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Studying the loading impact of silane grafted Fe2O3 nanoparticles on mechanical characteristics of epoxy matrix
Egyptian Journal of Petroleum xxx (xxxx) xxx
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Studying the loading impact of silane grafted Fe2O3 nanoparticles on mechanical characteristics of epoxy matrix Hamdy M. Naguib a,b, Mona A. Ahmed a, Z.L. Abo-Shanab a,⇑ a b
Department of Petroleum Applications, Egyptian Petroleum Research Institute (EPRI), Nasr City, 11727 Cairo, Egypt Key Laboratory for Advanced Technology in Environmental Protection of Jiangsu Province, Yancheng Institute of Technology, Yancheng 224051, Jiangsu Province, China
a r t i c l e
i n f o
Article history: Received 16 April 2018 Revised 20 September 2018 Accepted 23 October 2018 Available online xxxx Keywords: Iron oxide nanoparicles Epoxy nanocomposites Modulus Toughness Thermal stability
a b s t r a c t This study investigates the loading impact of iron oxide (IO) and silane treated iron oxide (SIO) nanoparticles on thermal, mechanical and morphological behavior of epoxy matrix. Both IO and SIO nanoparticles were loaded with 1, 3 and 5 wt% from the total weight of epoxy matrix. The morphology of IO, and SIO epoxy nanocomposites are investigated by TEM. FTIR spectra are successfully able to confirm the good chemical interaction between SIO nanoparticles and epoxy matrix. Thermal resistance of epoxy IO, and SIO nanocomposites is studied by TGA. The mechanical properties of prepared nanocomposites including storage modulus, tan d, stress-strain curves and toughness are studied using DMA at temperature range 25 °C–100 °C. The results approved that loading 3 wt% of SIO nanoparticles improved the morphological, thermal resistance and mechanical characteristics of epoxy matrix. Ó 2019 Egyptian Petroleum Research Institute. Production and hosting by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
1. Introduction Epoxy resin is one of the most important thermoset resins due to its high stiffness, thermal and chemical resistance that was attributed to the highly cross-linked structure [1,2]. However, the pure epoxy resin after curing becomes brittle and gives low wear resistance and low toughness that reduce its scope of applications. Reinforcing with nanofillers is currently considered as the main goal for improvement the fracture toughness of epoxy resin to get advanced and high-performance applications. Several fillers, such as SiO2, carbon nanotubes (CNTs), Al2O3 and TiO2, have been studied and incorporated into epoxy matrix, forming different filler-epoxy composites [3–13]. Among of them, organically modified Fe2O3 nanocomposites which are of particular interest due to the combining of properties from inorganic Fe2O3 filler and organic polymers. Different types of Fe2O3-grafted polymer nanocomposites have been synthesized, such as Fe2O3 based on poly(methyl methacrylate), Fe2O3-grafted polypropylene and Fe2O3 based on polystyrene, and so on [14–16]. Kim et al. synthesized polystyrene grafted Fe2O3 composite particles by using pickering emulsion polymerization method.
Peer review under responsibility of Egyptian Petroleum Research Institute. ⇑ Corresponding author at: Asphalt Laboratory in Petroleum Applications Department, Egyptian Petroleum Research Institute ‘‘EPRI”, 1 Ahmed El-Zomor Street, ElZohour Region, Nasr City, Cairo 11727, Egypt. E-mail address: [email protected] (Z.L. Abo-Shanab).
The obtained products show an improving in the rheological properties and solving the problem of sedimentation of Fe2O3 particles in industrial applications [14]. However, there still remain two factors greatly affecting the poor performance of polymer nanocomposite; the failure of good interfacial, in addition to the issues of dispersion [17]. Hence, the dispersion of nanofiller in epoxy resin is too difficult and is accompanied by formation of agglomerates due to the high specific surface area of the nanofiller and the high viscosity of epoxy resin. The agglomerates of fillers do not only affect the thermal and mechanical properties of the prepared epoxy nanocomposites, but also can initiate the crack progress and even worsen their mechanical properties. A lot of researches have been discussed to improve the problem of dispersion based on surface modification by using the proper surfactants, coupling agents and/or polymer coatings [18–24]. Heet et al. prepared good stabilized iron oxide NPs grafted with maleic anhydride-grafted polypropylene, they used maleic anhydride as a compatibilizer between the polypropylene matrix and nanofillers [25]. Naguib et al. [26] have applied silanated-iron oxide nanoparticles with epoxy after treatment of iron oxide nanoparticles with aminopropyltriethoxysilane (APTES) coupling agent, drawn in Scheme 1, and illustrated the effect of surface treatment on the general characteristics of the obtained epoxy nanocomposites. This study is considered as a continual work for the authors’ previous study [26], since the loading effect of untreated and silane-treated Fe2O3 NPs with percentages 1%, 3%, and 5 wt% on the surface,
https://doi.org/10.1016/j.ejpe.2018.10.001 1110-0621/Ó 2019 Egyptian Petroleum Research Institute. Production and hosting by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
Please cite this article as: H. M. Naguib, M. A. Ahmed and Z. L. Abo-Shanab, Studying the loading impact of silane grafted Fe2O3 nanoparticles on mechanical characteristics of epoxy matrix, Egyptian Journal of Petroleum, https://doi.org/10.1016/j.ejpe.2018.10.001
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H.M. Naguib et al. / Egyptian Journal of Petroleum xxx (xxxx) xxx
OEt EtO
OH Hydrolysis
OH
NH2
Si
APTES
OEt
NH2
Si
Silanol form
OH
Iron oxide surface O
O
epoxy chain
O
O
O
O
Si
Iron oxide surface O
O
H2 N
C
O
IO
Epoxy resin SIO O OH
epoxy chain
O
O
H N
Si
O
O C
I r o n o x id e s u r f a c e
NH2
SIO-epoxy nanocomposite Scheme 1. Reaction mechanism of iron oxide nanofiller (IO) with aminopropyltriethoxysilane (APTES) as coupling agent to obtain amino silane iron oxide nanofiller (SIO), followed by reaction of SIO with epoxy getting SIO-epoxy nanocomposite.
mechanical and thermal properties of the formed epoxy nanocomposites were clarified systematically. The surface properties of modified Fe2O3 NPs were confirmed by Fourier transform infrared (FTIR) spectroscopy. The quality of dispersion of the loaded Fe2O3 NPs in epoxy nanocomposite was analyzed by transmission electron microscopy (TEM). The mechanical and thermal properties of prepared nanocomposites including storage modulus, tan d, and toughness were studied as well.
2.2.2. Chemical and structural characteristics Fourier transforminfrared spectra FTIR analysis was applied to investigate the reaction between silane treated nanoparticles and epoxy matrix. The machine used for FTIR analysis is ‘‘Nicolet IS-10 FTIR spectrophotometerThermo Fisher Scientific” using the range of wavenumber of ‘‘400–4000 cm1”. Transmission electron microscope
2. Materials and methods 2.1. Materials Amino silane-treated iron oxide nanofiller (SIO) were synthesized as previously reported in the literature Naguib et al. [26]. The epoxy base is bisphenol-A diglycidyl ether epoxy, and the hardener is triethylenetetramine. The epoxy matrix grade is ‘‘635-thin epoxy, base:hardener as 2:1, US Composites”.
The structural morphology of prepared nanocomposites was observed by transmission electron microscope (TEM) using high resolution JEOL-2100FTEM at 200 kV. The samples were prepared in colloidal mixture diluted with ethanol by sonication for 15 min. The dispersed solution was positioned on the TEM grid. After drying, the grid was attached to the microscope and images were taken. Thermogravimetric analysis
2.2. Methods and characterization 2.2.1. Formulation of iron oxide/epoxy nanocomposites Six samples of IO and SIO epoxy nanocomposites were prepared by dispersing 1 wt%, 3 wt%, and 5 wt% by weight of IO and SIO nanoparticles into epoxy base using mechanical stirrer followed by direct exposure to ultrasonic waves till 10 min to ensure the complete dispersion into base epoxy. Then, the amine hardener was added carefully with gentle stirring. The obtained nanocomposites have been aged for seven days at the ambient temperature to complete the full curing process.
TGA1-Mettler Toledo was used to study the effect of ungrafted IO and silane grafted SIO iron oxide nanoparticles on thermal stability of prepared composites using (TGA) by heating from 25 °C to 600 °C at a rate of 5 °C/min.
2.2.3. Mechanical characteristics The mechanical characteristics including storage modulus (E0 ), damping factor (tan d), and stress-strain curves were measured for the prepared nanocomposites by using Triton Technology-TTDMA following ‘‘ASTM D-4065” standards [27]. Three point bending mode
Please cite this article as: H. M. Naguib, M. A. Ahmed and Z. L. Abo-Shanab, Studying the loading impact of silane grafted Fe2O3 nanoparticles on mechanical characteristics of epoxy matrix, Egyptian Journal of Petroleum, https://doi.org/10.1016/j.ejpe.2018.10.001
H.M. Naguib et al. / Egyptian Journal of Petroleum xxx (xxxx) xxx
with frequency of 1 Hz was applied, the dimension of specimens are (25 mm length, 10 mm width and 3 mm thickness), the samples were exposed to 100 °C with heating rate of 5 °C/min. 3. Results and discussion 3.1. Fourier transform infrared study FTIR spectra of epoxy, iron oxide grafted (IO) epoxy and silanated iron oxide grafted (SIO) epoxy nanocomposites samples
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were studied to illustrate the reaction between epoxy and silane treated iron oxide NPs as shown in Fig. 1. In SIO epoxy nanocomposite spectrum, the intensity of hydroxyl stretching peak in the range of 3350 cm1 is decreased compared with IO epoxy spectrum because of the reaction of ‘‘O–H” groups with APTES coupling agent that actually grafted on nanoparticles. Also the peak of N–H group near 1600 cm1 is absent due to consumption of amine groups in the curing process for epoxy [28]. In addition, the peak near 840 cm1 that characterized for ‘‘epoxide group” [29] showed a lower intensity compared with that of neat epoxy spectrum.
Fig. 1. FTIR spectra for pure epoxy, IO and SIO-epoxy nanocomposite.
Scheme 2. Mechanism of curing of SIO-epoxy nanocomposite in presence of amine hardener.
Please cite this article as: H. M. Naguib, M. A. Ahmed and Z. L. Abo-Shanab, Studying the loading impact of silane grafted Fe2O3 nanoparticles on mechanical characteristics of epoxy matrix, Egyptian Journal of Petroleum, https://doi.org/10.1016/j.ejpe.2018.10.001
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These spectra confirm the occurring of chemical reaction between SIO nanoparticles and epoxy matrix; so the reinforcement of epoxy with SIO was chemically performed. The reaction of iron oxide nanofiller (IO) with aminopropyltriethoxysilane (APTES) coupling agent to obtain amino silane iron oxide nanofiller (SIO), and then the reaction of SIO with epoxy getting the final SIO-epoxy nanocomposite are given in Scheme 1. Typically, APTES was hydrolyzed to silanol that reacted with IO to obtain SIO. The SIO itself caused a nucleophilic attack to the epoxy group in epoxy base, leading to formation of SIO-epoxy nanocomposite. The nanofiller in this case acts as hardener. However; with addition of the standard amine hardener (triethylenetetramine) in the presence of SIO nanofiller, a dual mechanism is suggested here as shown in Scheme 2. The amine group in the hardener (b) makes its nucleophilic attack to the epoxy ring that leading to ‘‘ring-opening reaction” and formation of new hydroxyl group (Ahmed et al.) [30]. At the same time, the NH2 in SIO as functionalized amino silane-treated iron oxide nanoparticles (a) can contribute to the curing reaction for epoxy. So, the scheme dis-
O
Fig. 2. TEM image of 1, 3, and 5%wt IO (a–c) and 1, 3, and 5%wt SIO (d–f) NPs dispersed in epoxy matrix.
cusses in details the reaction and curing mechanism that leading to formation of cured SIO-epoxy nanocomposite, which further subjected to the full curing conditions by aging for seven days at room temperature to obtain the final rigid form of nanocomposite. 3.2. Transmission electron microscope Dispersion of the fillers in epoxy matrix is the main factor which affects the behavior of nanocomposite. Hence, agglomerated fillers cause severe stresses concentration and interfacial cracks that negatively affecting the composite performance. Therefore, the dispersion of IO and SIO NPs in epoxy matrix was firstly investigated by TEM. TEM was used to examine the dispersion ability of loading 1%, 3%, and 5% by weight of untreated (IO) and silane treated Fe2O3 (SIO) NPs on epoxy matrix. As shown in Fig. 2a IO NPs is loaded with 1 wt%, the IO NPs were embedded in the epoxy matrix. However, with increasing the loading of IO to 3%, and 5 wt% as shown in Fig. 2b and c, the agglomeration was observed due to the large specific surface area and high surface energy. Fig. 2d and e (the loading of SIO NPs is 1 wt% and 3% respectively) showed good dispersion of SIO NPs into epoxy matrix and no agglomerates were observed. This advantage may be owe to the steric hindrance of SIO NPs and good interaction of silane group with epoxy matrix which resulted in improving the stiffness and failure strain. However, 5 wt% loading of SIO NPs shown in Fig. 2f gives complete saturation of SIO NPs in epoxy matrix and some of agglomeration is observed, so addition of more SIO was stopped for this ratio to avoid the inverse effect. 3.3. Dynamic mechanical characteristics The roles of surface modification and loading of Fe2O3 NPs on dynamic mechanical behavior of epoxy nanocomposites were studied. As seen in Fig. 3, the modulus of bending for the cured pure epoxy resin is about 1.45 GPa, and for IO-epoxy nanocomposites modulus of 1.48, 1.58, and 1.59 GPa were obtained with IO loading of 1, 3 and 5 wt%. While in the SIO-epoxy nanocomposites, they are 1.57, 1.74, and 1.69 GPa with the SIO loading of 1, 3, and 5 wt%, respectively. These data indicated that SIO NPs has been significantly enhanced the modulus of epoxy nanocomposites compare with IO NPs, which is attributed to the high cross linking degree between the epoxy matrix and fillers in addition to the good
Fig. 3. Effect of IO and SIO loading on modulus of epoxy nanocomposites.
Please cite this article as: H. M. Naguib, M. A. Ahmed and Z. L. Abo-Shanab, Studying the loading impact of silane grafted Fe2O3 nanoparticles on mechanical characteristics of epoxy matrix, Egyptian Journal of Petroleum, https://doi.org/10.1016/j.ejpe.2018.10.001
H.M. Naguib et al. / Egyptian Journal of Petroleum xxx (xxxx) xxx Table 1 Effect of IO and SIO loading on storage modulus and glass transition temperatures of epoxy nanocomposites. Sample
Modulus [GPa]
Tg [°C]
Epoxy 1% IO-epoxy 3% IO-epoxy 5% IO-epoxy 1% SIO-epoxy 3% SIO-epoxy 5% SIO-epoxy
1.45 1.48 1.58 1.59 1.57 1.74 1.69
43 43.1 44.3 43.6 43.3 46.2 43.6
interfacial force between silane treated NPs and epoxy matrix [26]. From Table 1, it is noticed that the modulus of SIO epoxy nanocomposites increases with the increase of loading of SIO NPs. When the nanoparticle loading increases to 3 wt%, the modulus of the epoxy nanocomposite raised to 60%. As well as, it can be noticed that the modulus of the obtained SIO epoxy nanocomposite firstly increases followed by a decrease with high loading 5 wt% of SIO (as shown in Fig. 3). This effect may be due to some of agglomerated areas at the
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SIO NPs-epoxy matrix interface that can occur with adding more and more of NPs content [31]. The effects of the surface modification and loading percent of Fe2O3 NPs on tan d were also discussed (as shown in Table 1, and Fig. 4). The results showed that as IO and SIO loading increases, the dissipated energy (tan d) decreases and consequently the main mechanical relaxation is enhanced and Tg of the nanocomposites increases linearly till 3% loading. Since the interfacial layers rising from the interaction between silane treated nanoparticles and epoxy during the curing process will give a different segmental dynamics from the neat epoxy. As shown in Table 1, there are higher Tg values for the SIO epoxy nanocomposites (43.3 and 46.2 °C for 1 and 3%) compared with that of IO epoxy nanocomposite (43.1 and 44.3 °C for 1 and 3%) or for epoxy (43 °C). The Tg value that began to decrease with adding 5% IO and SIO may be due to some of agglomerations created. Actually, the good dispersion of SIO nanoparticles into epoxy matrix, the free space among molecules decreases resulting in losing the mobility of chain segments [32]. On the other hand, loading epoxy with untreated IO didn’t significantly affect Tg value due to bad dispersion in epoxy. The
Fig. 4. Effect of IO and SIO loading on loss tangent (tan d) of epoxy nanocomposites.
Fig. 5. Stress-strain curves of epoxy nanocomposites loaded with different percentage of IO and SIO NPs.
Please cite this article as: H. M. Naguib, M. A. Ahmed and Z. L. Abo-Shanab, Studying the loading impact of silane grafted Fe2O3 nanoparticles on mechanical characteristics of epoxy matrix, Egyptian Journal of Petroleum, https://doi.org/10.1016/j.ejpe.2018.10.001
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H.M. Naguib et al. / Egyptian Journal of Petroleum xxx (xxxx) xxx
grafting of SIO NPs with loading 3 wt% into epoxy matrix is followed by high Tg value. The stress-strain curves of IO and SIO epoxy nanocomposites were plotted as shown in Fig. 5. It is noticed that addition of IO NPs to epoxy matrix improved stiffness of the prepared nanocomposites but lowered their strain. On the other side, addition of SIO NPs increased the stiffness with keeping the elastic properties (strain) for the epoxy matrix, especially with 3% SIO. The areas under the curves were measured to calculate the toughness of the prepared nanocomposites. The toughness data shown in Fig. 6 illustrated that epoxy nanocomposite loaded with 3% SIO NPs has the highest value of toughness, due to excellent dispersion and high crosslinks between SIO NPs and epoxy matrix. Addition of IO leads to stress increase and strain decrees, so the toughness (as calculated form area under the curve) has lower values till 3%, compared with neat epoxy. The 5% IO nanocomposite achieved higher stiffness due to the more stress, however the strain became
the least causing bad brittle character. On the other hand, Addition of SIO leaded to increasing of stress and strain together, so the toughness has increased in this case. However, 5% SIO nanocomposites began to decrease the toughness because of the agglomerated structures that obtained with this high loading percentage. Many studies on epoxy/nanofiller composites have reported this trend for mechanical properties with the difference in the loading percentages, depending on the type of epoxy and kind of organic grafted materials on iron oxide nanoparticles. Zahra et al. [33] studied the loading effect of organically treated by using 3-glyci doxypropyltrimethoxysilane (GPS) as coupling agent and untreated iron oxide nanoparticles on the modulus of prepared nanocomposites, it was found that addition of 8 wt% from treated iron oxide NPs give the highest modulus and further addition weaken the modulus of prepared composites. Tao Sun et al. [28] noticed that addition of 4 wt% of iron oxide nanoparticles treated with poly(N-vinyl-2-pyrrolidone) (PVP) and (3-aminopropyl)
Fig. 6. Toughness of epoxy nanocomposites loaded with different percentage of IO and SIO NPs.
Fig. 7. TGA for neat epoxy, IO-epoxy and SIO-epoxy nanocomposites.
Please cite this article as: H. M. Naguib, M. A. Ahmed and Z. L. Abo-Shanab, Studying the loading impact of silane grafted Fe2O3 nanoparticles on mechanical characteristics of epoxy matrix, Egyptian Journal of Petroleum, https://doi.org/10.1016/j.ejpe.2018.10.001
H.M. Naguib et al. / Egyptian Journal of Petroleum xxx (xxxx) xxx Table 2 Thermal degradation temperatures for neat epoxy and IO/SIO-epoxy nanocomposites. Sample
Epoxy
IO-Epoxy
SIO-epoxy
T0.1 [°C] T0.5 [°C]
194 369
196 372
199 377
T0.1 correlated to 10% weight loss in sample. T0.5 correlated to 50% weight loss in sample.
triethoxysilane (APTES) as modified agent to epoxy matrix increase the tensile strength by 50.2% and increase the fracture toughness by 106%. These general trends may be due to some of agglomerated areas at the SIO NPs-epoxy matrix interface that can occur with adding more and more of NPs content [32]. 3.4. Thermogravimetric analysis Fig. 7 represents the TGA curves for pure epoxy, IO and SIOepoxy nanocomposites loaded with 3% IO and SIO NPs respectively. All curves show the first thermal degradation process after 100 °C due to dehydration followed by combustion of epoxy between 300 and 430 °C and finally formation of char near 500 °C. It is clear that filling epoxy matrix with IO nanofiller caused some enhancement in the thermal stability compared with neat epoxy starting from 250 °C. However, the SIO-epoxy nanocomposite recorded the highest thermal stabilization through the noticeable increase in the temperatures of the thermal degradation steps as shown in the temperature range of 270 and 400 °C. In more details, Table 2 illustrates T0.1 and T0.5 temperatures for the epoxy, IO-epoxy and SIO-epoxy nanocomposites. T0.1 increased respectively from 194 °C for neat epoxy to 196 and 199 °C for IOepoxy and SIO-epoxy nanocomposites. Moreover, the T0.5 increased from 369 °C for neat epoxy to 372 and 377 °C for IOepoxy and SIO-epoxy nanocomposites respectively. Hence, more enhanced thermal stability was achieved after filling epoxy matrix with SIO NPs with shifting the mentioned degradation temperatures to higher values; the stronger SIO-epoxy interface is responsible for this advance. 4. Conclusion This work studies the effect of surface treatment and loading of Fe2O3 NPs with different doses (1, 3 and 5 wt%) on chemical, morphological, mechanical and thermal characteristics of epoxy matrix. The main findings of this work are: FTIR and TEM were considered as efficient tools to investigate the chemical structure of silanted-Fe2O3 NPs and their dispersion in epoxy matrix respectively. The results approved that loading with 3% of SIO NPs gave the best dispersion into epoxy matrix. The effect of silane surface treatment for Fe2O3 NPs on thermal degradation of epoxy nanocomposite was also studied using TGA, the results approved that silane coupling agent has a positive effect in increasing thermal stability of nanocomposites since T0.5 increased from 369 °C to 377 °C. DMA was conducted to study the dynamic mechanical behavior of the prepared nanocomposites including modulus of elasticity, Tg and toughness. The results approved that silane treated iron oxide NPs improved the modulus and Tg of epoxy nanocomposites more than untreated NPs. When 3 wt% SIO NPs were introduced, the modulus increased from 1.45 to 1.74 GPa, Tg increased from 43 to 46 °C and toughness from 300 to 500 MPa by comparing to pure epoxy resin system. This kind of epoxy nanocomposites with high mechanical, morphological and thermal performance could be used in many new
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Please cite this article as: H. M. Naguib, M. A. Ahmed and Z. L. Abo-Shanab, Studying the loading impact of silane grafted Fe2O3 nanoparticles on mechanical characteristics of epoxy matrix, Egyptian Journal of Petroleum, https://doi.org/10.1016/j.ejpe.2018.10.001
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[29] F.H. Rajabi, M.M. AlaviNikjeand, T. Taslimipour, Epoxidation of styrenebutadiene rubber (SBR) using in situ generated dimethyldioxirane (DMD): characterization and kinetic study, Des. Monom. Polym. 13 (2010) 535–546. [30] M.A. Ahmed, U.F. Kandil, N.O. Shaker, A.I. Hashem, The overall effect of reactive rubber nanoparticles and nano clay on the mechanical properties of epoxy resin, J. Radiat. Res. Appl. Sci. 8 (2015) 549–561. [31] M. Bhattacharya, Polymer nanocomposites – a comparison between carbon nanotubes, graphene, and clay as nanofillers, Materials 9 (2016) 262–296. [32] Z. Peng, L.X. Kong, S.D. Li, Dynamic mechanical analysis of polyvinylalcohol/ silica nanocomposite, Syn. Metals 152 (2005) 25–28. [33] Zahra Sekhavat Pour, Mousa Ghaemy, Thermo-mechanical behaviors of epoxy resins reinforced with silane-epoxide functionalized Fe2O3 nanoparticles, Prog. Org. Coat. 77 (2014) 1316–1324.
Please cite this article as: H. M. Naguib, M. A. Ahmed and Z. L. Abo-Shanab, Studying the loading impact of silane grafted Fe2O3 nanoparticles on mechanical characteristics of epoxy matrix, Egyptian Journal of Petroleum, https://doi.org/10.1016/j.ejpe.2018.10.001
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Full Length Article
Studying the loading impact of silane grafted Fe2O3 nanoparticles on mechanical characteristics of epoxy matrix Hamdy M. Naguib a,b, Mona A. Ahmed a, Z.L. Abo-Shanab a,⇑ a b
Department of Petroleum Applications, Egyptian Petroleum Research Institute (EPRI), Nasr City, 11727 Cairo, Egypt Key Laboratory for Advanced Technology in Environmental Protection of Jiangsu Province, Yancheng Institute of Technology, Yancheng 224051, Jiangsu Province, China
a r t i c l e
i n f o
Article history: Received 16 April 2018 Revised 20 September 2018 Accepted 23 October 2018 Available online xxxx Keywords: Iron oxide nanoparicles Epoxy nanocomposites Modulus Toughness Thermal stability
a b s t r a c t This study investigates the loading impact of iron oxide (IO) and silane treated iron oxide (SIO) nanoparticles on thermal, mechanical and morphological behavior of epoxy matrix. Both IO and SIO nanoparticles were loaded with 1, 3 and 5 wt% from the total weight of epoxy matrix. The morphology of IO, and SIO epoxy nanocomposites are investigated by TEM. FTIR spectra are successfully able to confirm the good chemical interaction between SIO nanoparticles and epoxy matrix. Thermal resistance of epoxy IO, and SIO nanocomposites is studied by TGA. The mechanical properties of prepared nanocomposites including storage modulus, tan d, stress-strain curves and toughness are studied using DMA at temperature range 25 °C–100 °C. The results approved that loading 3 wt% of SIO nanoparticles improved the morphological, thermal resistance and mechanical characteristics of epoxy matrix. Ó 2019 Egyptian Petroleum Research Institute. Production and hosting by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
1. Introduction Epoxy resin is one of the most important thermoset resins due to its high stiffness, thermal and chemical resistance that was attributed to the highly cross-linked structure [1,2]. However, the pure epoxy resin after curing becomes brittle and gives low wear resistance and low toughness that reduce its scope of applications. Reinforcing with nanofillers is currently considered as the main goal for improvement the fracture toughness of epoxy resin to get advanced and high-performance applications. Several fillers, such as SiO2, carbon nanotubes (CNTs), Al2O3 and TiO2, have been studied and incorporated into epoxy matrix, forming different filler-epoxy composites [3–13]. Among of them, organically modified Fe2O3 nanocomposites which are of particular interest due to the combining of properties from inorganic Fe2O3 filler and organic polymers. Different types of Fe2O3-grafted polymer nanocomposites have been synthesized, such as Fe2O3 based on poly(methyl methacrylate), Fe2O3-grafted polypropylene and Fe2O3 based on polystyrene, and so on [14–16]. Kim et al. synthesized polystyrene grafted Fe2O3 composite particles by using pickering emulsion polymerization method.
Peer review under responsibility of Egyptian Petroleum Research Institute. ⇑ Corresponding author at: Asphalt Laboratory in Petroleum Applications Department, Egyptian Petroleum Research Institute ‘‘EPRI”, 1 Ahmed El-Zomor Street, ElZohour Region, Nasr City, Cairo 11727, Egypt. E-mail address: [email protected] (Z.L. Abo-Shanab).
The obtained products show an improving in the rheological properties and solving the problem of sedimentation of Fe2O3 particles in industrial applications [14]. However, there still remain two factors greatly affecting the poor performance of polymer nanocomposite; the failure of good interfacial, in addition to the issues of dispersion [17]. Hence, the dispersion of nanofiller in epoxy resin is too difficult and is accompanied by formation of agglomerates due to the high specific surface area of the nanofiller and the high viscosity of epoxy resin. The agglomerates of fillers do not only affect the thermal and mechanical properties of the prepared epoxy nanocomposites, but also can initiate the crack progress and even worsen their mechanical properties. A lot of researches have been discussed to improve the problem of dispersion based on surface modification by using the proper surfactants, coupling agents and/or polymer coatings [18–24]. Heet et al. prepared good stabilized iron oxide NPs grafted with maleic anhydride-grafted polypropylene, they used maleic anhydride as a compatibilizer between the polypropylene matrix and nanofillers [25]. Naguib et al. [26] have applied silanated-iron oxide nanoparticles with epoxy after treatment of iron oxide nanoparticles with aminopropyltriethoxysilane (APTES) coupling agent, drawn in Scheme 1, and illustrated the effect of surface treatment on the general characteristics of the obtained epoxy nanocomposites. This study is considered as a continual work for the authors’ previous study [26], since the loading effect of untreated and silane-treated Fe2O3 NPs with percentages 1%, 3%, and 5 wt% on the surface,
https://doi.org/10.1016/j.ejpe.2018.10.001 1110-0621/Ó 2019 Egyptian Petroleum Research Institute. Production and hosting by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
Please cite this article as: H. M. Naguib, M. A. Ahmed and Z. L. Abo-Shanab, Studying the loading impact of silane grafted Fe2O3 nanoparticles on mechanical characteristics of epoxy matrix, Egyptian Journal of Petroleum, https://doi.org/10.1016/j.ejpe.2018.10.001
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H.M. Naguib et al. / Egyptian Journal of Petroleum xxx (xxxx) xxx
OEt EtO
OH Hydrolysis
OH
NH2
Si
APTES
OEt
NH2
Si
Silanol form
OH
Iron oxide surface O
O
epoxy chain
O
O
O
O
Si
Iron oxide surface O
O
H2 N
C
O
IO
Epoxy resin SIO O OH
epoxy chain
O
O
H N
Si
O
O C
I r o n o x id e s u r f a c e
NH2
SIO-epoxy nanocomposite Scheme 1. Reaction mechanism of iron oxide nanofiller (IO) with aminopropyltriethoxysilane (APTES) as coupling agent to obtain amino silane iron oxide nanofiller (SIO), followed by reaction of SIO with epoxy getting SIO-epoxy nanocomposite.
mechanical and thermal properties of the formed epoxy nanocomposites were clarified systematically. The surface properties of modified Fe2O3 NPs were confirmed by Fourier transform infrared (FTIR) spectroscopy. The quality of dispersion of the loaded Fe2O3 NPs in epoxy nanocomposite was analyzed by transmission electron microscopy (TEM). The mechanical and thermal properties of prepared nanocomposites including storage modulus, tan d, and toughness were studied as well.
2.2.2. Chemical and structural characteristics Fourier transforminfrared spectra FTIR analysis was applied to investigate the reaction between silane treated nanoparticles and epoxy matrix. The machine used for FTIR analysis is ‘‘Nicolet IS-10 FTIR spectrophotometerThermo Fisher Scientific” using the range of wavenumber of ‘‘400–4000 cm1”. Transmission electron microscope
2. Materials and methods 2.1. Materials Amino silane-treated iron oxide nanofiller (SIO) were synthesized as previously reported in the literature Naguib et al. [26]. The epoxy base is bisphenol-A diglycidyl ether epoxy, and the hardener is triethylenetetramine. The epoxy matrix grade is ‘‘635-thin epoxy, base:hardener as 2:1, US Composites”.
The structural morphology of prepared nanocomposites was observed by transmission electron microscope (TEM) using high resolution JEOL-2100FTEM at 200 kV. The samples were prepared in colloidal mixture diluted with ethanol by sonication for 15 min. The dispersed solution was positioned on the TEM grid. After drying, the grid was attached to the microscope and images were taken. Thermogravimetric analysis
2.2. Methods and characterization 2.2.1. Formulation of iron oxide/epoxy nanocomposites Six samples of IO and SIO epoxy nanocomposites were prepared by dispersing 1 wt%, 3 wt%, and 5 wt% by weight of IO and SIO nanoparticles into epoxy base using mechanical stirrer followed by direct exposure to ultrasonic waves till 10 min to ensure the complete dispersion into base epoxy. Then, the amine hardener was added carefully with gentle stirring. The obtained nanocomposites have been aged for seven days at the ambient temperature to complete the full curing process.
TGA1-Mettler Toledo was used to study the effect of ungrafted IO and silane grafted SIO iron oxide nanoparticles on thermal stability of prepared composites using (TGA) by heating from 25 °C to 600 °C at a rate of 5 °C/min.
2.2.3. Mechanical characteristics The mechanical characteristics including storage modulus (E0 ), damping factor (tan d), and stress-strain curves were measured for the prepared nanocomposites by using Triton Technology-TTDMA following ‘‘ASTM D-4065” standards [27]. Three point bending mode
Please cite this article as: H. M. Naguib, M. A. Ahmed and Z. L. Abo-Shanab, Studying the loading impact of silane grafted Fe2O3 nanoparticles on mechanical characteristics of epoxy matrix, Egyptian Journal of Petroleum, https://doi.org/10.1016/j.ejpe.2018.10.001
H.M. Naguib et al. / Egyptian Journal of Petroleum xxx (xxxx) xxx
with frequency of 1 Hz was applied, the dimension of specimens are (25 mm length, 10 mm width and 3 mm thickness), the samples were exposed to 100 °C with heating rate of 5 °C/min. 3. Results and discussion 3.1. Fourier transform infrared study FTIR spectra of epoxy, iron oxide grafted (IO) epoxy and silanated iron oxide grafted (SIO) epoxy nanocomposites samples
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were studied to illustrate the reaction between epoxy and silane treated iron oxide NPs as shown in Fig. 1. In SIO epoxy nanocomposite spectrum, the intensity of hydroxyl stretching peak in the range of 3350 cm1 is decreased compared with IO epoxy spectrum because of the reaction of ‘‘O–H” groups with APTES coupling agent that actually grafted on nanoparticles. Also the peak of N–H group near 1600 cm1 is absent due to consumption of amine groups in the curing process for epoxy [28]. In addition, the peak near 840 cm1 that characterized for ‘‘epoxide group” [29] showed a lower intensity compared with that of neat epoxy spectrum.
Fig. 1. FTIR spectra for pure epoxy, IO and SIO-epoxy nanocomposite.
Scheme 2. Mechanism of curing of SIO-epoxy nanocomposite in presence of amine hardener.
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These spectra confirm the occurring of chemical reaction between SIO nanoparticles and epoxy matrix; so the reinforcement of epoxy with SIO was chemically performed. The reaction of iron oxide nanofiller (IO) with aminopropyltriethoxysilane (APTES) coupling agent to obtain amino silane iron oxide nanofiller (SIO), and then the reaction of SIO with epoxy getting the final SIO-epoxy nanocomposite are given in Scheme 1. Typically, APTES was hydrolyzed to silanol that reacted with IO to obtain SIO. The SIO itself caused a nucleophilic attack to the epoxy group in epoxy base, leading to formation of SIO-epoxy nanocomposite. The nanofiller in this case acts as hardener. However; with addition of the standard amine hardener (triethylenetetramine) in the presence of SIO nanofiller, a dual mechanism is suggested here as shown in Scheme 2. The amine group in the hardener (b) makes its nucleophilic attack to the epoxy ring that leading to ‘‘ring-opening reaction” and formation of new hydroxyl group (Ahmed et al.) [30]. At the same time, the NH2 in SIO as functionalized amino silane-treated iron oxide nanoparticles (a) can contribute to the curing reaction for epoxy. So, the scheme dis-
O
Fig. 2. TEM image of 1, 3, and 5%wt IO (a–c) and 1, 3, and 5%wt SIO (d–f) NPs dispersed in epoxy matrix.
cusses in details the reaction and curing mechanism that leading to formation of cured SIO-epoxy nanocomposite, which further subjected to the full curing conditions by aging for seven days at room temperature to obtain the final rigid form of nanocomposite. 3.2. Transmission electron microscope Dispersion of the fillers in epoxy matrix is the main factor which affects the behavior of nanocomposite. Hence, agglomerated fillers cause severe stresses concentration and interfacial cracks that negatively affecting the composite performance. Therefore, the dispersion of IO and SIO NPs in epoxy matrix was firstly investigated by TEM. TEM was used to examine the dispersion ability of loading 1%, 3%, and 5% by weight of untreated (IO) and silane treated Fe2O3 (SIO) NPs on epoxy matrix. As shown in Fig. 2a IO NPs is loaded with 1 wt%, the IO NPs were embedded in the epoxy matrix. However, with increasing the loading of IO to 3%, and 5 wt% as shown in Fig. 2b and c, the agglomeration was observed due to the large specific surface area and high surface energy. Fig. 2d and e (the loading of SIO NPs is 1 wt% and 3% respectively) showed good dispersion of SIO NPs into epoxy matrix and no agglomerates were observed. This advantage may be owe to the steric hindrance of SIO NPs and good interaction of silane group with epoxy matrix which resulted in improving the stiffness and failure strain. However, 5 wt% loading of SIO NPs shown in Fig. 2f gives complete saturation of SIO NPs in epoxy matrix and some of agglomeration is observed, so addition of more SIO was stopped for this ratio to avoid the inverse effect. 3.3. Dynamic mechanical characteristics The roles of surface modification and loading of Fe2O3 NPs on dynamic mechanical behavior of epoxy nanocomposites were studied. As seen in Fig. 3, the modulus of bending for the cured pure epoxy resin is about 1.45 GPa, and for IO-epoxy nanocomposites modulus of 1.48, 1.58, and 1.59 GPa were obtained with IO loading of 1, 3 and 5 wt%. While in the SIO-epoxy nanocomposites, they are 1.57, 1.74, and 1.69 GPa with the SIO loading of 1, 3, and 5 wt%, respectively. These data indicated that SIO NPs has been significantly enhanced the modulus of epoxy nanocomposites compare with IO NPs, which is attributed to the high cross linking degree between the epoxy matrix and fillers in addition to the good
Fig. 3. Effect of IO and SIO loading on modulus of epoxy nanocomposites.
Please cite this article as: H. M. Naguib, M. A. Ahmed and Z. L. Abo-Shanab, Studying the loading impact of silane grafted Fe2O3 nanoparticles on mechanical characteristics of epoxy matrix, Egyptian Journal of Petroleum, https://doi.org/10.1016/j.ejpe.2018.10.001
H.M. Naguib et al. / Egyptian Journal of Petroleum xxx (xxxx) xxx Table 1 Effect of IO and SIO loading on storage modulus and glass transition temperatures of epoxy nanocomposites. Sample
Modulus [GPa]
Tg [°C]
Epoxy 1% IO-epoxy 3% IO-epoxy 5% IO-epoxy 1% SIO-epoxy 3% SIO-epoxy 5% SIO-epoxy
1.45 1.48 1.58 1.59 1.57 1.74 1.69
43 43.1 44.3 43.6 43.3 46.2 43.6
interfacial force between silane treated NPs and epoxy matrix [26]. From Table 1, it is noticed that the modulus of SIO epoxy nanocomposites increases with the increase of loading of SIO NPs. When the nanoparticle loading increases to 3 wt%, the modulus of the epoxy nanocomposite raised to 60%. As well as, it can be noticed that the modulus of the obtained SIO epoxy nanocomposite firstly increases followed by a decrease with high loading 5 wt% of SIO (as shown in Fig. 3). This effect may be due to some of agglomerated areas at the
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SIO NPs-epoxy matrix interface that can occur with adding more and more of NPs content [31]. The effects of the surface modification and loading percent of Fe2O3 NPs on tan d were also discussed (as shown in Table 1, and Fig. 4). The results showed that as IO and SIO loading increases, the dissipated energy (tan d) decreases and consequently the main mechanical relaxation is enhanced and Tg of the nanocomposites increases linearly till 3% loading. Since the interfacial layers rising from the interaction between silane treated nanoparticles and epoxy during the curing process will give a different segmental dynamics from the neat epoxy. As shown in Table 1, there are higher Tg values for the SIO epoxy nanocomposites (43.3 and 46.2 °C for 1 and 3%) compared with that of IO epoxy nanocomposite (43.1 and 44.3 °C for 1 and 3%) or for epoxy (43 °C). The Tg value that began to decrease with adding 5% IO and SIO may be due to some of agglomerations created. Actually, the good dispersion of SIO nanoparticles into epoxy matrix, the free space among molecules decreases resulting in losing the mobility of chain segments [32]. On the other hand, loading epoxy with untreated IO didn’t significantly affect Tg value due to bad dispersion in epoxy. The
Fig. 4. Effect of IO and SIO loading on loss tangent (tan d) of epoxy nanocomposites.
Fig. 5. Stress-strain curves of epoxy nanocomposites loaded with different percentage of IO and SIO NPs.
Please cite this article as: H. M. Naguib, M. A. Ahmed and Z. L. Abo-Shanab, Studying the loading impact of silane grafted Fe2O3 nanoparticles on mechanical characteristics of epoxy matrix, Egyptian Journal of Petroleum, https://doi.org/10.1016/j.ejpe.2018.10.001
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grafting of SIO NPs with loading 3 wt% into epoxy matrix is followed by high Tg value. The stress-strain curves of IO and SIO epoxy nanocomposites were plotted as shown in Fig. 5. It is noticed that addition of IO NPs to epoxy matrix improved stiffness of the prepared nanocomposites but lowered their strain. On the other side, addition of SIO NPs increased the stiffness with keeping the elastic properties (strain) for the epoxy matrix, especially with 3% SIO. The areas under the curves were measured to calculate the toughness of the prepared nanocomposites. The toughness data shown in Fig. 6 illustrated that epoxy nanocomposite loaded with 3% SIO NPs has the highest value of toughness, due to excellent dispersion and high crosslinks between SIO NPs and epoxy matrix. Addition of IO leads to stress increase and strain decrees, so the toughness (as calculated form area under the curve) has lower values till 3%, compared with neat epoxy. The 5% IO nanocomposite achieved higher stiffness due to the more stress, however the strain became
the least causing bad brittle character. On the other hand, Addition of SIO leaded to increasing of stress and strain together, so the toughness has increased in this case. However, 5% SIO nanocomposites began to decrease the toughness because of the agglomerated structures that obtained with this high loading percentage. Many studies on epoxy/nanofiller composites have reported this trend for mechanical properties with the difference in the loading percentages, depending on the type of epoxy and kind of organic grafted materials on iron oxide nanoparticles. Zahra et al. [33] studied the loading effect of organically treated by using 3-glyci doxypropyltrimethoxysilane (GPS) as coupling agent and untreated iron oxide nanoparticles on the modulus of prepared nanocomposites, it was found that addition of 8 wt% from treated iron oxide NPs give the highest modulus and further addition weaken the modulus of prepared composites. Tao Sun et al. [28] noticed that addition of 4 wt% of iron oxide nanoparticles treated with poly(N-vinyl-2-pyrrolidone) (PVP) and (3-aminopropyl)
Fig. 6. Toughness of epoxy nanocomposites loaded with different percentage of IO and SIO NPs.
Fig. 7. TGA for neat epoxy, IO-epoxy and SIO-epoxy nanocomposites.
Please cite this article as: H. M. Naguib, M. A. Ahmed and Z. L. Abo-Shanab, Studying the loading impact of silane grafted Fe2O3 nanoparticles on mechanical characteristics of epoxy matrix, Egyptian Journal of Petroleum, https://doi.org/10.1016/j.ejpe.2018.10.001
H.M. Naguib et al. / Egyptian Journal of Petroleum xxx (xxxx) xxx Table 2 Thermal degradation temperatures for neat epoxy and IO/SIO-epoxy nanocomposites. Sample
Epoxy
IO-Epoxy
SIO-epoxy
T0.1 [°C] T0.5 [°C]
194 369
196 372
199 377
T0.1 correlated to 10% weight loss in sample. T0.5 correlated to 50% weight loss in sample.
triethoxysilane (APTES) as modified agent to epoxy matrix increase the tensile strength by 50.2% and increase the fracture toughness by 106%. These general trends may be due to some of agglomerated areas at the SIO NPs-epoxy matrix interface that can occur with adding more and more of NPs content [32]. 3.4. Thermogravimetric analysis Fig. 7 represents the TGA curves for pure epoxy, IO and SIOepoxy nanocomposites loaded with 3% IO and SIO NPs respectively. All curves show the first thermal degradation process after 100 °C due to dehydration followed by combustion of epoxy between 300 and 430 °C and finally formation of char near 500 °C. It is clear that filling epoxy matrix with IO nanofiller caused some enhancement in the thermal stability compared with neat epoxy starting from 250 °C. However, the SIO-epoxy nanocomposite recorded the highest thermal stabilization through the noticeable increase in the temperatures of the thermal degradation steps as shown in the temperature range of 270 and 400 °C. In more details, Table 2 illustrates T0.1 and T0.5 temperatures for the epoxy, IO-epoxy and SIO-epoxy nanocomposites. T0.1 increased respectively from 194 °C for neat epoxy to 196 and 199 °C for IOepoxy and SIO-epoxy nanocomposites. Moreover, the T0.5 increased from 369 °C for neat epoxy to 372 and 377 °C for IOepoxy and SIO-epoxy nanocomposites respectively. Hence, more enhanced thermal stability was achieved after filling epoxy matrix with SIO NPs with shifting the mentioned degradation temperatures to higher values; the stronger SIO-epoxy interface is responsible for this advance. 4. Conclusion This work studies the effect of surface treatment and loading of Fe2O3 NPs with different doses (1, 3 and 5 wt%) on chemical, morphological, mechanical and thermal characteristics of epoxy matrix. The main findings of this work are: FTIR and TEM were considered as efficient tools to investigate the chemical structure of silanted-Fe2O3 NPs and their dispersion in epoxy matrix respectively. The results approved that loading with 3% of SIO NPs gave the best dispersion into epoxy matrix. The effect of silane surface treatment for Fe2O3 NPs on thermal degradation of epoxy nanocomposite was also studied using TGA, the results approved that silane coupling agent has a positive effect in increasing thermal stability of nanocomposites since T0.5 increased from 369 °C to 377 °C. DMA was conducted to study the dynamic mechanical behavior of the prepared nanocomposites including modulus of elasticity, Tg and toughness. The results approved that silane treated iron oxide NPs improved the modulus and Tg of epoxy nanocomposites more than untreated NPs. When 3 wt% SIO NPs were introduced, the modulus increased from 1.45 to 1.74 GPa, Tg increased from 43 to 46 °C and toughness from 300 to 500 MPa by comparing to pure epoxy resin system. This kind of epoxy nanocomposites with high mechanical, morphological and thermal performance could be used in many new
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