research article a novel method of mechanical oxidation of

Research ArticleA Novel Method of Mechanical Oxidation of CNT for PolymerNanocomposite Application Evaluation of Mechanical DynamicMechanical and Rheological Properties

Priyanka Pandey Smita Mohanty and Sanjay Kumar Nayak

Central Institute of Plastics Engineering and Technology (CIPET) TVK Industrial Estate Guindy Chennai 600032 India

Correspondence should be addressed to Sanjay Kumar Nayak papersjournalgmailcom

Received 16 January 2014 Accepted 30 March 2014 Published 17 April 2014

Academic Editor Donald L Feke

Copyright copy 2014 Priyanka Pandey et al This is an open access article distributed under the Creative Commons AttributionLicense which permits unrestricted use distribution and reproduction in any medium provided the original work is properlycited

A new approach of oxidation of carbon nanotubes has been used to oxidize the CNTs A comparative aspect of the mechanicaloxidation and acid oxidation process has been established FTIR analysis and titration method have shown the higher feasibilityof the mechanical oxidation method to oxidize the CNTs Comparatively less damage to the CNTs has been observed in caseof mechanically oxidized as compared to acid oxidized CNTs The mechanical properties of the nanocomposites reinforced withthe acid oxidized CNT (ACNT) and mechanically oxidized CNTs (McCNT) were analyzed and relatively higher properties in thenanocomposites reinforced withMcCNTwere noticedThe less degree of entanglement in theMcCNTswas noticed as compared toACNTs The dynamic mechanical analysis of the nanocomposites revealed much improved load transfer capability in the McCNTreinforced composites Further the rheological properties of the nanocomposites revealed the higher performance of McCNTreinforced composites

1 Introduction

Tremendously high mechanical properties with low densityof multiwalled carbon nanotubes (MWNT) have promptedinvestigation of these nanomaterials as filler in polymermatrix [1ndash3] The properties of MWNTs depend stronglyon the dispersion of the nanotubes inside polymer matrixHowever the hydrophobic inert nature of nanotubes causesbundling of tubes [4] The bundling of nanotubes can beminimized by modification of surface properties of tubes[5] Oxidation method is the most efficient method in thisregard [6 7] Further acids have been extensively utilized forthis purpose However the acid oxidation of nanotubes hasexhibited damage to the nanotube surface Hence this studywas aimed to establish an oxidation method to improve thedispersibility of nanotubes with minimized damage to thenanotube surface and its crystalline organization

The novel method used in this study to minimize thedamage was based on the mechanical oxidation of the nan-otubes [8 9] The confirmation of modification was carried

out via Fourier transform infrared spectroscopic (FTIR)analysis Raman spectra were analyzed to evaluate the effectof both modifications on CNT properties The concentrationof acidic groups on the modified (oxidized) CNTs was deter-mined using titration method The TEM micrographs havebeen analyzed in order to investigate the effect of both theoxidation methods on the surface characteristics of CNT andits bundling behavior Further in order to evaluate the effectof this oxidation method on the polymer matrix polymernanocomposites were prepared and an investigation of theproperties of the polymer nanocomposites was carried outPolypropylene has been used as the matrix materials sinceit has acquired a large space in the mainstream industry likeautomobile packaging and so forth [10] The major require-ment of the nanocomposites is the goodmechanical property[11] and hence a study on effect of these modificationson the mechanical properties was carried out Further thedynamic mechanical analysis technique was used to analyzethe thermomechanical performance of the nanocomposites

Hindawi Publishing CorporationInternational Journal of Chemical EngineeringVolume 2014 Article ID 623109 9 pageshttpdxdoiorg1011552014623109

2 International Journal of Chemical Engineering

and a comparative aspect of the effect of the mechanicaloxidation as compared to acid oxidation was establishedFurther the rheological property of the nanocomposites wasinvestigated to analyze the effect of this novel approachof modification on the microstructural characteristics ofthe nanocomposites This was further supported by TEMmicrographs of nanocomposites

2 Experimental

21 Oxidation of Carbon Nanotubes (CNTs) In a typicalprocedure 2mg of CNT sample was refluxed in 50mL of26MHNO

3 for 48 hrsThemixturewas diluted in 500mLof

distilledwater and functionalizedCNTwas collected throughfiltration This type of treated CNT is termed ACNT forfurther discussion

A mixture of 04 g of CNT and 8 gm of potassiumhydroxide and ethanol was stirred manually and the mixturewas allowed for intensive ball milling for 3 hrs using aball milling machine The obtained mixture was dissolvedin deionized water and centrifuged This dissolution andcentrifugation process was repeated to ensure the completeremoval of KOH residues The collected samples were driedfor 10 hrs at 100∘C This type of treated CNT is termedMcCNT for further discussion

22 Fabrication of Nanocomposites The masterbatch routewas employed to prepare the nanocomposites using microin-jection molding technique First the PPMAPP hybrid wassynthesized with a 5wt loading of MAPP using com-pounder Ms DSM explore Netherlands Micro 15 at a tem-perature of 180∘C for 10 minutes as obtained from previousstudy In the second step polypropylene (PP) nanocompositeswere prepared with 03 weight loading of ACNT andMcCNT at a temperature of 180∘C 185 ∘C and 180∘C in frontmiddle and rear zone respectively

23 Fourier Transform Infrared Spectroscopy (FTIR) For theconfirmation of successful modification of Na-MMT theFourier transform infrared spectroscopy (FTIR) was carriedout using thermoscientific FTIR (smart orbit ATR 400ndash4000 cmminus1 with microscope) The heat dried samples oftreated clays have been used for analysis

24 Raman Spectroscopy Raman scattering spectra wererecorded by Micro-Raman LabRam system in a back-scattering geometry A 6328 nm (196 eV) HeNe laser wasused as the light source and the power of the laser wasadjusted by optical filtersThe typical acquisition time for thespectra was 30 sec

25 Transmission Electron Microscope (TEM) TEM analysiswas of the samples carried using transmission electronmicroscope (JEOL 1200EX Japan) TEM imagingwas carriedout at an accelerating voltage of 100 kV Images were capturedusing a charged couple detector (CCD) camera for furtheranalysis using Gatan Digital Micrograph analysis software

26 Mechanical Properties The Izod impact strength of thePP and its nanocomposites have been evaluated using TiniusOlsen USA impactometer as per ASTMD 256 The sampleswere notched prior to the testing prior to loading withhammer of 2 J The notch depth was taken as 253mm witha notch angle of 45∘ The microinjection molded samples ofdiameter 635 times 127 times 3mm3 have been used for the testing7 numbers of samples of each composition have been testedin order to get the accuracy in the result

Further the microinjection molded dog-bone shapedsamples (5 samples of each composition) have been subjectedto tensile test Tensile properties of the virgin matrix as wellas the nanocomposites have been evaluated using UniversalTensile Machine (3382 Instron UK) as per ASTM D 638Samples of 127 times 127 times 3mm3 dimension were subjected totensile test at a gauge length of 50mm and with crossheadspeed of 5mmmin

27 Dynamic Mechanical Analysis (DMA) The samples weretested using dynamic mechanical analyzer (TA InstrumentsQ800) to determine the effects of modifications on thedispersion of clay in the nanocomposites The samples weretested at minus100∘C to 150∘C to obtain information acrosstransition temperature The DMA analysis was conducted ina dual cantilever mode The experiment was performed withthe injection molded samples having a dimension of 635 times127 times 3mm3

28 Rheological Analysis The samples were characterized bya modular advanced rheometer system (MARS III ThermoFisher Scientific Germany) in the frequency sweep modeusing parallel plate fixtures of 25mm in diameter at a gap of1mm In order to investigate the formation of silicate networkand extensive morphology frequency sweep method is mostoften used methodology Hence the dynamic frequencysweep test was performed at 220∘Cand frequency sweep from01 radsec to 200 radsec at a constant strain amplitude of1 Corresponding storagemodulus (1198661015840) loss modulus (11986610158401015840)and complex viscosity (120578lowast) were determined as a function offrequency and the data were analyzed and represented

3 Materials

Polypropylene (M110) was procured from Ms Haldia Petro-chemicals Kolkata India having a density of 094 gcm3and the MFI of 11 g10min Multiwalled carbon nanotubes ofgt98 purity and diameter of 80ndash100 nm used in this workwas purchased from Ms Nanoshel Intelligent MaterialsPvt Ltd India The compatibilizer used in this study wasmaleic anhydride grafted polypropylene (MAPP) (OPTIM-P425) having an anhydride content of 16ndash25 and density091 gcm3 was purchased fromMs Pluss Polymers Pvt LtdHaryana India

4 Results and Discussion

41 Analytical Characterization through Titration MethodThe total acidic sites were quantified by titration method

International Journal of Chemical Engineering 3

0080

0075

0070

0065

0060

0055

0050

0045

0040

0035

0030

0025

4000 3500 3000 2500 2000 1500 1000

2380 2360

2360

McCNT

ACNTCNT

Tran

smitt

ance

()

Wavenumber (cmminus1)

Figure 1 FTIR spectrum of pristine and treated CNTs

First 02mg of treated CNTs was sonicated in 25mL of 01MNaOH and the mixture was kept for stirring for 6 hrs underinert atmosphere The precipitation of CNTs was carried outby adding CaCl

2 Precipitate was separated from the solution

and removed upon washing Further 25mL of HCl wasadded to the filtrate with constant stirring for stirring underinert atmosphere for 12 hrs Excess of HCl was determinedby titration with NaOH [12] The relative concentration ofthe acidic group was found to be 17 34 and 46mmolg forCNT ACNT and McCNT respectively It was evident thatmechanical oxidation process results in higher concentrationof acidic sites as compared to that of acid treatment

42 Fourier Transform Infrared Spectroscopy (FTIR) Figure 1represents the FTIR spectra of as received CNT and oxidizedCNTs (ie ACNT and McCNT) A prominent absorptionband at 1574 cmminus1 in the spectra of as receivedCNT is relatedto the carbon skeleton of the nanotubes In case of McCNTthis peak was shifted to 1599 cmminus1 respectively indicatingthe increased density of surface oxygen [13] In case of boththe treated CNTs (ie ACNT andMcCNT) additional peaksnear 1084 cmminus1 and 1406 cmminus1 were observed exhibitingthe CndashOndashC stretching group (from ether alcohol and car-boxylic acid) and characteristic hydroxyl bond (OndashH) Abroad absorption band near 3434 cmminus1 (H-bond in hydroxylcarboxylic and phenol groups) was also present in bothoxidizedCNTs (ie ACNT andMcCNT)Therefore form theFTIR analysis it was found that oxygenated functional groupshave been introduced onto the surface of CNTs revealing theconfirmation of oxidation

Hence it is worth mentioning that both the modificationprocesses are feasible to incorporate the surface acidic groupin the CNTs The comparative investigation of the oxidationefficiency of both the methods is discussed in the furtherstudy

43 Raman Spectroscopy Figure 2 represents the Ramanspectra of CNTs excited with the 5145 nm laser line All thesamples exhibited three characteristic bands namely D-band

1200 1300 1400 1500 1600 1700 1800

Inte

nsity

()

McCNT

ACNT

CNT

Raman shift (cmminus1)

Figure 2 Raman spectrum of pristine and oxidized CNTs

sim1338 cmminus1 G-band sim1572 cmminus1 and D1015840-1608 cmminus1 [9 14]The D-band is a disorder induced carbon atoms resultingfrom the defects in the CNT [15 16] However G-band relatesto the structural intensity of sp2 hybridized carbon atoms ofCNT [17]

In case of treated CNTs higher D-band intensity wasnoticed as compared to neat CNT confirming the conversionof sp2 hybridization to the sp3 carbon This effect was morepronounced in McCNT revealing the transformation ofrelatively higher number of sp2 carbon atoms into sp3 carbonFurther higher ratio of relative intensity ofG-band toD-band(119868119866119868119863) of neat CNT as compared to treated CNTs exhibited

the increase in the degree of disorderness and presence of thedefects on the surface of treatedCNT arising from the foreignfunctionalities of the tube surface Further the lower relativeintensity (119868

119866119868119863) of the McCNT as compared to that of

ACNT revealed the higher number of defects on the McCNT


(a) (b) (c)

(d) (e)

Figure 3 TEMmicrographs of (a) pristine CNT (b) and (c) McCNT (d) and (e) ACNT

as compared to ACNT [18] Also the lower [119868119866(119868119866+ 119868119863)]

values (ie qualify factor) of McCNT as compared to thatof ACNT indicate the less cutting of the CNT length duringmechanochemicial oxidation treatment at applied conditions[19]

44 Transmission Electron Microscope (TEM) The surfaceof the CNTs was analyzed under TEM and reported inFigures 3(a)ndash3(e)The dispersedCNT samples were analyzedTEM micrographs of neat CNT exhibited various bundlesHowever individual fibers were visible in case of both treatedCNTs However in case of McCNT the bundling was foundto be minimized as compared to ACNT This may result inthe relatively better dispersion of McCNT in polymer matrixFurther the damage in the surface of ACNT as observedfrom previous characterization was also confirmed fromFigure 3(c) However no sign of surface damage could beseen in McCNT (Figure 3(e))

45 Mechanical Properties Table 1 represents themechanicalproperties of the PP and its nanocompositesThemechanicalproperties were evaluated through analyzing their tensileand impact properties and represented the injection moldedsample In order to maintain the accuracy of results fivesamples of each composition were tested Ductile fractureof the samples was noticed in all materials The mechanicalproperties of PPMAPPACNT and PPMAPPMcCNTwerefound considerably higher than that of neat PP This isattributed to the stress transfer ability in carbon nanotubepolymer composites [20] due to the tendency of nanotubesto align and bridge the crack when a tensile stress is appliedto the composites leading to load transfer across the poly-mer nanotube interface Wherein relatively higher tensile

properties of PPMAPPMcCNTrevealedmuch efficient loadtransfer properties betweenMcCNTandmatrix polymer [20]as compared to that of ACNT

This is ascribed to the relatively more even dispersion ofMcCNTs in the polymermatrix arising from less disentangledCNT fibrils as was noticed in TEM micrographs Thisfurther leads to more uniform bridging of crack This alsosupports the fact that ACNT reinforced nanocomposites dueto damaged structural integrity may have some loose inter-action leading to the relatively nonuniform stress transferacross polymer nanotube interface unlikeMcCNT reinforcednanocomposites

46 Dynamic Mechanical Analysis In order to confirm thefinding of filler dispersion as obtained from mechanicalanalysis the dynamic mechanical analysis is the preferredmethod wherein the storage modulus is related to thestiffness of the material and measures the elastic response ofthe polymer The loss modulus denotes the energy dissipatedby the system in the form of heat and measures the viscousresponse of the polymer material which in turn provides theinformation about the mechanical properties of the materialThe damping factor (tan 120575) is the ratio of the loss modulusto storage modulus and helps in estimating filler-polymerinteraction in case of composites

Figures 4(a) and 4(b) represent a variation of storagemodulus and loss modulus with respect to temperature InPP over the entire temperature range two main mechanicalrelaxation processes were evident namely high temp 120572relaxation related to the crystalline fraction present and a120573 process related to the glassrubber transition relaxation Ageneral falling trend was observed in all the cases

The higher initial value of storage modulus was observedfor each sample at a subambient temperature This supports


Table 1 Mechanical properties of PP and PP nanocomposites

Composition Yield strength (MPa) Youngrsquos modulus (MPa) Elongation at Break () Impact strength (jm)PPMAPP 3071 plusmn 018 1193 plusmn 32 gt500 37PPMAPPACNT 3598 plusmn 027 1630 plusmn 60 gt500 47PPMAPPMcCNT 3633 plusmn 041 1727 plusmn 57 gt500 51

0

1000

2000

3000

4000

5000

Stor

age m

odul

us (G

998400 )

0 50 100 150

PP

PPMAPPMcCNTPPMAPPACNT

Temperature (∘C)minus100 minus50

(a)

0 50 100 1500

50

100

150

200

250

300

PPPPMAPPMcCNTPPMAPPACNT

Loss

mod

ulus

(MPa

)Temperature (∘C)

minus100 minus50

(b)

Figure 4 Storage modulus and loss modulus of PP and its nanocomposites

the fact that molecules remain in a frozen state in thiscondition and hence they show high stiffness properties inglassy condition A clear transition was observed at 0∘CThis transition might be related to the glass (120573) transitionIn all the cases it was found that the storage modulusvalue decreases with the increase in temperature below glasstransition temperature This might be due to the fact that PPreaches its softening point and therefore reduces the elasticresponse of the material A considerable drop was noticedin the vicinity of glass transition temperature indicatingthe phase transition from the rigid glassy state where themolecular motions are restricted to a more flexible rubberystate and the molecular chains have more freedom to moveFurther with the increase of temperature to the meltingtemperature the storage modulus of composites is dominatedby matrix intrinsic modulus Storage modulus is higherwhen the molecular movement is limited or restricted andit consequently will cause the storage of mechanical energyto increase [21] The stiffening effect was more remarkable atlower temperature This phenomenon was explained by themismatch in coefficient of thermal expansion between thematrix and inorganic fillers which might allow better stresstransfer betweenmatrices and fillers at low temperatures [22]The similar observation was found in all cases of compositesalso

Further it was noticed that the storage modulus ofthe composites was higher as compared to the PP Thisconfirmed the reinforcing effect of ACNT and McCNT in

their individual composites Subsequently higher storagemodulus of PPMAPPMcCNT composites as compared toPPMAPPACNT revealed more evenly dispersed McCNTparticles in the PP matrix leading to the relatively moreeven distribution of the stress [23] This further exhibitedthe higher surface area of McCNT particles in PPg matrixarising from the relatively finer dispersion of McCNT insidethe PPg matrix [23] This further leads to the much moreevenly transferred applied stresses frommatrix onto the CNTparticles

The 120573 relaxation related to the local motion of amor-phous phase corresponding to glass transition temperature(119905119892) of PP was observed at 17∘C and no further change could

be noticed in that of composites revealing the equal level ofcrystallinity of PP and its composites Hence it is evidentthat incorporation of CNT and any type of treated CNTsdid not alter the relaxation mechanism of macromolecularchains This may be attributed to the rapid crystallization ofthe polymer and thus the anticipated effect of reinforcementis masked

Figure 5 represents the damping factor of PP and itsnanocomposites The damping in the polymeric material issensitive to segmental mobility of the polymer chains and incomposites is the indicative of interfacial interaction betweenthe polymer and the filler Strong interfacial interactionbetween the polymer and the filler tends to restrict thepolymermobility thereby reducing the damping wherein thelowest damping factor of PPMAPPMcCNT as compared to


003

006

009

012

015

018

021

0 50 100 150

PP



tan120575

Figure 5 Tan 120575 versus temperature of PP and its nanocomposites

PPMAPPACNT revealed the relatively strong interactionbetween McCNT and polymer matrix causing the restrictedpolymer mobility

47 Rheological Assessment The rheological properties canprovide information about the percolated network structureas well as the interaction between filler and polymer matrixMoreover it is important to evaluate the rheological behaviorin order to understand the effect of the nanotubes oninternal structures and processing properties of polymernanocomposites [24]

Figure 6 and Table 2 represent the complex viscosity ofPP and its nanocomposites as a function of frequency Fromthe figure it was depicted that the complex viscosities (120578lowast) ofPP and its nanocomposites were decreased with increasingfrequency indicating a non-Newtonian behaviour over thewhole frequency range measured

The shear thinning effect noticed in case of nanocompos-ites was ascribed to the random orientation and entangledmolecular chains in the nanocomposites during the appliedshear force The PP nanocomposites containing McCNT andACNT nanocomposites exhibited higher 120578lowast value than thatof neat PP at low frequency indicating the interconnectedand network structures formed as a result of particle-particle and particle-polymer interactions Further both thenanocomposites exhibited shear thinning behavior revealingthe breakdown of these interactions and network structureswith increase in the applied frequency Subsequently the 120578lowastof the PPMAPPMcCNT nanocomposites was found to berelatively higher as compared to PPMAPPACNT revealingthe strong interaction betweenMcCNT and polymer as com-pared to that of ACNT and Polymer Furthermore relativelymore distinct shear thinning behaviour and 120578lowast over thewholeapplied frequency range as compared to PPMAPPACNTmight be ascribed to better dispersion of McCNT and strongACNT polymer interaction [14ndash25]


PP

103

102

10

1E minus 4 1E minus 3 001 01 1

Com

plex

visc

osity

(120578lowast)

(Pa)

Frequency (120596) (rads)

Figure 6 Complex viscosity versus frequency of PP and nanocom-posites

Table 2 Variations of low frequency slopes of 120578lowast1198661015840 and11986610158401015840 versus120596 for PP and its nanocomposites

Materials Slope of 120578lowastversus 120596

Slope of 1198661015840versus 120596

Slope of 11986610158401015840versus 120596

PP minus011 121 097PPMAPPMcCNT minus014 105 091PPMAPPACNT minus016 087 089

Further the shear thinning exponent (119899) for the nano-composites was determined using

1003816100381610038161003816120578 sdot lowast asymp 120596

1198991003816100381610038161003816 (1)

From the analysis it was depicted that shear thinningbehavior of the nanocomposites was dependent on the pres-ence of McCNT and ACNT The incorporation of McCNTand ACNT resulted in decreased value of ldquo119899rdquo and this effectwas more pronounced in case of PPMAPPMcCNT Thiscan be again ascribed to the enhanced interfacial interactionbetween ACNT and polymer matrix The difference in the119899 value of both the nanocomposites depicted the variableefficiency of the modification Hence it is worth mentioningthat the McCNT is relatively better reinforcing agent for PPmatrix in presence of MAPP [14]

Figure 7 represents the frequency dependence of thestorage modulus (G10158401015840) and loss modulus (G10158401015840) for the PPand its nanocomposites measured at 220∘C The value ofstorage modulus (G1015840) and loss modulus (G10158401015840) of the PPand its nanocomposites showed an increasing tendency withincrease in the frequency This effect was more significant inthe low frequency region revealing the relaxation behaviorof polymer to a long time scale in the low frequency region[14] At low frequencies frequency dependence of modulusweakens clearly with the addition of the CNTs indicating thatthe long-range motion of the polymer chains is restrained by


PPPPMAPPACNTPPMAPPMcCNT

10

1

100

1000

10000

01 1 10 100

Frequency (rads)

Stor

age m

odul

us (G

998400 ) (Pa

)

(a)

01 1 10 100

100

1000

10000

PPPPMAPPC15APPMAPPMWNT

Loss

mod

ulus

(G998400998400

) (Pa

)

Frequency (rads)

(b)

Figure 7 (a) Storage modulus versus frequency (b) loss modulus versus frequency of PP and nanocomposites

PPMAPPACNT

(a)

PPMAPPMcCNT

(b)

Figure 8 TEM images of PP nanocomposites

the presence of the CNTs Further a decreased slope of G1015840and G10158401015840 of both the nanocomposites revealed the formationof interconnected and network like structure resulting fromnanotube-polymer interaction [14]

Further from the analysis it was depicted that the extentof increase in G1015840 of the PP and both the nanocompositeswas higher than that of G10158401015840 revealing that the rheologicalproperties of PP and both the nanocomposites can besensitively explained by G1015840 versus 120596 plot Subsequentlyit was depicted that the G1015840 and G10158401015840 value of PP and itsnanocomposites were higher as compared to neat PP in thelow frequency region and this increasing effect was morepronounced in case of PPMAPPMcCNT Greater G1015840 andG10158401015840 values of nanocomposites were ascribed to the formationof interconnected or networked structure formed due to

nanotube-polymer interaction Subsequently in the higherfrequency region both the nanocomposites exhibited thesimilar G1015840 and G10158401015840 values as that of neat PP This mightbe ascribed to the breakdown of interconnected networkstructure due to high level of shear force However the higherG1015840 and G10158401015840 value of PPMAPPMcCNT as compared toPPMAPPACNT confirmed the higher degree of interactionbetween McCNT and polymer matrix

48 Transmission Electron Microscopy (TEM) TEM micro-graphs of the nanocomposites are reported in Figure 8 Themicrographs showed the much uniform dispersion of thenanotubes in case of PPMAPPMcCNT revealing the betterdispersibility and interaction of the McCNT in the polymermatrix


5 Conclusions

From the study we may conclude that the mechanicaloxidation of the CNT via ball milling may be used as aneffective method in order to modify the CNT and henceto reduce the Vander wall interaction between the tubesFurther it was found that the mechanical oxidation methodof CNT may be advantageous in several aspects as comparedto acid oxidation method by reducing the damage to thetubes Hence the intrinsic properties of the nanotubes maybe intact Further since the CNTs are important as filler forpolymer nanocomposite application the polymer nanocom-posites of the mechanically oxidized and acid oxidized CNTwith polypropylene matrix were fabricated and investigatedThe investigation revealed the higher nucleating ability ofthe McCNT as compared to ACNT Also the highly uniformstress transfer ability in the PPMAPPMcCNT was noticedas compared to PPMAPPACNT Also the rheological prop-erties revealed the higher interaction between McCNT andpolymer matrix as compared to ACNT

Hence itmay be concluded that themechanical oxidationofCNTs can be used asmodification technique to improve themechanical and microstructural properties of the polymernanocomposites

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

References

[1] Y-S Shim B-GMin and S-J Park ldquoEffects of functional graft-ing on viscoelastic and toughness behaviors of multi-walledcarbon nanotubes-reinforced polypropylene nano-compositesrdquoMacromolecular Research vol 20 no 5 pp 540ndash543 2012

[2] K Saeed and I Khan ldquoPreparation and properties of single-walled carbon nanotubespoly(butylene terephthalate) nano-compositesrdquo Iranian Polymer Journal vol 23 no 1 pp 53ndash582014

[3] X Chen J Hu L Zhou W Li Z Yang and Y Wang ldquoPrepara-tion and crystallization of carbon nanotubemaleic anhydride-grafted polypropylene compositesrdquo Journal of Materials Scienceamp Technology vol 24 no 2 pp 279ndash284 2008

[4] W Xia Y Wang R Bergstraszliger S Kundu and M Muh-ler ldquoSurface characterization of oxygen-functionalized multi-walled carbon nanotubes by high-resolution X-ray photoelec-tron spectroscopy and temperature-programmed desorptionrdquoApplied Surface Science vol 254 no 1 pp 247ndash250 2007

[5] H Wang W Zhou D L Ho et al ldquoDispersing single-walledcarbon nanotubes with surfactants a small angle neutronscattering studyrdquoNano Letters vol 4 no 9 pp 1789ndash1793 2004

[6] T Kyotani S Nakazaki W-H Xu and A Tomita ldquoChemicalmodification of the inner walls of carbon nanotubes by HNO

3

oxidationrdquo Carbon vol 39 no 5 pp 782ndash785 2001[7] N V Naseh A A Khodadadi Y Mortazavi O A Sahraei

F Pourfayaz and M S Sedghi ldquoFunctionalization of carbonnanotubes using nitric acid oxidation and DBD plasmardquo Inter-national Journal of Chemical and Biological Engineering vol 2no 2 pp 66ndash68 2009

[8] I D Rosca F Watari M Uo and T Akasaka ldquoOxidation ofmultiwalled carbon nanotubes by nitric acidrdquo Carbon vol 43no 15 pp 3124ndash3131 2005

[9] A B Gonzalez-Guerrero E Mendoza E Pellicer F AlsinaC Fernandez-Sanchez and L M Lechuga ldquoDiscriminatingthe carboxylicgroups from the total acidic sites in oxidizedmulti-wall carbon nanotubes by means of acid-base titrationrdquoChemical Physics Letters vol 462 no 4ndash6 pp 256ndash259 2008

[10] M M Zamani A Fereidoon and A Sabet ldquoMulti-walledcarbon nanotube-filled polypropylene nanocomposites highvelocity impact response and mechanical propertiesrdquo IranianPolymer Journal vol 21 no 12 pp 887ndash894 2012

[11] G Z Papageorgiou1 M Nerantzaki I Grigoriadou DG Papageorgiou K Chrissafis and D Bikiaris ldquoIsotacticpolypropylenemulti-walled carbon nanotube nanocompositesthe effect of modification of MWCNTs on mechanical prop-erties and melt crystallizationrdquoMacromolecular Chemistry andPhysics vol 214 no 21 pp 2415ndash2431 2013

[12] Y-T Shieh G-L Liu H-H Wu and C-C Lee ldquoEffectsof polarity and pH on the solubility of acid-treated carbonnanotubes in different mediardquo Carbon vol 45 no 9 pp 1880ndash1890 2007

[13] C Bower A Kleinhammes Y Wu and O Zhou ldquoIntercalationand partial exfoliation of single-walled carbon nanotubes bynitric acidrdquo Chemical Physics Letters vol 288 no 2ndash4 pp 481ndash486 1998

[14] J Y Kim S I Han and SHong ldquoEffect ofmodified carbon nan-otube on the properties of aromatic polyester nanocompositesrdquoPolymer vol 49 no 15 pp 3335ndash3345 2008

[15] M S Dresselhaus G Dresselhaus R Saito and A JorioldquoRaman spectroscopy of carbon nanotubesrdquo Physics Reportsvol 409 no 2 pp 47ndash99 2005

[16] C Thomsen and S Reich ldquoDouble resonant Raman scatteringin graphiterdquo Physical Review Letters vol 85 no 24 pp 5214ndash5217 2000

[17] S Osswald E Flahaut H Ye and Y Gogotsi ldquoElimination ofD-band in Raman spectra of double-wall carbon nanotubes byoxidationrdquo Chemical Physics Letters vol 402 no 4ndash6 pp 422ndash427 2005

[18] T J Simmons J Bult D P Hashim R J Linhardt and PM Ajayan ldquoNoncovalent functionalization as an alternative tooxidative acid treatment of single wall carbon nanotubes withapplications for polymer compositesrdquo ACS Nano vol 3 no 4pp 865ndash870 2009

[19] N Pierard A Fonseca J-F Colomer et al ldquoBall milling effecton the structure of single-wall carbon nanotubesrdquo Carbon vol42 no 8-9 pp 1691ndash1697 2004

[20] P Liu ldquoModifications of carbon nanotubes with polymersrdquoEuropean Polymer Journal vol 41 no 11 pp 2693ndash2703 2005

[21] S K Samal S K Nayak and S Mohanty ldquoBananaglassfiber-reinforced polypropylene hybrid composites fabricationand performance evaluationrdquo Polymer-Plastics Technology andEngineering vol 48 no 4 pp 397ndash414 2009

[22] H Plaza B Reznik M Wilhelm O Arias and A Var-gas ldquoElectrical thermal and mechanical characterization ofpoly(propylene)carbon nanotubeclay hybrid compositemate-rialrdquoMacromolecular Materials and Engineering vol 297 no 5pp 474ndash480 2012

[23] V Vladimirov C Betchev A Vassiliou G Papageorgiou andD Bikiaris ldquoDynamic mechanical and morphological studiesof isotactic polypropylenefumed silica nanocomposites with


enhanced gas barrier propertiesrdquo Composites Science and Tech-nology vol 66 no 15 pp 2935ndash2944 2006

[24] K Prashantha J Soulestin M F Lacrampe P Krawczak GDupin and M Claes ldquoMasterbatch-based multi-walled carbonnanotube filled polypropylene nanocomposites assessment ofrheological andmechanical propertiesrdquoComposites Science andTechnology vol 69 no 11-12 pp 1756ndash1763 2009

[25] T Kashiwagi F Du J F Douglas K I Winey R H Harris Jrand J R Shields ldquoNanoparticle networks reduce the flammabil-ity of polymer nanocompositesrdquoNatureMaterials vol 4 no 12pp 928ndash933 2005

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and a comparative aspect of the effect of the mechanicaloxidation as compared to acid oxidation was establishedFurther the rheological property of the nanocomposites wasinvestigated to analyze the effect of this novel approachof modification on the microstructural characteristics ofthe nanocomposites This was further supported by TEMmicrographs of nanocomposites

2 Experimental

21 Oxidation of Carbon Nanotubes (CNTs) In a typicalprocedure 2mg of CNT sample was refluxed in 50mL of26MHNO

3 for 48 hrsThemixturewas diluted in 500mLof

distilledwater and functionalizedCNTwas collected throughfiltration This type of treated CNT is termed ACNT forfurther discussion

A mixture of 04 g of CNT and 8 gm of potassiumhydroxide and ethanol was stirred manually and the mixturewas allowed for intensive ball milling for 3 hrs using aball milling machine The obtained mixture was dissolvedin deionized water and centrifuged This dissolution andcentrifugation process was repeated to ensure the completeremoval of KOH residues The collected samples were driedfor 10 hrs at 100∘C This type of treated CNT is termedMcCNT for further discussion

22 Fabrication of Nanocomposites The masterbatch routewas employed to prepare the nanocomposites using microin-jection molding technique First the PPMAPP hybrid wassynthesized with a 5wt loading of MAPP using com-pounder Ms DSM explore Netherlands Micro 15 at a tem-perature of 180∘C for 10 minutes as obtained from previousstudy In the second step polypropylene (PP) nanocompositeswere prepared with 03 weight loading of ACNT andMcCNT at a temperature of 180∘C 185 ∘C and 180∘C in frontmiddle and rear zone respectively

23 Fourier Transform Infrared Spectroscopy (FTIR) For theconfirmation of successful modification of Na-MMT theFourier transform infrared spectroscopy (FTIR) was carriedout using thermoscientific FTIR (smart orbit ATR 400ndash4000 cmminus1 with microscope) The heat dried samples oftreated clays have been used for analysis

24 Raman Spectroscopy Raman scattering spectra wererecorded by Micro-Raman LabRam system in a back-scattering geometry A 6328 nm (196 eV) HeNe laser wasused as the light source and the power of the laser wasadjusted by optical filtersThe typical acquisition time for thespectra was 30 sec

25 Transmission Electron Microscope (TEM) TEM analysiswas of the samples carried using transmission electronmicroscope (JEOL 1200EX Japan) TEM imagingwas carriedout at an accelerating voltage of 100 kV Images were capturedusing a charged couple detector (CCD) camera for furtheranalysis using Gatan Digital Micrograph analysis software

26 Mechanical Properties The Izod impact strength of thePP and its nanocomposites have been evaluated using TiniusOlsen USA impactometer as per ASTMD 256 The sampleswere notched prior to the testing prior to loading withhammer of 2 J The notch depth was taken as 253mm witha notch angle of 45∘ The microinjection molded samples ofdiameter 635 times 127 times 3mm3 have been used for the testing7 numbers of samples of each composition have been testedin order to get the accuracy in the result

Further the microinjection molded dog-bone shapedsamples (5 samples of each composition) have been subjectedto tensile test Tensile properties of the virgin matrix as wellas the nanocomposites have been evaluated using UniversalTensile Machine (3382 Instron UK) as per ASTM D 638Samples of 127 times 127 times 3mm3 dimension were subjected totensile test at a gauge length of 50mm and with crossheadspeed of 5mmmin

27 Dynamic Mechanical Analysis (DMA) The samples weretested using dynamic mechanical analyzer (TA InstrumentsQ800) to determine the effects of modifications on thedispersion of clay in the nanocomposites The samples weretested at minus100∘C to 150∘C to obtain information acrosstransition temperature The DMA analysis was conducted ina dual cantilever mode The experiment was performed withthe injection molded samples having a dimension of 635 times127 times 3mm3

28 Rheological Analysis The samples were characterized bya modular advanced rheometer system (MARS III ThermoFisher Scientific Germany) in the frequency sweep modeusing parallel plate fixtures of 25mm in diameter at a gap of1mm In order to investigate the formation of silicate networkand extensive morphology frequency sweep method is mostoften used methodology Hence the dynamic frequencysweep test was performed at 220∘Cand frequency sweep from01 radsec to 200 radsec at a constant strain amplitude of1 Corresponding storagemodulus (1198661015840) loss modulus (11986610158401015840)and complex viscosity (120578lowast) were determined as a function offrequency and the data were analyzed and represented

3 Materials

Polypropylene (M110) was procured from Ms Haldia Petro-chemicals Kolkata India having a density of 094 gcm3and the MFI of 11 g10min Multiwalled carbon nanotubes ofgt98 purity and diameter of 80ndash100 nm used in this workwas purchased from Ms Nanoshel Intelligent MaterialsPvt Ltd India The compatibilizer used in this study wasmaleic anhydride grafted polypropylene (MAPP) (OPTIM-P425) having an anhydride content of 16ndash25 and density091 gcm3 was purchased fromMs Pluss Polymers Pvt LtdHaryana India

4 Results and Discussion

41 Analytical Characterization through Titration MethodThe total acidic sites were quantified by titration method


0080

0075

0070

0065

0060

0055

0050

0045

0040

0035

0030

0025

4000 3500 3000 2500 2000 1500 1000

2380 2360

2360

McCNT

ACNTCNT

Tran

smitt

ance

()









1200 1300 1400 1500 1600 1700 1800

Inte

nsity

()

McCNT

ACNT

CNT









(a) (b) (c)

(d) (e)














0

1000

2000

3000

4000

5000

Stor

age m

odul

us (G

998400 )

0 50 100 150

PP



(a)

0 50 100 1500

50

100

150

200

250

300


Loss

mod

ulus

(MPa

)Temperature (∘C)

minus100 minus50

(b)









003

006

009

012

015

018

021

0 50 100 150

PP



tan120575







PP

103

102

10


Com

plex

visc

osity

(120578lowast)

(Pa)





Slope of 1198661015840versus 120596

Slope of 11986610158401015840versus 120596




1198991003816100381610038161003816 (1)





10

1

100

1000

10000

01 1 10 100

Frequency (rads)

Stor

age m

odul

us (G

998400 ) (Pa

)

(a)

01 1 10 100

100

1000

10000


Loss

mod

ulus

(G998400998400

) (Pa

)

Frequency (rads)

(b)


PPMAPPACNT

(a)

PPMAPPMcCNT

(b)







5 Conclusions





References







3

























RoboticsJournal of





Journal of



RotatingMachinery





VLSI Design



Shock and Vibration







Journal of



Volume 2014


SensorsJournal of





Propagation










0080

0075

0070

0065

0060

0055

0050

0045

0040

0035

0030

0025

4000 3500 3000 2500 2000 1500 1000

2380 2360

2360

McCNT

ACNTCNT

Tran

smitt

ance

()









1200 1300 1400 1500 1600 1700 1800

Inte

nsity

()

McCNT

ACNT

CNT









(a) (b) (c)

(d) (e)














0

1000

2000

3000

4000

5000

Stor

age m

odul

us (G

998400 )

0 50 100 150

PP



(a)

0 50 100 1500

50

100

150

200

250

300


Loss

mod

ulus

(MPa

)Temperature (∘C)

minus100 minus50

(b)









003

006

009

012

015

018

021

0 50 100 150

PP



tan120575







PP

103

102

10


Com

plex

visc

osity

(120578lowast)

(Pa)





Slope of 1198661015840versus 120596

Slope of 11986610158401015840versus 120596




1198991003816100381610038161003816 (1)





10

1

100

1000

10000

01 1 10 100

Frequency (rads)

Stor

age m

odul

us (G

998400 ) (Pa

)

(a)

01 1 10 100

100

1000

10000


Loss

mod

ulus

(G998400998400

) (Pa

)

Frequency (rads)

(b)


PPMAPPACNT

(a)

PPMAPPMcCNT

(b)







5 Conclusions





References







3

























RoboticsJournal of





Journal of



RotatingMachinery





VLSI Design



Shock and Vibration







Journal of



Volume 2014


SensorsJournal of





Propagation










(a) (b) (c)

(d) (e)














0

1000

2000

3000

4000

5000

Stor

age m

odul

us (G

998400 )

0 50 100 150

PP



(a)

0 50 100 1500

50

100

150

200

250

300


Loss

mod

ulus

(MPa

)Temperature (∘C)

minus100 minus50

(b)









003

006

009

012

015

018

021

0 50 100 150

PP



tan120575







PP

103

102

10


Com

plex

visc

osity

(120578lowast)

(Pa)





Slope of 1198661015840versus 120596

Slope of 11986610158401015840versus 120596




1198991003816100381610038161003816 (1)





10

1

100

1000

10000

01 1 10 100

Frequency (rads)

Stor

age m

odul

us (G

998400 ) (Pa

)

(a)

01 1 10 100

100

1000

10000


Loss

mod

ulus

(G998400998400

) (Pa

)

Frequency (rads)

(b)


PPMAPPACNT

(a)

PPMAPPMcCNT

(b)







5 Conclusions





References







3

























RoboticsJournal of





Journal of



RotatingMachinery





VLSI Design



Shock and Vibration







Journal of



Volume 2014


SensorsJournal of





Propagation












0

1000

2000

3000

4000

5000

Stor

age m

odul

us (G

998400 )

0 50 100 150

PP



(a)

0 50 100 1500

50

100

150

200

250

300


Loss

mod

ulus

(MPa

)Temperature (∘C)

minus100 minus50

(b)









003

006

009

012

015

018

021

0 50 100 150

PP



tan120575







PP

103

102

10


Com

plex

visc

osity

(120578lowast)

(Pa)





Slope of 1198661015840versus 120596

Slope of 11986610158401015840versus 120596




1198991003816100381610038161003816 (1)





10

1

100

1000

10000

01 1 10 100

Frequency (rads)

Stor

age m

odul

us (G

998400 ) (Pa

)

(a)

01 1 10 100

100

1000

10000


Loss

mod

ulus

(G998400998400

) (Pa

)

Frequency (rads)

(b)


PPMAPPACNT

(a)

PPMAPPMcCNT

(b)







5 Conclusions





References







3

























RoboticsJournal of





Journal of



RotatingMachinery





VLSI Design



Shock and Vibration







Journal of



Volume 2014


SensorsJournal of





Propagation










003

006

009

012

015

018

021

0 50 100 150

PP



tan120575







PP

103

102

10


Com

plex

visc

osity

(120578lowast)

(Pa)





Slope of 1198661015840versus 120596

Slope of 11986610158401015840versus 120596




1198991003816100381610038161003816 (1)





10

1

100

1000

10000

01 1 10 100

Frequency (rads)

Stor

age m

odul

us (G

998400 ) (Pa

)

(a)

01 1 10 100

100

1000

10000


Loss

mod

ulus

(G998400998400

) (Pa

)

Frequency (rads)

(b)


PPMAPPACNT

(a)

PPMAPPMcCNT

(b)







5 Conclusions





References







3

























RoboticsJournal of





Journal of



RotatingMachinery





VLSI Design



Shock and Vibration







Journal of



Volume 2014


SensorsJournal of





Propagation











10

1

100

1000

10000

01 1 10 100

Frequency (rads)

Stor

age m

odul

us (G

998400 ) (Pa

)

(a)

01 1 10 100

100

1000

10000


Loss

mod

ulus

(G998400998400

) (Pa

)

Frequency (rads)

(b)


PPMAPPACNT

(a)

PPMAPPMcCNT

(b)







5 Conclusions





References







3

























RoboticsJournal of





Journal of



RotatingMachinery





VLSI Design



Shock and Vibration







Journal of



Volume 2014


SensorsJournal of





Propagation










5 Conclusions





References







3

























RoboticsJournal of





Journal of



RotatingMachinery





VLSI Design



Shock and Vibration







Journal of



Volume 2014


SensorsJournal of





Propagation















RoboticsJournal of





Journal of



RotatingMachinery





VLSI Design



Shock and Vibration







Journal of



Volume 2014


SensorsJournal of





Propagation









research article a novel method of mechanical oxidation of

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