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Transparent and Thermally Conductive Polycarbonate(PC)/Alumina (Al2O3) Nanocomposites: Preparation andCharacterizationsTvarit Patel a , Supratim Suin a , D. Bhattacharya a & B. B. Khatua aa Materials Science Center, Indian Institute of Technology , Kharagpur , IndiaPublished online: 27 Nov 2013.

To cite this article: Tvarit Patel , Supratim Suin , D. Bhattacharya & B. B. Khatua (2013) Transparent and ThermallyConductive Polycarbonate (PC)/Alumina (Al2O3) Nanocomposites: Preparation and Characterizations, Polymer-PlasticsTechnology and Engineering, 52:15, 1557-1565, DOI: 10.1080/03602559.2013.824464

To link to this article: http://dx.doi.org/10.1080/03602559.2013.824464

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Transparent and Thermally Conductive Polycarbonate (PC)/Alumina (Al2O3) Nanocomposites: Preparation andCharacterizations

Tvarit Patel, Supratim Suin, D. Bhattacharya, and B. B. KhatuaMaterials Science Center, Indian Institute of Technology, Kharagpur, India

We report the preparation and characterization of thermallyconductive and transparent polycarbonate (PC)/alumina (Al2O3)composites. First, nano Al2O3 powder was synthesized by flashpyrolysis process and calculated amount of Al2O3 was dispersed intothe methylmethacrylate (MMA) followed by bulk polymerization.PC/poly-(methylmethacrylate) (PMMA)-Al2O3 nanocompositeswith various amounts of Al2O3 was prepared by mixing bulk poly-merized PMMA-Al2O3 composites with PC through melt-mixing.Incorporation of Al2O3 in the bulk polymerized PMMA resultedin good dispersion of the Al2O3 particles in the PC matrix. Theeffect of particle size of Al2O3 on thermal conductivity, mechanicaland optical properties of the composites was investigated.

Keywords Al2O3; Mechanical property; Thermal conductivity;Transparent

INTRODUCTION

Over the last decade, automobile manufacturers havefocused on the improvements in vehicle lighting as a wayto improve vehicle safety. People should have a clear visionof the road, in which they are driving. When this conditionis not fulfilled, it results driving more complex, potentiallyreducing safety, as more than 60% of all traffic accidentstook place in poorly light conditions. However, consideringthe changes occurring in the headlamp beam pattern, mod-ern headlamps have less light directed upward, reducingroadway visibility on sag curves. Glass headlamp lensesbegan to be replaced with polycarbonate (PC) in the1980s. The use of plastic in headlamp applications enablesautomakers to reduce weight without sacrificing opticalperformance while increasing resistance to breakage.Replacement of the headlamp glass by polymers providesmany advantages. The versatility of plastic allows autoheadlights to incorporate designs and clarity, avoids safetyissues caused by the hazardous breakage of glass[1].

PC can be molded into very complex shapes, producingsmaller, more streamlined lights. This increased design

freedom makes more aerodynamic shapes possible. Butthe modern headlamps are more susceptible to degradationcompared to sealed beam headlamps that have lenses madeof glass. This is because PC is prone to yellowing, fogging,etc. caused by different factors like having very low thermalconductivity; acid rain, etc. This type of degradationdecreases the clarity and lifetime of PC headlamp[2]. Thisproblem can be avoided by developing the transparent,thermally conducting composites of PC using thermallyconductive fillers into the PC matrix[3–5].

Ceramics are electrically insulators and inherently lackof large amounts of free electrons. Due to the shortage ofelectrons, the heat transfer is predominantly through pho-nons. Even though free electrons are much more efficient atconducting heat, some ceramics have relatively high ther-mal conductivities. The thermally conductive nature ofceramics has been linked to the crystal structure.

Unlike ceramic materials, polymers typically havevery low thermal conductivities, approximately between0.2–0.3W=m-K[6]. Polymers with a higher degree of crystal-linity have been associated with greater thermal conductivi-ties, in comparison to those with an amorphous structure.Coordinated vibrations of molecular chains that occurwithin a crystalline state prove to be an effective methodof conducting heat[6]. In polymer composites, thermalconductivity has been known to improve through threedifferent techniques: (i) by forming continuous networks usingthermally conductive filler materials within the matrix[6–10], (ii)by decreasing the number of thermally resistant junctionsbetween adjacent filler particles by using particulates withincreased size[11], and (iii) by reducing the thermal contactresistance between fillers those are in contact[7].

In addition to the above considerations, it is recom-mended to select fillers with multimodal particle size distri-butions, and a polymer with a low melt viscosity to increasewetting and improve filler-matrix adhesion[8]. All thesesuggestions are based on the assumption that there shouldbe good adhesion between the polymer and filler, so as tominimize air gaps between the matrix polymer and fillerparticles that reduce the effective k-value. Therefore,

Address correspondence to B. B. Khatua, Materials ScienceCenter, Indian Institute of Technology, Kharagpur 721302, India.E-mail: khatuabb@matsc.iitkgp.ernet.in

Polymer-Plastics Technology and Engineering, 52: 1557–1565, 2013

Copyright # Taylor & Francis Group, LLC

ISSN: 0360-2559 print=1525-6111 online

DOI: 10.1080/03602559.2013.824464

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compatibility between the polymer and filler materialsis also recommended to decrease the possibility of voidformation. Alumina (Al2O3) has been considered as aneffective ceramic material for several years in variouspurposes[12,13].

Various attempts have been reported in the literaturebased on the improvement in the thermal conductivity inthe polymer nanocomposites. Xu et al.[7] investigated thethermal conductivity of polymer composite with differenttypes of filler. They reported that the thermal conductivityof the composites was increased with increasing fillervolume fraction regardless of the filler type. Jie et al.[14]

investigated the thermal conductivity and mechanicalproperties of PP=AlN (Al2O3 nanoparticles) composites.

They showed that the thermal conductivity of thecomposites was increased with the increasing AlN, andthe thermal conductivity of composites filled with 50 vol%modified AlN was 1.84W=mk. Cavalier et al.[15] preparedthe transparent polymer composite having mineralnanoparticles, which was partially coated with polymer.They also studied the co- chemical and physical inter-actions at the interface between the mineral nanoparticlesand the thermoplastic PC matrix. Benjamin et al.[16]

synthesized and investigated the mechanical properties ofPMMA=Al2O3 nanocomposites using 38 nm and 17 nmAl2O3 nanoparticles.

They suggested that, when a weak interface existsbetween nanoparticle and polymer, the room temperaturemode of yielding was changed from normal to shear, whichled to a brittle-to-ductile transition. Nahida and Marwa[17]

studied the optical properties of the PMMA=PC blend atdifferent blend compositions. Their results revealed thatPMMA=PC (1:1) binary blend showed the best opticalproperties and energy gap (Eg). Castrillo et al.[18] haveblended the fumed silica nanoparticles (14 nm of diameter)with PMMA, by high energy ball milling process.

They observed that the properties of the composite werehighly dependent on the active milling time. Hanemannet al.[19] investigated the physical properties of PC=Al2O3

nanocomposites. They reported that larger amounts ofthe nanosized filler caused slight polymer degradation.Although the Young’s modulus remained almost constant,the impact strength as well as the glass transition tempera-ture of this composite was reduced with increasingnanofiller content, which attributed to polymer chaindegradation effects. The addition of Al2O3 increased therefractive index due to particle agglomeration. Hakimelahiet al.[20] fabricated transparent nanocomposite films by in situpolymerization of PC in the presence of Al2O3 nanowhiskers.

The highly concentrated nanocomposites formed usingin-situ polymerization were diluted with high molecularweight PC to form nanocomposites which exhibiteda sharp improvement in mechanical properties with littleloss in transparency. Interestingly, these materials also

exhibited higher absorbance to the ultraviolet light(<400 nm) than plain PC. Chandra et al.[21] fabricatedthe low molecular weight poly-(styrene-maleic anhydride)(SMA) copolymers to coat spherical Al2O3 nanoparticlesto facilitate dispersion in a PC matrix. The combinationof a low molecular weight SMA polymer coating with ahigh intensity mixer generated nanocomposites with excel-lent nanoparticle dispersion, and thus semi-transparentlight transmittance was achieved even in 2mm thick sam-ples. This nanocomposite absorbed more energy beforefailure, thus resulting in higher impact strength. Thereare also various reports in the literature concerning inor-ganic fillers e.g., clay, TiO2, NiO etc. into the polymermatrix[22–38].

In summary, the retention of optical transparency byaddition of highly thermally conducting filler particles,and homogeneous dispersion and distribution of the fillerparticles in the transparent polymer matrix is a majorconcern. Thus, this problem leads to poor thermal conduc-tivity and optical transparency of the polymer composites.This provides the scope for further investigation ondeveloping transparent thermally conducting polymercomposites through homogenous dispersion of the nanofil-ler in the matrix polymer. The objective of this work is todevelop transparent PC=Al2O3 composites with improvedthermal and mechanical properties without significant lossin optical transparency.

Here we demonstrate an easy method that involves meltblending of PC and in-situ polymerized PMMA=Al2O3

composites to prepare PC=Al2O3 composites. The rationalebehind blending PC and PMMA was that low molecularweight PMMA is known to form miscible blend with PC.Thus, a-Al2O3 nanoparticles were synthesized by flash-pyrolysis method and PMMA-Al2O3 composites wasprepared by in-situ polymerization of methyl methacrylatemonomer in the presence of Al2O3. Finally, PMMA-Al2O3

nanocomposites were melt blended with PC at (70=30w=w)PC=PMMA-Al2O3 ratio to prepare the PC=Al2O3 compo-sites. Here, we discuss the detail of our findings.

EXPERIMENTAL

Materials Used

General purpose polycarbonate (PC, transparent gradeMakrolon 2205; MFI: 25 g=10min at 280�C and 2.16 kgload; Density at 23�C is 1.20 g=cc) was procured fromBayer Material Science AG, Germany. Synthesis gradealuminum nitrate (Al(NO3)3), extra pure citric acid mono-hydrate, purified glycine and methyl methacrylate (MMA)monomer used in this study were purchased from Merck,Germany. Poly(vinyl alcohol) (PVA) was supplied byLoba Chemie, Mumbai, India. All the starting materialsin the present experiment were used without any furtherpurification.

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Synthesis of Al2O3 Powder

In a cylindrical quartz container, 0.5M solution ofaluminum nitrate (Al(NO3)3) solution was prepared and10 g of citric acid was added. The pH of the solution wasmaintained at �6.0 via subsequent addition of liquidammonia and dilute HNO3. 5 g glycine containing 5 gpoly-(vinyl alcohol) (PVA) was added to the precursorsolution containing (Al(NO3)3). Then, 2 g ammoniumnitrate was added to the solution under stirring condition.The solution was then thermally dehydrated on a hotplate (� 80�C), resulting in a viscous liquid. The viscousprecursor was heated rapidly in a pre-heated pit furnacemaintaining the temperature at 350�C. Depending on thepH values of the taken mixer, the material undergoesfoam formation with concomitant the decomposition ofthe material, generating large volume of gases.

The spontaneous ignition, smoldering combustion andenormous swelling, produce a grayish, foamy, voluminousmass in different fashions. The whole process was com-pleted in less than 3 h. The voluminous and foamy combus-tion ashes were easily crushed to obtain the precursorpowders. The crushed precursor powders were transformedto pure c-Al2O3 and a-Al2O3 powders after calcinations at900�C and 1150�C for 2 h, respectively.

Preparation of the Composites

In-situ Polymerization of Al2O3-PMMA Composites

At first the MMA monomer was purified by applyingthe following procedure. First, 100mL MMA monomerwas taken in a 500mL separating funnel and 20mL of5% NaOH solution was added to it. The mixture wasshaken for 15min and the purified MMA was decantedinto a 250mL beaker. This process was continued five

times. Finally, after washing with deionized water, thepurified MMA was collected.

Based on the final requirement of Al2O3 loading in thefinal PC=PMMAblend, desired amount (1.26 and 2.56wt.%)of synthesized Al2O3 was dispersed in 40 g purified MMAmonomer in a 250ml three-neck, roundbottom flask. TheAl2O3=MMA dispersion was ultrasonicated for 1 h at roomtemperature. Then, the reactor, connected with the refluxingcondenser and nitrogen inlet to one of the three necks, wasimmediately placed on a hot plate magnetic stirrer. Requiredamount (1wt.%) of the benzoyl peroxide, as polymerizationinitiator, was added to the Al2O3=MMA dispersion in thereactor under constant stirring and the temperature of thereactor was gradually increased to �85�C.

The reaction was continued for 5 h under nitrogenatmosphere with constant temperature and stirring. TheAl2O3=PMMA composites, thus obtained through in-situbulk polymerization of Al2O3=MMAwere dried in air ovenat 60�C for 24 h. We assumed the conservation of mass ina chemical reaction. Thus, the resulting PMMA containedsimilar amount of Al2O3 as taken earlier before the reac-tion. The reaction scheme for the preparation of PMMA=Al2O3 composites is given in Figure 1.

Melt Blending for Al2O3 Polymer Composites

Composites of PC=PMMA=Al2O3 were prepared bymelt-mixing the PC and in-situ polymerized PMMA-Al2O3

composites in an internal mixer (Brabender Plasticorder,S. C. Dey & Co., Kolkata, India) at 280�C, 50 rpm for15min. To avoid moisture-induced thermal degradation,all the constituent polymers and the Al2O3 particleswere dried in an air oven at �100�C for 24 h before meltmixing. The melt mixed nanocomposites were cooled atroom temperature.

FIG. 1. Flow-chart of in-situ polymerization of Al2O3-PMMA composites.

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CHARACTERIZATIONS

X-Ray Diffraction Study

In this study, different phases of a-Al2O3 powder wasexamined by wide angle X-ray diffractometer (WAXD,Ultima-III, Rigaku, Japan) containing nickel-filteredCu-Ka X-ray tube (k¼ 0.154056 nm). The X-ray scans wereperformed between 2h values of 10�–80o.

TEM Analysis

The particle size of synthesized Al2O3 particles and theextent of dispersion and distribution of the filler (Al2O3)in the polymer matrix were studied by transmissionelectron microscopy (HRTEM: JEM-2100, JEOL, Japan).The operating accelerating voltages are 200 kV and 80 kVfor Al2O3 particles and Al2O3 filled polymer matrix compo-site, respectively. For the TEM sample preparation, synthe-sized Al2O3 was dried at 120�C for 24 h and then finelygrinded with mortar and pestle. A very small amount ofsample (0.05 g) was dispersed in ethanol by ultrasonication.One drop of this particulate dispersed solution was thencasted on copper grid and kept on filter paper for drying.The polymer composite samples were ultra-microtomed atcryogenic condition with a thickness of 60–80 nm. Sincethe Al2O3 particles have much higher electron density thanthe polymer; they appeared dark in the TEM images.

Measurement of Thermal Conductivity

Transverse thermal conductivity of a 1=8-inch thick by 2inch diameter disc-shaped of our test specimen of Al2O3

polymer composite was measured at 55�C temperatureusing a Holometrix Model TCA-300 Thermal ConductivityAnalyzer, which uses the guarded heat flow meter method(ASTM F433-98). Figure 2 illustrates the detail of the testmethod. To prepare these samples, 2.5-inch diameter

compression-molded disks were cut to a 2-inch diameterdisk using a water jet cutter. The samples were dried ina vacuum oven at 60�C for 2 h. After drying, thesecomposite samples were placed in sealed moisture-barrierbags, and subsequently tested dry as molded.

Thermogravimetric Analysis (TGA) Study

The thermal stability of the pure polymers, blends andnanocomposites was investigated with the help of thermo-gravimetric analyzer (TGA-209F; NETZSCH, Germany).The samples were heated from room temperature to600�C at a heating rate of 10�C=min under air atmosphere.

Differential Scanning Calorimetric (DSC) Study

The glass transition temperature (Tg) of PC and itscomposites were determined with differential scanningcalorimetry (DSC-7, Perkin Elmer) with a heating rate of10�C=min, under nitrogen atmosphere. The samples wereheated from room temperature to 175�C and then cooledto room temperature. The second heating curve wasanalyzed for the determination of Tg.

Microhardness Study

The Vickers hardness of the virgin PC and PC=(PMMA=Al2O3) nanocomposite of various compositionswere measured by microhardness analyzer, manufacturedby UHL VMHT, Germany. The dimension of thespecimens was 14� 12� 1.3mm3 and was tested with15 g=f load for a period of 12 s. The Vickers hardness wasautomatically computed and read at digital display.

Tensile Study

Tensile tests of the virgin polymers and the nano-composites samples were performed on Model M50HTTinius Olsen tensile testing machine (USA) with a cross-head speed of 1mm=min at room temperature. Specimenswere molded as a dog-bone shape through injection molding.

UV-Vis Spectroscopic Analysis

To study the optical transparency, thin sheets of 1.3mmthickness of melt processed pure PC, (80=20w=w) PC=PMMA-Al2O3 (0.25, 0.5wt.%) were prepared by com-pression molding. The optical transparency of the purePC, blends and the nanocomposites samples were studiedby UV-Vis spectroscopic study. The percent transmittancewas measured as a function of wavelength by using PerkinElmer, Lambda 750 spectrophotometer.

RESULTS AND DISCUSSION

Analysis of Al2O3 Nanoparticles

Phase Analysis of Synthesized Al2O3 Particles by XRD

The WAXD pattern of the Al2O3 was obtained byusing calcined Al2O3 nanopowder at 900�C and 1100�C

FIG. 2. Diagram of thermal conductivity test method. (Color figure

available online.)

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in oxygen environment, as shown in Figure 3. The XRDpatterns showed the peaks corresponding to differentphases of alumina. Most of the peaks of Al2O3 calcinedat 900�C represents the c-phase of the tetragonal structuredAl2O3 particles as reported in Joint Committee on PowderDiffraction Standards (JCPDS) card no. 16-0394.Additionally one more strong peak (at 2h¼ 74.54�) wasobserved which matches with tetragonal system of hightemperature unstable aluminum oxide (Al2O3) phase,as reported in JCPDS card no. 88-1609. All the peaks ofXRD pattern of the sample calcined at 1100�C are wellindexed to the a-phase of rhombohedra Al2O3 powder(JCPDS card no. 42-1468) and no peak from any otherphase of aluminum or other impurities was found,which indicates that high purity of the a-phase Al2O3

nanoparticles was formed in the synthesis.

TEM Analysis of Al2O3 Particles

Figure 4 shows the TEM images of a-Al2O3 particleswhich were calcined at 1100�C. The figure shows sphericalshaped particles in the range of 10–20 nm. These particleswere appeared as loosely bonded clusters due to strongvan der Waals forces between them. The Al2O3 nano-particles were not well dispersed into the solvent. Thismay be attributed to the absence of any stabilizer, as waspreviously reported to stabilize silver nanoparticles[39].

Analysis of PC/PMMA-Al2O3 Nanocomposites

Thermal Conductivity Analysis

The transverse thermal conductivity increases by theaddition of Al2O3 in the matrix polymer. Figure 5 showshysterisis diagram of thermal conductivity value for neatPC and its composites with PMMA-Al2O3 at different

loading of the Al2O3 (0.25 and 0.5wt.%). Thermal conduc-tivity value of 0.189 and 0.233W=mK were achieved inthe composites at Al2O3 loading level of 0.25wt.% and0.5wt.%, respectively. This difference in value of thermalconductivity is most likely due to the crystallinity differencebetween neat polymers and ceramic particulate filled poly-mer composites. Addition of Al2O3 particle increases thecrystallinity of polymer composites as Al2O3 particlesinherently display much more thermal conductivity thanthe matrix polymer. The increase in thermal conductivityappears to be linear due to uniform distribution of highlythermal conductive Al2O3 particles.

FIG. 3. X-ray diffractograms (using Cu Ka radiation) of Al2O3 powders

calcined at two different temperatures (900 and 1100�C).

FIG. 4. TEM micrographs of the synthesized a-Al2O3 powder.

FIG. 5. Variation of thermal conductivity for (1) Neat PC and PC=

PMMA-Al2O3 nanocomposites with (2) 0.25% Al2O3 and (3) 0.5 phr

Al2O3.

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Filler Dispersion Analysis by TEM

The TEM micrograph (Figure 6) shows the dispersion ofAl2O3 nanoparticles in melt blended (80=20w=w) PC=PMMA-Al2O3 (0.5 wt%) composites. As shown in the fig-ure, the small dark circles represent the Al2O3 particles.Figure 6 shows the morphology of polymer composites attwo different loadings. As can be seen, the filler particlesare highly dispersed into the matrix polymer. The reasonfor such dispersion of the nanoparticles into the polymermatrix (as they have inherent tendency to become agglom-erated) is due to our processing technique. As the Al2O3

particles were first dispersed into the MMA and then bulkpolymerized, the viscosity of the matrix might not allow thealumina particles to agglomerate. This results in a well dis-persed morphology of the filler particles into the polymermatrix. Moreover, during mixing PC with Al2O3 dispersedPMMA the top-down approach might restrict the aggre-gation of the fillers during the mixing process. In this pro-cess, the shear stress (hydrodynamic force) is induced in thepolymer melt by melt compounding method for breakingdown agglomerated Al2O3 particles and to achieve nano-scale dispersion of the particles in the matrix polymer.In general, the dispersion of inorganic fillers in the matrixpolymer depends largely on the internal shear stressesinduced by viscous drag on the fillers during melt-compounding process[40].

Microhardness Analysis

Figure 7 shows the Vickers hardness of the pure PC,pure PMMA, PC=PMMA blend, and PC=PMMA-Al2O3

nanocomposites at two different loadings of Al2O3 parti-cles. The micro hardness comparison of different composi-tions of Al2O3 shows that PC blended with PMMA-Al2O3

composites has higher hardness value than without Al2O3

mixed PMMA-blended PC composites. This is due to thefact that, the PMMA-Al2O3 composites was prepared byin-situ bulk polymerization technique in which the Al2O3

particles were finely dispersed in PMMA and then it wasmelt compounded with PC. Moreover, the miscibility of

the PMMA with PC allows the Al2O3 particles to disperseover the matrix polymer in a highly distributed mannerduring melt mixing.

Tensile Properties

The tensile properties of pure PC, (w=w 80=20) PC=PMMA Al2O3 filled nanocomposites at two different fillerloadings (0.25wt.% and 0.5wt.%) are shown in Figure 7.The tensile strength, modulus, and the percentage of elon-gation for PC=PMMA-Al2O3 are higher than the pure PC,indicating that Al2O3 particles were strongly bonded orinteracted with the PC. The high surface area of the incor-porated Al2O3 particles in nanometer scale favored theinteraction between the polymer and the very large surfacearea of the Al2O3 particles. As a result, the percent elonga-tion was increased without significant increase in brittlenessin the final nanocomposites.

Thermogravimetric Analysis

The TGA analyses of the PC=PMMA-Al2O3 nanocom-posites were carried out to compare their thermal stabilitywith that of neat PC. Figure 8 represents the TGA thermo-gramms of the pure PC and (80=20w=w) PC=PMMAnanocomposites containing 0.25 and 0.5wt.% of Al2O3.As observed, addition of Al2O3 particles increased thethermal stability of PC in the composites. Moreover, theincrease in thermal stability of PC was more in case ofPC=PMMA-0.5 wt.% Al2O3 composites as compared tothat of pure PC. The initial degradation temperature (T1�302�C) of PC=PMMA-0.5wt.% Al2O3 composites wasalmost 25�C higher than that of pure PC (T1� 278�C). Thisincrease in thermal stability may arise from the interactionbetween the polymer chains and the fillers surfaces.

DSC Analysis

The effect of the dispersion of Al2O3 particles on the Tg

of polymer matrix was studied using DSC analysis. Figure 9shows the DSC scans of the pure PC, (80=20w=w) PC=PMMA-(0.25–0.5wt.% Al2O3) nanocomposites. From theDSC scan, the Tg of the pure PC was found at �147�C.In case of the (80=20w=w) PC=PMMA-0.25wt.% Al2O3

nanocomposite, a single Tg (�149�C) was observed,suggesting the miscibility of the component polymers inthe blend nanocomposites. The Tg of the (80=20w=w)PC=PMMA-0.25wt.% Al2O3 nanocomposites was slightlyhigher than the pure PC. For instance, the Tg of pure PC(�147�C) was increased to �149�C and �155�C when0.25 and 0.5wt% of Al2O3 were incorporated in thecomposites. The increase in Tg of the (80=20w=w) PC=PMMA blend in presence of Al2O3 could be due to theinteraction of PC and PMMA chains with the surfaceof Al2O3 particles, which restricted the segmental motionsof polymer chains, consistent with the previous reports[16].

FIG. 6. TEM micrographs of (80=20w=w) PC=PMMA nanocomposites

with (a) 0.25wt.% Al2O3 and (b) 0.50wt.% Al2O3.

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UV-Vis Spectroscopy Analysis

The UV-Vis spectra of the neat PC and its compositeswith Al2O3 are shown in Figure 10. The path length foreach specimen was 1.3mm. To avoid any increase in thelight scattering behavior, the surface of the sampleswere polished to remove any surface dirt and impurities.The percentage transmittance of neat PC (� 80%) wasdecreased to �75% and �69% in (80=20w=w) PC=PMMA=Al2O3 composites containing 0.25 and 0.5wt.% Al2O3,

respectively. With the addition of Al2O3 particles, percent-age of transmittance was decreased more in pure PC.

The impact of quantitative loading and state ofdispersion of Al2O3 powder on the optical transparencyof hot compression molded sheet (thickness �1.3mm)was examined through direct visualization of the sheetplacing over the printed object. The digital images of purePC, (80=20w=w) PC=PMMA-0.25wt.% Al2O3 and with

FIG. 7. Comparison of mechanical properties (Vickers hardness no., tensile strength, Young modulus and elongation at break for (1) pure PC; (80=

20w=w) PC=PMMA-Al2O3 nanocomposites with (2) 0.25wt.% and (3) 0.5wt.% Al2O3.

FIG. 8. TGA thermograms of (a) pure PC; (80=20w=w) PC=PMMA-

Al2O3 nanocomposites with (b) 0.25wt.% and (c) 0.5wt.% Al2O3.. (Color

figure available online.)

FIG. 9. DSC heating scans of pure (a) pure PC, (80=20w=w) PC=

PMMA¼Al2O3 nanocomposites with (b) 0.25wt.% Al2O3, and (c)

0.5wt.% Al2O3. (Color figure available online.)

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0.5wt.% Al2O3 are shown in Figure 11. The optical clarityof composite decreased with increase in loading of Al2O3

particles. However, the optical clarity of PC=PMMA-0.25 -wt.% Al2O3 composites was almost similar to that ofpure PC, suggesting the possible use of the compositesfor transparent applications.

CONCLUSION

The a-Al2O3 particles were synthesized by flash pyrolysismethod along with heating the resultant pyrolyzed ashprecursor powder at 1100�C. Efficient dispersion ofAl2O3 particles in a polycarbonate matrix was achievedusing pre-synthesized in-situ polymerized, PMMA=Al2O3

composite by melt compounding method. Effectivedispersion a-Al2O3 in PC matrix was achieved by meltblending of PC and pre-dispersed Al2O3 in PMMAthrough in-situ bulk polymerization. The TEM images ofPC=PMMA-Al2O3 composites revealed homogeneousdispersion of Al2O3 particles in PC matrix. Thus, presenceof PMMA improves the dispersion of Al2O3 in PC matrix,which is considered to be due to the miscibility of PC andPMMA. The mechanical properties (i.e., Young’s modulus,

microhardness and the tensile strength) of the PC=PMMA-Al2O3 composites were also improved in comparison tothe pure PC, without significant loss in optical trans-parency of the pure PC. Moreover, the thermal conduc-tivity of pure PC was significantly improved in the PC=PMMA-Al2O3 composites.

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