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Effects of carbon nanotubes on mechanical and thermal properties of Epoxy Nanocomposites

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  • Save International Journal of M aterials Engineering 2013, 3(3): 36-40 DOI: 10.5923/j.ijme.20130303.02 Study the Influences of Carbon Nanotubes on the Mechanical and Thermal Properties of Epoxy Matrix Nanocomposite Mohamed A. Etman Adviser to the Nanotechnology for Housing & Building Research Center (HBRC),Al-Ahram higher institute for engineering and technology Abstract Carbon nanotube based epoxy co mposites have been fabricated at roo m temperature. To optimize the processing of the nanocomposites and to favor a homogeneous dispersion of the CNTs on the epoxy matrix, acetone was used to reduce epoxy viscosity and increasing diffusion of the CNTs in the matrix. Sonication principle was used in order to minimize entanglement of CNTs in the epoxy matrix nanocomposites. Epoxy based polymer co mposites are developed by dispersing of CNTs as reinforcement in different concentrations varying fro m 0.1 up to 0.5 wt% and found that with 0.5 wt% gives the best result. Detailed the rheological studies are carried out to know the dispersion of CNTs in matrix. SEM and TEM studies are carried out to observe the morphology of reinforcing materials as well as its dispersion in the epoxy matrix. The thermal stability of the epo xy nanocomposites were measured using thermo-gravimetric analysis (TGA ) and the result of which revealed that, co mposites made with CNTs showed higher thermal stability as compared with pure epoxy. Enhancement in flexu ral properties was observed with reinforced CNTs as well. Keywords Carbon Nanotubes, Dispersion, Nanocomposites, Flexural Properties, Thermal-grav imetric Analysis (TGA ), SEM and TEM 1. Introduction Carbon Nanotubes (CNTs), since their d iscovery in 1991 by lijima[1] have been attracted a great deal of interest[2]; in the field of nanotechnology related applications. Carbon Nanotubes (CNTs), one graphene layer (SWNT) or many graphene layers wrapped onto themselves (MWNT). The recent theoretical and experimental investigations indicate that they have properties suitable for applications in many fields. Their interesting mechanical propert ies such as axial Young modulus 1– 5 TPa[3–9], high flexib ility[8], bending fully reversible up to a 110_ crit ical angle for SWNT[10], and physical (meta llic or semi-conducting character[11, 12], field emission, high thermal and electrical conductiv ity, hydrogen adsorption) properties have been the subject of many research works. The CNTs-based composites, which may be one of the most promising applications, have been in tens ively stu d ied us ing d ifferent mat rix mat erials , polymers[13– 22], ceramics[23–25] and metals[26, 27]. A review paper has been published on the subject[26]. In the * Corresponding author: (Mohamed A. Etman) Published online at Copyright © 2013 Scientific & Academic Publishing. All Rights Reserved case of polymer matrix, most papers dealt with relat ively brittle and rig id matrix, such as cured epoxy resin. And often, only mechanical properties[17, 19] or physical properties[20, 22] were treated. The main purpose of this study is to obtain randomly oriented carbon nanotubes (CNTs)/epo xy nanocomposites using a minimu m amount of solvent, following a tip sonication and casting molding route, and to analyze the mechanical properties of the produced nanocomposites. Mechanical properties were investigated to evaluate the change introduced by the CNTs at different concentration varying fro m (0.1 to 0.5 wt %). 2. Experimental 2.1. Materials Carbon Nanotubes (CNTs) used for the preparation of nanocomposites was obtained from Nano Technology Lab in Housing and Building National Research Center (HBRC). They are produced by the author using plasma arc d ischarge technique between two graphene electrodes having high purity up to 99.9%. A lso, the epoxy used in this wo rk was supplied fro m LinForce RN075 LPL STRUCTURAL EPOXY SYSTEM consists of two parts resin and curing agent were mixed by mixing 2: 1 weight ratio. International Journal of M aterials Engineering 2013, 3(3): 36-40 37 2.2. Nanocomposites Preparati on Nanocomposites were prepared by dispersing CNTs in the epoxy matrix by ultrasonic method. In order to achieve best dispersion of CNTs in the epo xy matrix and remove the deagglomeration of CNTs by treated in the alcoholic med iu m as (acetone) and these tubes were then added to the epoxy resin and sonicated for 2 h at roo m temperature. Then the mixture was cured under vacuum at 90°C for 10 h followed by hardener addition and mechanical stirring. The CNTs/Epo xy matrix nanocomposite was allowed to set at room temperature. After that, the prepared nanocomposite were mo lded into sample mold as ASTM D790, shown in fig. 1, and then treated at 80°C for 6 h in the oven to remove the moisture content. Finally, those samples were placed between two metal plates under pressure to reduce the porosity that might be formed during hardening. The surfaces of these samples were mechanically polished to minimize the in fluence of surface flaws before carrying out mechanica l tests. analyzed by TGA technique. Test results were recommended in the table 1 and shown in fig. 6. 3. Result and Discussion 3.1. Microscopic Observations of CNTs CNTs samp les were synthesized and purified were observed and characterized by Transmission Electron Microscopy (TEM ) and Scanning Electron Microscopy (SEM) shown in fig. 2 and fig. 3(a, b) respectively. TEM and SEM results were depicted the numerous non-aligned spaghetti-like of carbon nanotubes having bends with different angles and through most of these samples with a few single tubes observed. The tubes showed kinks and bends can be confirm the mechanical nature of CNTs. The length of the tube could not be precisely measured while its diameter could be assessed with reasonable accuracy and found equal to 10 n m on the average. Figure 1. ASTM D790 sample mold (dimensions in mm) 2.3. Morphological Study Transmission Electron Microscopy (TEM ) observation was carried out using JEOL JEM 1200 EX operating at 120 kV was used to study the morphology and determine the sizes appro ximately of carbon nanotubes (CNTs). Also, Scanning Electron Microscope (SEM) (Joel JSM-6480 LV) was used to conduct the dispersion behavior and fractures surface topography characterizat ion for CNTs and CNTs/Epo xy matrix nanocomposites. 5500nnm Fi gure 2. TEM images for CNTs 2.4. Mechanical Test The flexural strength of a material is defined as its ability to resist deformation under load. Fo r materials that deform significantly but do not break, the load at yield strength, typically measured at the outer surface, is reported as the flexu ral strength or flexural yield strength. The test beam is under compressive stress at the concave surface and tensile stress at the convex surface shown in fig. 1 test geometry for ASTM D790 were carried out at Building Research Center Lab, at amb ient temperature. Flexural strength and flexu ral modulus were determined for each group by the average test result for five samples and shown in fig.5. 2.5. Thermal Gravi metric Measured The thermal stability of the synthesized carbon nanotubes and CNTs/epoxy matrix nanocomposite samples were Figure 3(a, b). SEM images of CNT s 3.2. Microscopic Observations for Epoxy Nanocomposite SEM of virg in epoxy is shown in Fig. 4a, was revealed structure in homogeneity with weak cross linking between base epoxy and hardener, as observed in the bright zone, although it fails in a ductile manner. The SEM of CNTs/epoxy nanocomposites containing 0.1 of CNTs is shown in Fig.4b. It illustrates the morphology of fractured surface of CNTs/Epo xy poly mer mat rix specimen. Ho mogeneous distribution of carbon nanotubes into the epoxy mat rix is observed. Figure 4c shows the different 38 M ohamed A. Etman: Study the Influences of Carbon Nanotubes on the M echanical and Thermal Properties of Epoxy M atrix Nanocomposite spots that confirm a reasonable bonding at the interface between the carbon nanotubes and epoxy matrix. Also, it is observed that the CNTs to enhancement the cross lin king of epoxy matrix nanocomposite to aug ment the mechanical p ro p erties . 3.3. Flexural Measurements Three bending tests were perfo rmed in order to evaluate the flexu ral strength and flexural modulus of epo xy and CNTs/epoxy nanocomposite. Figure 5 show the results of three points bend test is the relat ion between CNTs concentration and study the effect on the flexural strength and flexu ral modulus. Which clear that the flexural strength and flexural modulus of epoxy nanocomposite were improved by increasing the concentration of carbon nanotubes were just at 0.5wt% CNTs to epoxy nanocomposite were (120 MPa) and (1.95 GPa) which compared to values of virgin epo xy was (49 MPa) and (1.5 GPa). Which indicated that on increasing interfacial bonding between carbon nanotubes and epoxy composite to enables an effective on the stress due to fracture load was transferred through matrix. Figure 4. SEM images for CNT s/Epoxy nanocomposites(a) Virgin Epoxy matrix without CNTs.(b) Epoxy reinforced by 0.1 %wt. CNTs matrix.(c) Epoxy reinforced by 0.5 %wt. CNT s matrix 140 Flexural Strength (Mpa) 2.4 Flexural Modules (GPa) 120 Flexural Strength (Mpa) Flexural Modules (GPa) 100 2.1 80 1.8 60 40 1.5 20 0 1.2 0 0.1 0.2 0.3 0.4 0.5 0.6 Wt % of CNTs Figure 5. Flexural Strength and Flexural modules of CNT s/Epoxy International Journal of M aterials Engineering 2013, 3(3): 36-40 39 3.4. TGA of CNTs/epoxy Nanocomposites Thermo-gravimet ric analysis (TGA) was carried out of the carbon nanotubes and composites samples made with carbon nanotubes at ratio 0.5 wt% to know the thermal stability. Also, it was observed that the composites prepared with CNTs, which have only slightly affected the thermal decomposing temperature of epo xy resin whereas the CNTs have a great effect on the onset decomposing temperature. Introducing different CNTs to epoxy resin can increase the initial deco mposing temperature of virgin epo xy resin because of the strong interaction between the epoxy resin and carbon nanotubes, and the homogenous distribution of CNTs can be retarded under high thermal temperature. A lso, fig. 6 shows the release of weight loss percent due to the thermal degradation while heating up of the test samp le at a constant rate of 10oC/ min. A lso, TGA results were tabulated in Table 1 in wh ich the degradation temperatures corresponding to weight percent loss values of CNTs, virg in epoxy and CNTs/epoxy nanocomposite have been found 200, 330, 400, 490, 500, 550, 600, 700, and 929 oC, res p ectiv ely . 120 100 80 60 The epoxy polymer matrix nanocomposites have been adapted through the experimentation. Rheological studies that the viscosity of epoxy co mposites increase with increase the reinforced materials in the matrix, which can be useful for evaluating the dispersion in the matrix. The mechanical properties of CNTs/epoxy nanocomposites are improved significantly with the addition of CNTs due to the homogeneous dispersion of CNTs and the interfacial adhesion to the epoxy matrix. The most significant improvement of flexural strength and flexural modulus were (145% , 30%) at 0.5wt% content is observed. In addition TEM and SEM have been investigated to observed that the homogenous distribution of CNTs in epo xy matrix. 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