Paper Menu >>
Journal Menu >>
World Journ a doi: 10.4236/w j Copyright © 2 0 En h Abstract: Nanocompo s standard cal e epoxy resin man spectro epoxy resin c and Raman i laser power. toughness o f Keywords: 1. Introdu c Iijima discov e Single-walle d b ased structu r graphite rolle d and 1 nm in d (MWCNT) a r of graphite s h several micro pending on t h like structure , chanical pro p dynamics mo d His study su g CNT are not s the Young’s m be 0.45 TP a Yu et al [4] u measure the found the ten s of 11-63 GPa Their exc e length to dia m composite re i b ased compo s a l o f Nano Sc i j nse.2011.1100 1 0 11 SciRes. h ancem e Departmen t Recei v s ites consisti n e ndaring tec h by weight t o scopy tests w c omposite. T i ntensity also Also, nano h f epoxy resin Epoxy Resi n Elasticity c tion e red carbon n a d carbon nanot u r es that can b e d into a cylin d d iameter [2]. M r e similar to S W h eets in the cy l ns in length a h e number of l , CNT are ex p p erties. Lu [3] d el to predict t g gested that t h s ensitive to si z m odulus to be a , and the bul k u sed an atomi c mechanical p s ile strength a n and 270-950 G e llent mechan i m eter ratio m i nforcement. R s ites has focus e i ence and En g 1 Published On l e nt of E C t of Mechanic a v ed February 1 n g of multi w h nique. In t h o produce th e w ere used to T he results sh o affected wit h h ardness incr improved w i n ; Multiwall a notubes (CN u bes (SWCN T e viewed as a d er several m i M ultiwalled c WCNT but w l inder structur e a nd 5-50 nm i l ayers. Due t o p ected to hav e adopted an e t he elastic pro p h e elastic pro p z e and chirali t 1 TPa, the s h k modulus to c force micro s pr operties of n d modulus to G Pa respectiv e i cal propertie m ake CNT ve r R ecent researc e d on polyme r g ineerin g , 201 l ine March 201 1 E lastic M C arbo n Vijay K u a l Engineerin g E-mail: vij a 1 , 2011; revise d w all carbon n a h is study, 3 % e multiwall c a obtain the m o w that the R h the reinfor c eased with i n i th the additi o Carbon Nan o T) in 1991 [1 T ) are fulleren e single sheet o i crons in leng t arbon nanotu b ith many laye r e . MWCNT a r i n diameter d e o their graphit e e excellent m e e mpirical latti c p erties of CN T p e r ties of S W t y and predict e h ear modulus t be 0.74 TP s cope (AFM) t MWCNT a n be in the ran g e ly. s and superi o r y attractive f o h on nanotub e r matrix comp o 1, 1, ** 1 (http://www.s c M odul u n Nano t u mar Srivas t g , Indian I nstit u a yks210@gma d March 4, 20 a notubes (M W % multiwall a rbon nanot u m odulus of e R aman intens c ement of m u n crease of m o n of multiw a o tubes; Nan o ]. e - o f t h b e r s r e e - e - e - c e T . W - e d t o a. t o n d g e o r o r e - o - sites. Q showe d 42% i n in the t p osites electro n able t o reinfor c extrao r interfa c is ver y interfa c p redict using t calcul a b e in t h mole c u tions t o PS co m CNT f r cial fi b fibres i it was efficie n compo s strengt h c irp.org/journal / w u s of E p t ubes t ava u te of Techno l il.com 11; accepted M W CNT) and carbon nano u bes/epoxy c o e lasticity an d ity increased u ltiwall carb o m odulus of el a a ll carbon na n o hardness; R Q ian et al [5] c d that the addi t n crease in the t ensile strengt h . They observ n microscope o bridge the c r c ements in co m r dinary mecha n c ial bonding b e y critical. Wa n c ial shear str e the CNT- p o l t he critical le n a ted the CNT- p h e range of 50 u lar mechanic s o predict the i m posite syste m r om the matri x b re- p olymer s h i n epoxy matr i concluded th a n t interfacial s s ites. In addi t h , it was repo w jnse) p oxy R e l ogy, Varanasi , M arch 10, 201 epoxy resin tube particl e o mposite. N a d Raman int e with the inc r o n nanotubes a sticity, whi c n otubes. a man Spectr o c onducted an e t ion of 1 wt% elastic stiffne s h for polystyr e d CNT pull- o (TEM) that r ack in the P S m posites. In o r n ical properti e e tween CNT a n ger [6] obtai n e ngth to the c l ymer interfa c n gth from 10 0 p olymer inter f -250 MPa. Li o s simulations i nterfacial cha r m . They sim u x and calculat e h ear strength o f i x usually ran g a t a CNT- p oly m s tress transfer t ion to the i m r ted that Vic k e sin wi t , I ndia 1 were produ c e s were disp e a nohardness a e nsity of M W r ease of Ra m and 1% exp o c h indicated o scopy; Mo d e xperimental s t CNT resulte d s s and a 25% ene (PS) – b a s o ut in the tran s suggested C N S matrix and r der to fully u t e s of CNT, t h a nd the polym e n ed the fibre - ritical aspect c ial shear str e 0 to 500 nm. f acial bond st r o and Li [7] p e and elasticity r acteristics o f u lated the pu l e d the CNT-P S f high modul u g es from 50-1 m er can achi e than current a m provement i n k ers hardness o WJNSE t h c ed by a e rsed in a nd Ra- W CNTs/ m an shift o sure of that the d ulus of t udy and d in a 36- increase s ed com- s mission N T were serve as t ilize the h e strong e r ma t rix - polymer ratio, to e ngth by Wagner r ength to e rformed calcula- f a CNT- l l-out of S interfa- u s carbon 00 MPa, e ve more a dvanced n tensile o f epoxy V. K. SRIVASTAVA Copyright © 2011 SciRes. WJNSE increased by 20% with an additional 2 wt% CNT [8-12]. It is evident that CNT can be potentially used to rein- force the polymer and improve the mechanical properties. However, no experiment has come ever demonstrated a CNT based composite with better performance than cur- rent advanced polymer composites. For further advances in this area, researchers pointed out that several critical issues such as improvement in polymer interfacial bond- ing, MWCNT interwall sliding under tension, CNT dis- persion and alignment and polymer matrix shrinkage during the process must be addressed [11]. These issues may contribute to the uncertainty of manufacturing CNT/polymer composites with desired characteristics. Raman spectroscopy has historically played an impor- tant role in the study and characterization of graphite materials, being widely used over the last four decades to characterize pyrolytic graphite, carbon fibres, glassy and carbon nanotubes [12]. For sp2 nanocarbons such as Graphene and carbon nanotubes, Raman spectroscopy can give complete information about crystallite mate- rials. In this article, Raman spectroscopy, nanohardness and scanning electron microscopy were used to see the effect of multiwall carbon nanotubes in the elastic mod- ulus of epoxy resin. Our hypothesis is that the CNT will serve as an excellent reinforcement to toughen the epoxy resin due to its small scale, excellent mechanical proper- ties and good chemical compatibility with the composite adherends. 2. Experimental Details Araldite, LY-556 (55%), hardener, HY-917 (49%) and accelerator, DY-070 (0.28%) were used as epoxy resin. 3% multiwall carbon nanotubes filled epoxy resin (LY- 556) were produced using a lab-scale three-roll-mill (Ex- akt 120 E), which enables the introduction of very high shear forces (up to 200,000 s–1) throughout the suspen- sion. The pre-dispersed suspension was then given bat- chwise onto the roll with dwell times of 2 min. The dis- persive forces on the suspension were acting in the gap (5 µm) between the rolls. After dispersion of the nano- particles in the resin LY-556, the hardener and accelera- tor are usually added in a vacuum dissolver in order to avoid trapped air in the suspension. Then the mixture was placed in a vacuum chamber for 20 min to eliminate the bubbles introduced during the rolling process. Raman spectroscopy is nondestructive and readily available and measurements can be made over a wide range of temperature or pressures. It can provide unique information about vibrational and electron properties of the material. Even though it is not a direct method, it can also be used to determine the structure of the material and allows the identification of materials through the characteristics vibrations of certain structures. Because the Raman intensity of a vibration in a crystal depends on the relative directions of the crystal axis and the elec- tric wave polarization of the incident and scattered light. Therefore, Raman spectroscopy was used to determine the differences in Raman intensity of epoxy resin, MW- CNTs/epoxy resin composite and 1% laser power ex- posed MWCNTs/epoxy resin composite. The indentation method has become a standard way to measure the mechanical properties of thin-film and small- scale structures. A depth-sensing indenter, i.e. nanoin- denter, can measure the indentation displacement (h) and elastic contact stiffness (S) during a programmed inden- tation loading process, where S is defined as: d dc P Sh (1) where P is the indentation load, and ݄ is the elastic component of h. Using the data analysis method pro- posed by Oliver and Pharr [13], the contact depth, ݄, can be estimated by € cP hh S (2) where € is a constant, 0.75. Then, based on the predeter- mined indenter tip geometry, we can calculate the pro- jected contact area (A) from ݄. Finally, the elastic mod- ulus (E) and the hardness (H) of materials can be calcu- lated by 2 r J IS E A (3) P H A (4) Here ܧ is the reduced modulus defined as 2 21 1i ri EEE (5) where E and µ are Young’s modulus and Poisson’s ratio of the indented material respectively; and Ei and µi are the corresponding values of the indenter tip. H is the mean pressure under the indenter. The nanohardness and the elastic modulus of the epoxy resin and MSCNTs/epoxy resin composite were determined using a Nano Indentation tester (CSM in- strument). A triangular pyramid Berkovich indenter was used, its indent shape and side view angles were 65.3 and 77.05 respectively. The poisson’s ratio of the samples were estimated as µ = 0.3, because in the calculations of elastic modulus, an error in the estimation of the Poisson ratio does not produce a significant effect on the result- ing value of the elastic modulus. Three indentations were carried out to depth of 1000 nm where the indentation was kept for 10 s before unloading. The loading and the unloading rate were 10 mN min–1. Finally, scanning electron microscopy was used to identify the effect of MWCNTs in the epoxy resin. V. K. SRIVASTAVA Copyright © 2011 SciRes. WJNSE 3. Results and Discussion In this study MWCNT were dispersed by three mill roll- ing machine in an epoxy resin, with the aim of improving mechanical properties of MWCNTs/epoxy resin compo- site. First of all the effect of the presence of MWCNT in the epoxy resin was investigated by Raman spectroscopy technique. Figure 1 shows the Raman spectrum of epoxy resin, MWCNT/epoxy resin and 1% laser power exposed MWCNT/epoxy resin. These spectral features are clearly distinguishing the variation in Raman intensity. Because, when the bond lengths and angles of graphene are mod- ified by strain, caused by the interaction with a substrate or with other graphene layers or due to external perturba- tion, the hexagonal symmetry of graphene is broken. It was observed that the Raman spectra intensity increases with increasing the shift angle up to 300 cm–1 and gradu- ally decreases with increasing of shift angle after 400 cm–1. These spectral features are similar for epoxy resin, MWCNTs/epoxy resin and 1% exposed laser power MWCNTs/epoxy resin composites. Eight peak signal bands are identified from epoxy resin sample at different Raman shift values; 620, 835, 1140, 1240, 1460, 1600 cm–1. The height of these eight signals is gradually reduced with the addition of MWCNTs and exposure of laser power of epoxy resin, indicating a dilution effect of the MWCNTs when blended with epoxy resin. It is believe that epoxy resin exerts a pressure on the individual tubes, which leads to an increase of the breathing mode fre- quencies. Therefore bands are highly sensitive to micro- structure effects and can be used to probe any modifica- tion to the flat geometric structure of resin. The micro- structure effects induced by multiwall carbon nanotubes or by exposure of laser power. This shows the effect of CNTs and laser power exposure on epoxy resin, because, the interaction between nanotubes and resin polymer is reflected by a peak shift or peak width change. Visible change in the epoxy resin peak locations as a result of the insertion of nanotubes could be detected. The Raman intensity can vary when multiwall nano- tubes interact with elements; this can be used to examine the structure of the interface and obtain information about the nature, localization and force of the interaction. After the nanotubes were dispersed in epoxy resin, Ra- man intensity was observed towards lower intensities, evidence that MWCNTs were no longer in direct contact with one another tubes. Also, Raman intensities were decreased with the exposure of laser power. These show that Raman spectroscopy is a useful and reliable tool for the investigation of nanotubes dispersion in epoxy resin. The influence of scratch load on mechanical response of multiwall carbon nanotubes in epoxy resin was inves- tigated by nanoindentation test. Nanohardness and elastic modulus patterns of the epoxy resin and MWCNT/epoxy resin specimens are reported in Figure 2. The results show that the nanohardness increases with increase of elastic modulus. MWCNTs filled epoxy resin gives higher value than the epoxy resin, because MWCNTs improve the mechanical properties of epoxy resin [5-7]. Based on the experimental observation, one can derived that following expression to obtain modulus of elasticity from nardness, 12 4.9 0.86EH (6) where E and H are the elastic modulus and nanohardness. The micrograph shows the dispersion of MWCNT in an epoxy resin area as can be seen in Figure 3. Only few small aggregates are remaining, which are smeared out and well penetrated by the epoxy resin matrix. MWCNT/ epoxy resin composite containing 3% MWCNT exhibit a significant increase in fracture toughness and strength, as well as an enhancement of stiffness, due to resistance of cracks propagation [8], as can be identified from Figure 4. It is also clear that CNT particles resist the formation of crack path due to increase of toughness of MWCNT filled epoxy resin. The mechanisms of increasing the fracture toughness of polymers due to incorporation of particles have been extensively studied within the last three decades [14]. The application of micro-particles exhibits the highest effect in brittle matrix systems. A clear difference in the distribution pattern and agglome- rate sizes can be seen between MWCNT and epoxy resin and their interface appears to be much more homogene- ous, suggesting a greater dispersion. Figure 5 shows that MWCNT particles strongly bonded with the epoxy resin and it appears like sprouts, because of toughening effects of particle [7]. The epoxy resin is modified by the ad- dition of MWCNT, which participates in minimizing the crack initiation or the propagation by crack block- ing or bridging, as can be identified in Figure 4. The extensive MWCNT bridging seen in micrographs are well in agreement with the prior explained mechanisms, MWCNT-bridging effect enhanced the fracture tough- ness [6]. The most important micro-mechanical mechanism leading to an increase in fracture toughness are due to localized inelastic matrix deformation and void nuclea- tion, particle/fibre debonding and deformations [5]. The characteristics of the matrix polymer are also important for the reinforcing effect of nano-scaled fillers. In gener- al, the plastic zone size of brittle epoxy resin is relatively small. When a resin is filled with nano-particles, a signif- icant amount of particles occur in the plastic zone, while in a composite with micro-particles, only a minor num- ber of them are involved in the plastic zone deformation process. This is clear evidence that the main fracture mechanical mechanism is related to the enormous surface V. K. SRIVASTAVA Copyright © 2011 SciRes. WJNSE Figure 1. Variation of Raman intensity versus Raman shift from (a). epoxy resin, (b). MWCNTs/epoxy resin and (c). 1% laser power exposed MWCNTs/epoxy resin. Figure 2. Variation of nanohardness with elastic modulus of epoxy resin and MWCNTs/epoxy resin composites. area of nano-particles in general. Since, all composites exhibited a partly agglomerated dispersion of the filler, leading to increase in the toughness can be expected to localized inelastic matrix deformation, void nucleation and crack deflection at the agglomerates [7]. Therefore, it is clear from micrographs that resin rich area fractured due to the appearance of shear stress, which increases the adhesive bond strength of ceramic composites. This can be explained by the higher surface area of the double wall carbon nanotubes, which may result in a better load transfer efficiency at the interface region as well as amine functional groups over CNTs which is supposed to promote the dispersion and pronounced covalent bonding to some extent. 4. Concluding Remarks In this article, the effect of multiwall carbon nanotubes in epoxy resin was characterized by the Raman spectrosco- py and nanohardness indentation methods. The elastic 0.2 0.22 0.24 0.26 0.28 0.3 0.32 4.9555.05 5.1 5.15 5.2 5.255.3 5.35 Nanohardness,GPa Elasticmodulus,GPa Epoxy resin MWCNT with epoxy resin V. K. SRIVASTAVA Copyright © 2011 SciRes. WJNSE Figure 3. SEM micrograph showing the dispersion of MWCNT particles in the resin rich area. Figure 4. SEM micrograph showing the enhancement of cracks path with MWCNT particles. Figure 5. SEM micrograph shows the interface bond of MWCNTs with resin. V. K. SRIVASTAVA Copyright © 2011 SciRes. WJNSE modulus and nanohardness can be related as 12 4.9 0.86EH . Also, it was found that 3 wt% MWCNT loading showed good dispersion capability in the epoxy resin, which increases the elastic modulus of neat epoxy resin up to 15%. However, elastic modulus increases with increase of nanohardness, whereas Raman intensity reduces abruptly with the inclusion of MW- CNTs and exposure of 1% laser power. 5. References [1] S. Iijima, “Helical Microtubules of Graphite Carbon,” Nature, Vol. 354, No. 7, 1991, pp. 56-58. doi:10.1038/354056a0 [2] P. M. Ajayan, L. S. Schadler, C. Giannaris and A. Rubio, “Single Walled Carbon Nanotube Polymer Composites: Strength and Weakness,” Advanced Materials, Vol. 12, No. 10, 2000, pp. 750-753. doi:10.1002/(SICI)1521-4095(200005)12:10<750::AID- ADMA750>3.0.CO;2-6 [3] J. P. Lu, “Understanding of Carbon Nanotubes: From Basic to Applications,” Journal of Physics and Chemistry of Solids, Vol. 58, No. 11, 1997, pp. 1649-1655. doi:10.1016/S0022-3697(97)00045-0 [4] M. F. Yu, O. Lourie, M. Dyer, K. Moloni, T. F. Kelly and R. S. Ruoff, “Strength and Breaking Mechanism of Mul- tiwalled Carbon Nanotubes under Tensile Load,” Science, Vol. 287, No. 10, 2000, pp. 637-643. doi:10.1126/science.287.5453.637 [5] D. Qian, E. C. Dickey, R. Andrews and T. Rantell, “Load Transfer and Deformation Mechanisms in Carbon Nano- tubes-Poly-Styrene Composites,” Applied Physics Letters, Vol. 76, No. 20, 2000, pp. 2868-2670. doi:10.1063/1.126500 [6] H. D. Wanger, “Nano Composites: Issues at the Interface,” Materials Today, Vol. 7, No. 11, 2004, pp. 38-42. doi:10.1016/S1369-7021(04)00507-3 [7] K. Liao and S. Li, “Interfacial Characterization of a Car- bon Nanotube-Polystrene Composite System,” Applied Physics Letters, Vol. 79, No. 25, 2001, pp. 4225-4232. doi:10.1063/1.1428116 [8] K. T. Hsiao, J. Alms and S. G. Advani, “Use of Epoxy /Multiwalled Carbon Nanotubes as Adhesives to Join Graphite Fibre Reinforced Polymer Composites,” Nano- technology, Vol. 14, No. 8, 2003, pp. 791-793. doi:10.1088/0957-4484/14/7/316 [9] F. J. Gojny, M. H. G. Wichmann, U. Koupke, B. Fiedler and K. Schulte, “Carbon Nanotube-Reinforced Epoxy- Composites-Enhanced Stiffness and Fracture Toughness at Low Nanotubes Content,” Composite Science and Technology, Vol. 64, No. 15, 2004, pp. 2363-2371. doi:10.1016/j.compscitech.2004.04.002 [10] F. J. Gojny, M. H. G. Wichmann, B. Fiedler and K. Schulte, “Influence of Different Carbon Nanotubes on the Mechanical Properties of Epoxy Matrix Composites-A Comparative Study,” Composite Science and Technology, Vol. 65, No. 15-16, 2005, pp. 2300-2313. doi:10.1016/j.compscitech.2005.04.021 [11] M. H. G. Wichmann, J. Sumfletch, B. Fiedler, F. G. Goj- ny and K. Schulte, “Multiwall Carbon Nanotube/Epoxy Composites Produced by a Masterbatch Process,” Me- chanics of Composite Materials, Vol. 42, No. 5, 2006, pp. 395-405. doi:10.1007/s11029-006-0050-3 [12] J. Zhang and D. Jiang, “Interconnected Multiwalled Car- bon Nanotubes Reinforced Polymer-Matrix Composites,” Composite Science and Technology, Vol. 71, No. 4, 2011, pp. 466-470. doi:10.1016/j.compscitech.2010.12.020 [13] W. C. Oliver and G. M. Pharr, “An Improved Technique for Determining Hardness and Elastic-Modulus Using Load and Displacement Sensing Indentation Experi- ments,” Journal of Materials Research, Vol. 7, No. 9, 1992, pp. 1564-1572. doi:10.1557/JMR.1992.1564 [14] V. K. Srivastava and B. Harris, “Effect of Particles on Interlaminar Crack Growth in CrossPlied Carbon Fibre Epoxy Laminates,” Journal of Materials Science, Vol. 29, No. 2, 1994, 548-553. doi:10.1007/BF01162520 |