Study on Polycarbonate Multi Walled Carbon Nanotubes Composite Produced by Melt Processing

8/10/2019 Study on Polycarbonate Multi Walled Carbon Nanotubes Composite Produced by Melt Processing

1/5

Materials Science and Engineering A 457 (2007) 287291

Study on polycarbonate/multi-walled carbon nanotubes compositeproduced by melt processing

Li Chen a,, Xiu-Jiang Pang b, Zuo-Long Yu c,

a Key Lab of Rubber-Plastics, Qingdao University of Science & Technology (QUST), Ministry of Education, Qingdao 266042, ChinabDepartment of Chemistry & Molecular Engineering, QUST, Qingdao 266042, China

c Chengdu Institute of Organic Chemistry, Chinese Academy of Sciences, Chengdu 610041, China

Received 9 October 2006; received in revised form 6 December 2006; accepted 26 January 2007

Abstract

Multi-walled carbon nanotubes (MWCNTs) were filled into polycarbonate (PC) by large scale extruder, and some studies were carried out on

as-produced composite. The results showed PC composite containing 1 wt.% of MWCNTs had a tensile strength 4.5% higher than neat PC, and

the elastic modulus of PC/MWCNTs composite increased obviously with MWCNTs loadings. The electrical resistivity measurements indicated a

percolation of MWCNTs near 5wt.% (3.4 vol.%) for the composite. Either the decrease in the fluidity of the composite melts with the increase of

carbon nanotubes (CNTs) loadings or the unexpected shortening of CNTs in extrusion was supposed to have weakened the effects of CNTs as a

reinforcing agent or a conductive filler.

2007 Elsevier B.V. All rights reserved.

Keywords: Carbon nanotubes; Polymer-matrix composites (PMCs); Electrical properties; Mechanical properties; Electron microscopy

1. Introduction

Carbon nanotubes (CNTs) have diverse electrical proper-

ties [1,2], and have modulus and strength in the range of

2001000 GPa and 200900 MPa, respectively[3,4].So, CNTs

has been regarded as a good filler for producing new functional

polymer-based composite. Since the discovery of carbon nan-

otubes (CNTs), polymer-based CNTs composite have attracted

considerable attention in the research and industrial communi-

ties, due to their good electrical conductivity and high strength

at relatively low CNTs content[510].

A key issue in producing polymer/CNTscomposite is how to

achieve a homogeneous dispersion of CNTs in target polymer

base. Currently, three methods are commonly used to introduce

CNTs into polymers, i.e. solution processing[11],in situpoly-

merization of CNTspolymer monomer mixture[12],and melt

mixing of CNTs with polymers [13].In context with indus-

trial applications of polymerCNTs systems, melt mixing is

the preferred method of composite preparation. The tendency

Corresponding author. Tel.: +86 532 8402 2950; fax: +86 532 8402 3977. Corresponding author.

E-mail address:[email protected](L. Chen).

of nanotubes to form aggregates may be minimized by appro-

priate application of shearing force during melt mixing andstudies using melt processed thermoplastic polymer are increas-

ing gradually. For example, Haggenmuller et al.[11]applied a

method combining solvent casting and melt processing together

toproducefilmsof poly(methyl emthacrylate) (PMMA)contain-

ing single walled carbon nanotubes (SWCNTs). And the films

obtained by this melt processing technique had a more uniform

nanotube distribution than the cast film and led to much better

mechanical properties. Fergusonet al. [14] reported on kilogram

quantities of polycarbonate (PC)-based nanotube formulations

produced in a Buss Kneader. The results showed a better dis-

persion of the fibrils in as produced composite. Potschke et al.

[15]examined the rheological properties of MWCNTs filled PC

nanocomposite formed by melt extrusion.

Here we produced PC based composite incorporating MWC-

NTs by traditional large scale polymer manufacturing machines

like screw extruder. The electrical, mechanical, melt flowing

properties and microstructures of as-produced composite and

length change of CNTs before and after processing were exam-

ined. In the paper, the emphasis is put on the interrelationship

between properties and microstructures based on melt flowing

rate, and the influenceof the length change ofCNTs in melt mix-

ing on the properties of composite. Although the properties of

0921-5093/$ see front matter 2007 Elsevier B.V. All rights reserved.

doi:10.1016/j.msea.2007.01.107
mailto:[email protected]://localhost/var/www/apps/conversion/tmp/scratch_1/dx.doi.org/10.1016/j.msea.2007.01.107http://localhost/var/www/apps/conversion/tmp/scratch_1/dx.doi.org/10.1016/j.msea.2007.01.107mailto:[email protected]


2/5


3/5

L. Chen et al. / Materials Science and Engineering A 457 (2007) 287291 289

Table 1

The tensile properties of PC composite with different contents of MWCNTs

Specimen Content of CNTs (wt.%) Tensile strength (MPa) Elastic modulus (MPa) Elongation at break (%)

a 0 2350 60.84 105.00

b 1 2495 63.60 39.750

c 3 2641 54.83 4.087

d 5 2798 43.32 1.9620

e 8 4183 25.55 1.013

to obey the following equation:

Ecomposite = EPCVPC +EMWCNTVMWCNT (1)

whereEPCandEMWCNTare the elastic moduli of the two com-

ponents,VPCandVMWCNTare their volume fractions. In other

words, the elastic modulus of PC composite increased with the

content of MWCNTs. This might result from the restrictions of

the stronger interfacial adhesion to the movement of PC chains.

For example, the elastics modulus of the 8 wt.% composite was

78% higher than that of neat PC. The tensile strength of PCcomposite with 1 wt.% MWCNTs was 4.5% higher than that of

pure PC, but when the content of MWCNTs exceeded 3wt.%,

the tensile strengths of PC composite became lower and lower.

The elongation at break of PC/MWCNTs composite decreased

with the increase of CNTs content. The decreases in either ten-

sile strength or elongation at break of the PC composite might

be due to that the dispersion of MWCNTs in PC matrix became

less and less uniform when the content of CNTs became more

and more.

3.2.2. Electrical resistivity

In case of conductive fillers, electrical measurements are

suitable to detect the percolation composition unequivocally.Fig. 2shows the logarithm of volume resistivity (V) for the

PC/MWCNTs composite as a function of the MWCNTs con-

centration. In our studies the percolation was roughly estimated

atabout 5 wt.% (3.4 vol.%) MWCNTs in PC composite from the

curve inFig. 2.Near this value the volume resistivity changed

greatly. The great decrease in the volume resistivity of the

PC/MWCNTs should, presumably, result from the formation

of the conductive 3D CNTs network, and the composite with

CNTs contents higher than 8 wt.% (5.5 vol.%) can be regarded

Fig. 2. Influence of CNTs contents on PC composites volume resistivities.

as electrically conductive. The percolation threshold and vol-

ume resistivity were not advantageous compared to the results

reported for PCMWNT composite produced by melt mixing

in a small scale twin-screw extruder using a higher molecular

weight PC[15].This may be due to the relatively uneven dis-

persion of CNTs in the PC/MWCNTs composite resulting from

both the melt mixing process and the features of the MWCNTs

used in this study. Besides that, the small scale extruder used

in this literature was kind of different in mixing efficiency from

the larger scale extruder we used. What is more, the electrical

conductivity and the percolation threshold of composite varied

with host polymer [6]. It can be expected that the introduction of

some processing additives, the optimization of the mixing con-

ditions, the proper surface modification of CNTs might lower

the electrical resistivity and the percolation threshold value.

3.2.3. MFR of PCMWCNTs composite

You can also find the answer to the above phenomena from

the results of MFR inFig. 3.With the content of CNTs increas-

ing from 1 wt.% to 8 wt.%, the MFR of the PC composite

decreased from 59.1 g/10min to 0.5g/10min. Generally speak-

ing, the higher the MFR values of composite were, the less the

fluidity of the melts in the courseof processing. Thus, comparedwith the PC composite with a lower CNTs content, the PC com-

posite with a higher CNTs content were supposed to have less

uniform dispersion of CNTs, lower tensile strengths and higher

volume resistivities.

3.3. Dispersion of MWCNTs in composite

In order to make out the dispersion state of MWCNTs in

the PC matrix, SEM characterization was performed on the

Fig. 3. MFR of PC composite pellets with different contents of MWCNTs.


4/5

290 L. Chen et al. / Materials Science and Engineering A 457 (2007) 287291

Fig.4. SEMimagesof PC/MWCNTs composite: (a)PC/MWCNTs masterbatch

with 15 wt.% MWCNTs, (b) PC/MWCNTs pellets with 1wt.% MWCNTs, and

(c) PC/MWCNTs pellets with 5wt.% MWCNTs.

PC/MWCNTs composite pellets. As could be observed that

MWCNTs in Fig. 4a showed an uneven distribution in the

PC/MWCNTs masterbatch pellet. After diluting with PC, the

PC composite with 1wt.% MWCNTs (Fig. 4b) showed an more

evendistribution than that with 5 wt.% MWCNTs(Fig.4c).Indi-

vidual CNTs (white dot) inFig. 4bcould be distinguished from

each other and the fracture surface was rather rough, while in

Fig. 4csome CNTs agglomerated and the fracture surface was

smooth, which was in good agreement with the above results of

tensile tests.

Fig. 5. TEM images of shortened MWCNTs in melt extrusion.

3.4. Length change of MWCNTs in melt mixing

Fig. 5shows the TEM images of MWCNTs washed from

their PC composite pellets containing 5 wt.% MWCNTs. It

was found unexpectedly that the most of the MWCNTs were

much shorter than those inFig. 1and the shortest MWCNTs

inFig. 5were only about 400 nm long. The image of shorterCNTs appeared straighter due to the release of bending stress

coming from the entanglements of the pristine long CNTs. It

can be assumed that the MWCNTs were seriously shortened

by the violent rubbing forces and strong shearing forces

existing in producing PC/MWCNTs composite pellets via

melt extruding. Although the shortening of CNTs may exist

in other melt mixing processes as well, it would become more

serious especially for a melt mixing process without adding

any additives. The composites with more CNTs loadings were

supposed to result in more shorter CNTs after melt processing

[19]. This phenomenon could be used to explain the poor

strength and the higher volume resistivity of the PC/MWCNTs

composite we produced. In other words, the considerablereduction in CNTs length during extruding broke the large

aspect ratios of MWCNTs and weakened the effects of CNTs

as either a reinforcing agent or a conductive filler.

4. Conclusion

Generally speaking, the PC/MWCNTs composite could be

produced through traditional large scale plastics processing

machines. The composite containing 1 wt.% of MWCNTs

showedsome improvement in tensile strength.With the increase

of content of MWCNTs in composite, there were significant

increases in elastic modulus and obvious decreases in eithertensile strength or elongation at break. In the meantime, electri-

cal resistivity measurements indicated a percolation of MWNT

near 5 wt.% (3.4vol.%) for the composite. Besides that, the

decrease in the fluidity of the composite melts with the increase

of CNTs loadings became an obstacle to form a uniform

microstructure through the composite and the inhomogeneous

microstructure in return lowered the mechanical strengths and

electrical conductivities of the composite.

Especially, MWCNTs in PC composite pellets were found to

beshorteneddue to thestrong rubbing forcesand shearing forces

involved in melt extrusion. It was supposed that the shortening

of CNTs further weakened the effects of CNTs as a reinforc-


5/5

L. Chen et al. / Materials Science and Engineering A 457 (2007) 287291 291

ing agent or a conductive filler. It is also an important issue to

protect CNTs from being cut short in producing polymer/CNTs

composite on a large scale. The optimization of the melt condi-

tions like screw speed and mixing time and so on could make the

commercialization of polymer/CNTs composite with excellent

performances more promising.

Acknowledgement

The support from the Doctoral Fund of Qingdao University

of Science and Technology is gratefully acknowledged.

References

[1] J.W.G. Woldoer, L.C. Venema, A.G. Rinzler, R.E. Smalley, C. Dekker,

Nature 391 (6662) (1998) 5962.

[2] T.W. Odom, J.L. Huang, P. Kim, C. Lieber, Nature 391 (6662) (1998)

6264.

[3] D.A. Walters, L.M. Ericson, M.J. Casavant, J. Lui, D.T. Colbert, K.A.

Smith, R.E. Smalley, Appl. Phys. Lett. 74 (25) (1999) 38033805.

[4] F. Li, H.N. Cheng, S. Bai, G. Su, M.S. Dresselhaus, Appl. Phys. Lett. 77(20) (2000) 31613163.

[5] M.S.P. Shaffer, A.H. Windle, Adv. Mater. 11 (11) (1999) 937941.

[6] R. Andrews, D. Jacques, M. Minot, T. Rantell, Macromol. Mater. Eng. 287

(6) (2002) 395403.

[7] C.A. Cooper, D. Ravich, D. Lips, J. Mayer, H.D. Wagner, Compos. Sci.

Technol. 62 (7/8) (2002) 11051112.

[8] R. Haggenmueller, H.H. Gommans, A.G. Rinzler, J.E. Fischer, K.I. Winey,

Chem. Phys. Lett. 330 (3/4) (2000) 219225.

[9] Z. Jin, K.P. Pramoda, G. Xu,S.H. Goh, Chem. Phys. Lett. 337 (13) (2001)

4347.

[10] J.Sandler, M.S.P. Shaffer, T. Prasse, W. Bauhofer, K. Schulte,A.H. Windle,

Polymer 40 (21) (1999) 59675971.

[11] R. Haggenmuller, H.H. Gonmas, A.G. Rinzler, J.E. Fischer, K.I. Winey,Chem. Phys. Lett. 330 (3/4) (2000) 219225.

[12] Z.J. Jia, Z.Y. Wang, C.L. Xu, J. Liang, B.Q. Wei, D.H. Wu, S.W. Zhu,

Mater. Sci. Eng. A 271 (1/2) (1999) 395400.

[13] J.X. Jin, K.P. Pramoda, G.Q. Xu, S.H. Goh, Mater. Res. Bull. 37 (2) (2002)

271278.

[14] D.W. Ferguson, E.W.S. Bryant, H.C. Fowler, ESD thermoplastic prod-

uct offers advantages for demanding electronic applications, ANTEC98

(1998) 12191222.

[15] P. Potschke, T.D. Fornes, D.R. Paul, Polymer 43 (11) (2002) 3247

3255.

[16] M.S.P. Shaffer, X. Fan, A.H. Windle, Carbon 36 (11) (1998) 1603

1612.

[17] Z.M. Li, On in-situ fibrillation of GEP/PO blends and their morphology

and properties, Sichuan University, PhD thesis, 2003.

[18] L. Chen, M.Z. Qu, G.M. Zhou, B.L. Zhang, Z.L. Yu, Mater. Lett. 58 (29)(2004) 37373740.

[19] L. Chen, X.J. Pang, Q.T. Zhang, Z.L. Yu, Mater. Lett. 60 (2) (2006)

241244.

Study on Polycarbonate Multi Walled Carbon Nanotubes Composite Produced by Melt Processing

Documents

Transcript of Study on Polycarbonate Multi Walled Carbon Nanotubes Composite Produced by Melt Processing