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Copyright copy 2011 American Scientific PublishersAll rights reservedPrinted in the United States of America

Journal ofNanoscience and Nanotechnology

Vol 11 597ndash601 2011

Electrical Conductive CNT-PVAPCNanocomposites with High Tensile Elongation

Eun H Jung1 Seung I Cha2 Yong J Jeong1 and Soon H Hong1lowast1Department of Materials Science and Engineering Korea Advanced Institute of Science and Technology

373-1 Kusung-Dong Yusung-Gu Daejeon 305-701 Korea2Optoelectric Research Group Advanced Materials and Application Research Division

Korea Electrotechnology Research Institute (KERI) 70 Boolmosangil Changwon 641-120 Korea

Electrically conductive CNT reinforced polycarbonate matrix nanocomposites with high strain-to-failure were fabricated by inserting polyvinylalcohol as a surface modifier through a melt blendingprocess The addition of PVA by coating the CNT through a simple ball milling process beforemelt blending with a polycarbonate matrix resulted in an increased percolation limit as comparedto that prepared using uncoated CNTs while the electrical conductivity was maintained at a similarlevel of 2times10minus2 Scm However tensile elongation was considerably improved by the addition ofPVA and remained at 81 even though 5 wt of the CNTs were added for electrical conductivitywhile elongation dropped to 25 when the CNTs were not coated with PVA The addition of PVAinduces homogeneous dispersion of CNTs during the melt blending process and can enhance bothelectrical conductivity and mechanical durability

Keywords PVA Coating MWNT Polycarbonate Nanocomposites

1 INTRODUCTION

Carbon nanotubes (CNTs) are considered to provide pro-mising nanosized reinforcement due to their light weighthigh aspect ratio and excellent mechanical electrical andthermal properties12 They thus open a new area with highdriving force to develop nanocomposites reinforced withCNTs In particular CNTs has given rise to the possibil-ity of producing new polymeric materials capable of highmechanical performance and at the same time electricalconductivity34

Of the many polymers polycarbonate (PC) is one of themost important engineering plastics and is widely used forlaser optical data storage optical fibers membranes andstructural parts substituting metals due to its outstandingproperties including excellent toughness dimensional sta-bility transparency and thermal stability This wide rangeof applications of PC can be enlarged by obtaining electri-cal conductivity The addition of CNTs is one way to givePC electrical conductivity5ndash7

Previous studies on CNTPC nanocomposites gener-ally prepared by solution blending or melt blendingprocess have identified the problem of fracture toughnesseven though electrical conductivity has been obtained8ndash11

Although the addition of CNTs in PC can enhance strength

lowastAuthor to whom correspondence should be addressed

and promote electrical conductivity the strain-to-failureratio is considerably degraded and sometimes the PCbecomes very brittle It is generally accepted that thisdegradation comes from poor dispersion of CNTs withinthe PC matrix and weak interfacial adhesion between theCNTs and PC matrix Some modification of interface anddispersion by using epoxide-modified CNTs8 or a hybridcomposite with P3HT-g-PCL9 cannot improve their frac-ture toughness and can result in severe brittlenessHere we suggest a new melt blending-based process

using PVA as an interfacial modifier to disperse CNTshomogeneously and at the same time provide sound inter-facial strength The PVA at the interface between CNT andPC can provide much enhanced strain-to-failure in a ten-sile loading condition while at the same time having lit-tle affects on electrical conduction through CNT networkswithin the PC matrix In addition the CNTPC nanaocom-posites can be prepared by means of a simple melt blend-ing process suitable for mass production by the additionof a small amount of PVA during the blending step

2 EXPERIMENTAL PROCEDURES

21 Materials

The multi-walled CNTs (MWNTs) used in this study weresynthesized through the chemical vapor deposition method

J Nanosci Nanotechnol 2011 Vol 11 No 1 1533-4880201111597005 doi101166jnn20113215 597

Delivered by Ingenta toKorea Advanced Institute of Science amp Technology (KAIST)

IP 14324811055Thu 25 Oct 2012 113323

RESEARCH

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Electrical Conductive CNT-PVAPC Nanocomposites with High Tensile Elongation Jung et al

by Iljin Nanotech Co Ltd Korea Polyvinylalcohol (AcrosOrganics Mw 88000) and polycarbonate (Cheil Indus-tries) were used as purchased without further treatment

22 Fabrication Process forCNT-PVAPC Nanocomposites

For the homogeneous dispersion of CNTs and the soundinterface between the CNTs and the PC matrix PVA-coated CNTs are used following the melt blend processThe PVA coated CNTs were fabricated according to thefollowing process steps First the CNTs were dispersedin water by ultra-sonication and an aqueous PVA solutionwas added to the dispersed CNT while stirring at 80 CSecond the mixture was ball milled using zirconia ballsfor 24 hours The ball milled solution was then dried in avacuum oven at 100 C for 24 hoursThe dried CNT-PVA mixtures were mixed with PC pow-

der and ball-milled again for 24 hours The ball-milledCNT-PVAPC mixture powder was melt-blended using aBrabender mixer at 55 rpm at 260 C for 15 minutes andhot press at 260 C to 280 C

23 Characterization of CNTPolycarbonateNanocomposites

The microstructure of CNTPC nanocomposites wasobserved by scanning electron microscope (SEM HitachiS-4800) after Pt coating by sputter The mechanical prop-erties of the PCMWNT composites were investigated bytensile testing according to ASTM D638 using a universaltesting machine (Instron 5538) The speed of cross-headmovement for the tensile test was 100 mmmin and theaveraged value from at least 5 specimens was used Elec-trical conductivity measurement was performed using aprobe station (Semicondutor Characterization System 4200SCSF and Summit 11862B Keithley and Cascade) in thevoltage range of minus05 V to +05 V

3 RESULTS AND DISCUSSION

31 Microstructure and Electrical Conductivity

Coating CNTs with PVA contributes considerably to thehomogeneous dispersion of CNTs within the PC matrixin the melt-blending process as shown in Figure 1CNTPC nanocomposites without PVA coating haveseverely agglomerated CNTs in the PC matrix whichinduces a CNT-rich zone and a CNT-free zone Howeverwith the addition of PVA coated CNTs where the weightfraction of PVA and CNT is 110 the CNTs were homoge-neously dispersed within the PC matrix The role of PVAin dispersing CNTs in molten PC is not clear Howeverit could be expected that the coating of a small amountof PVA considerably suppresses the van der Waals forcebetween CNTs during the blending process It should be

(a) (b)

(c) (d)

Fig 1 SEM images of fracture surfaces of CNTPC nanocompositescontaining 2 wt CNT (a) low magnification of CNTPC nanocompos-ites without PVA coating have severely agglomerated CNTs in the PCmatrix (b) High magnification of CNTPC nanocomposites without PVAcoating have severely agglomerated CNTs in the PC matrix (c) Lowmagnification PVA-CNTPC nanocomposite where the weight fractionof PVA and CNT is 110 (d) High magnification of PVA-CNTPCnanocomposite where the weight fraction of PVA and CNT is 110 TheCNTs were homogeneously dispersed in the PC matrix

noted that the CNTs were not chemically treated for sur-face functionalizationIt is expected that coating each CNT with PVA degrades

the electrical conductivity of CNT-PVAPC nanocompos-ites as compared to CNTPC composites without PVAcoating Actually the relationship between electrical con-ductivity and the amount of CNTs added to the CNTPC orCNT-PVAPC nanocomposite shown in Figure 2 indicatesthat the percolation limit meaning the minimum CNT con-tent for electrical conductivity increased as an increasingamount of PVA coated the CNTs However the electricalconductivity of CNT-PVAPC nanocomposites is not much

Fig 2 Variations in electrical conductivity of CNTPC nanocompositeand PVA-CNTPC nanocomposite with varying CNT concentration andvarious weight fractions of PVA and CNTs

598 J Nanosci Nanotechnol 11 597ndash601 2011

Delivered by Ingenta toKorea Advanced Institute of Science amp Technology (KAIST)

IP 14324811055Thu 25 Oct 2012 113323

RESEARCH

ARTIC

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Jung et al Electrical Conductive CNT-PVAPC Nanocomposites with High Tensile Elongation

affected when the amount of CNT added exceeds the per-colation limitThere are several theories on the electrical conductiv-

ity of CNT reinforced polymer composites One of themconcerns the quantum tunneling of electrons between CNTnetworks jumping over the polymer matrix between eachCNT In this theory the distance between the CNTs shouldbe close to allow electrons to jump between them Theinsertion of PVA inhibits this electron movement by insert-ing an additional barrier between the CNTs However thehomogeneous dispersion of CNTs within the PC matrixdecreases the mean free path of the matrix ie the averagethickness of the PC matrix between the CNTs compen-sating for the additional PVA barrier By increasing theCNT content the CNTs are mechanically connected toeach other ultimately resulting in saturated electric con-ductivity It should be noted that the CNTs are not chemi-cally treated except for the PVA coating in the ball millingprocess Therefore CNTs are not severely damaged inmaintaining homogeneous CNT dispersion and saturatedelectrical conductivity obtained by keeping the CNTs incontact with each other shows little differences from thePVA coating

32 Mechanical Properties ofCNT-PVAPC Nanocomposites

The tensile deformation behaviors of CNT-PVAPCnanocomposites and CNTPC nanocomposites have showndramatic differences as illustrated in Figure 3 In thestressndashstrain relationship during the tensile test shown inFigure 3 stress increases and reaches a peak level and thendecreases rapidly to saturated stress with increasing strainAfter reaching saturated value the stress slightly increaseswith increasing strain until fracture The differences in thestressndashstrain curve in Figure 3 according to the addition

Fig 3 Mechanical properties of CNTPC nanocomposites Engineer-ing stressmdashengineering strain curves of CNTPC and PVA-CNTPCnanocomposites where the weight fraction of PVA and CNT is 110with varying CNT concentration 0 wt 1 wt 2 wt 5 wt CNTs

Table I Elongation of CNTPC nanocomposite and PVA-CNTPCnanocomposite

Contents of CNTs (wt) Elongation ()

CNTPC PVA-CNTPC0 179plusmn41 65plusmn20 134plusmn0742 38plusmn5 116plusmn1515 25plusmn2 81plusmn027

of CNT or PVA coated CNT to PC are shown mainly inelongation The elastic modules increase from 489 MPato 555 MPa with the addition of 5 wt of CNTs and to5645 MPa with the addition of 5 wt of PVA coatedCNTs Peaks stress improved 634 MPa to 669 MPa withthe addition of the same amount of CNT and to 70 MPawith the addition of PVA coated CNTs However elon-gation decreased from 179 to 25 with the addition of5 wt of CNTs to PC Just a 1 wt addition of CNTs toPC decreases elongation to 65Coating CNTs with a small amount of PVA dramatically

enhances the elongation of CNT-PVAPC nanocompositesElongation decreases to 81 with the addition of 5 wtof PVA coated CNTs which is a much higher elonga-tion than that of CNTPC nanocomposites with 1 wt ofuncoated CNTs When 1 wt of PVA coated CNTs areadded elongation is maintained 134 as shown in Table IThe enhancement of elongation by coating CNTs with

PVA is more clearly apparent in the relationship betweenpeak stress and elongation shown in Figure 4 In the caseof CNTPC nanocomposites elongation decreases rapidlywith increasing peaks stress and is maintained at high val-ues in the case of CNT-PVAPC nanocompositesThe role of PVA in the enhancement of elongation is

not clear because only a small amount of PVA is added

Fig 4 Relationship between peak stress and elongation of CNTPCand PVA-CNTPC nanocompostie where the weight fraction of PVA andCNT is 110 The range of CNTPC nanocomposite is 25 to 85 andthat of PVA-CNTPC nanocomposite is 81 to 135 with varying CNTcontent

J Nanosci Nanotechnol 11 597ndash601 2011 599

Delivered by Ingenta toKorea Advanced Institute of Science amp Technology (KAIST)

IP 14324811055Thu 25 Oct 2012 113323

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Electrical Conductive CNT-PVAPC Nanocomposites with High Tensile Elongation Jung et al

(a)

(b)

Fig 5 SEM images of the fracture surface of 5 wt PVA-CNTPCnanocomposites where the weight fraction of PVA and CNT is 110(a) Low magnification of fracture surface of 5 wt PVA-CNTPCnanocomposites (b) High magnification of fracture surface of 5 wtPVA-CNTPC nanocomposites

to the nanocomposites However in CNTPVA compositefibers it is expected that a small amount of PVA wouldgreatly improve strength and elongation by linking eachCNT with crystallized PVA which can be changed to longamorphous phase absorbing external mechanical energy8

Therefore it is expected that the interfacial PVA wouldabsorb strain energy during deformation Another possi-bility is that PVA simply makes the CNTs disperse morehomogeneously within the PC matrix In this case thehomogeneously dispersed CNTs prevent stress concentra-tion within the PC matrix which induces fracture dur-ing tensile loading The fractured surface of CNT-PVAPCnanocomposites does show evidence of strong bondingbetween the CNTs and the PC matrix In Figure 5 someCNTs are pulled out from the PC matrix after fracture andprovide rough surfaces as compared to PC without CNTreinforcement Therefore it can be expected that the PVAat the interface also enhances interfacial bonding strength

4 CONCLUSIONS

In this study CNTs were coated with PVA through aball milling process and PVA-CNTPC nanocomposites

were fabricated by a melt blending process The electri-cal morphological and mechanical properties of the PVA-CNTPC nanocomposites were investigated by electricalconductivity SEM and tensile strength measurementsFrom the results of the morphology of the PVA-CNTPC

nanocomposites it was observed that the CNTs were dis-persed homogeneously in the PC matrix The percolationthreshold of the PVA-CNTPC nanocomposite was shownto be in the range of 1 wt to 2 wt of the CNTsThe electrical conductivity of the 5 wt PVA-CNTPC

nanocomposite was about 20times 10minus2 Scm which wasalmost the same as that of the 5 wt CNTPC nanocom-posite This is because the PVA film on the surface of theCNTs inhibits electron movement by imposing an addi-tional barrier between the CNTs However as the CNTcontent increases the CNTs become connected to eachother and finally lead to saturated electric conductivityThe mechanical properties of PVA-CNTPC nanocom-

posites increased with increasing volume fraction ofadding CNTs Youngrsquos modulus of the PVA-CNTPCnanocomposite was increased from 4891 MPa to5643 MPa by increasing the carbon nanotube contentfrom 0 wt to 5 wt Tensile strength of the PVA-CNTPC nanocomposite was increased from 6337 MPato 6699 MPa The elongation of 5 wt PVA-CNTPCnanocomposite showed a very high elongation of 81 Itis suggested that the homogeneous dispersal of the CNTsprevents stress concentration within the PC matrix whichinduces fracture during tensile loading The mophology ofthe fractured surface of the CNT-PVAPC nanocompos-ites does show evidence of strong bonding between theCNTs and the PC matrix Therefore it can be expected thatthe PVA at the interface also enhances interfacial bondingstrengthFrom the above results PVA-CNTPC nanocomposite

can be a good candidate as an advanced electronic materialsuch as ESD and EMI shielding materials due to its highelectrical conductivity strength modulus and elongation

Acknowledgments This research was supported by agrant (KFR-2007-313-D00362) from the Korea ResearchFoundation and also partly supported by Nano RampD pro-gram through the Korea Science and Engineering Foun-dation funded by the Ministry of Science and Technology(Grant 2008-02631)

References and Notes

1 B Q W C L Xu R Z Ma J Liang X K Ma and D H WuCarbon 37 855 (1999)

2 Y Zhang C M Wang and B C Vincent J Nanosci Nanotechnol9 4870 (2009)

3 O U B T Kuzumaki H Ichinose and K Ito Adv Eng Mater2 416 (2000)

600 J Nanosci Nanotechnol 11 597ndash601 2011

Delivered by Ingenta toKorea Advanced Institute of Science amp Technology (KAIST)

IP 14324811055Thu 25 Oct 2012 113323

RESEARCH

ARTIC

LE

Electrical Conductive CNT-PVAPC Nanocomposites with High Tensile Elongation Jung et al

by Iljin Nanotech Co Ltd Korea Polyvinylalcohol (AcrosOrganics Mw 88000) and polycarbonate (Cheil Indus-tries) were used as purchased without further treatment

22 Fabrication Process forCNT-PVAPC Nanocomposites

For the homogeneous dispersion of CNTs and the soundinterface between the CNTs and the PC matrix PVA-coated CNTs are used following the melt blend processThe PVA coated CNTs were fabricated according to thefollowing process steps First the CNTs were dispersedin water by ultra-sonication and an aqueous PVA solutionwas added to the dispersed CNT while stirring at 80 CSecond the mixture was ball milled using zirconia ballsfor 24 hours The ball milled solution was then dried in avacuum oven at 100 C for 24 hoursThe dried CNT-PVA mixtures were mixed with PC pow-

der and ball-milled again for 24 hours The ball-milledCNT-PVAPC mixture powder was melt-blended using aBrabender mixer at 55 rpm at 260 C for 15 minutes andhot press at 260 C to 280 C

23 Characterization of CNTPolycarbonateNanocomposites

The microstructure of CNTPC nanocomposites wasobserved by scanning electron microscope (SEM HitachiS-4800) after Pt coating by sputter The mechanical prop-erties of the PCMWNT composites were investigated bytensile testing according to ASTM D638 using a universaltesting machine (Instron 5538) The speed of cross-headmovement for the tensile test was 100 mmmin and theaveraged value from at least 5 specimens was used Elec-trical conductivity measurement was performed using aprobe station (Semicondutor Characterization System 4200SCSF and Summit 11862B Keithley and Cascade) in thevoltage range of minus05 V to +05 V

3 RESULTS AND DISCUSSION

31 Microstructure and Electrical Conductivity

Coating CNTs with PVA contributes considerably to thehomogeneous dispersion of CNTs within the PC matrixin the melt-blending process as shown in Figure 1CNTPC nanocomposites without PVA coating haveseverely agglomerated CNTs in the PC matrix whichinduces a CNT-rich zone and a CNT-free zone Howeverwith the addition of PVA coated CNTs where the weightfraction of PVA and CNT is 110 the CNTs were homoge-neously dispersed within the PC matrix The role of PVAin dispersing CNTs in molten PC is not clear Howeverit could be expected that the coating of a small amountof PVA considerably suppresses the van der Waals forcebetween CNTs during the blending process It should be

(a) (b)

(c) (d)

Fig 1 SEM images of fracture surfaces of CNTPC nanocompositescontaining 2 wt CNT (a) low magnification of CNTPC nanocompos-ites without PVA coating have severely agglomerated CNTs in the PCmatrix (b) High magnification of CNTPC nanocomposites without PVAcoating have severely agglomerated CNTs in the PC matrix (c) Lowmagnification PVA-CNTPC nanocomposite where the weight fractionof PVA and CNT is 110 (d) High magnification of PVA-CNTPCnanocomposite where the weight fraction of PVA and CNT is 110 TheCNTs were homogeneously dispersed in the PC matrix

noted that the CNTs were not chemically treated for sur-face functionalizationIt is expected that coating each CNT with PVA degrades

the electrical conductivity of CNT-PVAPC nanocompos-ites as compared to CNTPC composites without PVAcoating Actually the relationship between electrical con-ductivity and the amount of CNTs added to the CNTPC orCNT-PVAPC nanocomposite shown in Figure 2 indicatesthat the percolation limit meaning the minimum CNT con-tent for electrical conductivity increased as an increasingamount of PVA coated the CNTs However the electricalconductivity of CNT-PVAPC nanocomposites is not much

Fig 2 Variations in electrical conductivity of CNTPC nanocompositeand PVA-CNTPC nanocomposite with varying CNT concentration andvarious weight fractions of PVA and CNTs

598 J Nanosci Nanotechnol 11 597ndash601 2011

Delivered by Ingenta toKorea Advanced Institute of Science amp Technology (KAIST)

IP 14324811055Thu 25 Oct 2012 113323

RESEARCH

ARTIC

LE

Jung et al Electrical Conductive CNT-PVAPC Nanocomposites with High Tensile Elongation

affected when the amount of CNT added exceeds the per-colation limitThere are several theories on the electrical conductiv-

ity of CNT reinforced polymer composites One of themconcerns the quantum tunneling of electrons between CNTnetworks jumping over the polymer matrix between eachCNT In this theory the distance between the CNTs shouldbe close to allow electrons to jump between them Theinsertion of PVA inhibits this electron movement by insert-ing an additional barrier between the CNTs However thehomogeneous dispersion of CNTs within the PC matrixdecreases the mean free path of the matrix ie the averagethickness of the PC matrix between the CNTs compen-sating for the additional PVA barrier By increasing theCNT content the CNTs are mechanically connected toeach other ultimately resulting in saturated electric con-ductivity It should be noted that the CNTs are not chemi-cally treated except for the PVA coating in the ball millingprocess Therefore CNTs are not severely damaged inmaintaining homogeneous CNT dispersion and saturatedelectrical conductivity obtained by keeping the CNTs incontact with each other shows little differences from thePVA coating

32 Mechanical Properties ofCNT-PVAPC Nanocomposites

The tensile deformation behaviors of CNT-PVAPCnanocomposites and CNTPC nanocomposites have showndramatic differences as illustrated in Figure 3 In thestressndashstrain relationship during the tensile test shown inFigure 3 stress increases and reaches a peak level and thendecreases rapidly to saturated stress with increasing strainAfter reaching saturated value the stress slightly increaseswith increasing strain until fracture The differences in thestressndashstrain curve in Figure 3 according to the addition

Fig 3 Mechanical properties of CNTPC nanocomposites Engineer-ing stressmdashengineering strain curves of CNTPC and PVA-CNTPCnanocomposites where the weight fraction of PVA and CNT is 110with varying CNT concentration 0 wt 1 wt 2 wt 5 wt CNTs

Table I Elongation of CNTPC nanocomposite and PVA-CNTPCnanocomposite

Contents of CNTs (wt) Elongation ()

CNTPC PVA-CNTPC0 179plusmn41 65plusmn20 134plusmn0742 38plusmn5 116plusmn1515 25plusmn2 81plusmn027

of CNT or PVA coated CNT to PC are shown mainly inelongation The elastic modules increase from 489 MPato 555 MPa with the addition of 5 wt of CNTs and to5645 MPa with the addition of 5 wt of PVA coatedCNTs Peaks stress improved 634 MPa to 669 MPa withthe addition of the same amount of CNT and to 70 MPawith the addition of PVA coated CNTs However elon-gation decreased from 179 to 25 with the addition of5 wt of CNTs to PC Just a 1 wt addition of CNTs toPC decreases elongation to 65Coating CNTs with a small amount of PVA dramatically

enhances the elongation of CNT-PVAPC nanocompositesElongation decreases to 81 with the addition of 5 wtof PVA coated CNTs which is a much higher elonga-tion than that of CNTPC nanocomposites with 1 wt ofuncoated CNTs When 1 wt of PVA coated CNTs areadded elongation is maintained 134 as shown in Table IThe enhancement of elongation by coating CNTs with

PVA is more clearly apparent in the relationship betweenpeak stress and elongation shown in Figure 4 In the caseof CNTPC nanocomposites elongation decreases rapidlywith increasing peaks stress and is maintained at high val-ues in the case of CNT-PVAPC nanocompositesThe role of PVA in the enhancement of elongation is

not clear because only a small amount of PVA is added

Fig 4 Relationship between peak stress and elongation of CNTPCand PVA-CNTPC nanocompostie where the weight fraction of PVA andCNT is 110 The range of CNTPC nanocomposite is 25 to 85 andthat of PVA-CNTPC nanocomposite is 81 to 135 with varying CNTcontent

J Nanosci Nanotechnol 11 597ndash601 2011 599

Delivered by Ingenta toKorea Advanced Institute of Science amp Technology (KAIST)

IP 14324811055Thu 25 Oct 2012 113323

RESEARCH

ARTIC

LE

Electrical Conductive CNT-PVAPC Nanocomposites with High Tensile Elongation Jung et al

(a)

(b)

Fig 5 SEM images of the fracture surface of 5 wt PVA-CNTPCnanocomposites where the weight fraction of PVA and CNT is 110(a) Low magnification of fracture surface of 5 wt PVA-CNTPCnanocomposites (b) High magnification of fracture surface of 5 wtPVA-CNTPC nanocomposites

to the nanocomposites However in CNTPVA compositefibers it is expected that a small amount of PVA wouldgreatly improve strength and elongation by linking eachCNT with crystallized PVA which can be changed to longamorphous phase absorbing external mechanical energy8

Therefore it is expected that the interfacial PVA wouldabsorb strain energy during deformation Another possi-bility is that PVA simply makes the CNTs disperse morehomogeneously within the PC matrix In this case thehomogeneously dispersed CNTs prevent stress concentra-tion within the PC matrix which induces fracture dur-ing tensile loading The fractured surface of CNT-PVAPCnanocomposites does show evidence of strong bondingbetween the CNTs and the PC matrix In Figure 5 someCNTs are pulled out from the PC matrix after fracture andprovide rough surfaces as compared to PC without CNTreinforcement Therefore it can be expected that the PVAat the interface also enhances interfacial bonding strength

4 CONCLUSIONS

In this study CNTs were coated with PVA through aball milling process and PVA-CNTPC nanocomposites

were fabricated by a melt blending process The electri-cal morphological and mechanical properties of the PVA-CNTPC nanocomposites were investigated by electricalconductivity SEM and tensile strength measurementsFrom the results of the morphology of the PVA-CNTPC

nanocomposites it was observed that the CNTs were dis-persed homogeneously in the PC matrix The percolationthreshold of the PVA-CNTPC nanocomposite was shownto be in the range of 1 wt to 2 wt of the CNTsThe electrical conductivity of the 5 wt PVA-CNTPC

nanocomposite was about 20times 10minus2 Scm which wasalmost the same as that of the 5 wt CNTPC nanocom-posite This is because the PVA film on the surface of theCNTs inhibits electron movement by imposing an addi-tional barrier between the CNTs However as the CNTcontent increases the CNTs become connected to eachother and finally lead to saturated electric conductivityThe mechanical properties of PVA-CNTPC nanocom-

posites increased with increasing volume fraction ofadding CNTs Youngrsquos modulus of the PVA-CNTPCnanocomposite was increased from 4891 MPa to5643 MPa by increasing the carbon nanotube contentfrom 0 wt to 5 wt Tensile strength of the PVA-CNTPC nanocomposite was increased from 6337 MPato 6699 MPa The elongation of 5 wt PVA-CNTPCnanocomposite showed a very high elongation of 81 Itis suggested that the homogeneous dispersal of the CNTsprevents stress concentration within the PC matrix whichinduces fracture during tensile loading The mophology ofthe fractured surface of the CNT-PVAPC nanocompos-ites does show evidence of strong bonding between theCNTs and the PC matrix Therefore it can be expected thatthe PVA at the interface also enhances interfacial bondingstrengthFrom the above results PVA-CNTPC nanocomposite

can be a good candidate as an advanced electronic materialsuch as ESD and EMI shielding materials due to its highelectrical conductivity strength modulus and elongation

Acknowledgments This research was supported by agrant (KFR-2007-313-D00362) from the Korea ResearchFoundation and also partly supported by Nano RampD pro-gram through the Korea Science and Engineering Foun-dation funded by the Ministry of Science and Technology(Grant 2008-02631)

References and Notes

1 B Q W C L Xu R Z Ma J Liang X K Ma and D H WuCarbon 37 855 (1999)

2 Y Zhang C M Wang and B C Vincent J Nanosci Nanotechnol9 4870 (2009)

3 O U B T Kuzumaki H Ichinose and K Ito Adv Eng Mater2 416 (2000)

600 J Nanosci Nanotechnol 11 597ndash601 2011

Delivered by Ingenta toKorea Advanced Institute of Science amp Technology (KAIST)

IP 14324811055Thu 25 Oct 2012 113323

RESEARCH

ARTIC

LE

Jung et al Electrical Conductive CNT-PVAPC Nanocomposites with High Tensile Elongation

affected when the amount of CNT added exceeds the per-colation limitThere are several theories on the electrical conductiv-

ity of CNT reinforced polymer composites One of themconcerns the quantum tunneling of electrons between CNTnetworks jumping over the polymer matrix between eachCNT In this theory the distance between the CNTs shouldbe close to allow electrons to jump between them Theinsertion of PVA inhibits this electron movement by insert-ing an additional barrier between the CNTs However thehomogeneous dispersion of CNTs within the PC matrixdecreases the mean free path of the matrix ie the averagethickness of the PC matrix between the CNTs compen-sating for the additional PVA barrier By increasing theCNT content the CNTs are mechanically connected toeach other ultimately resulting in saturated electric con-ductivity It should be noted that the CNTs are not chemi-cally treated except for the PVA coating in the ball millingprocess Therefore CNTs are not severely damaged inmaintaining homogeneous CNT dispersion and saturatedelectrical conductivity obtained by keeping the CNTs incontact with each other shows little differences from thePVA coating

32 Mechanical Properties ofCNT-PVAPC Nanocomposites

The tensile deformation behaviors of CNT-PVAPCnanocomposites and CNTPC nanocomposites have showndramatic differences as illustrated in Figure 3 In thestressndashstrain relationship during the tensile test shown inFigure 3 stress increases and reaches a peak level and thendecreases rapidly to saturated stress with increasing strainAfter reaching saturated value the stress slightly increaseswith increasing strain until fracture The differences in thestressndashstrain curve in Figure 3 according to the addition

Fig 3 Mechanical properties of CNTPC nanocomposites Engineer-ing stressmdashengineering strain curves of CNTPC and PVA-CNTPCnanocomposites where the weight fraction of PVA and CNT is 110with varying CNT concentration 0 wt 1 wt 2 wt 5 wt CNTs

Table I Elongation of CNTPC nanocomposite and PVA-CNTPCnanocomposite

Contents of CNTs (wt) Elongation ()

CNTPC PVA-CNTPC0 179plusmn41 65plusmn20 134plusmn0742 38plusmn5 116plusmn1515 25plusmn2 81plusmn027

of CNT or PVA coated CNT to PC are shown mainly inelongation The elastic modules increase from 489 MPato 555 MPa with the addition of 5 wt of CNTs and to5645 MPa with the addition of 5 wt of PVA coatedCNTs Peaks stress improved 634 MPa to 669 MPa withthe addition of the same amount of CNT and to 70 MPawith the addition of PVA coated CNTs However elon-gation decreased from 179 to 25 with the addition of5 wt of CNTs to PC Just a 1 wt addition of CNTs toPC decreases elongation to 65Coating CNTs with a small amount of PVA dramatically

enhances the elongation of CNT-PVAPC nanocompositesElongation decreases to 81 with the addition of 5 wtof PVA coated CNTs which is a much higher elonga-tion than that of CNTPC nanocomposites with 1 wt ofuncoated CNTs When 1 wt of PVA coated CNTs areadded elongation is maintained 134 as shown in Table IThe enhancement of elongation by coating CNTs with

PVA is more clearly apparent in the relationship betweenpeak stress and elongation shown in Figure 4 In the caseof CNTPC nanocomposites elongation decreases rapidlywith increasing peaks stress and is maintained at high val-ues in the case of CNT-PVAPC nanocompositesThe role of PVA in the enhancement of elongation is

not clear because only a small amount of PVA is added

Fig 4 Relationship between peak stress and elongation of CNTPCand PVA-CNTPC nanocompostie where the weight fraction of PVA andCNT is 110 The range of CNTPC nanocomposite is 25 to 85 andthat of PVA-CNTPC nanocomposite is 81 to 135 with varying CNTcontent

J Nanosci Nanotechnol 11 597ndash601 2011 599

Delivered by Ingenta toKorea Advanced Institute of Science amp Technology (KAIST)

IP 14324811055Thu 25 Oct 2012 113323

RESEARCH

ARTIC

LE

Electrical Conductive CNT-PVAPC Nanocomposites with High Tensile Elongation Jung et al

(a)

(b)

Fig 5 SEM images of the fracture surface of 5 wt PVA-CNTPCnanocomposites where the weight fraction of PVA and CNT is 110(a) Low magnification of fracture surface of 5 wt PVA-CNTPCnanocomposites (b) High magnification of fracture surface of 5 wtPVA-CNTPC nanocomposites

to the nanocomposites However in CNTPVA compositefibers it is expected that a small amount of PVA wouldgreatly improve strength and elongation by linking eachCNT with crystallized PVA which can be changed to longamorphous phase absorbing external mechanical energy8

Therefore it is expected that the interfacial PVA wouldabsorb strain energy during deformation Another possi-bility is that PVA simply makes the CNTs disperse morehomogeneously within the PC matrix In this case thehomogeneously dispersed CNTs prevent stress concentra-tion within the PC matrix which induces fracture dur-ing tensile loading The fractured surface of CNT-PVAPCnanocomposites does show evidence of strong bondingbetween the CNTs and the PC matrix In Figure 5 someCNTs are pulled out from the PC matrix after fracture andprovide rough surfaces as compared to PC without CNTreinforcement Therefore it can be expected that the PVAat the interface also enhances interfacial bonding strength

4 CONCLUSIONS

In this study CNTs were coated with PVA through aball milling process and PVA-CNTPC nanocomposites

were fabricated by a melt blending process The electri-cal morphological and mechanical properties of the PVA-CNTPC nanocomposites were investigated by electricalconductivity SEM and tensile strength measurementsFrom the results of the morphology of the PVA-CNTPC

nanocomposites it was observed that the CNTs were dis-persed homogeneously in the PC matrix The percolationthreshold of the PVA-CNTPC nanocomposite was shownto be in the range of 1 wt to 2 wt of the CNTsThe electrical conductivity of the 5 wt PVA-CNTPC

nanocomposite was about 20times 10minus2 Scm which wasalmost the same as that of the 5 wt CNTPC nanocom-posite This is because the PVA film on the surface of theCNTs inhibits electron movement by imposing an addi-tional barrier between the CNTs However as the CNTcontent increases the CNTs become connected to eachother and finally lead to saturated electric conductivityThe mechanical properties of PVA-CNTPC nanocom-

posites increased with increasing volume fraction ofadding CNTs Youngrsquos modulus of the PVA-CNTPCnanocomposite was increased from 4891 MPa to5643 MPa by increasing the carbon nanotube contentfrom 0 wt to 5 wt Tensile strength of the PVA-CNTPC nanocomposite was increased from 6337 MPato 6699 MPa The elongation of 5 wt PVA-CNTPCnanocomposite showed a very high elongation of 81 Itis suggested that the homogeneous dispersal of the CNTsprevents stress concentration within the PC matrix whichinduces fracture during tensile loading The mophology ofthe fractured surface of the CNT-PVAPC nanocompos-ites does show evidence of strong bonding between theCNTs and the PC matrix Therefore it can be expected thatthe PVA at the interface also enhances interfacial bondingstrengthFrom the above results PVA-CNTPC nanocomposite

can be a good candidate as an advanced electronic materialsuch as ESD and EMI shielding materials due to its highelectrical conductivity strength modulus and elongation

Acknowledgments This research was supported by agrant (KFR-2007-313-D00362) from the Korea ResearchFoundation and also partly supported by Nano RampD pro-gram through the Korea Science and Engineering Foun-dation funded by the Ministry of Science and Technology(Grant 2008-02631)

References and Notes

1 B Q W C L Xu R Z Ma J Liang X K Ma and D H WuCarbon 37 855 (1999)

2 Y Zhang C M Wang and B C Vincent J Nanosci Nanotechnol9 4870 (2009)

3 O U B T Kuzumaki H Ichinose and K Ito Adv Eng Mater2 416 (2000)

600 J Nanosci Nanotechnol 11 597ndash601 2011

Delivered by Ingenta toKorea Advanced Institute of Science amp Technology (KAIST)

IP 14324811055Thu 25 Oct 2012 113323

RESEARCH

ARTIC

LE

Electrical Conductive CNT-PVAPC Nanocomposites with High Tensile Elongation Jung et al

(a)

(b)

Fig 5 SEM images of the fracture surface of 5 wt PVA-CNTPCnanocomposites where the weight fraction of PVA and CNT is 110(a) Low magnification of fracture surface of 5 wt PVA-CNTPCnanocomposites (b) High magnification of fracture surface of 5 wtPVA-CNTPC nanocomposites

to the nanocomposites However in CNTPVA compositefibers it is expected that a small amount of PVA wouldgreatly improve strength and elongation by linking eachCNT with crystallized PVA which can be changed to longamorphous phase absorbing external mechanical energy8

Therefore it is expected that the interfacial PVA wouldabsorb strain energy during deformation Another possi-bility is that PVA simply makes the CNTs disperse morehomogeneously within the PC matrix In this case thehomogeneously dispersed CNTs prevent stress concentra-tion within the PC matrix which induces fracture dur-ing tensile loading The fractured surface of CNT-PVAPCnanocomposites does show evidence of strong bondingbetween the CNTs and the PC matrix In Figure 5 someCNTs are pulled out from the PC matrix after fracture andprovide rough surfaces as compared to PC without CNTreinforcement Therefore it can be expected that the PVAat the interface also enhances interfacial bonding strength

4 CONCLUSIONS

In this study CNTs were coated with PVA through aball milling process and PVA-CNTPC nanocomposites

were fabricated by a melt blending process The electri-cal morphological and mechanical properties of the PVA-CNTPC nanocomposites were investigated by electricalconductivity SEM and tensile strength measurementsFrom the results of the morphology of the PVA-CNTPC

nanocomposites it was observed that the CNTs were dis-persed homogeneously in the PC matrix The percolationthreshold of the PVA-CNTPC nanocomposite was shownto be in the range of 1 wt to 2 wt of the CNTsThe electrical conductivity of the 5 wt PVA-CNTPC

nanocomposite was about 20times 10minus2 Scm which wasalmost the same as that of the 5 wt CNTPC nanocom-posite This is because the PVA film on the surface of theCNTs inhibits electron movement by imposing an addi-tional barrier between the CNTs However as the CNTcontent increases the CNTs become connected to eachother and finally lead to saturated electric conductivityThe mechanical properties of PVA-CNTPC nanocom-

posites increased with increasing volume fraction ofadding CNTs Youngrsquos modulus of the PVA-CNTPCnanocomposite was increased from 4891 MPa to5643 MPa by increasing the carbon nanotube contentfrom 0 wt to 5 wt Tensile strength of the PVA-CNTPC nanocomposite was increased from 6337 MPato 6699 MPa The elongation of 5 wt PVA-CNTPCnanocomposite showed a very high elongation of 81 Itis suggested that the homogeneous dispersal of the CNTsprevents stress concentration within the PC matrix whichinduces fracture during tensile loading The mophology ofthe fractured surface of the CNT-PVAPC nanocompos-ites does show evidence of strong bonding between theCNTs and the PC matrix Therefore it can be expected thatthe PVA at the interface also enhances interfacial bondingstrengthFrom the above results PVA-CNTPC nanocomposite

can be a good candidate as an advanced electronic materialsuch as ESD and EMI shielding materials due to its highelectrical conductivity strength modulus and elongation

Acknowledgments This research was supported by agrant (KFR-2007-313-D00362) from the Korea ResearchFoundation and also partly supported by Nano RampD pro-gram through the Korea Science and Engineering Foun-dation funded by the Ministry of Science and Technology(Grant 2008-02631)

References and Notes

1 B Q W C L Xu R Z Ma J Liang X K Ma and D H WuCarbon 37 855 (1999)

2 Y Zhang C M Wang and B C Vincent J Nanosci Nanotechnol9 4870 (2009)

3 O U B T Kuzumaki H Ichinose and K Ito Adv Eng Mater2 416 (2000)

600 J Nanosci Nanotechnol 11 597ndash601 2011

Delivered by Ingenta toKorea Advanced Institute of Science amp Technology (KAIST)

IP 14324811055Thu 25 Oct 2012 113323

RESEARCH

ARTIC

LE

Jung et al Electrical Conductive CNT-PVAPC Nanocomposites with High Tensile Elongation

4 H S Kim S M Kwon K H Lee J S Yoon and H J JinJ Nanosci Nanotechnol 8 5551 (2008)

5 L Chen X J Pang and Z L Yu Mater Sci Eng A 457 287(2007)

6 B K Satapathy R Weidisch P Poumltschke and A Janke ComposSci Technol 67 867 (2007)

7 P Poumltschke T D Fornes and D R Paul Polymer 43 3247 (2002)

8 A Eitana F T Fisherb R Andrewsc L C Brinsonb and L SSchadler Compos Sci Technol 66 1159 (2006)

9 K H Kim and W H Jo Carbon 47 1126 (2009)10 S Pegel P Potschke G Petzold I Alig S M Dudkin and

D Lellinger Polymer 49 974 (2008)11 R Ramasubramaniama and J Chen Appl Phys Lett 83 2928

(2003)

Received 26 August 2009 Accepted 28 December 2009

J Nanosci Nanotechnol 11 597ndash601 2011 601