Article pubs.acs.org/IECR
Microencapsulated Ammonium Polyphosphate with Glycidyl Methacrylate Shell: Application to Flame Retardant Epoxy Resin Qinbo Tang,† Bibo Wang,† Yongqian Shi,† Lei Song,*,† and Yuan Hu*,†,‡ †
State Key Laboratory of Fire Science, University of Science and Technology of China, 96 Jinzhai Road, Hefei, Anhui 230026, People’s Republic of China ‡ Suzhou Key Laboratory of Urban Public Safety, Suzhou Institute for Advanced Study, University of Science and Technology of China, 166 Ren’ai Road, Suzhou, Jiangsu 215123, People’s Republic of China ABSTRACT: A new microcapsule containing ammonium polyphosphate (APP) and glycidyl methacrylate (GMA) as core and shell material was synthesized by in situ polymerization technology. The structure and performance of microencapsulated ammonium polyphosphate (MCAPP) were characterized by Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and water contact angle (WCA). The flame retardation of MCAPP and APP flame retarded epoxy resin (EP) composites were studied by limiting oxygen index (LOI), UL94 test, and cone calorimeter. The results indicated that the microencapsulation of APP with the GMA led to an improvement of the hydrophobicity. Results also revealed that the flame retardancy of the EP/MCAPP composite was better than that of the EP/ APP composite at the same additive loading. Moreover, the EP/MCAPP demonstrated better thermal stability, due to the stable char forming by APP and GMA shell and the better dispersion of MCAPP in the EP matrix.
1. INTRODUCTION Epoxy resin is considered to be one of the most important thermosetting polymers with many desirable properties, such as good heat and solvent resistance, remarkable adhesive strength, superior electrical and mechanical properties, ease of cure, and processing.1,2 These properties render it suitable for a wide range of potential applications such as structural compositions and electronic parts.3−7 However, the epoxy resin is difficult to meet those high heat resistance and flame retardant requirements and applications because of its poor fire resistance. Many methods have been developed to improve its thermal stability and flame retardancy.8−12 In recent years, 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) and its derivatives have received outstanding attention because of their high reactivity and applicability on epoxy resin.10 But the functionality of the flame retardant epoxy resins prepared by above methods is obviously decreased for the addition reaction of DOPO and its derivatives with epoxide groups. Consequently, it directly leads to a lesser cross-linking density in the cured epoxy resins and the low Tg of thermosets.13 Recently, various fillers have been used to improve the flame retardant properties of epoxy resin, intumescent flame retardants (IFRs) have been considered to be a promising method, which is due to the fact that they are low-toxicity, low-smoke, halogen-free, and very efficient.14−16 A typical intumescent system comprises an acid source (a dehydration catalyst for char formation), a carbon source (a carbonization agent), and a gas source (a blowing agent).17 The compounds used as an acid source are generally inorganic acids or precursor of the acids, for example, ammonium polyphosphate (APP), which is a common IFR. In despite of many advantages, IFRs may reduce the mechanical and other properties of the materials because of the rather different polarities of IFR and EP which makes them © 2013 American Chemical Society
thermodynamically immiscible. Meanwhile, the difference in polarity causes a weak interfacial adhesion, which plays an important role in the mechanical and other related properties. Furthermore, most IFR systems are moisture sensitive, thus they are easily attacked by water and exude during the service life, resulting in a decrease in the flame-retardant properties of the polymer composites. In order to overcome these problems, microencapsulation is a good choice. Microencapsulation is a process of enveloping microscopic amounts of matter in a thin film of polymer, which forms a solid wall.18 This core−shell structure allows isolation of the encapsulated substance from the surroundings and thus protects it from any degrading factors such as water. Even the proper shell can be used as a compatibilizer to improve the compatibility between the matrix and the flame retardants.19 Glycidyl ethers constitute an interesting and broad family of monomers as a great diversity of polymeric materials can be obtained by varying the nature of the ether side group attached to the epoxide. Glycidyl methacrylate (GMA) is a monomer of particular interest since it possesses two polymerizable groups: the epoxide and the methacrylate functions, which can be seen as a modified epoxy resin. In addition, the glycidyl methacrylate copolymers showed lower corrosivity to the equipment and could be used as a reactive compatibilizer, which could enhance the distubution of APP in EP matrix.20,21 So far, we have not found the report of using GMA as a microcapsule material. The schematic diagram of the MCAPP microcapsule is shown in Figure 1. Received: Revised: Accepted: Published: 5640
September 24, 2012 March 14, 2013 March 28, 2013 March 28, 2013 dx.doi.org/10.1021/ie302591r | Ind. Eng. Chem. Res. 2013, 52, 5640−5647
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spectrometer, with Al Kα excitation radiation (hν = 1253.6 eV) in ultrahigh vacuum conditions. Scanning Electron Microscopy (SEM). The morphology of the sample after gold-sputtered were studies by PHILIPS XL30E scanning electron microscope. The accelerated voltage was 20 KV. Water Contact Angle Measurements (WCA). The WCA of the samples was measured with a drop-shape analysis system (Krüss DSA100) at three different points for each. Limiting Oxygen Index. LOI was measured using a HC-2 oxygen index meter (Jiang Ning Analysis Instrument Company, China) on sheets 100 mm × 6.7 mm × 3 mm according to the standard oxygen index test ASTMD2863-2010. 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 mm × 12.7 mm × 3 mm according to UL-94 test ASTMD3801-2010. Cone Calorimeter Test. The combustion test was performed on the cone calorimeter (FTT, UK) tests according to ISO 5660 standard procedures, with 100 × 100 × 3 specimens. Each specimen was wrapped in an aluminum foil and exposed horizontally to 35 kW/m2 external heat flux. Thermogravimetric Analysis. Thermogravimetric analysis (TGA) was carried out using a Q5000 IR thermogravimetric analyzer (TA InstrumentsWaters, China) at a linear heating rate of 20 °C min−1 in N2 atmosphere. The weight of all the samples were kept within 5−10 mg. Samples in an open Pt pan were examined under an air flow rate of 6 × 10−5 m3/min at temperatures ranging from room temperature to 700 °C. Real-Time Fourier Transform Infrared Spectra (RT-FTIR). Real-time Fourier transform infrared (FTIR) spectra were recorded using a Nicolet MAGNA-IR 750 spectrophotometer equipped with a ventilated oven having a heating device. The untreated EP and flame retarded EP composites were mixed with KBr powders, and the mixture was pressed into a tablet, which was then placed into the oven. The temperature of the oven was raised at a heating rate of about 10 °C/min. Dynamic FTIR spectra were obtained in situ during the thermal oxidative degradation of the polymer and its composites. Dynamic Mechanical Analysis (DMA). Dynamic mechanical properties were measured with DMA Q800 (TA, USA). The dynamic storage modulus were determined at a frequency of 1 Hz and a heating rate of 10 °C/min over the range of 25−220 °C. The dimensions of the samples were approximately 1 mm thickness, 20 mm length, and 5 mm width.
Figure 1. Reaction scheme of MCAPP microcapsules.
In this paper, GMA was used as shell material to microencapsulate ammonium polyphosphate (MCAPP). Then MCAPP was used as an intumescent flame retardant for EP and considered the GMA microencapsulation technology on thermal and flame retardant properties of intumescent flameretardant systems.
2. EXPERIMENTAL SECTION 2.1. Materials. Epoxy resin (DGEBA, commercial name: E44) was supplied by Hefei Jiangfeng Chemical Industry Co. Ltd. (Anhui, China). Ammonium polyphosphate (APP) were supplied by Shandong Shian Chemical Co., Ltd. (Shangdong, China). Cyclohexane, benzoyl peroxide (BPO), butanone, and 4, 4′-diaminodiphenylmethane were standard laboratory reagents and provided by Sinopharm Chemical Reagent Co. Ltd., China. Glycidyl methacrylate (GMA, 96%, Janssen Chemicals) was distilled under vacuum in a flask. The purified monomer was kept in a fridge until use. 2.2. Preparation of Glycidyl Methacrylate Microencapsulated Ammonium Polyphosphate (MCAPP). A 100 g portion of APP and 200 mL cyclohexane were put into a three-neck bottle with mechanical stirring equipment and stirred at 50 °C. After stirring for 15 min, 12.5 g GMA was added and stirred for 15 min, the mixture was heated to 80 °C. A 0.125 g portion of BPO was dissolved in 20 mL butanone and added to the mixture. After that, the resulting mixture kept at 80 °C for 6 h. Finally, the obtained white slurry was cooled to room temperature, filtered, washed with cyclohexane and dried at 80 °C. Then, the MCAPP powder was finally obtained. 2.3. Preparation of Flame Retarded EP Composite. MCAPP and APP were mixed with epoxy resin in different ratios, 5, 10, and 15 wt %, respectively. The mixing progress was carried out in a 250 mL, one-neck bottle with magnetic stirring at 85 °C for 4 h. Then corresponding amount of curing agent (4, 4′-diaminodiphenylmethane) was added into it based on stoichiometric ratio and stirred rapidly for 3 min. Then, the mixture was cast in mold with appropriate temperature. 2.4. Measurements. Fourier Transform Infrared Analysis (FTIR). FTIR spectroscopy (MAGNA-IR 750, Nicolet Co. America) was employed to characterize MCAPP using thin KBr as the sample holder. Transition mode was used, and the wavenumber range was set from 4000 to 500 cm−1. X-ray Photoelectron Spectroscopy (XPS). The X-ray photoelectron spectroscopy measurement was carried out by using an ESCALABMK II (VG Co., Ltd., England)
3. RESULTS AND DISCUSSION 3.1. Characterization of MCAPP. The FTIR spectra of APP and MCAPP are shown in Figure 2. The typical absorption peaks of APP include 3200 (NH), 1249 (P O), 1088 (PO symmetric stretching vibration), 1012 (symmetric vibration of PO2 and PO3), 889 (PO asymmetric stretching vibration), and 802 (POP) cm−1. The spectrum of MCAPP shows new absorption peak at 908, 1260, and 1730 cm−1, which are corresponding to the CO stretching vibration of acrylate, and the CC double bond absorption peak (1640 cm−1) disappears, which indicates that GMA occurred the double bond polymerization in the synthesis progress and generated a macromolecular polymer to adsorb on the surface of APP. The XPS spectra of APP and MCAPP are shown in Figure 3. It can be observed that the peaks located at 134.7 and 190.9 eV 5641
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Table 2. Surface Elemental Compositions of APP and MCAPP sample
C (%)
O (%)
N (%)
P (%)
APP MCAPP
22.38 64.98
47.29 32.56
19.27 1.38
11.07 1.07
particles with the macromolecular polymer generated in the radical polymerization of glycidyl methacrylate, which indicates that APP is well coated by the resin.19,22 The surface morphologies of the APP and MCAPP particle are shown in Figure 4. It is clear that the surface of APP particle is very smooth. After microencapsulation, the MCAPP presents a comparably rough surface. The surface properties of MCAPP have been evaluated by water contact angle measurements, on coatings prepared by spin coating of particles suspensions. The water was absorbed immediately when the water drip on the surface of APP, and the WCA of pure APP is only 11.5°. The results indicated that the surface property of APP is hydrophilic. However, the double bond polymerization of GMA triggered by BPO results in the transformation of hydrophilic to hydrophobic MCAPP surface, with a WCA about 101.9°. The above results also suggest a coating exists on the surface of APP. 3.2. Flame Retardancy. LOI, UL-94, and cone calorimeter tests are widely used to determine the flammability of flame retardant materials. LOI, the minimum oxygen concentration by volume for maintaining the burning of a material, is an important parameter for evaluating the flame retardancy of a polymeric material. Usually, there is a poor correlation among LOI value, UL-94 rating, and cone result. The LOI values and UL-94 testing results of the EP composites are presented in Table 1. Pure EP is highly combustible, it cannot obtain a UL94 rating of V0, and the LOI value is only 21.5%. As the APP concentration is increased from 5 to 15 wt %, the LOI of the EP/APP composites increased from 27 to 36%, and EP with 15 wt % of APP can pass UL-94 V0 rating. Compared with the EP/APP composite, with the same loading, the EP/MCAPP composites demonstrate higher LOI values. With 15 wt % MCAPP, the sample EP-6 can pass the UL-94 test and the LOI value is as high as 38.5%. Furthermore, the combustion performance of EP/PGMA/APP blends has also been done according to the weight proportion of 10% and 15%, and the results are shown in Table 1. It can be seen that neither of EP-7 and EP-8 obtain a UL-94 rating of V0 and the LOI values are lower than that of EP-2 and EP-3. It is thus clear that the simple superposition of APP and PGMA did not have a synergistic effect. From the above results, it can be concluded that both APP and GMA-APP can form an intumescent system to protect the matrix from further burning, so the flame retardant
Figure 2. FTIR spectra of APP and MCAPP.
Figure 3. XPS spectra of APP and MCAPP.
are attributed to P2P and P2S of APP. For MCAPP, the intensities of peaks aforementioned decrease sharply, meanwhile the intensities of the C1S peak centered at 284.7 eV increase greatly. Table 2 shows the surface elemental compositions of MCAPP and APP particles. The P, N, and O atom content of MCAPP are 1.07, 1.38, and 32.56%, which are much lower than those of APP (11.07, 19.27, and 47.29%). And C atom content of MCAPP is 64.98%, higher than that of APP (22.38%). The changes of the above peaks and elemental compositions are due to the coverage of the outside APP Table 1. Formulation of Flame Retardant EP Composite sample
EP (wt %)
APP (wt %)
MCAPP (wt %)
PGMA (wt %)
LOI
UL-94
EP-0 EP-1 EP-2 EP-3 EP-4 EP-5 EP-6 EP-7 EP-8
100 95 90 85 95 90 85 90 85
0 5 10 15 0 0 0 8.9 13.3
0 0 0 0 5 10 15 0 0
0 0 0 0 0 0 0 1.1 1.7
21.5 27 30 36 28 31.5 38.5 28.5 32
no rating V1 V1 V0 V1 V0 V0 V1 V1
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Figure 4. SEM photographs of APP (a) and MCAPP (b) particles. The inset is a picture of the water contact angle.
properties of EP composites improved. Moreover, after microencapsulation with GMA, the MCAPP confers better flame retardant performance for EP. This may contribute to the better thermal stability of the shell materials and the better dispersion in EP than pure APP. Cone calorimetry is an effective approach to evaluate the combustion behavior of flame-retarded polymers. Time to ignition (TTI), peak heat release rate (PHRR), total heat release (THR), and time to peak heat release rate (TPHRR) are the main parameters to describe it. In addition, it is reported that there is a certain correlation between the value of fire performance index (FPI) of material and the time to flashover. When the value of FPI reduces, the time to flashover will be advanced. Thus, it is generally accepted that the value of FPI of a material is smaller and its fire risk is higher.23 The heat release rate (HRR) is one of the most significant parameters for fire retardancy evaluation which shows in Figure 5, and the main parameters obtained from the cone calorimeter
Table 3. Related Cone Date of EP and Flame Retardant EP Composites sample
TTI (S)
time to PHRR (S)
PHRR (KW/m2)
THR (MJ/m2)
FPI (m2 s/KW)
EP EP-3 EP-6
57 63 68
130 95 160
1730.27 397.89 283.09
114.16 35.49 44.00
0.03 0.20 0.24
time of the EP/15 wt % MCAPP prolongs to 640 s which is much longer than 340 s of the pure sample. Combined the value of FPI, the fire risk of EP-6 is lower than that of EP-3. But the THR of the EP-6 composite is a litter bigger than that of EP-3 composite, which may be due to the fact that the actual amount of flame retardant after microencapsulation is lower. Apparently, after microencapsulation, the additive confers better flame retardancy on the EP/MCAPP material. The residual char of EP, EP-3, and EP-6 after the cone calorimetry test are shown in Figure 6. Compare with pure EP and EP/APP composite, the residue of EP/MCAPP composite showed dramatic intumescentia during combustion and generated a compact carbon layer finally. The results demonstrate that MCAPP possesses the excellent intumescent effect. It can be concluded that MCAPP could promote the formation of intumescent carbonaceous char. As shown in Figure 7, the carbon monoxide and carbon dioxide production rates of flame-retardant EP significantly decreased compared with that of neat EP. In addition, from Figure 8, it can be seen that EP/MCAPP composites generated less toxic gases during combustion than those of EP/APP composites, which may be attributed to a better charring performance as the intumescent carbonaceous char can reduce the flue gas emission and slow the smoke release rate effective. Similarly, we can see the total smoke production rates which shown in Figure 9. The peak of EP/MCAPP composites is 0.09 m2/s, which is only one-third of the value of the peak of EP/ APP composites (0.27 m2/s) and one-sixth of the value of the peak of pure EP (0.54 m2/s). This indicated that added APP and MCAPP have excellent smoke suppression performance. And MCAPP demonstrated better smoke suppression than that of APP, which is fully confirmed that the microencapsulation not only imparted EP/MCAPP composites with higher LOI value and UL-94 rating but also could significantly improve the fire safety. 3.3. Morphology. The SEM image of fracture section of EP/APP and EP/MCAPP blends are shown in Figure 10. The
Figure 5. Heat release rate curves of EP and flame retardant EP composites.
tests of EP and flame retardant EP composites are in Table 3. It is obvious that the presence of the flame retardant additives in EP decreases the HRR value significantly when compared to the pure EP. In the case of EP/15%MCAPP composite, its peak HRR is 283.09 KW/m2, which is 38% lower than that of pure EP (1730 KW/m2) and 29% lower than that of EP/15%APP composite. Not only the TTI increases but also the combustion 5643
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Figure 6. Photos of residues of samples at the end of cone test: (a) EP, (b) EP-3, and (c) EP-6.
Figure 7. CO and CO2 production of the composites at an external heat flux of 50 kW/m2.
Figure 8. CO/CO2 ratios of the composites at an external heat flux of 50 kW/m2.
Figure 9. Smoke production rate (SPR) of the composites at an external heat flux of 50 kW/m2.
obvious distinctions between the EP/APP and EP/MCAPP blends are clearly found. Without microencapsulation, the interface between APP and the polymeric matrix is incompatibility. There are many large particles, cavities, and holes in the fracture section. After microencapsulation with GMA, the MCAPP particles have good dispersion in the matrix and almost no big holes are observed. As expected, the GMA shell can improve the dispersion of MCAPP in EP matrix, which is due to that they have the same similar polarity. More important is that the epoxy group on the surface of MCAPP can react with the curing agent, which can make the MCAPP have better compatibility with EP resin.
3.4. Dynamical Mechanical Properties. Dynamic mechanical analysis (DMA) gives the information about the viscoelastic properties of polymers. Figure 11 shows the storage modulus and tan δ curves of EP and EP composites. Compared with pure EP, the storage modulus of EP-3 decreases, as the same as the value of Tg. The poor interfacial adhesion between the EP matrix and APP tends to decrease the cross-linking density of the cured EP/APP systems, which may be responsible for the decrease of the storage modulus and Tg.24 However, EP-6 has a higher storage modulus and Tg value than that of EP and EP-3. Because the epoxy group on the surface of MCAPP can react with the curing agent, which makes the 5644
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Figure 10. SEM images of EP-3 (a) and EP-6 (b) composites with 15 wt % flame retardant.
Figure 11. Temperature dependence of tan δ and storage modulus of EP and flame retardant EP composites.
MCAPP have better compatibility with EP resin and increase the cross-linking density of the cured EP/MCAPP systems. 3.5. Thermal Stability. The typical Tg curves for EP and flame retardant EP composites under an air atmosphere are revealed in Figure 12. The initial decomposition temperature
Table 4. TGA Data of EP and Flame Retardant EP Composites temperature of 5% sample weight loss (°C) EP0 EP-3 EP-6
352 327 332
temperature of 50% weight loss (°C)
residue at 700 °C (wt %)
439 423 452
0 20.8 24.4
As for pure EP, the thermal oxidative degradation process has two stages in air atmosphere. The first stage is in the temperature range of 300−490 °C and the weight loss is 18.2 wt %. These indicate that some complex chemical reactions take place at the first stage of thermal oxidative degradation, including the free radical chain scission of the isopropylidene linkage and the branching and cross-linking reactions of molecular chains induced by oxygen, besides the elimination of the hydration water.25 The second stage is in the temperature range of 490−690 °C, and the peak of the maximum thermal degradation is 586 °C, corresponding to 78.7% weight loss, which is the main decomposition process. During this stage, the macromolecular chains of EP are further oxidized and many small molecular degradation products are released. The thermal oxidative degradation progress of the flame retardant EP composite has the similar two decomposition stages as the pristine EP. It can be observed that the flame retardant has noticeable influence on the thermal degradation of EP. Compared with the pure EP, the initial decomposition temperature of the flame retardant EP composites reduced. This can be explained by the fact that the poor thermal stability of APP. However, the EP/MCAPP composite demonstrate
Figure 12. TGA curves of EP and flame retardant EP composites in air.
can be considered as the temperature at which the weight loss is 5 wt %. The relative thermal stabilities of the cured resins are compared by the temperature of 5 and 50 wt % weight loss, and the fraction of the char residue at 700 °C are obtained from the TGA curves. These data are listed in Table 4. 5645
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Figure 13. Dynamic FTIR spectra of sample (a) EP and (b) EP-6 with different pyrolysis temperatures.
As seen from Figure 13, the peak at 1400 cm−1 can be assigned to the deformation vibration of NH4+. It disappeared at 350 °C because of the elimination of NH3 from ammonium salt complexes.26 At room temperature, the peaks at 1255, 1087, and 886 cm−1 are attributed to the O = P, P−O−P absorption of APP. It is clearly seen from Figure 13 that the peak at 1255 cm−1 moves to the relatively higher wave numbers (1285 cm−1) when temperature increases to 350 °C. This could be due to the formation of pyrophosphate caused by the dehydration of polyphosphoric acids. At 450 °C, the peaks at 1280, 1080, and 886 cm−1 as shown in the spectrum, indicate that the residue contains P = O and P−O−P groups, which lead to the formation of a more dense carbon layer than pure EP.
higher initial decomposition temperature and 50 wt % weight loss temperature than those of EP/APP composite. The residue of pure epoxy resin at this temperature is 0 at 700 °C. While the residue of EP/APP and EP/MCAPP is 20.8% and 24.4%, respectively. The degradation of phosphorus-containing groups generates heat-resistant residues to result in high char yields. Therefore, the char yield of the flame retardant EP composites increased, resulting in a reduced heat release rate and a lower rate of degradation of the epoxy resin by working as a heat barrier and a thermal insulator, which limit the production of combustible gases and then interfere the combustion of the materials. Compared with the EP/APP composites, the microencapsulated sample has higher initial degradation temperature, 50 wt % weight loss temperature, and char residue. This is due to the fact that the EP/MCAPP generated more compact char residue than that of EP/APP composite and the GMA shell materials have a higher thermal stability than APP. 3.6. Thermal Degradation Mechanism. The thermal degradation behavior of sample EP and EP-6 are investigated using real-time FTIR spectroscopy. Figure 13 shows the changes in the dynamic FTIR spectra obtained from the sample EP and EP-6 at different pyrolysis temperatures. As shown in Figure13a, at room temperature (25 °C), the peaks at 3392 (O−H stretching vibration of water or phenol), 2930 (−CH3 and −CH2− stretching vibration), 1607, 1513, 1458 (C−C stretching vibration of aromatic ring), 1240, 1035 (C−H vibration of −C6H4−O−CH2−), and 1177 (C−O stretching vibration) are all the characteristic absorptions of EP. The relative intensities of other characteristic peaks do not change below 350 °C. When the temperature is up to 350 °C, it is found that the absorption peaks at 2930, 1607, 1458, 1240, and 1035 cm−1 disappear, indicating that the main decomposition happens at this stage, which is consistent with the TGA results. The FTIR spectra of the EP-6 at different degradation temperatures are shown in Figure 13b, too. From Figure 13b, it can be noted that the characteristic peaks of EP are not obvious, which is because its characteristic bands probably coincide with the characteristic bands of the EP matrix. It can be observed that at 350 °C the intensities of most peaks decreased sharply, which means that the presence of MCAPP catalyzes the thermal degradation of EP and formation of char. The residual char can prevent the materials from further degradation during combustion.
4. CONCLUSIONS In this study, GMA was used as the shell material for microencapsulated APP, the microcapsule was successfully prepared and showed excellent hydrophobicity. And the GMA shell could improve the dispersion of MCAPP and enhance the compatibility between EP matrix and MCAPP. According to LOI values, UL-94 tests, TG tests, and cone calorimeter results, it could be concluded that the EP/MCAPP composite demonstrated a better flame retardancy and thermal stability than those of the EP/APP composite at the same loading. Furthermore, the EP/MCAPP composite revealed excellent smoke suppression performance during combustion and an intumescent char layer is formed to protect the inner polymer matrix.
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AUTHOR INFORMATION
Corresponding Author
*Fax: +86-551-3601664. E-mail address:
[email protected] (Y.H.);
[email protected] (L.S.). Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS The work was financially supported by the National Basic Research Program of China (973 Program) (2012CB719701), the joint fund of NSFC and Guandong Province (U1074001), and Specialized Research Fund for the Doctoral Program of Higher Education.
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REFERENCES
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dx.doi.org/10.1021/ie302591r | Ind. Eng. Chem. Res. 2013, 52, 5640−5647
