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7/28/2019 Oxygen Barrier of Multiwalled Carbon Nanotube%2FPolymethyl Methacrylate Nanocomposites Prepared by in Situ

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J. Mater. Sci. Technol., 2012, 28(5), 391395.

Oxygen Barrier of Multiwalled Carbon Nanotube/Polymethyl

Methacrylate Nanocomposites Prepared by in situ Method

Ajaya K. Pradhan1) and Sarat K. Swain1,2)

1) Department of Chemistry, North Orissa University, Takatpur, Baripada 757003, India

2) Department of Chemistry, Veer Surendra Sai University of Technology, Burla, Sambalpur 768018, India

[Manuscript received June 13, 2011, in revised form December 29, 2011]

Multiwalled carbon nanotubes (MWCNTs)/poly(methyl methacrylate) (PMMA) nanocomposites were pre-pared by ultrasonic assisted emulsifier free emulsion polymerization technique with variable concentrationof functionalized carbon nanotubes. MWCNTs were functionalized with H2SO4 and HNO3 with continu-ing sonication and polished by H2O2. The appearance of Fourier transform infrared absorption bands in thePMMA/MWCNT nanocomposites showed that the functionalized MWCNT interacted chemically with PMMAmacromolecules. The surface morphology of functionalized MWCNT and PMMA/MWCNT nanocompositeswere studied by scanning electron microscopy. The dispersion of MWCNT in PMMA matrix was evidenced byhigh resolution transmission electron microscopy. The oxygen permeability of PMMA/MWCNT nanocompos-ites gradually decreased with increasing MWCNT concentrations.

KEY WORDS: Nanocomposites; Morphology; Permeability; Dispersion

1. Introduction

Carbon nanotubes (CNTs) can consist of singleor multiple concentric graphene cylinders. Since itsdiscovery[1], CNTs are ideal fillers for polymer com-posites due to high Youngs modulus combined with

low density, good electrical and thermal conductiv-ity. The very high aspect ratio (approximately 10000)of the CNTs makes possible the addition of a smallamount (5 wt%) of CNTs for the strong improve-ment of the electrical[2,3], thermal[4] and mechanical[5]

properties of the polymer matrix. However, the effec-tive usefulness of nanotubes as fillers in polymer com-posites depends on the capacity to obtain a good dis-persion of CNTs in the matrix[6,7]. In the preparationof good CNT/polymer composites, an appropriatesurface modification of CNTs is essential for achievinga homogeneous dispersion of CNTs and strong bond-ing between CNTs and polymer matrices[8].

Different methods are commonly used to incor-

Corresponding author. Prof.; Tel.: +91 9937082348;E-mail address: [email protected] (S.K. Swain).

porate nanotubes into polymers: (i) film casting ofsuspensions of nanotubes in dissolved polymers, (ii)polymerization of nanotube with monomer mixtures,(iii) melt mixing[9,10], (iv) solution blending[11], and(v) in situ polymerization[12,13]. Film casting wasused to investigate the properties of polymers con-taining CNTs including the effect of dispersion andorientation[1416] and interfacial bonding[17]. Meltmixing cannot achieve homogeneous dispersion ofCNTs in polymer matrices where as solution blend-ing does not form strong chemical bonding betweenCNTs and polymer. The in situ polymerization tech-nique is a preferred method of composite formationas per earlier reports[1820].

The mechanical properties, electrical conductiv-ity and morphology of poly(methyl methacrylate)(PMMA)/multiwalled carbon nanotube (MWCNT)composites have been reported previously[21,22].Schmidt et al.[23] prepared the thin transparent film of

MWCNTs in PMMA matrix and the results showedincreased electrical conductivity. Park et al.[24] syn-thesized MWCNT/PMMA nanocomposites using insitu bulk polymerization with ultrasonication and re-


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392 A.K. Pradhan et al.: J. Mater. Sci. Technol., 2012, 28(5), 391395.

Fig. 1 Flow sheet for synthesis of PMMA/MWCNT nanocomposites

ported the increase in electrical conductivity of thecomposites. Pande et al.[25] reported the improvedmechanical properties of MWCNT/PMMA nanocom-posites prepared by in situ polymerization method.Ormsby et al.[26] prepared the polymethylmethacry-late bone cement/MWCNT nanocomposites in dif-ferent methods. The improved mechanical proper-ties of the nanocomposites cement and the decreasein thermal properties were attributed to the methodof incorporation of MWCNT. Jin et al.[27] prepared

the thin films by compressing the well dispersedMWCNT/PMMA nanocomposites through miniaturemixture-molder and reported the increase in elec-trical conductivity of the composites. Valentinoet al.[28] studied the influence of polymer structureand nanotube concentration on conductivity of poly-ethylene/MWCNT nanocomposites by melt mixingprocess and found the enhanced electrical propertiesof the composites. The MWCNT/PMMA nanocom-posites may be applicable for electronic packaging ma-terial and corrosion resistance materials in engineer-ing applications[27,28].

In this work, the PMMA/MWCNT nanocompos-ites were synthesized in aqueous medium through insitu polymerization under ultrasonication techniquefor good dispersion and debundling of the MWCNTs.The morphology and dispersion of MWCNTs wereinvestigated by scanning electron microscopy (SEM)and high resolution transmission electron microscopy(HRTEM). The influence of the MWCNT concentra-tions on thermal properties and oxygen permeabilitywere studied as compared to the virgin PMMA.

2. Experimental

The MWCNTs that have been used during thisexperiment were purchased from Sigma Aldrich, USAand they had diameters ranging from 10 to15 nm andlength ranging from 0.1 to 10 m. Methyl methacry-late (MMA) was purchased from Merck, Germanyand used after purification with solution of phos-phoric acid, sodium hydroxide and double distilledwater. Potassium persulphate (KPS) was obtainedfrom Merck, Germany and used as received. All otherreagents such as H2SO4, HNO3, and ammonium fer-rous sulphate were of analytical grade and used asreceived.

The MWCNTs were cut and functionalized bytreatment in a mixture of concentrated H2SO4 andHNO3 in a volume ratio of 3:1 and sonicated by anultrasonic cleaner (120 W/60 kHz) for 24 h at about

40 C in a flask. The solution was then dilutedwith double distilled water and filtered. The residuewas washed with distilled water. Further the openend tubes were polished with hydrogen peroxide andH2SO4 in a volume ratio of 1:4 with stirring at 70

Cfor 30 min. The resultant solution was diluted withdistilled water and centrifuged to get the functional-ized multiwalled carbon nanotubes (f-MWCNT) andcontinued till no acid remain in the f-MWCNT.

The f-MWCNTs with distilled water were soni-

cated in a two necked flask for 20 min. Then MMAmonomer was added into the flask and stirred for10 min, which were further sonicated for 10 min.The stock solution of KPS of 0.1 mol/L as initia-tor was added and nitrogen gas was purged into theflask to remove oxygen. It was allowed to polymerizefor 3 h with constant stirring at 63 C. Ammoniumferrous sulphate of 0.1 mol/L solution was added toarrest the polymerization process. The precipitatewas filtered to get PMMA/MWCNT nanocompos-ites and dried in hot air oven for characterization ofits properties. The concentration of MMA and KPS

were optimized by weight percent conversion of poly-merization and [MMA]=1.41 moldm3, [KPS]=1102 moldm3 were kept constant for variation ofMWCNT. The schematic representation of synthesisof PMMA/MWCNT nanocomposites is illustrated asFig. 1.

The chemical structure and interaction of MW-CNT with polymer matrix were detected witha Fourier transform infrared (FTIR) spectrometer(Perkin-Elmer Paragon 500) in the range of 400 to4000 cm1 using KBr powder. The morphology anddispersion of MWCNT in PMMA matrix were in-vestigated by using SEM (JEOL, JSM-5800, Japan).The high resolution transmission electron microscopy(Tec-nai 12, Philips), operating at 120 kV was usedto study the dispersion of MWCNT in PMMA matri-ces. Thermogravimetric analysis (TGA) of powderedcomposites was performed for the samples in nitro-gen flow at a heating rate of 10 C/min using a TGAapparatus (Model DTG-60, Shimadzu Corporation,Japan). Oxygen permeability of the nanocompositeswere measured with ASTM F 316-86 by using oxy-gen permeation analyzer (PMI instrument, GP-201-A, NY, USA)

3. Results and Discussion

3.1 FTIR analysis

The FTIR spectra of MWCNT, f-MWCNT,


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A.K. Pradhan et al.: J. Mater. Sci. Technol., 2012, 28(5), 391395. 393

4 0 0 0 3 5 0 0 3 0 0 0 2 5 0 0 2 0 0 0 1 5 0 0 1 0 0 0 5 0 0

4 0 0 0 3 5 0 0 3 0 0 0 2 5 0 0 2 0 0 0 1 5 0 0 1 0 0 0 5 0 0

T

r

a

n

s

m

t

t

a

n

c

e

W a v e n u m b e r / c m

M W C N T

f - M W C N T

3 4 1 0

3 5 0 0

1 7 1 0

T

r

a

n

s

m

t

t

a

n

c

e

W a v e n u m b e r / c m

M M A / f - M W C N T

1 7 3 5

2 3 6 4

2 9 5 3

1 4 5 4

Fig. 2 FTIR spectra of MWCNT, f-MWCNT, PMMAand PMMA/f-MWCNT nanocomposites

PMMA and PMMA/f-MWCNTs were studied toidentify the functional groups proving interaction ofMWCNT with PMMA in Fig. 2. MWCNT beforefunctionalization exhibits as OH stretching band at3410 cm1 which is induced by the carboxyl and hy-droxyl group attached to the open ends of MWCNT.After being sonicated in the H2SO4/HNO3 (3:1) byvolume mixture solvent, MWCNTs show two absorp-

tion bands at 3500 and 1710 cm1 (Fig. 2 (inset))associating with OH stretching and C=O stretch-ing in carboxyl group, respectively. The results in-dicate that MWCNTs bonded to COOH groups areobtained. The peak at 1735 cm1 shows the charac-teristics C=O stretching from the carboxyl and car-

bonyl groups introduced by the acid treatment on theMWCNT surface by which PMMA macromoleculesare grafted onto the surface of functionalized MW-CNT.

3.2 Morphology study

The morphology and the degree of dispersion ofraw MWCNT (Fig. 3(a)), f-MWCNT (Fig. 3(b)) andPMMA/f-MWCNT composites (Fig. 3(c)) have beenanalyzed by SEM. The SEM micrograph in Fig. 3(c)of PMMA/f-MWCNT nanocomposites at concentra-

tion of 0.70 wt% of MWCNT shows homogeneous dis-persion of the carbon nanotubes throughout the poly-mer matrices and nanotubes have been interconnectedat this concentration and form a nanotube network.Carbon nanotubes are observed as bright spots lyingover the dark PMMA matrix and explain the gooddispersion of MWCNT in PMMA matrix. Fig. 3(d)indicates the HRTEM image of PMMA/f-MWCNTnanocomposite sample which clearly shows a uniform

Fig. 3 SEM images: (a) MWCNT, (b) f-MWCNT, (c) PMMA/f-MWCNT nanocomposites with 0.70 wt% ofMWCNT; (d) HRTEM image of PMMA/f-MWCNT nanocomposites


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394 A.K. Pradhan et al.: J. Mater. Sci. Technol., 2012, 28(5), 391395.

1 0 0 2 0 0 3 0 0 4 0 0 5 0 0 6 0 0

W

e

g

h

t

p

e

r

c

e

n

t

T e m p e r a t u r e /

f - M W C N T

P M M A / f - M W C N T

P M M A

Fig. 4 TG curves of PMMA, PMMA/f-MWCNTnanocomposites with 0.70 wt% of MWCNT

PMMA coating around the tube core. This is con-sidered as a clear evidence for the interaction of f-MWCNT with PMMA matrix. The MWCNT over-laid with PMMA confirms that the interaction be-tween MWCNT and PMMA is not a physical contactbut strong adhesion due to chemical bond.

3.3 TG analysis

The thermal stability of PMMA, f-MWCNT andPMMA/f-MWCNT composites are shown in Fig. 4. Itis observed that in comparison to PMMA the decom-

position of PMMA/f-MWCNT composites are shiftedtowards a higher temperature. The thermal decom-position of PMMA occurs in three steps reaction withmaximum decomposition at 270 C, the first stepdue to water loss, second step due to degradationof polymer chain and third step due to oxidationof PMMA macromolecules above 400 C. Two stepchange of MWCNT is observed because of water lossfrom 80 to 130 C and dehydroxylation of functional-ized MWCNT from 200400 C. From TG analysis itis observed that PMMA macromolecules decomposealmost completely, whereas for wrapped PMMA/f-MWCNT composites, a residue of about 50% is ob-tained due to MWCNT content. The thermal sta-bility of PMMA/f-MWCNT composites is more thanthat of the PMMA due to grafting of MWCNT withPMMA macromolecules. Further it is seen from Fig. 4that the plot of virgin polymer is sharper than that ofits composites, thus the addition of f-MWCNTs canslower the degradation rate of PMMA matrix. Thisindicates that the dispersion of the MWCNT into thepolymer matrix also improves the thermal stability ofthe composites.

3.4 Oxygen permeability

The oxygen permeability of virgin PMMA andPMMA/f-MWCNT nanocomposites has been stud-ied as shown in Fig. 5. At 3.447 kPa (0.5 Psi)

0 . 0 0 0 . 3 5 0 . 7 0 1 . 0 5 1 . 4 0 1 . 7 5

O

x

y

g

e

n

p

e

r

m

e

a

b

t

y

/

(

c

m

2

/

m

n

)

M W C N T / w t %

Fig. 5 Oxygen permeability of PMMA/f-MWCNTnanocomposites at constant pressure of 3.447 kPa(0.5 Psi)

pressure, the oxygen permeability of PMMA/f-MWCNT nanocomposites with 1.75 wt% of MWC-NTs loading is about eight times less than that ofvirgin PMMA. The reduction of permeability arisesfrom the longer diffusive path of the penetration ofthe oxygen in the presence of MWCNTs. The incor-poration of MWCNT in PMMA matrix is particularlyefficient at maximizing the path length due to the highaspect ratio. Further, the presence of MWCNT intro-duces a torturous path for which the oxygen travelslonger diffusive path. Hence oxygen permeability ofPMMA/MWCNT nanocomposites is less than that of

PMMA matrix. The tremendous decrease in oxygenpermeability with increasing MWCNT (wt%) is dueto good dispersion of MWCNTs in polymer matrixof PMMA/f-MWCNT composites which is supportedwith Fig. 3(c). The substantial reduction in oxygenpermeability of PMMA/f-MWCNT may enable thecomposites for coating industry.

4. Conclusion

PMMA/f-MWCNT nanocomposites were synthe-sized by emulsion polymerization process providing

good dispersion of carbon nanotubes in the polymermatrix. Dispersion and morphology of MWCNT inthe polymer matrix were explained by HRTEM andSEM micrographs. The decrease in oxygen permeabil-ity of the PMMA/f-MWCNT nanocomposites withaddition of the MWCNT would make the materialsbe more applicable in the industrial coatings.

Acknowledgements

The authors are thankful to Department ofAtomic Energy, BRNS, Government of India forproviding financial support under Grant OM #2008/20/37/5/BRNS/1936.

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