Journal of Scientific & Industrial Research Vol 74, December 2015, pp. 685-689 Experimental Investigations of Influence of Halloysite Nanotube on Mechanical and Chemical Resistance Properties of Glass Fiber Reinforced Epoxy Nano Composites R Ramamoorthi 1 * and P S Sampath 2 *1 Department of Mechanical Engineering, Sri Krishna College of Engineering and Technology, Coimbatore-641008, India 2 Department of Mechanical Engineering, K.S.R.College of Technology, Tiruchengode -637215, India Received 17 October 2014; revised 5 July 2015; accepted 18 September 2015 In this paper bi-directionally woven E-glass fabric/epoxy nanocomposite with different loading of halloysite nanotube (EP/GF/HNT) were made by hand layup followed by compression molding processes. Effectiveness of HNT addition on mechanical properties of the glass fiber reinforced epoxy nanocomposites were investigated by performing tensile and flexural property analysis as per ASTM standards. The results show that the addition of HNT significantly improved the mechanical properties compared with unfilled epoxy/glass fiber (EP/GF) composites and the maximum improvements in the properties were obtained at 4wt% addition of HNT. A further increase in the HNT content deteriorates the mechanical behaviour. The XRD, and scanning electron microscopy (SEM) were used to investigate the reinforcement mechanism and dispersion states of HNT in the nano composite. The results indicate that the compatibility between glass fiber and epoxy were obviously enhanced by the addition of HNT in the EP/GF composites. The chemical resistance properties EP/GF/HNT nanocomposites were also studied by using various chemical regents. It was found that all the composites are resistant to almost all the chemicals used. Keywords: HNT, Polymer nanocomposites, Mechanical Properties, Epoxy, Chemical resistance Introduction In the last two decades, some studies have shown that the potential improvement in properties and performances of fiber-reinforced polymer matrix materials in which nano scale particles were incorporated 1-5. Among various kind of nano particles CNTs are primly used as they drastically improve the mechanical properties of polymer composites. Many researchers investigated the effect of CNT s on the mechanical and thermal properties of fiber reinforced epoxy composites and proved that the addition of CNT s enhances the properties of composites 6-8. Halloysite nanotubes (HNT) are newly invented nanofillers which has recently become the subject of research attention as a new type of nano filler for improving the mechanical properties of polymers. HNT s are derived from naturally deposited aluminosilicate (Al 2 Si 2 O 5 (OH) 4 2H 2 O), HNT s resembles that of carbon nanotubes (CNTs) in terms of aspect ratio.some of the researchers also justified that HNTs are the new type of additive for enhancing the Author for correspondence E-mail:ramamecad@gmail.com mechanical and thermal performance of polymers 9,10. Compared to other nanosized inorganic fillers, naturally occurring HNTs are easily available and much cheaper. So based on various aspects from the literature findings it is concluded that halloysite nanotubes can be used as the ideal materials for preparing polymer nanocomposites 11,12. Among various kinds of fibers, glass fibers are the foremost wide used as reinforcement in polymer composites due to their low cost and fairly sensible mechanical properties 13. Although good works has been reported on polymer nanocomposites, works on epoxy/glass fiber composites strengthened with nano fillers is in the infant stage and has not been absolutely explored. Also no literature could be cited on the effect of HNT addition on mechanical and chemical resistance properties of epoxy/glass fiber composites. Hence, there is a necessity to explore these aspects. So the objective of this study is to disperse the HNT in epoxy then manufacture the Epoxy/Glass fiber/hnt (EP/GF/HNT) nanocomposite laminates by hand layup method and to investigate the effectiveness of different weight proportions of HNT reinforcement on the mechanical and chemical resistance performances
686 J SCI IND RES VOL 74 DECEMBER 2015 of the composite. These polymer matrix nano composites are expected to be used in lightweight and high strength structural applications. Experimental details Materials Due to several advantages over other thermo set polymers, epoxy LY 556 resin is selected as the matrix material for this research work and corresponding hardener is HY 951 both were supplied by Vantigo. The resin hardener ratio is 100:10 by weight as recommended by the supplier. Plain woven type E-glass fabrics are used as major reinforcement which was supplied by Binani, Goa. The halloysite nano tube (HNT) was procured from Natural nano, Inc. NewYork. Dispersion of HNT For the preparation of nanocomposites, one of the challenging tasks is dispersion. A certain amount of HNT was agitated in acetone for 30 min with the help of high intensity probe type ultrasonicator to de-agglomerate the HNTs. Epoxy LY556 grade resin was preheated to lower the viscosity and to enable better wetting of the particles. Pre-calculated amount of pristine HNTs and epoxy resin was mixed together by mechanical stirrer for one hour and the temperature of the resin was maintained at 70 O C then the mixture was sonicated for one hour by using the ultrasonicator. The sonication process was carried out in an ice/water bath to maintain the temperature throughout the process. To reduce the chances of voids, the HNT dispersed resin is kept under vacuum for 60 min. Once bubbles were trapped, proportionate amount of hardener HY951 was added and manually mixed for 5 min. Fabrication of Composite Laminates Composite laminates were prepared by hand layup technique. The stacking procedure consists of placing resin system (epoxy+hardner+hnt) impregnated fabrics one above another. To ensure the uniform thickness of the sample, a spacer of size 3mm was used. The mould plates were sprayed with release agent. The whole assembly was kept in a hydraulic press at 10MPa pressure and a temperature of 100 o C was applied for 2 hours. At the end of the process, the complete setup was cooled slowly to room temperature and allowed to cure for a day in order to minimize the thermal residual stress. The obtained laminate thickness was approximately 3mm. The fiber volume fraction of this composite laminate was approximately 36%. The unfilled epoxy/glass-fiber composite was also fabricated in the same manner except that there were no HNT fillers. The HNT contents varied as 0,1,2,4,6,8 and 10 wt% based on the weight of the matrix, to study the effect of HNT weight fraction on performance of composite. Material Characterisation Tensile properties were tested by universal testing machine (M/s Kalpak, Pune) according to the procedure described in standard ASTM D3039-76.Flexural tests under three-point bend configuration were performed according to the ASTMD790 standard to evaluate flexural modulus and strength of each of the laminates.to study chemical resistance of EP/GF/HNT nanocomposites, the test method ASTM543-95 was employed. The X-ray diffraction (XRD) was performed with a diffractomer (RIKAGU- Japan). The XRD measurements were made directly from HNT powder and the nanocomposites. The fractured surfaces of EP/GF/HNT nanocomposites were investigated using Scanning electron microscope (SEM; JEOL JSM -6390) The fractured surface of the samples was sputter-coated with a thin gold layer in vacuum chamber for conductivity before examination. Results and Discussion The data related to the mechanical properties of EP/GF/HNT composite systems have been presented and discussed in the following sections. Tensile Properties It is evident from Table 1 that the tensile properties are rapidly increasing upto 4wt% of HNT content and reached the utmost values of 361.004MPa and 9.217GPa respectively (Which are 33.71% and 31.01% higher than unfilled EP/GF composite), then decreases as HNT content increased upto 10wt%. However, it is interesting to note that in all the cases HNT Content (Wt%) Table 1 Tensile and Flexural properties of EP/GF/HNT nanocomposites Tensile Properties Strength (MPa) Modulus (MPa) Flexural Properties Strength Modulus (MPa) (GPa) 0 270 7032 310.67 10.82 1 297.74 7356 335.49 11.80 2 310.61 8242 373.01 15.57 4 361.00 9217 485.29 27.13 6 345.49 9088 420.85 22.31 8 300.61 8705 351.26 14.07 10 294.15 8003 309.96 12.31
RAMAMOORTHI & SAMPATH: EXPTAL INVESTIGATIONS OF HALLOYSITE NANOTUBE 687 duo properties of nanocomposites are found to be significantly higher than that of unfilled EP/GF suggesting a better compatibility between HNT and epoxy. The increase in the strength of the composites up to 4wt% of HNT may be due to the well-dispersed nano tube and this will increases the resistance of crack propagation by the bonding effect. The decrease in the tensile strength of the EP\GF\HNT nanocomposites beyond 4 wt% of HNT addition can be attributed to the amendment in morphology from exfoliated to intercalated structure (Which is evidenced by XRD analysis). This inturn leads to increase in viscosity of the resin system that, results in formation of micro bubbles throughout sample preparation. This is also in agreement with the findings of Siriwardena S et al 14. The improvement in tensile modulus of the EP/GF/HNT nanocomposite is credited to the exfoliation and uniform dispersion of HNT as well as the interfacial bonding between the epoxy matrix and the nanotube. Because of this, the flexibility of the matrix is restricted under loading, so the nanocomposites resin becomes stiffer leading to higher modulus. But beyond 4wt%, the dispersion of HNT in epoxy results the agglomeration of nanotube and cross link density is lowered. Consequently, the filler matrix interaction becomes poorer resulting decrease of the tensile strength and modulus. Flexural Properties It can be seen from Table 1that the duo properties are increased upto 4wt% HNT addition then the gradually decrease as HNT content increased further. This enhancement in flexural strength ascertains the compatibility of HNT with epoxy and presence of HNT at the surface of glass fiber, which can uphold the interfacial adhesion between epoxy and glass fiber. Similarly, the enhancement in flexural modulus may be due to the reinforcing-ability and stiffness of the HNT. However, as more HNT (>4wt%) was loaded into the nanocomposites, the flexural properties are seems to be reducing. This can be attributed to incompatibility between epoxy resin and a HNT particle which leads to poor bonding of epoxy with glass fiber also the nano tube agglomeration reduces the effectiveness of the intercalated and exfoliation structure, which may degrade the flexural properties. According to Yasmin A et al 15, the reduction of modulus at higher content of clay can be associated to the presence of un-exfoliated aggregates or clay tactoids. Chemical Resistance Table 2 shows the weight gain (+) and weight loss(-) of experimental results of the unfilled EP/GF composites and EP/GF/HNT nanocomposites as a function of HNT weight fraction when the samples are immersed in acids, alkalis and solvents. From the results it is clearly evident that weight gain is observed when immersed in almost all the chemical regents. This weight gain indicates that the nanocomposites are swollen due to absorbtion of the chemical reagents rather than dissolving 16. This chemical resistance study clearly indicates that the EP/GF/HNT nanocomposites can be used for handling chemicals in various engineering fields. Morphological Studies X-Ray Diffraction Studies (XRD) The XRD analysis results of HNT and EP/GF/HNT nanocomposites with various weight proportions of HNT are shown in Figure 1. For the HNT, an obvious characteristic peak at 2 = 12.004 O (consequent to the d-spacing of 7.37Å) is detected. XRD of 6wt% - 10wt% EP/GF/HNT nanocomposites shows less uniform dispersion than that of 1wt% to 4wt% HNT dispersed nanocomposites as indicated by the distinct peaks shown in Figure 1. Thus, it is concluded that intercalation occurred in 6wt% to 10wt% HNT dispersed nanocomposites, where as exfoliation occurred in 1wt% to 4wt% HNT dispersed nanocomposites. It is interpreted that at higher HNT loading (>4wt %) the resin molecules could only Table 2 Chemical Resistance Properties of EP/GF/HNT nanocomposites Name of Chemical EP/GF/HNT nanocomposites (HNT wt%) 0 1 2 4 6 8 10 HCl(10%) +1.47 +0.65 +0.58 +0.57 +0.62 +0.46 +0.77 CH 3 COOH(5%) +2.20 +1.09 +2.66 +1.11 +2.04 +2.40 +2.69 HNO 3 (40%) +1.59 +0.93 +0.92 +0.80 +2.02 +2.52 +3.08 NaOH(10%) +0.83 +1.15 +0.82 +0.26 +0.72 +0.96 +0.48 Na 2 CO 3 (20%) +0.16-0.62-0.54 +0.23 +0.42 +0.65 +0.70 Benzene +0.904 +8.340 +8.282 +6.060 +18.177 +19.120 +19.870 H 2 O +1.763 +1.062 +0.596 +2.022 +0.898 +1.027 +1.125
688 J SCI IND RES VOL 74 DECEMBER 2015 Fig. 1 - XRD patterns of a)pure HNT b)1wt% c) 2wt% d)4wt% e)6wt% f)8wt% g) 10wt% HNT dispersed nanocomposites, scanned from 2 O to 15 O in 2-theta scan. Fig. 2 - SEM micrographs of (a) 4 wt% and (b) 10wt% HNT filled epoxy/glass specimens infiltrate in between the nanotubes causing intercalation, and could not delaminate the platelets. Lakshmi M.S et al 17 states that, if in the XRD pattern of epoxy filled with organically modified caly particles did not show any interlayer spacing characteristics then it indicates that the clay has moved from intercalated to exfoliated region. Similar results were reported by Woo R.S.C et al 18. According to Liu T et al 19, it is possible deduce that an increase in d-spacing leads to decrease in attraction forces between clay platelets and intercalation of the epoxy resin and curing agent monomers into the galleries of nanoclay. SEM Studies Scanning electron micrographs (SEM) provides good evidence of the binding between the resin and the fiber. Figure 2a & 2b, shows the damage surface morphology along the cross-section of fractured specimens of EP/GF/HNT nanocomposites with 4wt% and 10wt% HNT content. Fiber breaking is the dominant failure mode in all the composite specimens. In the specimens with 4wt%, a strong interlocking of the HNT-filled resin and the glass fiber could be observed which is shown in Figure 2a. The specimens with 10wt% HNT shows greater degree of fiber pull-out as presented in Figure 2b. This may be due to the presence of agglomerated HNT in the resin system (the XRD plot also suggested that there is change in the morphology after 4wt% addition of HNT as explained in the earlier section). Greater levels of nanoparticle loading may increase the viscosity of the resin and result in reduced wetting out of the laminate 20. Also higher fractions of HNT results in micro voids which act as stress concentration points; they facilitate shear yielding in the system and therefore, reduce the mechanical properties. Energy dispersive X-ray (EDX) analysis was performed on the nanocomposite specimen in order to determine the elements presented, where five elements has been observed, i.e. O, Al, Si, Fe and Ti, which are the elements of HNT so it can be understood that the spot is the agglomerated HNT. Conclusion The present work deals with fabrication of EP/GF/HNT nano composites and characterisation by mechanical property (Tensile, & Flexural) testing s. Incorporation of HNT as a reinforcement in epoxy/glass fiber composites improves the mechanical properties of the composites by a significant level. The maximum improvement in properties are obtained at 4wt% HNT addition, this is due to the uniform reinforcing effect of HNT. The adhesion between epoxy and glass fiber was highly enhanced in the presence of 4wt% HNT, as evidenced by morphological analysis. The chemical resistance property is also enhanced by the incorporation of HNT. References 1 Hussain M, Nakahira A & Niihara K, Mechanical property improvement of carbon fiber reinforced epoxy composites by Al 2 O 3 filler dispersion, Mater Lett, 26 (1996) 185-191. 2 Chowdhury F H, Hosur M V & Jeelani S, Studies on the flexural and thermomechanical properties of woven carbon/nanoclay-epoxy laminates, Mater Sci Eng A, 421 (2006) 298-306. 3 Suresha B, Chandramohan G, Sadananda Rao P R, Sampathkumaran P & Seetharamu S, Influence of SiC Filler on Mechanical and Tribological Behavior of Glass Fabric Reinforced Epoxy Composite Systems, J Reinf Plast Compos, 26 (2007) 565-578.
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