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Carbon 45 (2007) 2621–2627

Reinforcement of styrene–butadiene–styrene tri-block copolymerby multi-walled carbon nanotubes via melt mixing

Lan Lu, Zhen Zhou, Yong Zhang *, Shifeng Wang, Yinxi Zhang

State Key Laboratory of Metal Matrix Composites, School of Chemistry and Chemical Technology,

Shanghai Jiao Tong University, 200240 Shanghai, PR China

Received 17 November 2006; accepted 7 August 2007Available online 28 August 2007

Abstract

Styrene–butadiene–styrene tri-block copolymer (SBS) was reinforced with multi-walled carbon nanotubes (MWCNTs) by the inter-action through melt mixing. The tensile strength of SBS/MWCNT composites increased with increasing MWCNT content. The inter-actions between SBS and MWCNTs were characterized by solubility of MWCNTs in tetrahydrofuran, dynamic mechanical analysis,X-ray photoelectron microscope, ultraviolet spectra and transmission electron microscopy. The results showed that there were interac-tions between MWCNTs and SBS occurred during melt mixing, leading to an improvement of the mechanical properties of SBS/MWCNT composites, as well as the homogeneous dispersion of MWCNTs in SBS. The interactions between MWCNTs and SBS weresupposed to consist of the p–p interaction between MWCNTs and the phenyl groups of SBS, as well as the chemical bonding of poly-butadiene segments with MWCNTs.� 2007 Elsevier Ltd. All rights reserved.

1. Introduction

Since the discovery of carbon nanotubes (CNTs) in 1991by Iijima [1], CNTs have been regarded as the ultimatefibers and under considerable researches [2–4]. Judicialblending of the strength, stiffness, electrical and thermalproperties of the CNTs with the flexibility, resilience andextendibility of thermoplastic will lead to the developmentof a gamut of new materials which are of commercialimportance [5,6].

There are several ways to prepare polymer/CNT com-posites including solution processing, melt mixing, in situ

polymerization, etc. [7–9]. Because solution processingwould employ a large amount of solvent, it is not suitablefor industrial production. Melt mixing is a good alternativeto prepare polymer/CNT composites because of its speedand simplicity [3,10]. However, CNTs tend to aggregatetogether owing to the strong Van der Waals forces between

0008-6223/$ - see front matter � 2007 Elsevier Ltd. All rights reserved.doi:10.1016/j.carbon.2007.08.025

* Corresponding author. Fax: +86 21 54741297.E-mail address: yong_zhang@sjtu.edu.cn (Y. Zhang).

CNTs. Therefore, many researches have been carried outto improve the dispersion of CNTs in polymers as well asto increase the interfacial bonding between CNTs andpolymers [11–13].

Chemical and physical interactions between inorganicfillers and polymers often occur during melt mixing. Thesephenomena have been confirmed by both theoretical andexperimental researches [14–17]. The interactions betweenCNTs and polymers during melt mixing were investigatedby many researchers [18–20]. For instance, Zhang et al.[20] studied the effect of melt mixing on the interactionbetween MWCNTs and polystyrene (PS). They found thatthe melt mixing led to an enhanced interaction betweenMWCNTs and PS which dramatically increased the solu-bility of MWCNTs in some solvents. However, the mecha-nism of the interactions between MWCNTs and polymersduring melt mixing is still unclear and needs to be furtherstudied.

Styrene–butadiene–styrene tri-block copolymer (SBS) asa thermoplastic elastomer has many commercial applica-tions. PS segments are hard domains and polybutadiene

2622 L. Lu et al. / Carbon 45 (2007) 2621–2627

(PB) segments are soft domains in SBS. PS domains asphysical crosslinks disperse in SBS. There are both phenylgroups and carbon–carbon double bonds in the structureof SBS, which may have certain interactions withMWCNTs. These interactions could improve the disper-sion of MWCNTs in SBS matrix as well as increase theirinterfacial adhesion. In this work, the reinforcement effectof MWCNTs on SBS was studied. In addition, the interac-tions between MWCNTs and SBS during melt mixing wereinvestigated and their effects on the improvement ofmechanical properties were discussed.

2. Experimental

2.1. Materials

The MWCNTs were produced using chemical vapor depositionmethod by Tsinghua Nafine Nano-Power Commercialization EngineeringCentre, China. The average diameter of MWCNTs is about 20 nm and thepurity is higher than 95%. SBS (791H, Mn = 5.9 · 104 and the styrene con-tent is 30%) was purchased from Yueyang General Petrochemical Co.,China.

2.2. Sample preparation

SBS/MWCNT composites were prepared at 120 �C on a two roll mill,with the MWCNT content of 0, 1%, 3% and 7% by weight.

SBS/MWCNT composites were prepared by solution processing as fol-lowing procedures. SBS was dissolved in the tetrahydrofuran (THF) withthe ratio of 1:9 by weight to form a solution. MWCNTs were separatelydispersed in THF under ultrasonication to form a mixture. The SBS solu-tion was poured into the mixture of MWCNTs/THF. The mixture wasunder continuous stirring for 4 h. Meanwhile THF was removed fromthe mixture. After all the THF evaporated, resulting SBS/MWCNT com-posites were obtained. The concentrations of MWCNTs in SBS are 3%and 7% by weight.

0 100 200 300 400 500 600 700

0

4

8

12

16

20

Str

ess

(MP

a)

Strain (%)

0 wt% 1 wt% 3 wt% 7 wt%

Fig. 1. Strain–stress curves of SBS/MWCNT composites prepared bymelt mixing.

2.3. Characterization of SBS/MWCNT composites

The tensile test was carried out on an Instron 4465 tensile machine(Instron Co., UK) at a crosshead speed of 500 mm/min. The dumbbellshape samples were 75 mm in length, 1 mm in thickness, and 4 mm inwidth. Field emission scanning electron microscopy (FESEM) (JSM-7401F, JEOL Co., Japan) was used to observe the frozen fracture surfaceof composites.

Dynamic mechanical analysis (DMA) was performed with DMA 242C(Netzsch, Germany) under nitrogen at a heating rate of 5 �C/min from�140 �C to 150 �C and a frequency of 1 Hz.

Optical microscopy (Leica-Dmlp, Leica, Germany) was used to char-acterize the morphology of SBS/MWCNT composites which were dis-solved in THF in macroscopical scale. For the measurement ofultraviolet spectra, after SBS/MWCNT composites were dissolved inTHF, their solution was centrifuged for 15 min at the speed of14,000 rpm. The supernatant liquid was decanted. The precipitate was dis-solved in THF, and the same centrifuge procedures were repeated 10 timesto remove free SBS. The final precipitate was collected (hereinafterreferred as f-MWCNTs). The ultraviolet (UV) spectra of SBS, pristineMWCNTs and f-MWCNTs in THF were recorded on an UV spectropho-tometer (TU-1901, Pgeneral Co., China). Furthermore, X-ray photoelec-tron microscope (XPS) and transmission electron microscopy (TEM)were used to characterize f-MWCNTs. XPS experiments were carriedout on a Perkin–Elmer PHI 5000C ESCA system using AlKa radiation.The anode voltage and current were set at 12 kV and 10 mA. The vacuum

of the specimen chamber was maintained at 5 · 10�7 Pa and the bindingenergy of 285.0 eV for the C1s was taken as reference. TEM images weretaken on a JEM2010 (JEOL Co., Japan).

3. Results and discussion

3.1. Mechanical properties

Fig. 1 shows representative strain–stress curves for pureSBS and SBS/MWCNT composites prepared by melt mix-ing. The addition of MWCNTs can reinforce the compos-ites significantly without sacrificing their deformability. Asseen in Fig. 1, the modulus at 100% elongation and tensilestrength of SBS/MWCNT composites increase withincreasing MWCNT content. The tensile strength of SBS/MWCNT composite containing 7 wt% MWCNTs is17.1 MPa, about 66% higher than that of pure SBS.

However, composites prepared by solution processinghave poorer mechanical properties than that by melt mix-ing, as shown in Fig. 2. The tensile strength of the compos-ite prepared by melt mixing is 4 MPa higher than that ofthe composite prepared by solution processing at a givenMWCNT content of 7 wt%. There are two reasons for thisdifference in tensile strength. One reason is that high shearforce during melt mixing could improve the dispersion ofMWCNTs in SBS. Another reason is that interactionsbetween SBS and MWCNTs might occur during melt mix-ing, so that the stress applied to the composites could beefficiently transferred to the MWCNTs and allowed themto take a disproportionate share of load. Further discus-sion about the interactions is in the following context.

3.2. Morphology of MWCNTs in SBS/MWCNT composites

FESEM images of the frozen fracture surface of SBS/MWCNT composites with 3 wt% MWCNTs prepared bysolution and melt processing are shown in Fig. 3. All thewhite spots and small fibrils must be the end or pulled-out

0 1 2 3 4 5 6 7 88

10

12

14

16

18

20

Ten

sile

str

engt

h (M

Pa)

MWCNT weight fraction (%)

Melt Solution

Fig. 2. Tensile strength of composites prepared by melt and solutionprocessing as a function of MWCNT content.

L. Lu et al. / Carbon 45 (2007) 2621–2627 2623

part of MWCNTs on the fracture surface. As shown inFig. 3a, although the dispersion of MWCNTs is uniform,there are still several aggregates existed in the compositeprepared by solution processing. As shown in Fig. 3b, thedispersion of MWCNTs in the SBS/MWCNT compositeprepared by melt mixing is more homogeneous and uniformthan the composite prepared by solution processing. Thisphenomenon means that the dispersion of MWCNTs inSBS is improved via melt mixing, resulting in good mechan-ical properties of composites as mentioned before. Fig. 3c isa high magnification image of the composite prepared bymelt mixing. The average diameter of MWCNTs calculatedfrom the scale bar is about 42 nm which is roughly twice lar-ger than the pristine MWCNTs. This phenomenon may beattributed to the polymer layers wrapped on the surface ofMWCNTs which were charged by the high electron beam inthe electrical field [21].

Fig. 3. FESEM images of frozen fracture surface of SBS/MWCNTcomposites with 3 wt% MWCNTs prepared by solvent (a) and melt (b)processing. High magnification image of composite prepared by meltmixing (c).

3.3. Interactions between SBS and MWCNTs

DMA was used to measure the glass transition temper-atures (Tg) of pure SBS and SBS/MWCNT composites,and the results of pure SBS and SBS composite with3 wt% MWCNTs are shown in Fig. 4. SBS has two Tg

peaks at around �113 �C and +85 �C assigned to the PBand PS domains. After adding MWCNTs into SBS, bothTg peaks shifted towards higher temperatures. The twoTg peaks of SBS/MWCNT composites are around�109 �C and +93 �C, which increase 4 �C and 8 �C com-pared with that of pure SBS. The increasing of Tg is prob-ably because the movement of SBS polymer chains can behindered by the presence of MWCNTs.

To reveal the effect of melt mixing on the interactionsbetween SBS and MWCNTs, two SBS/MWCNT compos-ites with 3 wt% MWCNTs prepared by solution and meltprocessing were separately dissolved in THF. The disper-sion of MWCNTs in composites was observed by optical

microscopy (Fig. 5). The composite prepared by solutionprocessing contained many black spots, indicating the exis-tence of many aggregations of MWCNTs in the composite

-150 -100 -50 0 50 100 1500.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

0.40

0.45

tanδ

Temperature (oC)

0 wt% 3 wt%

Fig. 4. Dynamic mechanical analyses of SBS and SBS/MWCNT com-posite with 3 wt% MWCNTs prepared by melt mixing.

1000 900 800 700 600 500 400 300 200 100 0

O 1

s C 1

s

c

b

a

Inte

nsity

(a.

u.)

Binding Energy (eV)

Fig. 6. XPS full-scan spectra of pristine MWCNTs (a), f-MWCNTs (b)and SBS (c).

2624 L. Lu et al. / Carbon 45 (2007) 2621–2627

(Fig. 5a). On the contrary, the composite prepared by meltmixing was homogeneous and nearly transparent (Fig. 5b).After the centrifugation of these two suspensions, thesupernatant liquids were collected. The photos of thesesupernates are shown in Fig. 5c and d. The supernate ofthe sample prepared by solution processing is colorlessand transparent (Fig. 5c), suggesting that little MWCNTsexist in the supernatant liquid. However, the supernate ofthe sample prepared by melt mixing is black and opaque(Fig. 5d). The dark-colored supernate has remained stable

Fig. 5. Optical microscopy images of SBS/MWCNT composites prepared by sthe supernate obtained by centrifugation of the THF solutions of SBS/MWC

and homogeneous for more than 6 months. It is very obvi-ous that melting mixing could increase the interactionbetween SBS and MWCNTs so as to improve the solubilityof MWCNTs in THF.

XPS was employed to determine the surface composi-tions of MWCNTs and f-MWCNTs. Fig. 6 shows theXPS survey spectra of MWCNTs, f-MWCNTs and pureSBS treated by melt mixing. Three spectra reveal the pres-ence of carbon and oxygen. For pristine MWCNTs, thebinding energy of carbon is 284.6 eV and the relativeatomic concentrations of carbon and oxygen are 89.9%

olution (a) and melt (b) processing after dissolved in THF; Photograph ofNT composites prepared by solution (c) and melt (d) processing.

Table 1Summary of the relative percentage of carbon and assignation

MWCNTs f-MWCNTs

Assignation C–C C–O C@O CO–O C–C C–O C@O CO–OBinding

energy(eV)

284.6 286.2 287.6 288.9 284.8 286.3 287.9 290.6

Percentage(%)

69.6 17.6 6.6 6.1 71.7 18.7 6.0 3.6

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

Abs

orba

nce

SBS MWNTs f-MWNTs

L. Lu et al. / Carbon 45 (2007) 2621–2627 2625

and 10.1%. For f-MWCNTs, the binding energy of carbonis 284.9 eV and the atomic concentration of carbonincreased to 91.2%, while the concentration of oxygendecreased to 8.8%. The slight changes of atomic concentra-tion support that MWCNTs are coated with a SBS layer[22]. For SBS, the binding energy of carbon is 286.6 eVand the existence of oxygen in spectrum of SBS indicatesthat thermal oxidative degradation of SBS occurred duringmelt mixing.

The carbon component C1s can be decomposed intofour contributions appearing at 284.6, 286.2, 287.6 and288.9 eV (Fig. 7). The C1s peak observed at 284.6 eV isinterpreted as the combination of the sp2 C@C and sp3

C–C structure of MWCNTs [23]. The respective percentageand assignation are summarized in Table 1. It is very inter-esting to notice that each binding energy of f-MWCNTs ishigher than the corresponding binding energy ofMWCNTs. This is probably because of the coating ofSBS on the surface of MWCNTs changed the chemicalenvironment of carbon, leading to the increase of bindingenergy.

The UV/vis absorption spectra of SBS, pristineMWCNTs and f-MWCNTs are shown in Fig. 8. There is

292 290 288 286 284 282 280

Inte

nsity

(a.

u.)

Binding Energy (eV)

294 292 290 288 286 284 282 280

Inte

nsity

(a.

u.)

Binding Energy (eV)

Fig. 7. C1s XPS spectra of pristine MWCNTs (a) and f-MWCNTs (b).

200 300 400 500 600 700 8000.0

Wavelength (nm)

Fig. 8. UV spectra of SBS, MWCNTs and f-MWCNTs.

no obvious peak in spectrum of pristine MWCNTs, whilethere are two peaks in the spectrum of SBS. The weak peakof SBS at 235 nm is q-band characteristic of phenyl groups,while the strong peak in 260 nm is a-band as another char-acteristic peak of phenyl groups. There are two strongpeaks in 235 nm and 276 nm in the spectrum of f-MWCNTs. The absorbance of q-band of f-MWCNTsintensifies significantly compared with that of pure SBS.In addition, the a-band in the spectrum of f-MWCNTsshifts from 260 nm to 276 nm, indicating that there was ap–p interaction between MWCNTs and the phenyl groupsof SBS [20,24].

It has been reported that both small molecular radicalsand polymer chain radicals are able to effectively function-alize CNTs [25–27]. In the present study, XPS results showthat SBS was thermally degraded during melt mixing.According to the previous studies [28,29], PB segments areconsidered more liable to degradation than PS segmentsbecause the low Tg of PB promotes permeability towardoxygen diffusion. Free radicals were formed on the sites ofa-H on PB segments during melt mixing owing to their highactivity. Because open-ends and the defects on the sidewallof MWCNTs provide the active sites for chemical reaction,these active sites on MWCNTs are able to react with thefree radicals on PB segments, resulting in the grafting ofSBS on the surface of MWCNTs. The reaction of PB seg-ments with MWCNTs is considered as the main reactionbetween SBS and MWCNTs during melt mixing, leading

Fig. 9. TEM images of pristine MWCNTs (a) and f-MWCNTs (b).

2626 L. Lu et al. / Carbon 45 (2007) 2621–2627

to the chemical bonding of SBS to MWCNTs. On the otherhand, it is generally recognized for many kinds of solid inor-ganic powders, such as carbon black, graphite, quartz, silicaand marble, under grinding or ball milling, a large amountof instantaneous active free radicals are generated on thesurface of the powders because of the mechanochemicaleffect, and these active sites are capable to initiate polymer-ization of many monomers as well as to graft alreadyformed polymer chains [30–32]. It is possible that somenew active sites generate on the surface of MWCNTs undermilling. These active sites could also react with polymerchains [33,34]. Therefore, it is much possible that somedegraded SBS chains have been grafted to the surface ofMWCNTs during the melt mixing in present study.

The microstructure of pristine MWCNTs and f-MWCNTs was observed by TEM (Fig. 9). There is aSBS layer wrapped on the surface of MWCNTs, and itsthickness is about 13 nm (Fig. 9b). It is obvious that poly-mer layers could not be removed by the washing procedure,indicating that the presence of irreversible coating of SBSon the surface of MWCNTs. However, the amount of f-MWCNTs is small. There are still some MWCNTs withoutany polymer coating according to Fig. 9b. It is probablybecause of the amount of free radicals generated duringmelt mixing were very small so that only parts of SBSchains could be grafted to MWCNTs.

4. Conclusions

MWCNTs can be used to reinforce the SBS. The tensilestrength of SBS/MWCNT composite containing 7 wt%MWCNTs was 17.1 MPa, about 66% higher than that ofpure SBS. MWCNTs were uniformly dispersed in theSBS/MWCNT composites according to the FESEMimage. The presence of MWCNTs could lead to an increaseof glass transition temperatures of PS and PB domains.The intensification of q-band at 235 nm and the shift ofa-band from 260 nm to 276 nm in UV spectra indicatedthat there was p–p interaction between MWCNTs and

SBS prepared by melt mixing. The chemical interactionsbetween MWCNTs and SBS were supposed to occur dur-ing melt mixing.

References

[1] Iijima S. Helical microtubules of graphitic carbon. Nature 1991;354(6348):56–8.

[2] Baughman RH, Zakhidov AA, de Heer WA. Carbon nanotubes – theroute toward applications. Science 2002;297(5582):787–92.

[3] Breuer O, Sundararaj U. Big returns from small fibers: a review ofpolymer/carbon nanotube composites. Polym Compos 2004;25(6):630–45.

[4] Coleman JN, Khan U, Gun’ko YK. Mechanical reinforcement ofpolymers using carbon nanotubes. Adv Mater 2006;18:689–706.

[5] Koerner H, Liu W, Alexander M, Mirau P, Dowty H, Vaia RA.Deformation-morphology correlations in electrically conductive car-bon nanotube-thermoplastic polyurethane nanocomposites. Polymer2005;46(12):4405–20.

[6] Li Z, Li S, Yang M, Huang R. A novel approach to preparing carbonnanotube reinforced thermoplastic polymer composites. Carbon2005;43:2413–6.

[7] Frogley MD, Ravich D, Wagner HD. Mechanical properties ofcarbon nanoparticles-reinforced elastomers. Compos Sci Technol2003;63:1647–54.

[8] Potschke P, Fornes TD, Paul DR. Rheological behavior of multi-walled carbon nanotube/polycarbonate composites. Polymer2002;43(11):3247–55.

[9] Velasco-Santos C, Martinez-Hernandez AL, Fisher FT, Ruoff R,Castano VM. Improvement of thermal and mechanical properties ofcarbon nanotube composites through chemical functionalization.Chem Mater 2003;15(23):4470–5.

[10] Andrews R, Jacques D, Minot M, Rantell T. Fabrication of carbonmultiwall nanotube/polymer composites by shear mixing. MacromolMater Eng 2002;287(6):395–403.

[11] Schadler LS, Giannaris SC, Ajayana PM. Load transfer in carbonnanotube epoxy composites. Appl Phys Lett 1998;73(26):3842–4.

[12] Qian D, Dickey EC, Andrews R, Rantell T. Load transfer anddeformation mechanisms in carbon nanotube–polymer composites.Appl Phys Lett 2000;76(20):2868–70.

[13] Ruan SL, Gao P, Yang XG, Yu TX. Toughening high performanceultrahigh molecular weight polyethylene using multiwalled carbonnanotubes. Polymer 2003;44(19):5643–54.

[14] Cataldo F. The role of fullerene-like structures in carbon black andtheir interaction with dienic rubber. Fullerene Sci Technol 2000;8(1–2):105–12.

L. Lu et al. / Carbon 45 (2007) 2621–2627 2627

[15] Ginzburg VV, Gendelman OV, Manevitch LI. Simple ‘‘kink’’ modelof melt intercalation in polymer–clay nanocomposites. Phys Rev Lett2001;86(22):5073–5.

[16] Pan H, Liu L, Guo ZX, Dai L, Zhang F, Zhu D, et al. Carbonnanotubols from mechanochemical reaction. Nano Lett2003;3(1):29–32.

[17] Wang Z, Liu C, Liu Z, Xiang H, Li Z, Gong Q. p–p Interactionenhancement on the ultrafast third-order optical nonlinearity ofcarbon nanotubes/polymer composites. Chem Phys Lett2005;407:35–9.

[18] Zhang WD, Shen L, Phang IY, Liu T. Carbon nanotubes reinforcednylon-6 composite prepared by simple melt-compounding. Macro-molecules 2004;37:256–9.

[19] Wong M, Paramsothy M, Xu XJ, Ren Y, Li S, Liao K. Physicalinteractions at carbon nanotube–polymer interface. Polymer2003;44(25):7757–64.

[20] Zhang Z, Zhang J, Chen P, Zhang B, He J, Hu GH. Enhancedinteractions between multi-walled carbon nanotubes and polystyreneinduced by melt mixing. Carbon 2006;44:692–8.

[21] Hu G, Zhao C, Zhang S, Yang M, Wang Z. Low percolationthresholds of electrical conductivity and rheology in poly(ethyleneterephthalate) through the networks of multi-walled carbon nano-tubes. Polymer 2006;47(1):480–8.

[22] Xu H, Wang X, Zhang Y, Liu S. Single-step in situ preparation ofpolymer-grafted multi-walled carbon nanotube composites under60Co c-ray irradiation. Chem Mater 2006;18:2929–34.

[23] Okpalugo TIT, Parakonstantinou P, Murphy H, McLaughlin J,Brown NMD. High resolution XPS characterization of chemicalfunctionalized MWCNTs and SWCNTs. Carbon 2005;43:153–61.

[24] Star A, Han TR, Gabriel JCP, Bradley K, Gruner G. Interaction ofaromatic compounds with carbon nanotubes: correlation to theHammett parameter of the substituent and measured carbon nano-tube FET response. Nano Lett 2003;3(10):1421–3.

[25] Qin S, Qin D, Ford WT, Herrera JE, Resasco DE, Bachilo SM, et al.Solubilization and purification of single-wall carbon nanotubes inwater by in situ radical polymerization of sodium 4-styrenesulfonate.Macromolecules 2004;37(11):3965–7.

[26] Peng H, Alemany LB, Margrave LJ, Khabashesku VN. Sidewallcarboxylic acid functionalization of single-walled carbon nanotubes. JAm Chem Soc 2003;125(49):15174–82.

[27] Ying Y, Saini RK, Liang F, Sadana AK, Billups WE. Functional-ization of carbon nanotubes by free radicals. Org Lett 2003;5(9):1471–3.

[28] Xu J, Zhang A, Zhou T, Cao X, Xie Z. A study on thermal oxidationmechanism of styrene–butadiene–styrene block copolymer (SBS).Polym Degrad Stab 2007;92:1682–91.

[29] Allen NS, Edge M, Wilkinson A, Liauw CM, Mourelatou D, BarrioJ, et al. Degradation and stabilisation of styrene–ethylene–butadi-ene–styrene (SEBS) block copolymer. Polym Degrad Stab2001;71:113–22.

[30] Hasegawa M, Kimata M, Kobayashi SI. Mechanochemical polymer-ization of styrene initiated by the grinding of quartz. J Appl PolymSci 2001;82(11):2849–55.

[31] Xu H, Li B, Wu C. Polymer grafting onto carbon black by solid statemethod. Polym J 2006;38(8):807–13.

[32] Ruan WH, Zhang MQ, Rong MZ, Friedrich K. Mechanicalproperties of nanocomposites from ball milling grafted nano-silica/polypropylene block copolymer. Polym Polym Compos2004;12(4):257–67.

[33] Baibarac M, Baltog I, Lefrant S, Godon C, Mevellec JY. Mechanico-chemical interaction of single-walled carbon nanotubes with differenthost matrices evidenced by SERS spectroscopy. Chem Phys Lett2005;406:222–7.

[34] Beyer MK, Clausen-Schaumann H. Mechanochemistry: the mechan-ical activation of covalent bonds. Chem Rev 2005;105(8):2921–48.