, proves the emergence of Sb2O3 in the EVA, coinciding with the literature value (Joint Committee on Powder Diffraction Standards file card no. 431071).8 Dispersion of nanofillers in a polymer matrix is very important to obtain property enhancements. In order to investigate the inner structure of the composites, the composites with the β-FeOOH, MoO3, or Sb2O3 loading of 5.0 wt % were cryogenically broken after immersion in liquid nitrogen and the fractured surfaces were characterized by SEM (Figure 2). Figure 2a,c show that β-FeOOH and Sb2O3 have good interfacial adhesion with EVA matrix in the composite, B

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FeOOH, EVA/MoO3, and EVA/Sb2O3 formulations. For the FTIR spectrum of EVA (Figure 3a), the peak around 3436 cm−1 is assigned to the stretching vibration of −OH groups.9 The peaks at 2925, 2854, and 1470 cm−1 are attributed to −CH2−. The peaks at 1241, 1100, and 1020 cm−1 suggest the existence of C−O−C. The peak at 1736 cm−1 indicates the presence of CO. The peak at 720 cm−1 corresponds to the bending vibration of C−C. Also, the peak at 610 cm−1 is responsible for the stretching vibration of the C−H group.10 For the FTIR spectrum of EVA/β-FeOOH (Figure 3b), there are many peaks corresponding to EVA. In addition, two typical bands at 860 and 675 cm−1 can be ascribed to Fe−O−H bending vibrations in β-FeOOH. The Fe−O stretching vibrations are responsible for the bands at 438 cm−1.11 In the FTIR spectrum of EVA/MoO3 (Figure 3c), there are also many peaks for EVA. The absorption peaks between 500 and 600 cm−1 indicate the appearance of the vibration of the Mo−O bond. Also, the sharp and broad peaks in the region 1100−900 cm−1 are attributed to the stretching vibration of the MoO bond.12 In the FTIR spectrum of EVA/Sb2O3 (Figure 3d), apart from the peaks of EVA, the absorption band at 710 and 590 cm−1 are assigned to the Sb−O stretching mode of Sb2O3.13 3.2. Thermal Stability of EVA, EVA/β-FeOOH, EVA/ MoO3, and EVA/Sb2O3 Formulations. The thermogravimetric analysis (TGA) and differential thermogravimetric (DTG) curves of EVA and EVA composites under nitrogen atmosphere are shown in Figure 4, and the data are summarized in Table 1. It is defined that the initial decomposition temperature as T−10 means the temperature at 10 wt % mass loss, and T−50 means the temperature at 50 wt % mass loss. It is clearly found that the thermal degradation of the pure EVA and EVA composites are composed of two main steps. The first step is generally accepted to be loss of acetate groups. The second step results from decomposition of the chain-stripped polyene.14 Compared with pure EVA, the EVA/ 5% MoO3 and EVA/5% Sb2O3 exhibit an enhanced thermal behavior at the initial temperature and have residues about 6.3% and 4.3% at 700 °C, respectively. The addition of 5% βFeOOH leads an enhanced thermal behavior at temperatures above 380 °C and improves the yield of residue to 6.5%. The reason could be explained that during the course of EVA degradation, the catalytic property of Fe3+ ion would promote the cross-linking of EVA to form extra char, which prevents the

Figure 2. SEM of (a) EVA/β-FeOOH, (b) EVA/MoO3, and (c) EVA/ Sb2O3 composites.

which exhibits uniformly dispersed morphology. However, MoO3 in EVA (Figure 2b) matrix has a small amount of agglomeration. The composition of the products were analyzed by FTIR spectroscopy. Figure 3 is the FTIR spectra of EVA, EVA/β-

Figure 3. FTIR of (a) EVA, (b) EVA/β-FeOOH, (c) EVA/MoO3, and (d) EVA/Sb2O3 composites.

Figure 4. TGA and DTG curves of (a) EVA, (b) EVA/β-FeOOH, (c) EVA/MoO3, and (d) EVA/Sb2O3 composites under nitrogen atmosphere at a heating rate of 20 °C/min. C

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Figure 5. (a) Tan δ versus temperature curves and (b) storage modulus of EVA, EVA/β-FeOOH, EVA/MoO3, and EVA/Sb2O3 as a function of temperature.

Table 2. Cone Calorimeter Data for EVA, EVA/5% βFeOOH, EVA/5% MoO3, and EVA/5% Sb2O3 Formulationsa

composites from decomposing. However, the Fe3+ ion would also have the same catalytic property that can increase the rate of EVA deacetylation, promote the onset time of the degradation, and reduce the thermal stability of the composite.15 So β-FeOOH reduces the thermal stability of EVA in the initial decomposition temperatures and improves the thermal stability and char residue above 380 °C. 3.3. Dynamic Mechanical Properties of EVA, EVA/βFeOOH, EVA/MoO3, and EVA/Sb2O3 Formulations. Dynamic mechanical thermal analyses (DMTA) as a very versatile technique can provide a convenient and sensitive testing system for rapid determination of thermo-mechanical properties of polymers and polymer-based materials as a function of frequency, temperature, or time, using only small amounts of the material.16 The glass transition temperature (Tg) is defined as the peak of the tan δ curve. The tan δ versus temperature curves for EVA, EVA/5% β-FeOOH, EVA/5% MoO3, and EVA/5% Sb2O3 are plotted in Figure 5a. It is clear that the glass transition temperatures of the composites are higher than that of the pure EVA, attributed to the restricted chain motion of polymer near the nanofiller.17 The plot of storage modulus versus temperature in Figure 5b illustrates that the storage modulus of the composites are also higher than that of the pure EVA. This suggests that addition of β-FeOOH, MoO3, or Sb2O3 nanoparticles gives a favorable impact on the storage modulus of the EVA. Generally, the storage modulus for the composites depends on the inorganic phase, the interfacial interaction, and the cross-linking density of the polymer matrix.18 Therefore, this behavior can be mainly explained that these rigid fillers have imparted stiffness behavior to the EVA.18 3.4. Cone Calorimeter Tests (CCTs) Date of EVA,EVA/ β-FeOOH, EVA/MoO3, and EVA/Sb2O3 Formulations. The cone calorimeter (CONE) has been widely used to evaluate the flammability characteristics of materials; it can provide a wealth of information on the combustion behavior and give a measure of the size of the fire. Table 2 and Figures 6−8 show data and plots of pure EVA and EVA with β-FeOOH, MoO3, or Sb2O3 obtained from the cone calorimeter test at an incident heat flux of 35 kW m−2. The peak rate of heat release (PHRR) of a polymer is considered to be one of the most important parameters in assessing potential behavior in a real fire. From Table 2, PHRR for EVA is high at 1286.0 kW m−2. The largest amount of total heat release (THR) can reach 95.5 MJ m−2 kg−1. The EVA

sample

TTI (s)

EVA1 EVA2 EVA3 EVA4

55 50 50 49

tp(s)

PHRR (kW/m2)

THR (MJ/m2)

sample

170 140 180 175 AMLR (10−2g/s/m2)

1286.0 948.7 1285.4 972.6 AEHC (MJ/kg)

95.5 77.5 72.6 74.6 ASEA (m2/kg)

EVA1 EVA2 EVA3 EVA4

4.5 4.0 4.2 4.0

36.4 27.9 28.7 29.6

395.9 215.8 261.9 341.9

FPI (10−2)

FGI (10−1)

4.2 5.3 3.9 5.0 ACOY (10−3) 32.1 27.3 46.1 67.5

75.8 63.2 71.4 55.6

CY (%)

0.3 7.4 7.0 4.8 ACO2Y (10−1) 19.0 19.9 17.0 17.6

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; FPI, proportion of TTI and PHRR; FGI, proportion of PHRR and the time to peak HRR; CY, char yield, ±0.5%; AMLR, average mass loss rate, ±0.1 g/s/m2; AEHC (MJ/kg), average effective heat of combustion; ASEA, average specific extinction area, ±20 m2/ kg; ACOY, average CO yield, ±0.005 kg/kg; ACO2Y, average CO2 yield, ±0.008 kg/kg. a

Figure 6. SPR curve of (a) EVA, (b) EVA/β-FeOOH, (c) EVA/ MoO3, and (d) EVA/Sb2O3 composites.

containing β-FeOOH, MoO3, or Sb2O3 has a slightly lower peak rate of heat release. For example, the PHRR for EVA/5% D

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can clearly be seen that SPR of the EVA2 composite during the first stage is lower than that of during the second stage, and the maximum of SPR of EVA2 is the lowest among all samples. Total smoke production (TSP) (Figure 7) of EVA2 composites

Figure 8. PCOR curve of (a) EVA, (b) EVA/β-FeOOH, (c) EVA/ MoO3, and (d) EVA/Sb2O3 composites.

β-FeOOH reduces to 948.7 MJ m−2 kg−1, which is less than that for EVA/5% MoO3 or EVA/5% Sb2O3. Also, the THR for EVA/5% β-FeOOH decreases to 77.5 MJ m−2 kg−1, which can be considered as a significant reduction. The fire performance index (FPI) and fire growth index (FGI) are parameters calculated from the directly measured data of cone calorimeter experiments and can be used to give an overall assessment of the fire safety of a material in the cone calorimeter test.19,20 The higher the value of the FPI or the lower the value of the FGI, the higher is the product’s safety rank.21 The comparison for the values of FPI and FGI of four specimens has been shown in Table 2. The FPI values of the EVA/5% β-FeOOH and EVA/5% Sb2O3 are higher, and their FGI values are lower than that of the pure EVA, which are different from these for EVA/5% MoO3.These mean that fire risks of EVA/5% β-FeOOH and EVA/5% Sb2O3 become smaller. Average mass loss rate (AMLR) is recognized to be the primary parameter responsible for influencing the HRR and the smoke production rate (SPR) of a material during combustion.22 The data contained in Table 2 clearly demonstrate that adding β-FeOOH, MoO3, and Sb2O3 can decrease the AMLR of the pure EVA, which show that they are effective agents in the EVA system. It is also observed that all these metal oxides improve the char yield (CY) from combustion of the EVA, which is consistent with the results of TGA. Average effective heat (av-EHC) means the average heat released by burning volatiles produced during the combustion of materials per unit mass, which is considered to be an important parameter to evaluate the flammability.23 Compared with that of EVA, the av-EHC of EVA2, EVA3, and EVA4 composites reduces; and that of EVA2 is the lowest. The emission of smoke and toxic gas is considered as another important parameter for evaluating materials.21 The smoke from EVA during burning is mainly the pyrolyzed product including carbon particles, the acid gas, and water vapor, etc. formed by the polymerization of olefin fragments cyclization. Smoke production rate is defined as the rate at which smoke is produced per unit time. Curves of the smoke production rate (SPR) of the sample are shown in Figure 6. There is a distinction of the smoke release behavior between EVA and its composites. SPR of all samples can be divided into two steps: the one is before the ignition of the samples, and the other is during the flaming processes at the basis of the time scale.23 It

Figure 7. TSP curve of (a) EVA, (b) EVA/β-FeOOH, (c) EVA/ MoO3, and (d) EVA/Sb2O3 composites.

is reduced by 25.8% compared with that of EVA1. It can be considered that β-FeOOH plays the role of smoke suppressant in the combustion of EVA2 composites, which may be attributed to the formation of char.24 From Figure 8, carbon monoxide production rate (PCOR) of EVA2 during combustion is far less than that of the pure EVA. Also, the average CO yield (ACOY) of EVA2 can reduce to 0.0273 kg/ kg compared with that of the pure EVA. The average CO2 yield (ACO2Y) of EVA2 is the highest in the samples. The results of the average smoke extinction area (av-SEA) are also listed in Table 2. The average smoke extinction area means the smoke which is produced per unit mass of volatiles. It can be noticed that av-SEA of EVA is 395.9 m2 kg−1 and decreases to 215.8 m2 kg−1 when adding β-FeOOH to EVA. It is attributed to the presence of β-FeOOH, which may change the components of volatiles and lead to the decrease of total smoke production. 3.5. Structure Analysis of the Purified Char Residue. Laser Raman spectroscopy (LRS) was used to characterize the structure of residual char which was collected after cone calorimeter testing. Three samples are chosen for comparative research, and they all contain two obvious vibrating peaks. The first peak around 1360 cm−1 is attributed to the E2g vibrational mode, while the second one around 1600 cm−1 represents defects in the structure.25 Figure 9 and Table 3 show different results of char with the addition of β-FeOOH, MoO3, and Sb2O3. Relative intensity ratios between 1596 cm−1 and 1364 cm−1 with the addition of β-FeOOH, MoO3, and Sb2O3, which is inversely proportional to an in-plane microcrystalline size and/or an in-plane phonon correlation length obtained from Raman spectroscopy,26 are presented in Table 3. The content ratio of ordered carbon with the addition of β-FeOOH is highest in the three samples, and that of Sb2O3 is higher than that of MoO3. It is well-known that the ordered carbon can improve the flame retardancy of the system.27 What is more, the addtion of β-FeOOH to EVA brings the highest amount of the char, according to the data of the cone calorimeter (CONE) and TGA. So the combustion performance of EVA is improved, and the smoke is inhibited after adding β-FeOOH. Although the amount of the char of EVA/Sb2O3 is less than E

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reduction of toxic gases, which is in agreement with the data of CCTs. What’s more, the amount of the hydrocarbon evolved products for EVA/5% β-FeOOH composite has reduced compared with those evolved by pure EVA. The reduced amount of the hydrocarbon volatiles further leads to the inhibition of smoke, because the organic volatiles may crack into smaller hydrocarbon molecules and smoke particles. The gaseous hydrocarbons are condensed and the smoke particles are aggregated to form smoke.28 However, it is also found that the general intensity of acetate evolved product for EVA/5% βFeOOH is slightly higher than that for EVA, which means that β-FeOOH promotes the loss of acetate by chain-stripping of EVA,14 in agreement with the data of TGA. In combination with the results of LRS and TGA-IR, it is indicated that compared with MoO3 and Sb2O3, β-FeOOH play the largest role in terms of inhibiting the combustion and the release of smoke and toxic gas, due to the highest amount of the char residue and ordered carbon formed during thermal degradation or combustion of EVA/β-FeOOH composites.

Figure 9. Raman spectra of the purified char residue of (a) EVA/βFeOOH, (b) EVA/MoO3, and (c) EVA/Sb2O3 composites.

Table 3. Position and Area Ratio of Peaks in the Char sample

peak 1 (cm−1)

peak 2 (cm−1)

area ratio (peak 1/peak 2)

EVA2 EVA3 EVA4

1600 1603 1606

1358 1361 1362

0.678 0.314 0.360

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CONCLUSIONS

In this paper, EVA with β-FeOOH, MoO3, or Sb2O3 were fabricated through a melt blending process. Apart from MoO3, β-FeOOH and Sb2O3 nanoparticles are uniformly dispersed in the EVA matrix. The TGA results show that in comparison with pure EVA, MoO3 and Sb2O3 can enhance thermal behavior of EVA at start temperatures, whereas β-FeOOH only improves its thermal stability at high temperatures and has the largest amount of residues. The data of DMTA indicate that there is a increase in the glass transition temperature (Tg) and the storage modulus for the samples containing β-FeOOH, MoO3, or Sb2O3 compared with the pure EVA. In the CONE testing, the relevant flammability parameters of the composites remarkably drop after adding these oxides. The results of TGAIR show that the total, hydrocarbon, and CO evolved products of EVA/β-FeOOH become less, but β-FeOOH promotes the loss of acetate of EVA, which are agreement with the cone calorimeter (CONE) and TGA data. LRS and TGA-IR analysis indicates that EVA/β-FeOOH composite can form the largest amount of the char residue and ordered carbon during thermal degradation or combustion, retarding the combustion and lessening the release of smoke and toxic gas. Moreover, the char of EVA/5% Sb2O3 composite possesses a better graphitization degree than that of EVA/5% MoO3. So β-FeOOH and Sb2O3 can be considered to be used in EVA to improve the thermal and combustion properties and suppress the smoke and toxic gas.

that of EVA/MoO3, the content ratio of ordered carbon in the char of EVA/Sb2O3 is more. So the fire risk of EVA/Sb2O3 is smaller than that of EVA/MoO3. 3.6. Volatilized Products of EVA and EVA/β-FeOOH Formulations. To investigate the influence of β-FeOOH on the evolved gaseous volatiles during pyrolysis, the volatile components of EVA and EVA/5% β-FeOOH composite are investigated by the thermogravimetric analysis-Fourier transform infrared spectrometry (TGA-FTIR) technique. The 3D diagrams of EVA and EVA/5% β-FeOOH composite are shown in Figure 10. It shows that the typical thermal degradation process of the composite is similar to pure EVA. Figure 11 gives the intensity of the total and typical gaseous volatiles of pure EVA and EVA/5% β-FeOOH composite in different times. The typical gaseous volatiles, such as CO, hydrocarbon, and acetate are identified easily by their characteristic absorbance: CO, hydrocarbon, and acetate correspond to 2180, 2985, and 1736 cm−1, respectively. The maximum intensity of the total evolved products for EVA/5% β-FeOOH composite has reduced compared with those evolved by pure EVA, which implies that the amount of the volatiles released from the EVA/5% β-FeOOH composite is much less than that from the pure EVA. The decrease of the CO emission for EVA/5% β-FeOOH composite indicates the

Figure 10. 3D diagrams of the evolved gaseous volatiles of (a) EVA and (b) EVA/5%β-FeOOH composites. F

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Figure 11. Volatilized products analysis (a) the total, (b) CO, (c) hydrocarbon, and (d) acetate of EVA and EVA/β-FeOOH composites.

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AUTHOR INFORMATION

Corresponding Author

*Fax: 86-551-3601664 (Y.H.); 86-551-3601642 (L.S.). E-mail: [email protected] (Y.H.); [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 the National Natural Science Foundation of China (Grant No. 51036007) and China Postdoctoral Science Foundation Grant 2012M521246.

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