rheological and dynamic-mechanical behavior of carbon ...macromolecular nanotechnology rheological...

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European Polymer Journal 43 (2007) 2836–2847

www.elsevier.com/locate/europolj

POLYMERJOURNAL

Macromolecular Nanotechnology

Rheological and dynamic-mechanical behaviorof carbon nanotube/vinyl ester–polyester suspensions

and their nanocomposites

A.T. Seyhan a, F.H. Gojny b, M. Tanoğlu a,*, K. Schulte b

a Izmir Institute of Technology (IZTECH), Mechanical Engineering Department, 35430 Izmir, Turkeyb Polymer Composites, Technical University Hamburg-Harburg (TUHH), Denickestrasse 15, D-21073 Hamburg, Germany

Received 10 December 2006; received in revised form 16 March 2007; accepted 10 April 2007Available online 1 May 2007

Abstract

Rheological properties of vinyl ester–polyester resin suspensions containing various amounts (0.05, 0.1 and 0.3 wt.%) ofmulti walled carbon nanotubes (MWCNT) with and without amine functional groups (–NH2) were investigated by utili-zation of oscillatory rheometer with parallel plate geometry. Dispersion of corresponding carbon nanotubes within theresin blend was accomplished employing high shear mixing technique (3-roll milling). Based on the dynamic viscoelasticmeasurements, it was observed that at 0.3 wt.% of CNT loadings, storage modulus (G 0) values of suspensions containingMWCNTs and MWCNT–NH2 exhibited frequency-independent pseudo solid like behavior especially at lower frequencies.Moreover, the loss modulus (G00) values of the resin suspensions with respect to frequency were observed to increase withan increase in contents of CNTs within the resin blend. In addition, steady shear viscosity measurements implied that ateach given loading rate, the resin suspensions demonstrated shear thinning behavior regardless of amine functional groups,while the neat resin blend was almost the Newtonian fluid. Furthermore, dynamic mechanical behavior of the nanocom-posites achieved by polymerizing the resin blend suspensions with MWCNTs and MWCNT–NH2 was investigatedthrough dynamic mechanical thermal analyzer (DMTA). It was revealed that storage modulus (E 0) and the loss modulus(E00) values of the resulting nanocomposites increased with regard to carbon nanotubes incorporated into the resin blend.In addition, at each given loading rate, nanocomposites containing MWCNT–NH2 possessed larger loss and storage mod-ulus values as well as higher glass transition temperatures (Tg) as compared to those with MWCNTs. These findings wereattributed to evidences for contribution of amine functional groups to chemical interactions at the interface between CNTsand the resin blend matrix. Transmission electron microscopy (TEM) studies performed on the cured resin samplesapproved that the dispersion state of carbon nanotubes with and without amine functional groups within the matrix resinblend was adequate. This implies that 3-roll milling process described herein is very appropriate technique for blending ofcarbon nanotubes with a liquid thermoset resin to manufacture nanocomposites with enhanced final properties.� 2007 Elsevier Ltd. All rights reserved.

Keywords: Carbon nanotubes; Thermosets; Rheology; Nanocomposites; Thermal properties; TEM

0014-3057/$ - see front matter � 2007 Elsevier Ltd. All rights reserved.doi:10.1016/j.eurpolymj.2007.04.022

* Corresponding author. Tel.: +90 232 750 7806/7890.E-mail address: [email protected] (M. Tanoğlu).

mailto:[email protected]

A.T. Seyhan et al. / European Polymer Journal 43 (2007) 2836–2847 2837

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1. Introduction

Addition of nano-scale particles into polymershas been the recent study of interest in materials sci-ence to develop functional nanocomposites offeringenhanced properties as compared to conventionalpolymer based composites that contains micro-scaleparticulates such as carbon black (CB) or glassmicro spheres [1–3]. Due to their high aspect ratioas well as excellent mechanical, thermal and electri-cal properties, CNTs have been recently consideredas an ideal nano-filler to fabricate various types ofpolymer based nanocomposites [1–4]. However,the poor dispersion states of CNTs within the sur-rounding resin matrix due to their huge surface areaand inert surfaces leads to some limitations for han-dling and processing [1–5]. Therefore, achievementof homogeneous dispersion of CNTs within poly-mers is the key for the realization of the desiredenhancement in the final properties of nanocompos-ites. The degree of dispersion is commonly regardedas functions of the size of the dispersed particles,wettability by disperse medium, and nature of theattractive forces between the corresponding constit-uents [7]. From that point of view, some physicaland chemical surface treatments have been appliedfor CNTs to improve their dispersion state andcompatibility with the surrounding matrix resin[2–4]. Direct mixing and sonication have been themost common techniques to disperse CNTs withinthermoset polymer resins such as epoxy, polyesteror vinyl ester [2,3]. However, these methods werefound to be ineffective to prevent the agglomeratesof CNTs [1–7]. Shear intensive 3-roll milling processhas been recently applied for the same purpose.Gojny et al. [4] revealed that double walled carbonnanotubes (DWCNTs) exhibited adequate disper-sion within the epoxy resins through 3-roll millingtechnique, based upon transmission electronmicroscopy (TEM) investigations. In the samestudy, they also showed that blending of DWCNTswith very low content (0.1 wt.%) of epoxy resin via3-roll milling process improved the mechanicalproperties such as Young’s modulus and strain tofailure ratio of the corresponding epoxy resins.

In addition to microscopic techniques such asTEM, rheological examination of polymer suspen-sions containing CNTs has been also recently per-formed to investigate the dispersion state of CNTsin the corresponding resin media [7–9]. It wasrevealed that the Brownian motion of CNT particleswith huge aspect ratio results in more considerable

viscoelastic rheological behavior as compared tothose of micrometer size short fiber or particles suchas carbon black [7,8]. However, the number ofworks reported in the literature on the rheologicalbehavior of CNT/polymer systems is quite limited[6–11]. The rheological behavior of concentratedaqueous nanotube dispersions was studied by Kin-loch et al. [7]. They found that the dispersion stateof MWCNTs is highly sensitive to the applied strainin the linear viscoelastic region and the storage andloss modulus were independent of frequency. Mitch-ell et al. [10] investigated the linear viscoelasticproperties of polystyrene (PS) nanocomposites con-taining SWCNTs with and without surface func-tional groups. They found that the nanotubes withfunctional groups have better dispersion in PS thanthose without any functional group. The authorsalso revealed that nanocomposites with functional-ized nanotubes gave higher storage modulus andcomplex viscosity values at low frequency level.Kim et al. [8] studied the rheological behavior ofepoxy resin suspensions containing amine, acidand plasma treated carbon nanotubes. It was foundthat the surface modified CNT/epoxy suspensionsexhibited a very strong shear thinning behaviorand higher shear viscosity than those with untreatedCNTs due to the enhanced interfacial bondingbetween CNTs and the corresponding epoxy resin.Song and Youn [9] also performed a similar studyand claimed that poorly dispersed CNTs withinepoxy resin leads to higher storage, loss modulusand complex viscosity in the resulting resin suspen-sions compared to homogenously dispersed CNTs.

Measuring the temperature dependent materialproperties is also critical for determination ofappropriate processing conditions to predict thebehavior of polymeric components during their ser-vice life [2–12]. The dispersion state of carbon nano-tubes influences the dynamic mechanical propertiesof the resulting nanocomposites. Fidelus et al.[12] investigated the dynamic mechanical propertiesof the epoxy based nanocomposites containingMWCNTs and SWCNTs. They found an 8%increase of storage modulus in the nanocompositeswith SWCNTs relative to the neat epoxy, whilethose with MWCNTs showed almost no substantialchange in the elastic modulus values. They alsorevealed that glass transition temperature of thenanocomposites containing SWCNTs or MWCNTsincreases slightly with respect to nanotube contents.

In this study, the rheological behavior of vinylester/polyester based suspensions containing

2838 A.T. Seyhan et al. / European Polymer Journal 43 (2007) 2836–2847

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MWCNTs and MWCNT–NH2 was determinedmeasuring dynamic viscoelastic and steady shearproperties of the suspensions via parallel plate oscil-latory rheometer. Furthermore, the correspondingCNT/polymer suspensions were cross-linked usingperoxide (MEKP) initiator. Dynamic mechanicalbehavior of the resulting nanocomposites was inves-tigated by dynamic mechanical thermal analyzer(DMTA) to relate the influence of dispersion stateof CNTs within the blend with final mechanicaland thermal properties of the corresponding nano-composites. Transmission electron microscopy(TEM) was employed to investigate the dispersionstate of CNTs within nanocomposites. The effectof the amine functional groups on the surfaces ofcarbon nanotubes upon their dispersion state andchemical interactions at the interface between CNTsand the resin blend were discussed in details consid-ering the liquid and solid state of each involved resinblend, respectively.

2. Experimental

2.1. Materials

Thin multiwalled carbon nanotubes (MWCNTs)and amino-functionalized multiwalled carbon nano-tubes (MWCNT–NH2) were obtained from Nano-cyl (Namur Belgium) and used as nanofillerswithin the corresponding resin blend. CNTs havean average diameter of 15 nm with a length ofapproximately 50 lm. Styrene-free polyester (Poliya420) and vinyl ester resin (Polives 701, a bisphenolA epoxy based vinyl ester resin with 35 wt.% of sty-rene) were obtained from Poliya Polyester, Turkey.Styrene emission agent BKY 740, purchased fromAlton Chemie, Germany, was employed to preventthe styrene evaporation from the resin blend duringthe polymerization reaction. The formulized resinblend was composed of 25 wt.% of Poliya 420 and75 wt.% of Polives 701. BKY 740 was furtherintroduced to the prepared suspension at a ratioof 1 wt.%. To polymerize each corresponding resinblend suspension, Cobalt naphtanate (CoNAP)and methyl ethyl kethone peroxide (MEKP) wereintroduced to the system as accelerator and initia-tor, respectively.

2.2. Three (3)-roll milling process

Various amounts of MWCNTs and MWCNT–NH2 (0.05, 0.1 and 0.3 wt.%) were first dispersed

in the styrene free (Poliya 420) polyester resin byshear intensive blending via 3-roll milling technique.The collected CNT/polyester resin mixture was sub-sequently blended with vinyl ester resin at a weightratio of (1/3) by hand mixing for about 10 min fol-lowed by mechanical stirring for about 15 min.After the addition of the styrene emission agent(BKY 740, 1 wt.%) into the prepared resin mixture,the CoNAP and MEKP were introduced into thesystem at a ratio of 0.2 and 1 wt.%, respectively.The resin suspensions were allowed to cure at roomtemperature followed by post curing at 75 �C and120 �C for 2 h, respectively. Prior to the additionof CoNAP and MEKP into the mixture, liquid sam-ples from each type of the resin suspensions weretaken for the rheological characterization. Pleasenote that a special resin blend was used to manufac-ture nanocomposites because of the fact that someserious problems with commercial unsaturatedpolyester resin. During 3-roll milling processing,instant styrene evaporation encountered due to heatevolved on the rolls caused increase of the viscosityof resin. Therefore, to overcome these difficulties,the CNTs were first dispersed in specially synthe-sized high viscous styrene-free polyester resin withthe application of high shear forces between gapsof the rolls to break up the agglomerates of theCNTs.

2.3. Rheological measurements

A oscillatory rheometer (TA Instruments) withparallel plate geometry (500 micrometer gap, and50 mm plate diameter) was used to analyze the vinylester/polyester resin blend suspensions with differ-ent amounts of carbon nanotubes with and withoutamine functional groups. Tests were performed inboth dynamic and steady modes at room tempera-ture in order to avoid extreme styrene evaporationduring the measurements. All measurements weretaken in linear viscoelastic region (LVR) in whichthe storage modulus (G 0) and loss modulus (G00)were independent of strain amplitude. Dynamic fre-quency sweeps (DFS) were then conducted in theLVR to investigate the structure of the suspensions.In the DFS, the strain amplitude was remained con-stant 35% through whole frequency range. Pleasenote that prior to main experiments, the corre-sponding value of strain amplitude was proved tobe in the LVR conducting Dynamic Strain Sweeps(DSS) at a constant frequency. During the DFS,the frequency varied stepwise from 0.1 to 80 rad/s.


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Storage modulus (G 0) and loss modulus (G00) valueswere then measured as a function of frequency. Fur-thermore, steady shear sweeps (SSS) were employedto investigate the flow properties of the suspensionsby considering the viscosity as a function of increas-ing shear rates.

2.4. Dynamic mechanical characterization of the

nanocomposites

Dynamic mechanical properties of the nanocom-posites prepared after curing of each type of theresin suspension were investigated by dynamicmechanical thermal analyzer, (DMTA, GABOEPLOXOR 500 N). For the measurements, rectan-gular specimens of 50 mm in length, 5 mm in widthand 2 mm in thickness were sectioned from largersamples. The tests were performed in tensile modeat a frequency of 10 Hz with a static strain of0.6% and dynamic strain of 0.1%, in a temperaturerange between �50 and 200 �C with a heating rateof 3 �C/min. The storage modulus (E 0), loss modu-lus (E00) and the loss tangent (tan d) were determinedas a function of temperature.

2.5. Transmission electron microscopy

The transmission electron microscopy (TEM)was conducted to investigate the dispersion stateof CNTs with and without amine functional groups

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Fig. 1. The frequency dependence of the storage modulus (G 0) for

within the resulting nanocomposites. The TEMimages were taken using a Philips EM 400 at120 kV. Ultra thin films of each type of composites(50 nm) were obtained by ultra microtome cutting.

3. Results and discussion

3.1. Rheological behavior of the suspensions

The storage modulus (G 0) of the resin suspen-sions with different concentrations of MWCNTand MWCNT–NH2 is shown in Figs. 1 and 2,respectively. Consequently, storage modulus valueswere observed to increase with an increase in theoscillatory frequency. Moreover, as the concentra-tions of the CNTs were increased in the correspond-ing resin blend, higher storage modulus values wereobtained. At 0.3 wt.% CNT contents, the flowregime of the resin suspensions was significantlyaltered at low frequencies and a pseudo-solid likebehavior was more visible. We referred this aspseudo-solid like behavior since in true-solid likebehavior the storage modulus (G 0) is fully indepen-dent of frequency [11]. In addition, suspensions with0.1 and 0.3 wt.% of MWCNTs exhibited slightlyhigher storage modulus values especially at low fre-quencies as compared to those with MWCNT–NH2.It was also reported that the CNTs with very smallsizes are very likely to produce strong particle–poly-mer interactions even at very low filling rates

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0.3 wt.% MWCNT

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the CNT/resin suspensions with various MWCNT contents.

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Fig. 2. The frequency dependence of the storage modulus (G 0) for the CNT/resin suspensions with various MWCNT–NH2 contents.


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because of the huge interfacial area between the par-ticles and polymers [8–10]. So, the high aspect ratioand huge surface area of CNTs raise the storagemodulus of the resin suspensions. Figs. 3 and 4show the loss modulus values of polymer suspen-sions containing MWCNTs and MWCNT–NH2,respectively. It was observed that the loss modulusvalues as a function of angular frequency increases

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Fig. 3. The frequency dependence of the loss modulus (G00) for t

with the incorporation of carbon nanotubes. Inaddition, at 0.3 wt.% loading rate, resin suspensioncontaining untreated CNTs exhibits viscous behav-ior (G00 > G 0), whereas those with amino functional-ized CNTs shows viscoelasticity (G00 � G 0). Thisverifies that amine functional groups over CNT sur-faces alter the flow characteristic of resin suspen-sions as well.

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he CNT/resin suspensions with various MWCNT contents.

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Fig. 4. The frequency dependence of the loss modulus (G00) for the CNT/resin suspensions with various MWCNT–NH2 contents.


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Figs. 5 and 6 give shear viscosity as a function ofshear rate for the neat resin blend and resin suspen-sions containing MWCNTs and MWCNT–NH2,respectively. In principle, shear viscosity of a purepolymer is divided into two distinct regions includ-ing the Newtonian and shear thinning regions[9–11]. At low shear rates, the Newtonian regionindependent of shear rate is observed followed by

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shear thinning region through which shear viscositylinearly declines with shear rate. As seen in the fig-ures, shear thinning behavior was observed for eachresin suspensions with nanotubes such that the vis-cosity is reduced with an increase in shear rates.Moreover, the neat resin blend showed almost theNewtonian fluid behavior. In other words, the New-tonian region disappeared even if very low content

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lend and CNT/resin suspensions with MWCNTs.

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Fig. 6. Shear rate dependency of viscosity of resin blend and CNT/resin suspensions with MWCNT–NH2.


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of CNTs (0.05 wt.%) is added into the resin blend.This implies that strong particle–particle interactionof CNTs is one major factor that leads to anincrease in shear viscosity of the corresponding sus-pensions. On the other hand, at 0.1 wt.% loadingrate, the initial shear viscosity of the resin suspen-sion with amino-functionalized nanotubes wereslightly lower than those of the suspensions withnon-functionalized nanotubes. Moreover, resin sus-pensions containing 0.3 wt.% of MWCNTs andMWCNT–NH2 exhibited similar initial viscosityvalues. So, based on the experimental findings, itwas observed that amine functional groups do notsignificantly contribute to enhancement of disper-sion state of CNTs within the corresponding resinblends. In fact, it is not easy to claim a single andprecise comment on rheological behavior of poly-meric suspensions because it is extremely dependon dispersing state of fillers inside, particle–particleinteractions, and interaction between particles anddisperse medium (polymer). In the present case,since CNTs have high aspect ratio, surface areaand amine functional groups over their surfaces,both particle–polymer resin blend and particle–par-ticle interactions became more crucial, as elucidatedin details during analysis of rheological data above.Please note that the amino-functionalized nano-tubes used in our experiments were processed inammonia solution via ball milling process, duringwhich CNTs are broken in length and their aspect

ratios are partially diminished. According to infor-mation provided by the manufacturer of CNTs(Nanocyl, Belgium), the aspect ratio of multi wallednanotubes with amine functional groups is eventu-ally five times lower than those without any surfacetreatment. From that point of view, the incorpora-tion of amino-functionalized nanotubes (MWCNT–NH2) with their reduced aspect ratio into the resinsystem is expected to result in relatively lower stor-age and loss modulus values in addition to reducedshear viscosity in their corresponding resin suspen-sions as compared to those with MWCNTs.However, in our case, the effect of the surface func-tionalization on the rheological behavior is rela-tively insignificant especially at higher loading rateof CNTs embedded into the resin blend. Thisimplies a conceivable occurrence of chemical inter-actions between CNTs and disperse medium (resinblend) through the amine functional groups overthe CNTs surfaces. So, the effects of interfacialinteractions and particle–particle interactions viadistinct aspect ratios of CNTs upon the shear vis-cosity and dynamic rheological properties of theCNT/resin systems needs further investigations.Therefore, it is interesting to monitor the thermo-mechanical properties of the resulting nanocompos-ites (solid state) prepared for each correspondingresin suspensions containing MWCNTs andMWCNT–NH2 in order to further follow ourapproach. Furthermore, TEM was also conducted


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to characterize the dispersion state of CNTs withand without amine functional group within thecured resin blends.

3.2. Thermo-mechanical properties of the resulting

nanocomposites

Figs. 7 and 8 give storage modulus (E 0) and lossfactor (tan d) values as a function of temperatureobtained from dynamic mechanical measurementsfor the nanocomposites containing MWCNT andMWCNT–NH2, respectively. The addition of non-functionalized and amino-functionalized carbonnanotubes into the polymer system has some con-siderable effects on the storage modulus in boththe glassy and the rubbery states, depending onthe nanotube contents within the resin blend. Thisis due to the stiffening effect of CNTs and interfacialinteractions along a huge interfacial area betweenthe CNTs and the polymer matrix. Consequently,CNTs reduced the mobility of the surrounding poly-mer matrix to some extent leading to an increase inthe modulus values. This effect is more pronouncedin the glass transition region. As mentioned above,amino-functionalized nanotubes have shorter length(lower aspect ratios) as compared to that withoutsurface treatment as a result of the functionalizationprocess (ball milling process). So, one can expect rel-atively lower elastic modulus values from the nano-composites containing MWCNT–NH2 as compared

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Fig. 7. Storage modulus and loss factor of nanocomposites

to those with MWCNTs. However, we obtainedopposing results in the present case. As an example,the storage modulus values at 20 �C for the nano-composites containing 0.3 wt.% of MWCNT–NH2and MWCNTs were found to be 3170 and2930 MPa, respectively, which are also higher thanthat of the neat resin blend (2430 MPa). Theseresults revealed that relatively enhanced dispersionstate of the MWCNT–NH2 within the matrix com-pensates the lower aspect ratio of these tubes andprovides higher modulus values to their resultingnanocomposites.

In Figs. 9 and 10, the loss modulus (E00) values ofthe nanocomposites containing MWCNTs andMWCNT–NH2 were given as a function of temper-ature, respectively. It was found that the loss mod-ulus values at the peak points gets higher, as thenanotube contents increases. In addition, nanocom-posites containing amino-functionalized nanotubesresults in somewhat higher peak values as comparedto those with non-functionalized nanotubes. Inbrief, the loss modulus indicates the energy con-verted into heat and can thus be used as a measure-ment of viscous component or unrecoverableoscillation energy dissipated per cycle. From thatpoint of view, we can further conclude that the sat-isfactorily dispersed nanotubes with and withouttreatment would assist in dissipating energy undervisco-elastic deformation of the surrounding resinblend matrix. Moreover, higher loss modulus values

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Fig. 8. Storage modulus and loss factor of nanocomposites containing amino-functionalized nanotubes (MWCNT–NH2).

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Fig. 9. Loss modulus values of nanocomposites containing non-functionalized nanotubes (MWCNT).


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of the nanocomposites with MWCNT–NH2 as com-pared to those with MWCNTs showed that aminefunctional groups promotes the involved chemicalinteractions at the interface in some extend, owingto the same reasons as previously explained.

Fig. 11 shows the glass transition temperature(Tg) values of the nanocomposites with MWCNTand MWCNT–NH2 obtained from the slope of

the storage modulus values in the glass transitionzone. As seen in the figure, the addition of nano-tubes within the resin blends increased the corre-sponding Tg values significantly. The mobility ofthe polymer matrix around the nanotubes is reduceddue to the presence of the nanotubes. In fact, inter-facial strong bonds are expected to occur betweenthe polymer matrix and the amino-functionalized

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Fig. 10. Loss modulus values of nanocomposites containing amino-functionalized nanotubes (MWCNT–NH2).

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Fig. 11. Glass transition temperatures of the nanocomposites as a function of nanotube content with and without any functional groups.


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nanotubes, thus a enhanced bonding at the interfacefurther increases the Tg. In addition, the reducedaspect ratio of amino-functionalized nanotubesmay also have some effects on the degree of poly-merization. Gryschuk et al. [13] stated that thelower aspect ratio of MWCNTs (achieved by ballmilling process) would give better results for highlycross-linked thermoset resins such as vinyl-esters.

3.3. Dispersion state of carbon nanotubes within the

nanocomposites

Figs. 12-a and 12-b are the TEM micrographsshowing achieved dispersion state of MWCNTand MWCNT–NH2 at 0.3 wt.% loading withinthe corresponding resin systems, respectively. Func-tionalized nanotubes exhibited relatively good

Fig. 12-a. TEM image showing the dispersion state of MWCNTs (0.3 wt.%) within the vinyl ester/polyester resin matrix. No condensedagglomerates, but individual nanotubes are noticeable.

Fig. 12-b. TEM image showing the dispersion state of amino-functionalized multi walled nanotubes (MWCNT–NH2) (0.3 wt.%) withinthe corresponding vinyl ester/polyester resin matrix. A better dispersion of functionalized nanotubes within the resin is visible.


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dispersion within the matrix resin blend without anysignificant agglomerates. The TEM characteriza-tions also support our findings that amine func-tional groups over CNTs improve their dispersionstate within the resins enhancing their compatibilitywith resin blend matrix.

4. Conclusions

In this study, the rheological behavior of thevinyl ester/polyester resin blend suspensions con-taining different weight percentage of MWCNTs

and MWCNT–NH2 was investigated. CNTs withand without amine groups were dispersed withinthe corresponding resin blend using 3-roll millingmethod. These resin suspensions were then polymer-ized to reveal the effects of amine functional groupsover the CNTs surfaces on the chemical interactionsat the interface. The interactions were monitored byconsidering the rheological behavior (liquid state) incomparison with the properties of their matchingnanocomposites (solid state). In that manner,dynamic mechanical behavior of the resulting nano-composites was also investigated. Linear dynamic


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viscoelastic measurements revealed that storagemodulus (G 0) and loss modulus (G00) values of resinsuspensions as a function of angular frequencyincreased with respect to CNTs regardless of aminefunctional groups. Moreover, as a consequenceof steady shear viscosity measurements, it wasobserved that each resin suspension containingnanotubes exhibited shear thinning behavior, whilethe neat resin blend was almost the Newtonian fluid.On the other hand, the storage (E 0) and loss modu-lus (E00) values of the resulting nanocomposites werefound to increase with an increase in contents ofCNTs. In addition, at 0.3 wt.% loading rate, resinsuspensions showed pseudo solid like behavior atlower frequency. Furthermore, the incorporationof nanotubes into the resin blend shifted the corre-sponding Tg of the nanocomposites to higher valuesas compared to those of neat resin blend due to thereduced mobility of the surrounding resin blendmatrix by CNTs. Furthermore, TEM was con-ducted to highlight the dispersion state of CNTswith and without amine functional groups withinthe cured resin samples. It was found that CNTswere dispersed adequately within the resin blend,which also proved that 3-roll milling techniquewas capable of providing homogenous dispersionof nano-fillers within thermoset resins to manufac-ture nanocomposites.

In brief, we found similar rheological propertiesfrom resin suspensions independent of aminegroups. We also obtained relatively higher storageand loss modulus values as well as higher glass tran-sition temperatures from the nanocomposites con-taining MWCNT–NH2. This is the corroboratingevidence that enhanced dispersion state of amino-functionalized nanotubes within the resin blendmatrix compensates their lower aspect ratio pro-moting the chemical interactions at the interfacebetween CNTs and resin blend matrix.

Acknowledgements

Authors acknowledge the supports of The Scien-tific and Technical Research Council of Turkey

(TÜB_ITAK) and JUL_ICH Research Center of Ger-many for the financial support for Tubitak-Julich 5project.

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Rheological and dynamic-mechanical behavior of carbon nanotube/vinyl ester-polyester suspensions and their nanocompositesIntroductionExperimentalMaterialsThree (3)-roll milling processRheological measurementsDynamic mechanical characterization of the nanocompositesTransmission electron microscopy

Results and discussionRheological behavior of the suspensionsThermo-mechanical properties of the resulting nanocompositesDispersion state of carbon nanotubes within the nanocomposites

ConclusionsAcknowledgementsReferences

rheological and dynamic-mechanical behavior of carbon ...macromolecular nanotechnology rheological...

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