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Materials Science and Engineering A 528 (2011) 8517– 8522

Contents lists available at SciVerse ScienceDirect

Materials Science and Engineering A

jo ur n al hom epage: www.elsev ier .com/ locate /msea

hermal and mechanical interfacial properties of epoxy composites based onunctionalized carbon nanotubes

an-Long Jina, Chang-Jie Mab, Soo-Jin Parkc,∗

School of Chemical and Materials Engineering, Jilin Institute of Chemical Technology, Jilin City 132022, People’s Republic of ChinaApplied Chemical Engineering Department, Jilin Vocational College of Industry and Technology, Jilin City 132013, People’s Republic of ChinaDepartment of Chemistry, Inha University, Nam-Gu, Incheon 402-751, South Korea

r t i c l e i n f o

rticle history:eceived 4 April 2011eceived in revised form 23 July 2011ccepted 26 August 2011vailable online 2 September 2011

a b s t r a c t

Carbon nanotubes (CNTs) were treated by a mixture of acid and functionalized subsequently by aminetreatment to improve interfacial interactions and dispersion of CNTs in epoxy matrix. The thermal sta-bilities and mechanical interfacial properties of epoxy/CNT composites were investigated using severaltechniques. The dispersion state of CNTs in the epoxy matrix was observed by scanning electron micro-scope (SEM) and transmission electron microscopy (TEM). As a result, the glass transition temperature

eywords:poxy resinarbon nanotubeshermal stabilitieslass transition temperature

of epoxy/CNT composites increased by about 11 ◦C compared to neat epoxy resins. The mechanical inter-facial property of the composites was significantly increased by the addition of amine treated CNTs. TheSEM and TEM results showed that the separation and uniform dispersion of CNTs in the epoxy matrix.

© 2011 Published by Elsevier B.V.

echanical interfacial properties

. Introduction

Epoxy resins have been widely used for coatings, electronicaterials, adhesives, and matrices for fiber-reinforced compos-

tes due to their outstanding mechanical properties ranging fromxtreme flexibility to high strength and hardness, high adhesiontrength, good heat resistance, and high electrical resistance [1].owever, cured epoxy resins are inherently brittle due to highrosslinking density, thus posing a constraint on many engineer-ng applications. Epoxy resins are commonly modified by liquidlastomers, thermoplastics, and inorganic particles [2–4].

Since Iijima discovered carbon nanotubes (CNTs) in 1991, CNTsave attracted extensive research attention widely due to itsxcellent mechanical, electrical, and thermal properties [5,6]. CNTggregation has been found to dramatically hamper the mechanicalroperties of fabricated CNT composites. Functionalization of CNTsy polymers may be divided into two categories, involving eitheron-covalent or covalent bonding between CNT and polymer [7].

Several researchers have prepared epoxy resin/CNT compositeso obtain outstanding mechanical and physical properties. Chen

t al. fabricated epoxy resin/CNT composites by resin transfer mold-ng [8]. The results indicated that the mechanical and electricalroperties of the composites were dramatically improved with the

∗ Corresponding author. Tel.: +82 42 860 7234; fax: +82 42 861 4151.E-mail address: sjpark@inha.ac.kr (S.-J. Park).

921-5093/$ – see front matter © 2011 Published by Elsevier B.V.oi:10.1016/j.msea.2011.08.054

addition of the CNTs. Kim et al. studied the effects of surface modifi-cation on rheological and mechanical properties of epoxy resin/CNTcomposites [9]. They concluded that the rheological properties ofCNT-containing epoxy resin and mechanical properties of epoxyresin/CNT composites were improved due to the improved disper-sion of CNTs in epoxy matrix and interactions between the CNT andthe epoxy resin.

In this study, CNTs were treated by a mixture of concen-trated sulfuric and nitric acid and functionalized subsequently byamine treatment. The functionalization effect on the thermal andmechanical interfacial properties of diglycidylether of bisphenol-A (DGEBA)/CNT composites was investigated by a differentialscanning calorimeter (DSC), a thermogravimetric analysis (TGA),a dynamic mechanical analysis (DMA), and an universal testingmachine. The morphologies of the DGEBA/CNT composites wereobserved using a scanning electron microscope (SEM) and a trans-mission electron microscopy (TEM).

2. Experimental

2.1. Materials

The epoxy resin used in this study was diglycidylether of

bisphenol-A (DGEBA), supplied by Kukdo Chem. of Korea, whichhad an epoxide equivalent weight of 185–190 g/eq and a den-sity of about 1.16 g/cm3 at 25 ◦C. Multi-walled carbon nanotubesused in this work were purchased from Nano Solution Co. Ltd.

8 nd Engineering A 528 (2011) 8517– 8522

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5% weight loss, Td5) of the P-CNT is 735 ◦C, which indicates thatthe CNT is thermally stable up to 735 ◦C, as shown in Table 2. Incontrast, the weight loss of the A-CNT sample at 735 ◦C is 8.7%,

Table 1Elemental composition of CNTs at different stages.

518 F.-L. Jin et al. / Materials Science a

f Korea, which had a average diameter of 10–25 nm, a length of0–50 �m, and a purity rating of 90%. The composition of remaining0% was metal catalyst granules, amorphous carbon granules, andraphite carbon fragments. 4,4′-Diaminodiphenyl methane (DDM)urchased from Aldrich Chem., was selected as a curing agent.odecylamine was used as an organic amine agent, supplied byldrich Chem.

.2. Acid treatment of CNT (A-CNT)

Pristine CNT (P-CNT) was treated with a 3:1 mixture of concen-rated sulfuric and nitric acid by stirring at 40 ◦C for 4 h. The mixtureas filtered and the remaining solid was washed by repeated rins-

ng with deionized water. Finally, the acid treated CNTs were driedt 100 ◦C for 12 h in a vacuum oven.

.3. Dodecylamine treatment of CNT (D-CNT)

1 g A-CNT was dispersed in ethyl alcohol using an ultrasonic gen-rator. And then 0.2 g dodecylamine was added into the mixture,nd the reaction was performed at 80 ◦C for 24 h. The remainingolid was washed with ethyl alcohol several times to remove unre-cted organic compound. The amine treated CNTs were dried at00 ◦C for 12 h in a vacuum oven.

.4. Sample preparation

The weight content of CNTs was 1 wt%. The desired amounts ofGEBA and CNTs were mixed by a magnetic stirring bar at 80 ◦C

or 1 h and was ultrasonic treated for 30 min. And then DDM wasdded into the mixture. The bubble-free mixture was poured into

preheated mold, which was sprayed with a mold release agent.uring was performed at 110 ◦C for 1 h, at 140 ◦C for 2 h, and at70 ◦C for 1 h in a convection oven.

.5. Characterization and measurements

Elemental composition of CNTs before and after surface modifi-ation was measured using an elemental analyzer (CE EA-1110).

The Raman spectra were obtained with a Bruker model RFS00/S at a wavelength of 600 nm and a power of 500 mV.

The cure behaviors of DGEBA/CNT samples were investigatedsing a differential scanning calorimeter (NETZSCH, DSC 200 F3) at

heating rate of 10 ◦C/min from 30 to 300 ◦C under a nitrogen flowf 30 ml/min.

The thermal stabilities of DGEBA/CNT composites were studiedith a NETZSCH TG 209 F3 analyzer at a heating rate of 10 ◦C/min

rom 30 to 850 ◦C under a nitrogen atmosphere.The dynamic mechanical properties of the composites were

etermined with a dynamic mechanical analyzer (RDS-II, Rhemet-ics Co.) at a frequency of 1 Hz, the temperature range from 35 to50 ◦C, and a heating rate of 5 ◦C/min. The specimen dimensionsere 2 mm × 12 mm × 35 mm.

The critical stress intensity factor (KIC) of the composites washaracterized by single edge notched (SEN) testing in three-pointending flexure. The three-point bending test was conducted on aniversal testing machine (Instron Model 1125) according to theSTM E-399.

The fracture surfaces of the composites after the KIC testsere investigated using a scanning electron microscope (FE-SEM

-4300/HITACHI). Transmission electron microscopy photographsere obtained using a field emission-transmission electron micro-

cope (FE-TEM, JEM2100/JEOL) with an accelerating voltage of00 kV.

Fig. 1. SEM image of pristine carbon nanotube (P-CNT).

3. Results and discussion

3.1. Characterization of CNTs

Fig. 1 presents typical morphology of pristine carbon nanotubes(P-CNTs). As can be seen, aggregation of CNTs is formed due tohigh specific surface area and cotton-like entanglements [10]. Aneffective method to prevent aggregation of nanotubes is function-alization of CNTs. In this study, CNTs were functionalized by aminetreatment, and changes of surface morphology by functionalizationare shown in Fig. 2. The outer shell of dodecylamine functional-ized carbon nanotube (D-CNT) covered with a thin layer of someamorphous materials [11].

The elemental composition of CNTs before and after surfacemodification is summarized in Table 1. The O/C ratio of P-CNT andA-CNT samples is 1.6% and 5.5%, respectively, which confirms theeffectiveness of acid treatment process in generating carboxylicgroups on the CNT surfaces. The oxygen content decreased from5.5% to 3.6% after dodecylamine functionalization due to the cou-pling reaction between the amine and carboxylic groups on the CNTsurfaces. The N content of D-CNT sample is 0.9%, which indicatedthat the attachment of nitrogen-containing groups on CNTs [12].

Raman spectroscopy was employed to probe the structuraldestruction of CNTs. As shown in Fig. 3, the disorder-induced Dband and tangential G band in Raman spectra are appeared at wavenumbers of 1285 cm−1 and 1600 cm−1, respectively. The intensityratio of the D and G bands, ID/IG, is often used as a measure of defectintroduction. Intensity ratio of ID/IG of A-CNTs increased from 1.56to 1.71, which due to covalent bonds are formed between car-bon nanotube walls and functional groups, owing to the formationof sp3 hybridized carbon defect sites [13,14]. After dodecylaminefunctionalization, intensity ratio of ID/IG of CNTs is not significantlyvaried, confirming that the functionalization did not generatedefects on the CNTs.

Fig. 4 shows the TGA thermograms of P-CNT, A-CNT, and D-CNTsamples. The initial decomposing temperature (the temperature of

Element (atomic %) C O N O/C (%)

P-CNT 94.8 1.5 0 1.6A-CNT 92.0 5.1 0 5.5D-CNT 92.5 3.3 0.9 3.6

F.-L. Jin et al. / Materials Science and Engineering A 528 (2011) 8517– 8522 8519

Fig. 2. TEM images of P-CNT (a) and dodecylamine functionalized carbon nanotube(D-CNT) (b).

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Fig. 4. TGA thermograms of CNT samples.

Table 2Thermal stability of CNT samples obtained from TGA thermograms.

Sample Td5 (◦C) Weight loss at 735 ◦C

P-CNT 735.0 5%A-CNT 494.6 8.7D-CNT 353.3 15.2

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Fig. 5. DSC thermograms of DGEBA/CNT samples.

which was come from the decomposition of carboxylic groups andbroken structure during acid treatment. The weight loss of the D-CNT sample at 735 ◦C is 15.2%, which was mainly attributed to thedecomposition of dodecyl groups [11,15].

DGEBA/CNT samples cured with DDM were subjected todynamic DSC evaluation to investigate their curing behaviors. Fig. 5shows the dynamic DSC curves for the samples at a heating rate of10 ◦C/min. The obtained DSC thermogram data, such as maximumpeak temperature (Tp) and enthalpy of cure reaction (�H), are sum-marized in Table 3. As can be seen, the T of epoxy resins increased

p

by the addition of CNTs, which indicated that CNTs retarded thecure reaction of epoxy resins. The retardation effect of the P-CNT on the cure reaction was more remarkable than that of the

Table 3Peak maximum temperature (Tp) and reaction enthalpy (�H) of DGEBA/CNTcomposites.

Composite Tp (◦C) �H (J/g)

DGEBA/DDM 163.2 384.3DGEBA/P-CNT/DDM 167.2 426.9DGEBA/A-CNT/DDM 164.1 367.1DGEBA/D-CNT/DDM 164.0 338.9

8520 F.-L. Jin et al. / Materials Science and Engineering A 528 (2011) 8517– 8522

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Fig. 8. KIC values of DGEBA/CNT composites; A: DGEBA/DDM, B: DGEBA/P-CNT/DDM, C: DGEBA/A-CNT/DDM, D: DGEBA/D-CNT/DDM.

Temperature (ºC)

Fig. 6. TGA thermograms of DGEBA/CNT composites.

-CNT or D-CNT. The �H of the DGEBA/P-CNT sample is higher thanhat of the DGEBA/DDM sample, and the �H of the DGEBA/A-CNTnd DGEBA/D-CNT samples is lower than that of the DGEBA/DDMample. This means that the acid treated CNTs and dodecylamineunctionalized CNTs in the epoxy network structure absorb heatnd act as a heat sink in the systems [16–18].

.2. Thermal and mechanical interfacial properties of DGEBA/CNTomposites

The thermal stabilities of DGEBA/CNT composites were studiedy TGA at a heating rate of 10 ◦C/min under a nitrogen atmosphere,nd the results are presented in Fig. 6. Thermal stability factors,ncluding initial decomposing temperature (the temperature of 5%

eight loss, Td5) and statistic heat-resistant index temperature (Ts),an be determined from TGA thermograms [13,19]. The Ts was cal-ulated from the Td5 and the temperature of 30% weight loss (Td30)alues according to the following equation [20–22]:

s = 0.49[Td5 + 0.6 × (Td30 − Td5)] (1)

The values of Td5, Ts, and char at 800 ◦C for the DGEBA/CNTomposites are summarized in Table 4. As observed, the Td5 ands values of the cured epoxy resins decreased by the addition ofhe P-CNT. However, the thermal stability of the DGEBA/A-CNT andGEBA/D-CNT composites is similar to neat epoxy resins. The chart 800 ◦C increased by the addition of CNTs [23]. These results indi-ated that the acid treated and functionalized CNTs have little effectn the decomposition temperature of epoxy resins.

Dynamic mechanical properties of the DGEBA/CNT compos-tes were measured by DMA over a spectrum of temperature. Thetorage modulus and glass transition temperature (Tg) of the com-osites as a function of temperature are presented in Fig. 7. The Tg

alue can be derived from DMA results through investigating the-relaxation temperatures. The data of storage modulus and Tg areummarized in Table 5.

It can be seen that the Tg value of DGEBA/P-CNT composites slightly higher than that of neat epoxy resins, as shown inable 5. The Tg value of DGEBA/A-CNT and DGEBA/D-CNT compos-tes increased by about 11 ◦C compared to neat epoxy resins. The

able 4hermal stability factors of DGEBA/CNT composites obtained from TGAhermograms.

Composite Td5 (◦C) Ts (◦C) Char at 800 ◦C

DGEBA/DDM 362.1 182.5 14.3DGEBA/P-CNT/DDM 352.0 179.0 15.9DGEBA/A-CNT/DDM 359.6 181.6 15.7DGEBA/D-CNT/DDM 360.2 181.8 16.9

Table 5Glass transition temperature (Tg) and storage modulus of DGEBA/CNT compositesobtained from DMA results.

Composite Tg (◦C) Storage modulus (MPa)

Glassyregiona

Rubberyregionb

DGEBA/DDM 170.4 1513 37.7DGEBA/P-CNT/DDM 173.5 1509 34.4DGEBA/A-CNT/DDM 179.4 1474 43.5DGEBA/D-CNT/DDM 181.6 1433 41.4

a Storage modulus at 35 ◦C.b Storage modulus at Tg + 30 ◦C.

F.-L. Jin et al. / Materials Science and Engineering A 528 (2011) 8517– 8522 8521

Fig. 9. SEM images of the fracture surface in DGEBA/CNT composites; (a) DGEBA/P-CNT/DDM, (b) DGEBA/A-CNT/DDM, (c) DGEBA/D-CNT/DDM.

Fig. 10. TEM photographs of DGEBA/CNT composites; (a) DGEBA/P-CNT/DDM, (b) DGEBA/A-CNT/DDM, (c) DGEBA/D-CNT/DDM.

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522 F.-L. Jin et al. / Materials Science a

torage modulus of the composites in the glassy region is lowerhan that of neat epoxy resins. However, the storage modulus ofpoxy resins in the rubbery region increased by the addition of acidreated and functionalized CNTs. This may be mainly attributedo the reduced mobility of the epoxy matrix around the nan-tubes by the interfacial interactions [24–27]. Similar observationsere reported by Ma and Gojny et al. using silane and amino-

unctionalized CNTs [28,29].The mechanical interfacial properties of the DGEBA/CNT com-

osites were investigated by the critical stress intensity factor (KIC)easurement. For the three-point flexural test, the KIC value was

alculated by following equation [30,31]:

IC = PBW1/2Y (2)

here P is the rupture force (in kN), B the specimen thickness (inm), W is the specimen width (in cm), and Y is the geometricalactor.

Fig. 8 shows the KIC values of the DGEBA/CNT composites. Asan be seen, the KIC value of the DGEBA/CNT composites wasmproved by the addition of CNTs. The neat DGEBA was very brit-le, exhibiting a KIC value of 0.71 MPa m1/2. In contrast, the attainedIC values of the DGEBA/P-CNT, DGEBA/A-CNT, and DGEBA/D-CNTomposites are 17% higher with 0.83 MPa m1/2, 22% higher with.87 MPa m1/2, and 38% higher with 0.98 MPa m1/2, respectively.he KIC value of the DGEBA/D-CNT composite is 18% higher thanhat of the DGEBA/P-CNT composite. These results indicated thathe functionalization of CNTs significantly increased the fractureroperties of the DGEBA/CNT composites, which was attributed tohe improved dispersion of CNTs in epoxy matrix and interfacialnteractions between the functional groups on the CNT surfacesnd the epoxy matrix. Similar results have been reported by Kimnd Chen et al. using octadecylamine and acid treated CNTs [9,32].

Fig. 9 shows SEM photographs of the DGEBA/CNT compositesfter KIC tests. For untreated CNTs, both properly dispersed CNTsnd agglomerates can be observed in the epoxy matrix, as shownn Fig. 8(a). By contrast, the acid treated and functionalized CNTsre dispersed well in the epoxy matrix. In addition, the acid treadNTs are pulled out slightly and the functionalized CNTs are pulledut slightly or broken during KIC tests, as shown in Fig. 8(b and c)9,33].

The dispersion state of CNTs in the epoxy resins was furthernvestigated by TEM. Fig. 10 shows typical TEM micrographs ofhe DGEBA/CNT composites. As observed, when P-CNT was useds a reinforcement agent, the CNTs agglomerated in the epoxyatrix. After acid treatment of CNTs, agglomerates of CNTs were

till remaining, as shown in Fig. 10(b). In the TEM micrograph ofGEBA/D-CNT composite (Fig. 10(c)), the CNTs are separated andispersed uniformly in the epoxy matrix [34–36].

. Conclusions

CNTs were functionalized by acid and amine treatmentsnd the thermal stabilities and mechanical interfacial proper-ies of DGEBA/CNT composites were investigated using several

[

[

ineering A 528 (2011) 8517– 8522

techniques. As a result, the thermal stability of the DGEBA/A-CNTand DGEBA/D-CNT composites was similar to neat epoxy resins.The Tg value of the DGEBA/A-CNT and DGEBA/D-CNT compositesincreased by about 11 ◦C compared to neat epoxy resins. The KICvalue of the DGEBA/D-CNT composite was 38% higher than thatof neat epoxy resins. From the SEM and TEM images of DGEBA/D-CNT composite, separation and uniform dispersion of CNTs in epoxymatrix can be observed. All of the results indicated that the Tg andmechanical property improvements were achieved by the additionof functionalized CNTs.

Acknowledgement

This work was supported by the Carbon Valley DevelopmentProject of Korea.

References

[1] R.S. Bauer, Epoxy Resin Chemistry, Advanced in Chemistry Series, No. 114.American Chemical Society, Washington, DC, 1979, p. 1.

[2] S.K. Lee, B.C. Bai, J.S. Im, S.J. In, Y.S. Lee, J. Ind. Eng. Chem. 16 (2010) 891.[3] K.S. Kim, S.J. Park, Carbon Lett. 11 (2010) 102.[4] E. Serrano, A. Tercjak, G. Kortaberria, J.A. Pomposo, D. Mecerreyes, N.E.

Zafeiropoulos, M. Stamm, I. Mondragon, Macromolecules 39 (2006) 2254.[5] S. Goossens, B. Goderis, G. Groeninckx, Macromolecules 39 (2006) 2953.[6] S. Xue, M. Reinholdt, T.J. Pinnavaia, Polymer 47 (2006) 3344.[7] S. Iijima, Nature 354 (1991) 56.[8] P.M. Ajayan, O. Stephan, C. Colliex, D. Trauth, Science 265 (1994) 1212.[9] Z. Spitalsky, D. Tasis, K. Papagelis, C. Galiotis, Prog. Polym. Sci. 35 (2010) 357.10] Y. Zhou, F. Pervin, L. Lewis, S. Jeelani, Mater. Sci. Eng. A 475 (2008) 157.11] K.S. Kim, K.Y. Rhee, K.H. Lee, J.H. Byun, S.J. Park, J. Ind. Eng. Chem. 16 (2010)

572.12] Q.F. Cheng, J.P. Wang, J.J. Wen, C.H. Liu, K.L. Jiang, Q.Q. Li, S.S. Fan, Carbon 48

(2010) 260.13] W. Zou, Z. Du, Y. Liu, X. Yang, H. Li, C. Zhang, Compos. Sci. Technol. 687 (2008)

3259.14] R.Y. Sato-Berrú, E.V. Basiuk, J.M. Saniger, J. Raman Spectrosc. 37 (2006) 1302.15] J.A. Kim, D.G. Seong, T.J. Kang, J.R. Youn, Carbon 44 (2006) 1898.16] E.V. Basiuk, M. Monroy-Peláez, I. Puente-Lee, V.A. Basiuk, Nano Lett. 4 (2004)

863.17] P.C. Ma, S.Y. Mo, B.Z. Tang, J.K. Kim, Carbon 48 (2010) 1824.18] J. Bae, J. Jang, S.H. Yoon, Macromol. Chem. Phys. 203 (2002) 2196.19] W.S. Choi, A.M. Shanmugharaj, S.H. Ryu, Thermochim. Acta 506 (2010) 77.20] J. Tarrío-Saavedra, J. López-Beceiro, S. Naya, R. Artiaga, Polym. Degrad. Stab. 93

(2008) 2133.21] J.L. Chen, F.L. Jin, S.J. Park, Macromol. Res. 18 (2010) 862.22] R.S. Lehrle, R.J. Williams, Macromolecules 27 (1994) 3782.23] B. Jiang, J. Hao, W. Wang, L. Jiang, X. Cai, Eur. Polym. J. 37 (2001) 463.24] M.R. Grimbley, R.S. Lehrle, Polym. Degrad. Stab. 49 (1995) 223.25] Q.P. Feng, J.P. Yang, S.Y. Fu, Y.W. Mai, Carbon 48 (2010) 2057.26] F.L. Jin, S.J. Park, J. Polym. Sci. Part B: Polym. Phys. 44 (2006) 3348.27] R.J. Varley, W. Tian, Polym. Int. 53 (2004) 69.28] P.C. Ma, J.K. Kim, B.Z. Tang, Compos. Sci. Technol. 67 (2007) 2965.29] F.H. Gojny, K. Schulte, Compos. Sci. Technol. 64 (2004) 2303.30] F.L. Jin, S.J. Park, Polym. Degrad. Stab. 92 (2007) 509.31] F.L. Jin, S.J. Park, Mater. Sci. Eng. A 475 (2008) 190.32] Z.K. Chen, J.P. Yang, Q.Q. Ni, S.Y. Fu, Y.G. Huang, Polymer 50 (2009) 4753.33] J.M. Park, D.S. Kim, S.J. Kim, P.G. Kim, D.J. Yoon, K.L. DeVries, Composites Part B

38 (2007) 847.

35] F.H. Gojny, J. Nastalczyk, Z. Roslaniec, K. Schulte, Chem. Phys. Lett. 370 (2003)820.

36] B. Fiedler, F.H. Gojny, M.H.G. Wichmann, M.C.M. Nolte, K. Schulte, Compos. Sci.Technol. 66 (2006) 3115.