J. Mater. Sci. Technol., Vol.25 No.2, 2009 247

Electrical and Mechanical Properties of PMMA/nano-ATO

Composites

Wei Pan†, Huiqin Zhang and Yan ChenInstitute of Materials and Chemical Engineering, Zhongyuan University of Technology, Zhengzhou 450007, China

[Manuscript received December 24, 2007, in revised form July 1, 2008]

Conducting nanocomposites of poly (methyl methacrylate) (PMMA) and antimony doped tin oxide (ATO)were prepared by solution blending. The influences of ATO content on the electrical conductivity, thermalstability, and mechanical properties of the nanocomposites were investigated. A homogeneous dispersionof silane coupling agent modified ATO was achieved in PMMA matrix as evidenced by scanning electronmicroscopy. The resultant PMMA/silane-ATO nanocomposites were electrically conductive with significantconductivity enhancement at 4 wt pct. It was found that the composition at 4 wt pct ATO gave the highertensile strength. Furthermore, it gave the largest elongation at break value among all the compositions.Thermal stability of the nanocomposites was remarkably enhanced by the incorporation of silane-ATO.

KEY WORDS: Antimony doped tin oxide; PMMA; Nanocomposites; Structure and properties

1. Introduction

Polymers can be compounded with a variety ofcommon and special fillers, reinforcements, and mod-ifiers to yield specific properties in a wide range ofapplications[1,2]. Among these, additives that areelectrically and thermally conductive can provide pro-tection against static accumulation, electrostatic dis-charge and molding cycle reduction. Various fillers,some of metallic, are used to improve the conduc-tive properties of the neat polymer. However, highconcentrations of filler (e.g. 30% carbon black), cantake a toll on physical and esthetical properties of thepolymer: selection of conductive material has ofteninvolved compromises[3,4]. The preparation of poly-mer composites by dispersion of small loadings ofnanosized fillers in a polymeric matrix has lately at-tracted much attention in the academia and the indus-try for its potential in improving the performance ofmacromolecular materials. Nanoparticles may makethe matrix′s physical-mechanical properties much im-proved with respect to traditional micro-sized fillers,due mainly to maximization of the polymer-filler in-terfacial region[5–7].

Particularly interesting conductive filler is anti-mony doped tin oxide (ATO) as it possesses goodelectrical conductivity with optical transparency[8–10].When used as antistatic agent, ATO shows better per-formance than currently used carbon blacks, metal-lic pigment and organic polymer binders[11]. ATOhas been used to increase the electrical conductivityof polyvinyl acetate-acrylate copolymer coatings[12],gelatine and acrylate films[13], and urethane and poly-ester coatings[14]. For different matrices, the mini-mum amount of ATO to obtain the aimed increase inconductivity varied roughly from 5 to 20 vol. pct.

PMMA is an important commercial plastic, whichhas extensive application in many sectors such asin aircraft glazing, signs, lighting, architecture,transportation and merchandising. However, thelow conductivity, less than 10−14 S/cm and the

† Corresponding author. Assoc. Prof., Ph.D.;E-mail address: panwei@zzti.edu.cn (W. Pan).

static problem restrict its further applications.PMMA/ATO conducting system has not yet beenexplored but it is a competitive system for mak-ing conducting polymer. In our study, PMMA/ATOnanocomposites were prepared by a solution-mixingmethod. The relationship between the electrical prop-erties and the morphology of the composites was stud-ied. The effects of mixing fillers on thermal propertiesof the nanocomposites were also investigated.

2. Experimental

2.1 Materials

The PMMA (LX-025) employed in this study waspurchased from Shanghai Petroleum Chemical Co.,Ltd. (Shanghai, China). The untreated nano-ATOparticles (specific surface area: 80 m2/g, antimonydoping level: 15%, average particles size: 40 nm) werepurchased from Shanghai Huzheng Technology Co.,Ltd. (Shanghai, China). The silane coupling agent(KH570, commercial grades) supplied by ShanghaiYaohua Chemical Plant (Shanghai, China), was usedto treat the nano-ATO particles. Other agents andprocess assistants (commercial grades) were obtainedfrom the market.

2.2 Nano-ATO particle surface treatment

Silane coupling agent (0.1 g) was mixed with 5.0 gdistilled water and 95.0 g absolute ethanol. Then10.0 g ATO powder was added into the solvent mix-ture. The suspension was dispersed in an ultrason-icator for 1 h, and then was refluxed at 120◦C for24 h. After surface treatment, the ATO particles werewashed with ethanol three times in order to removeany unreacted silane coupling agent.

2.3 Composites preparation

The silane-ATO or untreated-ATO was dispersedin THF (tetrahydrofuran) to prepare a suspendingdispersion with certain nano-ATO content. ThePMMA was dissolved in THF by heating to a back-

248 J. Mater. Sci. Technol., Vol.25 No.2, 2009

Fig. 1 SEM micrographs of freeze fractured surfaces of PMMA/ATO nanocomposites: (a) 4 wt pct untreated-ATO, (b) 4 wt pct silane-ATO, (c) 8 wt pct untreated-ATO, (d) 8 wt pct silane-ATO

flow temperature of THF (about 80◦C). The ATOsuspending dispersion was added drop by drop intothe PMMA solution at the backflow state, keepingthe total concentration of the ATO and the PMMAas 20 wt pct mass ratio. The mixture solutions werecast and left to dry in vacuum at 60◦C for 48 h.

2.4 Testing methods

Morphological studies were performed by SEM(scanning electron microscopy). Microphotographswere taken of the surface made by fracturing the spec-imen in liquid nitrogen and then sputtered with gold.A JSM5600LV scanning electron microscope was usedfor morphological observation. Electrical conductiv-ity of the composites was measured by four-probemethod. Five measurements in three different sam-ples of each composition were carried out, and thestandard deviation was always less than 1%. Wideangle X-ray diffraction (XRD) was carried out us-ing a BRUKER-AXC08 X-ray diffractmeter and fil-tered CuKα radiation. The diffraction patterns ofthe composite powder of the ATO and PMMA wereobtained by scanning the samples in an interval of2θ=5◦–60◦. Thermogravimetric analyses (TGA) ofpure PMMA and PMMA/ATO nanocomposites wereperformed with a TA Instruments Du Pont l090 at10◦C/min in nitrogen atmosphere. Room tempera-ture tensile testing of the composites was conductedon an Instron1122 testing machine at a crossheadspeed of 50 mm/min. Five samples were tested foreach case.

3. Results and Discussion

3.1 Morphology observation

The cross-section SEM micrographs of the

PMMA/untreated-ATO and PMMA/silane-ATOnanocomposites containing 4 and 8 wt pct ATO areshown in Fig. 1. The dark regions are PMMA phasewhile the bright regions are conductive ATO phase.Figure 1(a) and 1(c) show the poor particle disper-sion in PMMA matrix. Raw ATO is agglomeratedinto large size. On the other hand, the silane-ATOparticles are homogeneously dispersed in the PMMAmatrix (Fig. 1(b) and (d)). This is because the pres-ence of the silane group on the ATO surface is likelyto give the strong interfacial interaction between thepolymer matrix and the ATO in polymer composites.

3.2 Electrical conductivity

The electrical conductivity of the PMMA/ATOnanocomposite as a function of ATO content is shownin Fig. 2. Figure 2 shows that the conductivity ofthe PMMA/silane-ATO composites increased with in-creasing the ATO content. The sharp increase in theconductivity for ATO up to 4 wt pct suggested thatthe percolation threshold in the conductivity of thenanocomposites is around 4 wt pct content. Whenthe ATO content was increased further, the electricconductivity increased slowly. This demonstrates avery low percolation threshold value for a conduct-ing nanocomposite prepared with silane-ATO, whichis much smaller than that of conventional conductingmacro-composites. The augmentation of the electri-cal conductivity can be ascribed to the uniform dis-persion of silane-ATO within the polymer matrix andthe formation of conducting network at very low fillerloading. With very low inorganic filler content, theresulted nanocomposites can remain the superior in-herent mechanical strength of polymeric matrix. Thenanocomposites exhibit high polymeric performanceand electrical conductivity.

Figure 2 also shows that the electrical conductivity

J. Mater. Sci. Technol., Vol.25 No.2, 2009 249

0 5 10 15 2010-14

10-10

10-6

10-2

PMMA/untreated-ATO PMMA/silane-ATO

Content of ATO / %

Con

duct

ivity

/ S

cm

-1

Fig. 2 Electrical conductivity of PMMA/ATO compos-ite vs ATO content

10 20 30 40 50 60

ATO

12 wt pct ATO8 wt pct ATO4 wt pct ATO

PMMA

2 / deg.

Fig. 3 X-ray diffractrograms of PMMA, silane-ATO andPMMA/silane-ATO

of the PMMA/untreated-ATO composites was lowerthan that of the silane-ATO composites at identicalATO content. As a result, the electrical current ofthe composites filled with the well dispersed ATO washigher than that of composites filled with the poorlydispersed ATO. It was easier for the well dispersedATO to form electrical paths due to their relativelyhomogeneous dispersion of nanoparticles than for thepoor dispersion ATO.

3.3 Wide-angle X-ray diffraction

It is known that the crystal structure of thematrix has a key role in determining the proper-ties of polymer-based composites[15,16]. The XRDpatterns of silane-ATO, the pure PMMA and thePMMA/silane-ATO nanocomposites with 4, 8 and12 wt pct of nano-ATO content are shown in Fig. 3.The XRD patterns of the nano-ATO display five peaksat 2θ=26.5◦, 33.7◦, 37.7◦, 51.7◦ and 54.7◦ correspond-ing to the diffraction from (110), (101), (200), (220)and (211) plane, respectively[17]. PMMA showed abroad diffraction peak at 2θ=14◦, which indicatedthat PMMA is amorphous.

The XRD patterns of the PMMA/ATO nanocom-posites showed that combine peaks appeared in theATO and pure PMMA. Moreover, the intensity ofthe peaks assigned to the ATO in the composite in-creased with increasing the content of ATO. However,

0 5 10 15 20

40

50

60

70

Elo

ngat

ion

to b

reak

/ %

Silane-ATO content / %

1.0

1.5

2.0

2.5

Tens

ile s

treng

th /

MP

a

Fig. 4 Effect of silane-ATO content on tensile strengthand elongation to break of composites

100 200 300 400 500 6000

20

40

60

80

100

Wei

ght /

%

Temp. / oC

Der

ivat

iva

/ % m

in-1

417oC -60

-40

-20

0

20

Fig. 5 TGA curves of PMMA/ATO (12 wt pct)

the position of the peaks corresponding to the twoconstituents of the nanocomposite was the same asthe individual of PMMA and nano-ATO, which illus-trated that either the orientation of the PMMA chainsor the structure of ATO was not influenced each otherduring the process of preparation.

3.4 Tensile measurement

The tensile strength and elongation at break of thePMMA/silane-ATO composites with different ATOcontents are shown in Fig. 4. The tensile strength ofPMMA/silane-ATO nanocomposites increased withincreasing silane-ATO content up to 4 wt pct and thendecreases at higher loading. The elongation at breakbehaves in a similar way. With slightly adding ofsilane-ATO, the filler is uniformly dispersed in PMMAmatrix. The filler has high aspect ratio, which tendsto improve interfacial bonding and form filler-polymerinteraction because of high specific surface area of thefiller[18,19]. The lower tensile strength of nanocompos-ites at a higher silane-ATO loading may be due to theinevitable aggregation of ATO nanoparticles. Theseaggregates are the weakest point in the composite,which leads to earlier tensile break.

3.5 Thermal analysis

The thermal stability of the pure PMMA andPMMA/silane-ATO nanocomposites with 12 wt pctnano-ATO content was characterized by TGA. Theweight loss curves as a function of temperature isshown in Figs. 5 and 6. In the present study, 50%of the total weight loss was considered as the thermal

250 J. Mater. Sci. Technol., Vol.25 No.2, 2009

100 200 300 400 500 600

0

20

40

60

80

100W

eigh

t / %

Der

ivat

iva

/ % m

in-1

Temp. / oC

-40

-20

0

392oC

Fig. 6 TGA curves of pure PMMA

decomposition temperature of the system, which usu-ally coincides with the peak of the derivative curves.It is observed that the thermal decomposition tem-perature of PMMA/ATO is around 417◦C, whereasthat of pure PMMA is only 392◦C. This clearlydemonstrates that the PMMA/silane-ATO system isthermally more stable than the corresponding neatPMMA system. The existence of inorganic materialsin polymer matrix, generally, enhances the thermalstability of the composite[20]. The thermal stabilityalso increases due to the presence of the inorganicphase and its interaction with the polymer.

4. Conclusion

PMMA/silane-ATO and PMMA/ATO compositesand the morphology were prepared by solution blend-ing. Electrical properties and mechanical propertiesof the composites and the morphology were charac-terized by SEM, XRD and TGA. The results showedthat the silane coupling agent onto the ATO surfaceimproved the dispersion of ATO in PMMA along withmuch enhanced electrical property of composites com-pared to those containing ATO without treated. Itwas found that the 4 wt pct silane-ATO sample gavethe highest tensile strength and elongation at break

value amongst all the ATO compositions from 0 to20 wt pct. Thermal stability of the nanocompos-ites was remarkably enhanced by the incorporationof silane-ATO.

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