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Polymer Testing 30 (2011) 155–160

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Polymer Testing

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Material Properties

Studies on Microstructural and Thermophysical properties of polymernanocomposite based on polyphenylene oxide and Ferrimagneticiron oxide

K. Agarwal a, M. Prasad a, R.B. Sharma b, D.K. Setua a,*

aDefence Materials and Stores Research and Development Establishment, DMSRDE (Post Office), G. T. Road, Kanpur 208013, IndiabDefence Institute of Advanced Technology, Girinagar, Pune 411025, India

a r t i c l e i n f o

Article history:Received 17 September 2010Accepted 14 November 2010

Keywords:Magnetic polymer nanocompositePolypheylene oxideg-Fe2O3

Vibrational sample magnetometerSEM-EDXThermal analysis

* Corresponding author. Tel.: þ91 512 2451759 72450404.

E-mail address: dksetua@rediffmail.com (D.K. Se

0142-9418/$ – see front matter � 2010 Elsevier Ltddoi:10.1016/j.polymertesting.2010.11.009

a b s t r a c t

Nanocomposites of polyphenylene oxide (PPO) filled with nanoparticles of organicallymodified g-Fe2O3, in varied concentration from 0 to 20 wt. %, were prepared. Thermalstability of these nanocomposites was evaluated by thermo-gravimetric analysis (TGA) andtheir dimensional stability was measured at sub-ambient as well as at elevated tempera-tures by thermo-mechanical analysis (TMA). The glass transition temperature (Tg) of thenanocomposites, measured by differential scanning calorimeter (DSC), was found todecrease with increasing weight fraction of g-Fe2O3. Phase morphology of the nano-composites was analyzed by scanning electron microscope (SEM). The distribution ofg-Fe2O3 in PPO matrix was studied by determining the iron using a X-ray energy dispersivespectroscope (EDX) attached to the SEM. These analyses reveal that the nanoparticles ofg-Fe2O3with an average diameter of 20 nmwere dispersed uniformly in the PPOmatrix andalso that there was very good matrix-filler adhesion. A detailed morphological study usinga Gatan hot stage attachment with the SEM showed that there was no change in the surfacemorphology from ambient to high temperature up to 280 �C, beyond which segregation ofthe nanoparticles took place. Measurements by vibrational sample magnetometer (VSM)showed that the degree of saturation magnetization increased with increasing fillerconcentration from 0% to 10wt. % of g-Fe2O3. Themagnetic nanocomposites, in general, alsoshowed very good mechanical strength and high temperature resistance.

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1. Introduction

Recent years have witnessed a rapid growth in thedevelopment of smart materials and devices consisting ofpolymers and elastomers carrying magnetically polarizableparticles e.g., iron [1]. Composites based on ferromagneticor superparamagnetic nanoparticles in polymers canfind application in flexible magnetic devices, magneto-

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tua).

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rheological (MR) elastomers, active vibration dampingmaterials, magnetic recording media, conductive seals/gaskets etc for missiles [2–9]. Composites to be used inthese components/devices should have good mechanicalstrength and high temperature resistance. The relationshipbetween microstructure of iron particles and the MR effectin elastomers has been reported [10,11]. Conductingcomposites comprising of nano particles of Fe2O3 andpolyaniline have been demonstrated to reduce the dielec-tric loss and dielectric permittivity to achieve maximalabsorption of electromagnetic energy [12]. In order togenerate magnetic susceptibility along with high temper-ature resistance, polymer nanocomposites require addition

Table 1Mechanical and Thermal properties of the Nanocomposites.

Sample Tensile strength(Ts), MPa

Elongation atbreak (Eb), %

Peak degradationtemperature, �C

Glass transitiontemperature(Tg), �C

Neat PPO 68.5 15.1 480.9 208.0PPO: g-Fe2O3 (100:1) 71.5 15.0 479.2 205.8PPO: g-Fe2O3 (100:2) 72.1 13.5 477.1 202.5PPO: g-Fe2O3 (100:3) 73.0 12.1 475.7 196.3PPO: g-Fe2O3 (100:5) 75.2 11.6 471.1 184.7PPO: g-Fe2O3 (100:10) 75.6 11.1 469.7 163.7PPO: g-Fe2O3 (100:20) 74.5 10.2 468.7 154.9

K. Agarwal et al. / Polymer Testing 30 (2011) 155–160156

of magnetic nanofillers to high temperature resistantpolymers. The polymer should also enable proper disper-sion of the nanoparticles in the matrix as well as very goodpolymer-filler adhesion to prevent agglomeration of thefiller particles during processing or annealing/storage ofthe polymer/elastomer compounds. Modification of thesurface of the iron particles by surfactants e.g., by use ofsilane coupling agents, has also been reported to benecessary for proper polymer-filler interactions andimprovement of the tensile strength of the composites [13].

Poly(p-phenylene oxide)(PPO) is a high temperatureengineering thermoplastic stable up to 400 �C and hasa high glass transition temperature (Tg ¼ 210 �C). It has,therefore, been chosen to prepare conducting polymernanocomposites by addition of nanosized Maghemiteg-Fe2O3 [14–16]. The surfaces of g-Fe2O3 particles werecoated with a suitable organic surfactant and their homo-geneous dispersion in PPO matrix was obtained by select-ing appropriate polymer processing techniques.

Fig. 1. TGA Thermograms of Polypheylene oxide with 10 wt.% of g-Fe2O3.

2. Experimental details

g-Fe2O3 with an average particle size of 20 nm wassupplied by Macwin Pvt. Ltd., New Delhi, India. PPO (grade803) was obtained from GE plastic, Bangalore, India. Thesurface of the filler particles were coated with organicnonionic surfactant Sorbitol-monoleate gel (PH: 7, g-Fe2O3:gel ¼ 1:1 wt. ratio) at room temperature (25�2 �C) by trit-urating with a pestle and mortar for about 15 min. Theagglomerates/lumps of g-Fe2O3 were broken into finepowder and a homogeneous paste of the g-Fe2O3 in sorbitolgel was obtained. The composites containing 1,2,3,5, 10 &20 wt. % of the modified g-Fe2O3 were prepared in a micro-compounder (model Haake Mini Lab-II of ThermoscientificCo., Karlsruhe, GmbH,Germany)with amini-extruder usingconical intermeshing co-rotating screws at 280 �C for 5min.

The processing conditions were optimized to achieveuniform dispersion of the nanoparticles in the polymermatrix as cross checked by SEM. A micro injection moldingmachine (Type 557-2286) of Thermoscientific Co.,Germany was used to prepare tensile dumb-bell specimenswith temperature of the cylinder at 280–295 �C, holdingtime 20 s and injection pressure of 1000 bar in molds keptat 80–100 �C. Both the tensile strength (TS) and elongationat break (Eb) of the samples were measured in a UniversalTesting Machine (UTM, Model H10 kS, Tinius Olsen, UK) atstrain rate of 10 mm/min at room temperature. A DSC 2910(TA Instruments Inc., New Castle, NJ, USA) was used to

determine the glass transition temperature (Tg) of thecomposites at heating rate of 20 �C/min and temperaturerange from�150 �C to 50 �C using a liquid nitrogen coolingaccessory. 5–10 mg of a sample was put in a platinum panand heated from ambient to 800 �C at a constant rateof 20 �C/min in nitrogen gas purge of 60 ml/min in aHi-Resolution TGA 2950 (TA Instruments Inc., USA) formeasurement of thermal stability. For dimensional stabilityof the composites, a TMA 2940 (TA Instruments Inc., USA)with an expansion probe was used and samples of size4 � 4 mm and thickness 4 � 0.01 mmwere heated at a rateof 5 �C/min from 5 �C to 150 �C. Phase morphology of thenanocomposites was evaluated using a Carl Zeiss EVO 50Scanning Electron Microscope (SEM). The cross-section ofthe tensile fractured surfaces of the samples, without anygold coating, was used. For elemental analysis of thenanoparticles present on the fracture surface, X-ray energydispersion spectroscopy (EDX, Genesis 2000) attached tothe SEM was utilized. A vibrational sample magnetometerEV7-VSM (ADE-DMS, USA) was used to determine themagnetic properties of the samples. In VSM, the sampleunder study was kept in a constant magnetic field tomagnetize the sample by aligning the magnetic dipoles orthe individual magnetic spins of the magnetic particlesalong the direction of the applied magnetic field. Thestronger the applied field, the larger is the magnetization.As the sample is moved up and down, this magnetic strayfield is also changed and can be sensed by a set of pick-upcoils. The alternating magnetic field will cause an electricfield in the pick-up coils resulting in variation of theinduction current (I) proportional to the extent of

-3

-2

-1

0

Hea

t Flo

w (W

/g)

-40 50 100 150 200 250 300 350 400

Exo Up

(a)

(b)

(c)

(d)

(e)

(f)

(g)

Temperature (ºC)

Fig. 2. DSC overlay of PPO nanocomposites, (a) Neat PPO, (b) 1 wt.% filler, (c)2 wt.% filler, (d) 3 wt.% filler, (e) 5 wt.% filler, (f) 10 wt.% filler and (g) 20 wt.%filler.

Fig. 4. SEM Photographs of Phase Morphology of the Neat PPO.

K. Agarwal et al. / Polymer Testing 30 (2011) 155–160 157

magnetization of the sample. This was then amplified bya trans-impedance lock-in amplifier and measured.

3. Results and discussion

Values of Ts and Eb, degradation peak temperature andTg measured by UTM, TGA and DSC, respectively, are givenin Table 1. PPO filled with g-Fe2O3 shows enhancement ofTs up to 10 wt. % but it is then reduced at 20 wt. %. However,the Eb has been found to be reduced consistently due tofiller addition from 1 to 20 wt. %. The lowering of Eb isbecause of increasing hardness and adherence of themacromolecular chains to the surface of the nanoparticlesby polymer- filler interaction and, thereby, their mobility isrestricted. Both the enhancement of Ts and change of Eb arenot significant beyond 5 wt% of g-Fe2O3. This is because ofsaturation of the filler surface by bound polymer chains andformation of a stagnant polymeric ‘thin film’ encapsulatingfiller particles on the nanoscale. The observation is

Fig. 3. TMA overlay of PPO nanocomposites (a) Neat PPO, (b) 1 wt.% filler, (c)2wt.% filler,(d) 3 wt.% filler, (e) 5 wt.% filler, (f) 10 wt.% filler and (g) 20 wt.%filler.

supportive of our earlier reports on different polymer-layered clay nanocomposites [17,18].

TGA degradation peak temperatures of neat PPO and allthe nanocomposites showed very good thermal stability,and addition ofg-Fe2O3 did not significantly vary the peaktemperatures. A representative TGA plot for PPO with10 wt. % g-Fe2O3 having peak temperature at 469.74 �C hasbeen shown in Fig. 1. Thermal conductivity of g-Fe2O3 ishigher than PPO and, therefore, its presence in the PPOmatrix resulted in inductive heating in the compositespecimen when subjected to heating at a constant rate inthe DSC experiments. The resultant softening of the matrixis much faster than observed in the case of other nanofillerse.g., Montmorillonite, Closite, Laponite etc. [19]. Therefore,the addition of different proportions of g-Fe2O3 to PPOresulted in a gradual decrease of Tg with increasing filler

Fig. 5. SEM Photographs of Phase Morphology of the PPO with 3 wt.% g-Fe2O3.

Fig. 6. SEM Photographs of Phase Morphology of the PPO with 5 wt.% g-Fe2O3.

Fig. 8. SEM Photographs of Phase Morphology of the PPO with 5 wt.% g-Fe2O3 at 140 �C.

K. Agarwal et al. / Polymer Testing 30 (2011) 155–160158

concentration from 1% to 20% (a representative DSC plothas been shown in Fig. 2, and the Tg values are given inTable 1). A previous study made on damping properties ofmagnetorheological cis-polybutadiene rubber also sup-ports this result [20]

Addition of filler increased hardness proportional tofiller concentration and the extent of reinforcement issignificant up to 10 wt. % filler. The thermo-mechanicalanalysis (TMA) results show an improvement of dimen-sional stability of the nanocomposites effective up to 10 wt% filler, then the dimensional change is much faster in thecase of 20 wt. % filler [compare plot (g) and those of plots(a to f) in Fig. 3].

Fig. 4 is an SEM image of the tensile fracture surface ofneat PPO (without addition of any nanofiller). The fracturetype resembles brittle failure in layered planes (slate type).Presence of some cracks and slip lines in comet type oftrajectories are also observed. Addition ofg-Fe2O3 causedmarked changes in the fracture surface topography. Figs. 5

Fig. 7. SEM Photographs of Phase Morphology of the PPO with 5 wt.% g-Fe2O3 at 40K magnification.

and 6 are the representative photomicrographs of thetensile fractured surface of the composite samples with3 and 5 wt. % of nanofiller, respectively. Both of them showthe presence of rough surfaces and occurrence of manyshort rounded tear lines, the extent of which increases withincreasing filler concentration. The filler particles, due tobetter polymer-filler interaction and adhesion, act as stressraisers and hinder smooth propagation of the stress paths.As a result, the elastic stored energy and tensile strengthwere found to be concomitantly improved with filler

Fig. 9. SEM Photographs of Phase Morphology of the PPO with 5 wt.% g-Fe2O3 at 280 �C.

Fig. 10. EDX plot of 5 wt.% nanocomposites.

K. Agarwal et al. / Polymer Testing 30 (2011) 155–160 159

concentration up to 5 wt. % of g-Fe2O3. Excellent dispersionwithout any agglomeration of particles or their segregationetc. in the polymers matrix can be observed at highermagnification of the composite with 5 wt.% filler (Fig. 7). Inorder to substantiate the DSC observations on matrixsoftening given above, the SEM studies were also con-ducted at elevated temperatures using a hot-stage attachedto the SEM. Matrix softening was visible at 140 �C (Fig. 8).There also occurred some major changes in the morpho-logical pattern at 280 �C where the sample shows matrixsoftening, with migration and agglomeration of the fillerparticles (Fig. 9). Genesis 1000 Energy dispersive X-rayanalysis with detection of iron containing particles furtherconfirmed that the round shaped g-Fe2O3 particles areuniformly dispersed on the tensile fractured surface of thenanocomposites, thus effecting very good mechanicalproperties (Fig. 10). VSM results (Fig. 11) show marginalincrease of the saturation magnetism (SM) up to 3 wt.% ofg-Fe2O3. However, there is a sharp rise in SM between 3 and10 wt.% followed by flattening of the SM values between 10and 20 wt.% of filler.

0

1

2

3

4

5

6

7

8

1 2 3 5 10 20

)g/ume(

noitazitengam

noitarutaS

2O3 Concentration (wt%)γFe

Fig. 11. Magnetic property of the nanocomposites.

4. Conclusions

Novel polymer nanocomposites based on high temper-ature matrix resin combined with magnetic nanofillershave been developed. The high temperature resistance andthermal stability of the PPO-g-Fe2O3 nanocomposites werefound to be very good in TGA. The improvement ofmechanical properties was significant up to 5 wt.% ofoptimum filler concentration. Development of magneticsusceptibility of these nanocomposites shows promise forelectro-magnetic interference (EMI) shielding and otherapplications.

Acknowledgements

The authors acknowledgewith thanks toDr. K.U. BhaskarRao, Director, DMSRDE, Kanpur for his suggestion andpermission for publication of this paper and Prof. K.K. Kar ofIIT, Kanpur for providing Vibrational SampleMagnetometer(VSM) facility.

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