Modification of the Epoxy Resin Mechanical and Thermal Properties ...

Modification of the Epoxy Resin Mechanical and Thermal Properties with Silicon Acrylate and Montmorillonite Nanoparticles

Modification of the Epoxy Resin Mechanical and Thermal Properties with Silicon Acrylate and Montmorillonite Nanoparticles S.M. Mousavi*1, O. Arjmand2, S.A. Hashemi3, and N. Banaei4 1Department

of Chemical Engineering, School of Chemical and Petroleum Engineering, Shiraz University, Shiraz 71345, Iran 2Young Researchers and Elite Club, Nourabad Mamasani Branch, Islamic Azad University, Nourabad, Iran 3Department of Mechanical Engineering, Najafabad Branch, Islamic Azad University, Najafabad, Iran 4Department of Applied polymer, yazd Branch, Islamic Azad University, yazd, Iran Received: 17 June 2015, Accepted: 18 April 2016

Summary In this study we have investigated the effect of montmorillonite with alkyl quaternary ammonium salt that had been doped into the silicon acrylate (AC-Si)/ Epoxy Cresol Novolac (ECN)/ montmorillonite nano composites on structural, mechanical and thermal properties of composite samples. Moreover the effect of increase in weight percentages of fillers at 0.01, 0.02, 0.03 and 0.04 wt% on the amount of Impact and flexural strength had been investigated. Also impact and flexural strength were performed on two different systems namely (a) ECN filled nanoclay and (b) AC-Si ECN filled with nano montmorillonite as a function of clay respectively. By increase in the weight percentage of filler in the context of matrix up to the 0.03 wt%, the amount of flexural and impact strength were increased but by adding filler more that 0.03 wt%, the amount of flexural and impact strength will decrease. The resulting nanocomposites have optimal mechanical properties at 0.03 wt% montmorillonite content. Addition of The AC-Si will increase the interlamellar distance due to better dispersion of the clay within the matrix. Cross section of fracture surfaces that had been shown by SEM micrographs, specifies that, increase in viscosity had caused due to aggregation that is the main cause of fluctuation in samples properties.

* Author to whom correspondence should be addressed: seyyed mojtaba mousavi. Email:[email protected] ©Smithers

Information Ltd, 2016

Polymers from Renewable Resources, Vol. 7, No. 3, 2016

101

S.M. Mousavi, O. Arjmand, S.A. Hashemi, and N. Banaei

In addition the produced samples were characterized by X-ray diffraction (XRD) differential scanning calorimetry, Thermal gravimetric analysis, scanning electron microscopy and mechanical testing (impact and flexural). Keywords:, Epoxy Cresol Novolac, , Silicon Acrylate, Nano montmorillonite

Introduction Epoxy resins are thermoset polymers that have broad practical applications [1]. The superior adhesive and mechanical characteristics of 3D crosslinked epoxy polymers make them suitable materials for numerous industrial applications such as aerospace, coatings, marine vessels, space vehicles, adhesives, electronics, automotive, and biotechnology [2, 3]. Epoxy resins constitute a large class of composites that contain two or more epoxy groups. Epoxy resins are generally complicated 3D network structures. The epoxies can be reacted with other components in conjunction with hardeners or curing agents. Hardeners typically have active hydrogens including amines and anhydrides. The resultant composites exhibit a series of exceptional performances, such as low creep, high-temperature performance, high modulus, and fracture strength [4]. Comprehensive high performance epoxy nanocomposites Co reinforced by two dimensionally different nanoscale particles were successfully prepared. In the nanocomposites, 2D MMT mono platelets and 0D spheres SiO2 nanoparticles formed intermingled structure and caused non natural conformations of epoxy chains before and during crosslinking due to specific absorption on the mixed filler surface [5]. Manufacturers fill polymers with particles in order to improve the stiffness and the toughness of the materials and also to enhance their barrier properties, resistance to fire and ignition or simply to reduce the final cost. Addition of particulate fillers, sometimes imparts drawbacks to the resulting composites such as brittleness or opacity. Nanocomposites are a new class of composites, that are particle-filled polymers for which at least one dimension of the dispersed particles is in the nanometer range. One can distinguish three types of nanocomposites, depending on how many dimensions of the dispersed particles are in the nanometer range. When the three dimensions are in the order of nanometers, we are dealing with isodimensional nanoparticles, such as spherical silica nanoparticles [6, 7] or by polymerization promoted directly from their surface [8], but also it can include semiconductor nanoclusters [9] and others [7]. When two dimensions are in the nanometer scale and the third is larger, forming an elongated structure, [10, 11] which are extensively studied as reinforcing nanofillers yielding materials with exceptional properties. The third type of nanocomposites is characterized by only one dimension in the nanometer range. In this case, the filler is present in the form of sheets 102



by one to a few nanometer thick and hundreds to thousands nanometers long. This family of composites can be gathered under the name of polymerlayered crystal nanocomposites, and studying their properties will constitute the main object of this contribution. These materials are almost exclusively obtained by the intercalation of the polymer (or a monomer subsequently polymerized) inside the galleries of layered host crystals. Amongst all the potential nanocomposite precursors, those based on clay and layered silicates have been more widely investigated probably because the starting clay materials are easily available and their intercalation chemistry has been studied for a long time [12]. Owing to the nanometer-size particles obtained by dispersion, these nanocomposites exhibit markedly improved mechanical, thermal, optical and chemical properties when compared with the pure polymer. Clay-epoxy cresol novalac nanocomposites have attracted considerable technological and scientific attention, because these materials offer a wide array of property improvements at very low filler content. Also The effects of organoclay on modulus of elasticity have been investigated [13]. In this study, Epoxy cresol novalac /silicon acrylate /MMT/ nanocomposites Co_reinforced by dimensional MMT platelets and spheres were prepared. They exhibited considerable improvements over neat epoxy cresol novalac in modulus, strength, toughness and thermal resistance.

Experimental Section

Materials The epoxy cresol novalac resin (ECN) 9500 and Hardener Di ethylen tri amine (DETA), had been supplied by Sana company (from Iran). The nanoclay organically had been modified by montmorillonite that have been supplied by Southern, USA. The surface treatment of nanoclay, make it suitable for dispersion in an amine cured epoxy cresol novalac resin (ECN). All other chemicals materials that had been used in this study, had AR grades. Figure 1 depicts the diagram of clay nanoparticles size (PSA). The size of the nanoparticles is determines to be 36 nm.

Sample Production Method In the first stage we have put the montmorillonite and epoxy cresol novalac resin (ECN) in humidity absorbing chamber for further humidity reduction for about 2 hours. The montmorillonite particles have a narrow range of particle-


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Figure 1. Diagram of nanoparticle size (PSA) of the montmorillonite nanoparticles

size distribution and excellent dispersion in the epoxy cresol novalac. Different amounts 0.00, 0.01, 0.02, 0.03 and 0.04 wt% of montmorillonite were mixed with the epoxy cresol novalac by means of a mechanical mixer stirring for 30 minutes under vacuum at room temperature. Then the resulting suspension had been mixed by ultra-sonic mixer for 10 minutes (under 120w of instrument magnitude and by temperature limit: 30°C to obtain a homogenous mixture. Then the mixture was degassed under vacuum for about 2 hours. Upon completion of degassing, the vacuum was released and hardener was added at a weight ratio of 10:1 while the suspension was stirring slowly. Then the resulting suspension was molded and cured at room temperature for 24 hours. Moreover the second curing step was handled at 140°C for 10 hours. The post cured epoxy plates were left in the oven and allowed to cool gradually to ambient temperature before removal from the moulds. The cured epoxy cresol novalac laminates were machined into different test specimens for characterization. Also a view of manufacturing process can be seen in Figure 2.

Results and Discussion

Mechanical Properties Bending tests were carried out with an Gotech, Tiwan universal testing machine under a strain rate of 5 mm/min at 25°C. All test specimens were made according to ASTM D 790. Minimum five samples were tested at room temperature for each formulation and an average values were reported. Impact tests were carried out with a Gotech, Tiwan universal testing machine. All 104



Figure 2. A view of above mentioned manufacturing process

test specimens were made according to ASTM D 256, minimum five samples were tested at room temperature for each formulation and an average values were reported.

Impact Strength Impact strength of fully cured composite samples can be seen in Table 1 and Figure 3. Impact strength of neat ECN (4.2 J/m) is lower than the reinforced composite samples with filler. By increase in the weight percentage of fillers, the amount of impact strength increase significantly. Sample containing 0.03 wt% filler shows The highest amount of impact strength in comparison with other samples. In addition by increase in the weight percentage of montmorillonite nanoparticles to 0.04 wt%, the amount of impact strength decreased. The decrease in impact strength at higher clay content is due to the existence of aggregates. The impact result show that AC-Si/ECN/ montmorillonite nano composites provide better impact properties than ECN/clay nanocomposites. This behavior is attributed to the extraordinarily large aspect ratio of the silicate layer in AC-Si/ECN/ montmorillonite nanocomposites. Better compatibility between AC-Si/ECN with montmorillonite is the possible reason for high impact strength for AC-Si/ECN/ montmorillonite nanocomposites than ECN/ montmorillonite nanocomposites.


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Table 1. Impact strength of nanocomposites Name of the sample

Impact strength (J/m)

ECN

4.2

ECN/1 wt% montmorillonite

5.9


7


7.6


7.2

AC-Si/ECN/1 wt% montmorillonite

6.3


8.1


8.9


8.3

Figure 3. Impact strength of nanocomposites

Flexural Strength Figure 4 shows the effect of montmorillonite addition on flexural strength. The flexural strength of pure ECN is about 58.1 MPa. Also by increase in clay weight percentage up to 0.03 wt% in the context of matrix, the amount of flexural strength increased significantly. Moreover by adding montmorillonite nanoparticles more than 0.03 wt%, the amount of flexural strength will decrease. The decrease in flexural strength at higher filler content is due to existence of aggregations. The flexural result show that AC-Si/ECN/ montmorillonite nanocomposites provide better flexural properties than ECN/montmorillonite nanocomposites, as you can see in Figure 4. 106



Figure 4. Flexural strength of nanocomposites

X-ray Diffraction (XRD) In this study we have examined the nanocomposite structure and filler distribution in the context of epoxy cresol novolac resin by X-ray diffraction as you can see in Figures 5 and 6. Figure 5 shows the X-ray diffraction result of ECN-montmorillonite nanocomposites and Figure 6 shows the X ray diffraction result of ECN(AC Si)-montmorillonite nanocomposites. From Figures 5 and 6, we have observed that the reflections related to the 0.01 wt% of the montmorillonite shows a peak in 2Θ=4.8 and nanocomposites shows this basal plane peak indicating that exfoliation or intercalation has occurred in the system. Moreover by comparing the XRD spectrum of Figures 5 and 6, we can clearly see that addition of the silicon acrylate to the epoxy cresol novolac resin can increase the interlamellar distance.

Thermal Gravimetric Analysis (TGA) The thermal stability of the epoxy cresol novolac nanocomposites have been evaluated using Mettler Toledo instrument. About 10 mg of sample was subjected to dynamic TGA scans at a heating rate of 10°C/min in the temperature range of ambient to 700°C in N2 atmosphere. The TG curves were analysed as percentage weight loss as a function of temperature, thermal properties of ECN and nanocomposites were investigated. Figure 7 shows the


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TGA thermograms of the neat ECN and AC-Si/ECN nanocomposite with 0.01, 0.02 and 0.03 wt% of montmorillonite. In general, major weight losses were observed in the range of ~300-400ºC for ECN and nanocomposites, which may be related to the structural decomposition of polymers. It can be seen

Figure 5. XRD spectra of AC-Si /ECN/cloisite (30B)

Figure 6. XRD spectra of AC-Si /ECN

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in Figure 7 that the Td (the temperature of degradation) for nanocomposites containing 0.02 wt% filler has shifted toward the higher temperature range in comparison to the pure ECN. However the Td of 0.03 wt% nanocomposite is lower than neat ECN due to the catalytic effect of nano montmorillonite on the crosslinking reaction of the ECN resin with curing agent. Result shows ECN/AC-Si/ montmorillonite nanocomposite has better thermal stability than ECN/ montmorillonite nano composite, This behavior is attributed to the extraordinarily large aspect ratio of the silicate layer in AC-Si/ECN/ montmorillonite nanocomposites.

Figure 7. TGA tests of composite samples containing 0.01, 0.02 and 0.03 wt% cloisite 30B in the context of ECN and AC-Si/ECN

Differential Scanning Calorimetry Test In this section, we have examined and compared the glass transition temperature and thermal gravimetric curves for different composite samples. Comparison between differential scanning calorimetry tests of composite samples containing 0.01, 0.02 and 0.03 wt% cloisite 30B in the context of ECN and AC-Si/ECN can be seen in Figure 8. As showed in this figure, different amounts of titanium acrylate won’t change the composite samples glass transition temperature significantly. This is due to the compatibility of acrylate resin and epoxy resin in the same amounts of nanofiller. After comparison between sample containing pure resin and other samples, we have observed that by increase in the weight percentage of nanofiller, the order of the crystal crosslink will disrupted and glass transition temperature will decreases.


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Figure 8. DSC tests of composite samples containing 0.01, 0.02 and 0.03 wt% montmorillonite in the context of ECN and AC-Si/ECN

Scanning Electron Microscope (SEM) SEM analysis shows the reason that caused change in mechanical properties of composite samples in different weight percentage of fillers. SEM analysis had done for different fracture surfaces of nanocomposites as shown in Figures 9 and 10. As depicted in the Figure 9 part (a), smooth fracture surfaces that had been observed on the pure ECN surface indicate the relatively brittle fracture. In Figure 9 part b and c and d and e and Figure 10 part f and g, the nanocomposites exhibited a rougher fracture surface. Figure 10 part h and i depicts high montmorillonite concentration, relatively higher fractions of montmorillonite aggregations were observed. as a result, it can causes micro voids which act as a stress concentration factors and facilitates shear yielding in the system and thus reduces the impact and flexural strength. SEM images clearly shows the fracture cross sections.

Conclusions In this study we have used a multi stage manufacturing process for fabrication of composite samples containing montmorillonite nanoparticles. Two different samples of ECN/ montmorillonite nanocomposites (with and without AC-Si) were prepared and then we have measured the effect of fillers in different weight percentages on the amount of impact and flexural strength. Moreover 110



we have observed that by increase in weight percentages of filler until 0.03 wt%, the amount of both impact and flexural strength will increase but by increasing in the weight percentages of fillers more than 0.03 wt%, this properties decreased that can be due to aggregation of fillers in the context of matrix. Also the amount of impact and flexural strength were increased for

Figure 9. SEM micrographs from fractured surfaces of nanocomposites at same (3.00k x) magnifications for (a)-Neat ECN; (b)-ECN/1 wt% montmorillonite; (c)-AC-Si/ ECN/1 wt% montmorillonite; (d)-ECN/2 wt% montmorillonite; (e)-AC-Si/ ECN/2 wt% montmorillonite


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Figure 10. SEM micrographs from fractured surfaces of nanocomposites at same (3.00k x) magnifications for (f)-ECN/3 wt% montmorillonite; (g)-AC-Si/ ECN/3 wt% montmorillonite; (h)-ECN/4 wt% montmorillonite; (i)-AC-Si/ECN/4 wt% montmorillonite.

samples containing ECN/ montmorillonite and AC-Si/ECN/ montmorillonite (at 0.03 wt%) about 81%,162% and 112%, 181% respectively. In addition for examination of composite samples structure and fillers distribution, the XRD and SEM analysis were taken from the samples. Also the TGA and DSC tests for samples containing filler at different weight percentages shows that by increasing in the weight percentage of filler in the context of the matrix, the thermal stability will increase.

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