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DOI: 10.1177/0892705710391394

published online 31 December 2010Journal of Thermoplastic Composite MaterialsSeena Joseph, V. V. Shertukade, P. A. Mahanwar and V. A. Bambole

of Poly(ethersulfone) and Poly(ether-ether-ketone)Effect of Concentration of Mica and Microsilica on Particulate Composites

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Effect of Concentration of Micaand Microsilica on Particulate

Composites of Poly(ethersulfone) andPoly(ether-ether-ketone)

Seena Joseph, V. V. Shertukade and P. A. Mahanwar*

Department of Polymer Engineering and Surface Coating Technology,Institute of Chemical Technology, Matunga, Mumbai 400019, India

V. A. Bambole

Department of Applied Physics, Institute of Chemical Technology,Matunga, Mumbai 400019, India

ABSTRACT: High performance polymers, poly(ether-ether-ketone) (PEEK) andpoly(ethersulfone) (PES), were filled with mica and silica particulate fillers atdifferent filler contents and the properties of the composites have been compared.The performance of these composites was analyzed in terms of the tensile, flexural,and impact properties and hardness measurements, and the properties were found toincrease with increase in filler content. The scanning electron microscopy studiesrevealed that filler dispersion is good even at higher loadings. The dielectric strength,arc resistance, and heat distortion temperature of both mica- and microsilica-filledPEEK and PES composites are found to have better performance compared tounfilled polymers. Mica filler is found to be a better filler for PEEK than silica, whilesilica imparts better properties for PES than mica does.

KEY WORDS: particulate composites, poly(etheretherketone), poly(ethersulfone),mechanical properties, silica, mica

Journal of THERMOPLASTIC COMPOSITE MATERIALS, Vol. 00—2010 1

0892-7057/10/00 1–16 $10.00/0 DOI: 10.1177/0892705710391394� The Author(s), 2010. Reprints and permissions:

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*Author to whom correspondence should be addressed.E-mail: [email protected] 2, 5, 6 appear in color online http://jtc.sagepub.com



INTRODUCTION

HIGH PERFORMANCE POLYMERS like poly(ether-ether-ketone) (PEEK)and poly(ethersulfone) (PES) evoke a lot of interest due to a large

number of industrial applications because of their excellent properties evenat high temperatures [1,2]. Particulate-filled polymer composites are mostwidely used composite materials than fibrous or any other filled materials.Property improvement in composites is found to be very much dependent onfiller size and filler content. Micro and nanosized materials are found toinfluence the material properties more efficiently compared to fibrousreinforcements [3–5]. Mechanical, thermal, and electrical properties, barrierproperties, and flame retardance of the polymer could be improved byproper selection of fillers [6–9].

High performance exfoliated poly(methyl methacrylate) (PMMA)/claynanocomposites were prepared by in situ polymerization technique by Cuiet al. [10]. The incorporation of a small amount of clay into PMMA matrixresulted in the enhancement of thermal properties and mechanical proper-ties, retaining the optical properties of PMMA. Wang et al. [11,12] preparedPEEK composites using micron-sized silicon carbide and silicon carbidewhiskers. They reported that SiC whisker-reinforced PEEK exhibited lowerfriction coefficient compared to pure PEEK and wear rate was effectivelyreduced [11]. Goyal et al. analyzed the tribiological properties of PEEK/Al2O3 composites. Microscopic studies showed that wear of pure PEEKoccurs mainly by mechanism of adhesion, whereas for PEEK composites, itoccurs by microploughing and abrasion [13]. At low stress, there is theexistence of particle network in the suspension increasing the elasticity of thematerial. Quadrini and Squeo [14] fabricated an injection molded bush madeof tribological PEEK and analyzed it to correlate the wear behavior andmolded material structure. They reported that the bush geometry and theinjection molding process should be optimized to allow the best tribologicalbehavior of the molded material under working conditions. Du et al. [15]found that the alignment and dispersion of the nanotubes and the molecularweight of polymer matrix have a strong influence on the rheologicalbehavior of the nanocomposites.

There are different parameters like types of fillers and polymers, fillerparticle size, filler/matrix interaction, etc. that affect the properties of thecomposites. Here, microsilica and mica have been used as filler in PES andPEEK matrices and the properties of individual composites have beenanalyzed and compared. The composites were fabricated by melt mixing intwin screw extruder, followed by injection molding at different fillercontents. The effect of filler content on tensile, flexural, and impact

2 S. Joseph et al.



properties, and hardness of the PEEK and PES composites have beenanalyzed. Transmission electron microscopy (TEM) studies showed theeffect of silica and mica fillers on the morphology of the composites. Thedielectric strength, arc resistance, and heat distortion temperatures ofboth mica- and microsilica-filled PEEK and PES composites have beenanalyzed.

EXPERIMENTAL

Materials

PEEK of grade 5300 was supplied by Gharda Chemical, Panoli, India;microsilica of grade Ultrasil R-600 and mica of grade Mica MF wereobtained from M/s HMP Mumbai.

Preparation of Composites

Before compounding, the filler and PEEK powder were mixed in a highspeed mixer of speed 600 rpm for half an hour at 808C. The composites wereprepared by varying the concentration of fillers from 0 to 30wt%. Thepremixed compositions of PEEK and fillers were melt blended usingco-rotating twin scew ZE twin scew, Ze-25 Berstott, Italy, with L/D 40:1with a screw speed of 60 rpm. In all compositions, 0.25% antioxidant(Ultranox) is used. The temperature profiles used for melt mixing of PEEKand fillers are as follows: Zone-1,3508C, zone-2,3708C, zone-3,3808C, anddie 3808C. The extruded samples were quenched in cooling tank containing20–308C water and pulled with a speed of 20–30 rpm/min and thenpalletized. The resulting pallets were used for further study. The granuleswere then predried for 3 h at 180� 58C in an air circulating oven. Thetest specimens used for tensile, flexural, and impact tests, as per ISOstandards, were injection molded using microprocessor injection moldingmachine (LTM – Demang Italy).The processing parameters are zone 1,3408C; zone 2, 3608C; zone 3, 3708C; and nozzle 3908C. The cooling of moldwas controlled by hot water maintained at 80–858C to avoid suddenquenching.

Mechanical Properties of the Composites

The dumbbell-shaped tensile strength specimens were injection moldedand tensile properties were evaluated according to the ISO 527 using Instron

Effect of Concentration of Mica and Microsilica 3



universal tester at a crosshead speed of 5mm/min and the average value ofseven results was reported. Flexural properties were measured using Instronuniversal tester according to ISO 178. Jaw speed of 2.8mm/min wasmaintained for a three-point flexural test and the span was 200mm. All thereported values were the averages of five values. The rectangular samples forimpact testing as per ISO 179 were injection molded. The notch was cut onrectangular bar specimen using a motorized notch-cutting machine, NotchVis Ceast, Italy. The impact strength was determined using Resil 25 impacttester Ceast Italy, with a striking velocity of 3.46m2/s and 2.7 J striker andthe average value of five results is reported.

The rectangular bars for hardness as per ASTD 785 standards wereinjection molded and samples were free from sink marks, burrs, and parallelsurfaces. The hardness scale is M and the test is carried out using Rockwellhardness tester. The average value of five results is reported.

Scanning Electron Microscopy

A JEOL-JSM 6400 scanning electron microscope (SEM) equipped withenergy dispersive spectrometry (EDS) was used to evaluate the microparticledispersion condition. Small particles were cut parallel to the axial directionof molded bars and mounted on a block of denture base polymer resin. Theobtained sample surfaces were manually ground and polished withsuccessive finer grades of sandpapers followed by cloth (mounted onwheel) polishing using water/alumina suspension to remove scratchesdeveloped during sand polishing. These polished samples were used forSEM study.

Dielectric Strength

Dielectric strength was measured by Saran Elctrical Instruments, India, asper ASTM D 149.

Arc Resistance

Arc resistance was measured by Acrvis, Ceast Italy as per ASTM D 495.

Heat Distortion Temperature

Heat distortion temperature was measured using Vicant softening pointmachine, Davenport, UK, as per ISO 75. The sample position was edgewise,test span, 80mm and surface stress, 1.82MPa.

4 S. Joseph et al.



RESULTS AND DISCUSSION

PEEK Composites

MECHANICAL PROPERTIESSandlera et al. [16] reported that carbon nanofiber (CNF)-filled PEEK

nanocomposites showed a linear increase in tensile stiffness and strengthwith increase in CNF content up to 15wt% maintaining the tensile ductility,up to 10% carbon nanofiller content. The effects of mica and microsilicacontent on the tensile and flexural properties of PEEK are given in Tables 1and 2. The tensile strength and modulus values are found to increase withincrease in mica content. The addition of 30% mica has increased the tensilestrength of PEEK matrix by 18% and Young’s modulus by 83%. Theelongation of the PEEK matrix is considerably reduced by incorporatingmica filler. The elongation value is found to have 78% decrease by theincorporation of 30% mica. Similar behavior is obtained for microsilicacomposites. Increase in tensile strength is almost the same for silica-filledcomposites, but the increase in modulus of PEEK by incorporating silica isless compared to mica. There is only 52% increase in Young’s modulus bythe incorporation of 30% silica filler. The percentage elongation is alsodecreased with increase in silica content. Comparing the tensile behavior ofmica and microsilica composites, though the trends in properties are thesame, the mica composites are found to have higher modulus value andhigher elongation compared to misrosilica. Silica filler increases the britilityof the PEEK matrix compared to mica filler. Lapcik et al. reportedimprovement of tensile properties of talc/PP composites. With increase infiller content, higher crystal-like morphologies were created, which resultedin the increase in tensile strength [17].

Table 1. Tensile and flexural properties of mica-filled PEEK composites.

Wt% ofmica

Tensilestrength(MPa)

Young’smodulus

(MPa)

Elongationat break

(%)

Flexuralstrength(MPa)

Flexuralmodulus

(MPa)

0 90 3552 80 126 30935 93 4147 75 134 366210 96 4873 64 137 387615 98 4833 52 139 415220 99 4964 39 143 463025 103 6093 22 149 491030 107 6522 17 154 5369




The flexural strength and modulus of the composites also increase withincrease in filler content. The increase in flexural strength is higher for mica-filled composites compared to silica, while flexural modulus increased by120% on incorporation of 30% silica filler, while the same mica content

(a)

(c)

(b)

Figure 1. The scanning electron micrographs of mica-filled PEEK composites at differentfiller contents: (a) 5%, (b) 15%, and (c) 30%.

Table 2. Tensile and flexural properties of microsilica-filled PEEKcomposites.

Wt% ofmica


Young’smodulus

(MPa)

Elongationat break

(%)


Flexuralmodulus

(MPa)

0 90 3552 80 126 30935 93 4386 84 138 364610 95 4428 86 139 388615 98 4607 44 143 484120 103 4964 16 145 532525 104 5095 12 148 647930 108 5419 10 149 6805

6 S. Joseph et al.



could increase the flexural modulus by 73% compared to neat PEEKmatrix. The scanning electron micrographs of tensile fracture surface ofmica- and microsilica-filled nanocomposites at different filler contents areshown in Figures 1 and 2, respectively. It is clear from the SEM that thedegree of dispersion of fillers in the matrix is not much affected by increasein filler content. In both the composites, though the filler density increaseswith increase in filler content, agglomeration is not much. The particle size isnot much affected by increasing filler content. This may be due to the stronginterface in this system. If the composite were to have a weak filler/matrixinteraction, there would have been a boundary region between matrix andfiller. But here, such a boundary is not present and hence there can beefficient stress transfer between filler and matrix. So, increase in fillercontent increases the mechanical properties of the composites.

Figure 3 shows the variation in impact strength of silica- and mica-filledPEEK composites. Silica and mica fillers increase the impact strength withincrease in filler content. The mica filler is found to impart higher toughnessto PEEK matrix compared to silica filler at lower filler loading. At 30%loading, both mica and silica fillers are found to have same impact strength.

(c)

(b)(a)

Figure 2. The scanning electron micrographs of microsilica-filled PEEK composites atdifferent filler contents: (a) 10%, (b) 20%, and (c) 30%.




100

105

110

115

120

125

Har

dnes

s

Filler content (%)

Mica/PEEK composites Silica/PEEK composites

0 5 10 15 20 25 30

Figure 4. Effect of filler loading on hardness value of mica- and silica-filled PEEKcomposites.

0 5 10 15 20 25 302

3

4

5

6

7

8

9

10

11

Impa

ct s

tren

gth

(KJ/

m2 )

Filler loading (wt%)

Mica/PEEK compositesSilica/PEEK composites

Figure 3. Effect of filler loading on impact strength of mica- and silica-filled PEEKcomposites.

8 S. Joseph et al.



Figure 4 shows the hardness values of mica- and silica-filled PEEKcomposites. The hardness is found to increase with increase in filler contentfor both mica- and silica-filled PEEK composites. Mica is found to imparthigher hardness to nanocomposites compared to silica filler. There is 19%increase in hardness value for 30% mica/PEEK composites, compared to15% increase for silica/PEEK, when compared to PEEK. Mina et al.prepared TiO2-filled polypropylene by multiple molding (using extruder andcompression molding) and single extrusion process. The hardness value washigher for multiple extrusion process compared to single extrusion becauseof good filler/matrix interaction [18]. Here, mica is found to impart higherhardness to nanocomposite compared to silica filler due to higher interfacialinteraction in mica/PEEK system.

ELECTRICAL AND THERMAL PROPERTIES OF COMPOSITESTable 3 gives the dielectric strength, arc resistance, and heat distortion

temperature of mica-filled and microsilica-filled PEEK composites. Thedielectric strengths of both mica- and silica-filled composites are found toincrease with increase in filler contents. The increase is more prominent atlower filler contents. Incorporation of 5% mica and microsilica hasincreased the dielectric strength of the PEEK by 70% and 64%, respectively.Dielectric strengths of 30% mica and silica nanocomposites are 108% and154% higher than neat PEEK matrix, respectively.

A polymer resin reinforced with nanosized inorganic particulates isexpected to have improved thermal stability and resistance to flammability.Kuo et al. [19] observed that thermal stability of filled PEEK matrix ishigher than PEEK matrix by 408C. Here, thermal stability of the PEEK isalso found to increase with increase in mica and silica contents. Both heatdistortion temperature and arc resistance of the composites increase with

Table 3. Dielectric strength, arc resistance, and heat distortion temperatureof mica-filled and microsilica-filled PEEK composites.

Fillercontent(%)

Dielectric strength (kV/mm) Arc resistance (s)Heat distortion

temperature (8C)

Mica Silica Mica Silica Mica Silica

0 11 11 120 126 153 1535 18 19 140 158 168 16210 19 21 161 169 173 17415 19 23 176 175 182 17920 20 25 178 181 196 18825 21 26 182 182 213 19630 24 28 184 189 225 212




increase in filler content. The arc resistance is found to be comparable forboth silica- and mica-filled composites. The heat distortion temperature ishigher for silica-filled composites compared to mica composites at all fillerloadings.

PES Composites

MECHANICAL PROPERTIESTables 4 and 5 gives the tensile strength, modulus, flexural strength, and

modulus of mica- and silica-filled PES composites at different filler contents.For both silica- and mica-filled composites, tensile strength increases withincrease in filler content. The variation of tensile strength with filler contentis found to be similar in both silica and mica composites, but the modulusvalue is higher for silica-filled composites than mica filled in PEScomposites. About 29% increase in tensile strength is obtained by adding30% of filler in the PES matrix. Tensile modulus is also found to increase

Table 4. Tensile and flexural properties of mica-filled PES composites.

Wt% ofmica


Young’smodulus

(MPa)

Elongationat break

(%)


Flexuralmodulus

(MPa)

0 86 2800 25 120 26005 94 3415 8.3 137 316610 96 3685 8.7 140 334315 99 3825 6.8 144 346320 103 4080 6.2 149 367425 107 4329 6 152 400630 111 4521 5 156 4423

Table 5. Tensile and flexural properties of microsilica-filled PES composites.

Wt% ofmica


Young’smodulus

(MPa)

Elongationat break

(%)


Flexuralmodulus

(MPa)

0 86 2800 25 120 26005 94 3289 3.5 142 334010 96 3641 4.5 147 360015 102 3876 5.7 149 394320 105 4237 5 154 468725 108 4893 4 158 500830 110 5632 3.5 163 5432

10 S. Joseph et al.



with increase in filler volume fraction; 100% increase in tensile modulusvalue is obtained for 30% microsilica-filled PES composites. Incorporationof mica also increased the modulus of the PES matrix. Percentageelongation decreases with increase in filler content for both silica- andmica-filled composites and the decrease is higher for silica-filled compositesthan that of mica-filled ones.

The scanning electron micrographs of the surface of mica- and silica-filledcomposites at different filler loadings are shown in Figures 5 and 6. It isclear from the TEM that filler agglomeration is low in both mica and silicacomposites. Initially, at low filler content, fillers are dispersed uniformly.As the filler loading increases, the fillers start to form a continuous networkin the composite. The filler loading at which network formation occursdepends on the type of filler and matrix and the filler/matrix interaction.At high fiber loadings, if fiber/matrix adhesion is poor, the fillers getagglomerated rather than forming a continuous network. In this case,property improvement will be lower. Microsilica particles are found to forma continuous network-like structure at higher filler contents (25 and 30).

(a) (b)

(d)(c)

Figure 5. The scanning electron micrographs of mica-filled PES composites at different fillercontents: (a) 5%, (b) 10%, (c) 20%, and (d) 30%.




But mica-filled ones like to remain in an agglomerated state rather than anetwork structure. So, the filler surface area is lower and stress transfer frommatrix to filler is lower than silica composites. So, silica composites showhigher properties at higher filler content (25% and 30%).

Flexural strength and modulus of both mica- and silica-filled compositesincrease with increase in filler content. The flexural strength and modulusvalues are found to be higher for silica-filled composites than that of mica-filled ones. This is because of the higher interfacial interaction in silica-filledcomposites as seen from SEM.

Variation of impact strength with filler content is shown in Figure 7. Forboth silica- and mica-filled composites, the impact strength is found toincrease with increase in filler content. By incorporating 30% mica, theimpact strength is increased by 100%, whereas the same amount of silicacould increase the impact strength by 200%.

Variation of the hardness values of mica- and silica-filled composites isshown in Figure 8. Hardness increases with increase in concentration of

(a) (b)

(b) (d)

Figure 6. The scanning electron micrographs of microsilica-filled PES composites atdifferent filler contents: (a) 5%, (b) 15%, (c) 20%, and (d) 30%.

12 S. Joseph et al.



3

4

5

6

7

8

910

11

12

13

14

15

16

17

Impa

ct s

treng

th (K

J/m

2 )

Filler content (wt%)

Mica/PES composites Silica/PEScomposites

0 5 10 15 20 25 30

Figure 7. Effect of filler loading on impact strength of mica- and silica-filled PES composites.

80

90

100

110

120

130

Har

dnes

s

Filler content (Wt%)

Mica/PES composites Silica/PES composites

0 5 10 15 20 25 30

Figure 8. Effect of filler loading on hardness value of mica- and silica-filled PES composites.




both the fillers. It is seen that the surface area of the filler and filler/matrixinteraction contributes to the total hardness of the composites.

ELECTRICAL AND THERMAL PROPERTIES OF PESPARTICULATE COMPOSITES

Table 6 gives the dielectric strength, arc resistance, and heat distortiontemperature of mica- and silica-filled composites. It is observed that thedielectric strength and arc resistance of ultrafine silica-filled PES increasesdrastically with increase in the concentration of mica. In silica-filledcomposites, the dielectric strength and arc resistance increase drastically bythe addition of 5% silica and thereafter increases marginally. At higherloadings, the rate of change in properties is found to be low, compared tothat at lower loading.

CONCLUSIONS

Addition of mica and silica fillers to both PEEK and PES matricesincreased the performance of both the matrices. The tensile, flexural, andimpact properties, and hardness values were found to increase with increasein filler loading. The mica-filled composites are found to impart highertensile and flexural properties and toughness to PEEK compared to silica-filled ones. In both mica- and silica-filled composites, filler dispersion isbetter even at higher filler contents, indicating good filler/matrix interaction.Dielectrical strength, arc resistance, and distortion temperature of thecomposites are also increasing with increase in filler content.

Silica filler is found to impart higher tensile, flexural, and impactproperties in PES matrix than mica. Like PEEK composites, the filleragglomeration is low in PES composites also. But at higher filler contents,

Table 6. Dielectric strength, arc resistance, and heat distortion temperatureof mica- and microsilica-filled PES composites.

Fillercontent(%)

Dielectric strength (kV/mm) Arc resistance (s)Heat distortion

temperature (8C)

Mica silica Mica silica Mica silica

0 8 8 70 70 200 2005 9 11 80 128 221 21410 11 13 83 131 229 22615 12 16 89 148 238 22820 15 17 98 150 247 23625 17 18 119 156 262 24830 18 21 124 162 274 257

14 S. Joseph et al.



agglomeration starts in mica composites, indicating a higher filler/matrixinteraction in the later. In PES composites also, dielectrical strength, arcresistance, and distortion temperature of the composites increase withincrease in filler content.

ACKNOWLEDGMENT

One of the authors, Seena Joseph thanks University Grant Commission,New Delhi, India for granting the Dr D.S. Kothari Post DoctoralFellowship.

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