theinvestigationofantistaticeffectsof1-ethyl- 2,3

The investigation of antistatic effects of 1-ethyl-2,3-dimethylimidazolium ethyl sulphate foracrylic-based polymer filmY. Seki∗1, N. Yıldız1, M. Ince1, S. Sengül2, K. Sever3, M. Sarıkanat4 and T. Dikici5

This study aims to produce a long-term antistatic acrylic-based film by incorporating ionic liquid(IL), 1-ethyl-2,3-dimethylimidazolium ethyl sulphate (EIL) into acrylic resin. After loading,characterisations of samples were conducted by mechanically, thermally and morphologically.In order to determine antistatic properties, surface resistivity of samples was measured byusing at different time intervals. The results indicated that IL loaded polymers showed a goodantistatic property for a long time. The effect of incorporation on tensile strength, tensilemodulus, flexural strength and flexural modulus of polymer were also obtained. After loadingprocess, tensile strength, tensile modulus, flexural strength and flexural modulus valuesdecreased considerably. The decrement in tensile strength of polymer is much less than thatin flexural strength. The effect of EIL incorporation into acrylic resin on thermal conductivityand surface wettability was also investigated. From scanning electron microscopy images, EILparticles in nano-size range were observed in polymer structure.Keywords: Antistatic, Additives, Films, Thermogravimetric analysis (TGA), Polymer

IntroductionPolymers have very high surface resistivities in the range1012–1014 Ω sq−1.1 Therefore, polymers are good electri-cal insulators. Such electrical insulating properties gener-ate static electricity. Static charges may form theconditions for sparkling caused by an electrostatic dis-charge. This may create electrical shock. Electricalshock is not directly dangerous for humans, but cangive severe damage for electronic devices.2 Moreover,electrical shocks and electrical discharge cause fire orexplosion.3 One of the other effects of static electricityis the tendency for surfaces to gather up dust or tostick to each other.4

In order to overcome these problems, antistatic addi-tives are used to modify the electrical properties of thepolymer, reducing the electric resistance of its surfaceallowing quick dissipation of the electrostatic charge.3–5

Antistatic additives reduce surface resistivity of a polymerto the range of 1010–1012 Ω sq−1. A decrease in surfaceresistivity of polymer provides a slow static decay rate6

and contributes protection against the chargeaccumulation.7

Antistatic additives can be divided into two groups:the electronic conduction-based additives and theionic conduction-based additives.8 Carbon-based fillers(carbon nanofiber, graphene nanosheet etc.) and inor-ganic fillers (ZnO whisker etc.) for electronic conduc-tion, and surfactants (ionic liquids (ILs) etc.) andintrinsically conductive polymers (polypyrrole etc.) forionic conduction have been used to obtain antistaticproperties.8–13 Antistatic effects of the agents arerealised by ion or electron conduction mainly occurredthrough successive conduction paths formed by addi-tives or moisture adsorbed on the surfaces of thepolymer.12

ILs have been reported to be useful antistatic agents onplastics.2,14 ILs are potential organic salts due to their lowglass transition temperature (Tg).

15 Since many ILs arehighly dissociable and Tg of ILs are quite lower thanthat of inorganic salts, ILs are expected to be superb addi-tives to prepare ionic conductive polymers.16 Effectiveantistatic effects are supported by the anion migrationof ILs.8

In this study, ethyl-2,3-dimethylimidazolium 1-ethylsulphate (EIL) was used as IL and the acrylic polymer/EIL were prepared by solution casting method. The aimof this study is to evaluate the effect of IL as an antistaticagent on the thermal properties, and surface resistivity ofthe acrylic polymer.

1Department of Chemistry, Dokuz Eylul University, Izmir, Turkey2DYO Boya Fabrikaları San.ve Tic. A.S., Izmir, Turkey3Department of Mechanical Engineering, Izmir Katip Çelebi University,Izmir, Turkey4Department of Mechanical Engineering, Ege University, Izmir, Turkey5Department of Material Science and Engineering, Izmir Katip ÇelebiUniversity, Izmir, Turkey

∗Corresponding author, email [email protected]

© 2016 Institute of Materials, Minerals and MiningPublished by Taylor & Francis on behalf of the InstituteReceived 21 May 2016; accepted 6 June 2016DOI 10.1080/14658011.2016.1201258 Plastics, Rubber and Composites 2016 1

mailto:[email protected]

Material and methodsMaterialsCommercial products, acrylic resin (882-8192), n-butylacetate (solvent) and R76936 hardener were suppliedfrom DYO Paints Manufacturing and Trading Company,Turkey. EIL as IL was purchased from Sigma-AldrichCorp.

Manufacturing of films0.1 g of EILwas firstly dissolved in 10 g of n-butyl acetateby mixing for an hour. Acrylic resin was added to the sol-ution and mixed for half an hour. Then, hardener, 35 wt-% of acrylic resin, was added to the mixture and mixed fora while. The mixture was cast into petri dish and placedinto oven at 80°C for 2 h. This procedure was repeatedfor 0.25 and 0.5 g of EILs. The samples were coded asPoly-0.1EIL, Poly-0.25EIL, Poly-0.5EIL by taking themasses of EIL into account.

Electrical resistivity measurementElectrical resistivity measurements of films were madeaccording to ASTM-D-257-9 standard by using 6517B/E Keithley Electrometer/High Resistance Meter. Surfaceresistivities were given as Ω sq−1.

TGATGA was conducted by using TGA (Perkin-Elmer Dia-mond TG/DTA Analyzer) at a heating rate of 15°C min−1 in the range of 30–600°C under nitrogenatmosphere.

Thermal conductivityThermal conductivity and effusivity measurements of filmsamples were performed by using C-Therm TCi ThermalConductivity Analyzer. The results were given as averagevalue of eight successful measurements.

Mechanical analysisThe tensile strength and Young’s modulus of films weredetermined by tensile tests. Flexural strength and flexuralmodulus values were obtained by three point bendingtests. The stated-tests were made by using tensile testingmachine with a 50 N load cell at a crosshead speed of5 mm min−1. A Shimadzu Autograph AG-IS Series uni-versal testing machine was used in analyses.

SEM analysisSEM analyses were conducted by using FEI Quanta FEG250 SEM instrument operated at 5 kV. Before analyses,the filmswere coatedwith gold by the help of plasma sput-tering method.

Contact angle measurementsThe surface wettability was determined by the water con-tact angle measurements. These measurements were per-formed using a manual optical tensiometer (Theta Lite).The measurements were made by using 5 mL of the sessiledrop at three different points on the surface.

Resistance to chemicals, alcohol and fuelThe varnishes containing acrylic resin, solvent, IL, etc.,were applied by means of an applicator on metal panels.The panels were dried at 80°C for 30 min. Resistance tochemicals, alcohol and fuel were also investigated accord-ing to ASTMD 1308, FIAT 9.55842/01–2.16 and ASTMD 2792 standards, respectively. All samples demonstrateda resistivity to chemicals and alcohols. However, a smallsoftening was observed after fuel application.

Results and discussionsElectrical resistivity measurementsThe surface resistivity of acrylic polymer at various timeintervals is given in Fig. 1. The surface resistivity ofacrylic polymer was obtained to be 3.03 × 1014 Ω sq−1.The surface resistivity of acrylic polymer increases withday. The highest value was obtained on 90th day as1.70 × 1016 Ω sq−1. The surface resistivities of Poly-0.1EIL, Poly-0.25EIL and Poly-0.5EIL at various timeintervals are given in Figs. 2–4. The resistivity values forPoly, Poly-0.1EIL, Poly-0.25EIL and Poly-0.5EIL on90th day are 1.70 × 1016, 2.83 × 1013, 2.73 × 1013 and6.87 × 1010 Ω sq−1, respectively. With the inclusions of0.1 EIL, 0.25 EIL and 0.5 EIL, surface resistivity ofacrylic polymer on first day decreased to 1.21 × 1010,1.06 × 1010 and 5.02 × 109 Ω sq−1, respectively. The high-est surface resistivity values for Poly-0.1EIL, Poly-0.25EIL and Poly-0.5EIL were obtained to be 3.16 ×

1 Electrical resistivity of polymer surface

2 Electrical resistivity of Poly-0.1EIL surface

Seki et al. The investigation of antistatic effects of 1-ethyl-2,3-dimethylimidazolium ethyl sulphate

2 Plastics, Rubber and Composites 2016

1013 Ω sq−1 on 60th day, 4.68 × 1013 Ω sq−1 on 60th dayand 1.18 × 1011 Ω sq−1 on 30th day, respectively. The res-istivity values of Poly, Poly-0.1EIL, Poly-0.25EIL andPoly-0.5EIL on 90th day (at 50% r.h.) were measured tobe 3.03 × 1014, 2.83 × 1013, 3.73 × 1013 and 6.87 ×1010 Ω sq−1, respectively. It can be noted that long-termantistatic acrylic polymer was achieved with the inclusionof EIL into acrylic polymer. Among these acrylic poly-mer, one loaded with 0.5 EIL achieved the best perform-ances in terms of long-term antistatic property. It isknown that ILs have high ion density, high ionic mobility,and extremely high ionic conductivity and thus mayimprove the conductivity of polymers.17,18 Since increas-ing the weight fraction of EIL in polymer increases thenumber of charge carriers, Poly-0.5EIL has the lowest sur-face resistivity value. In summary it can be noted thatantistatic ability of the acrylic polymer results from theformation of continuous ion-conductive phases in acrylicpolymer.17

TGA analysisThe effect of EIL on thermal stability of Poly films wasinvestigated by TG analysis. TGA curves and data forthose samples are also given in Table 1 and Fig. 5, respect-ively. The mass losses up to 110°C due to evaporation ofwater are less than 1% for EIL loaded polymer samples.Initial decomposition temperatures were reported as255, 236, 250 and 256°C for Poly, Poly-0.1EIL, Poly-0.25EIL and Poly-0.5EIL, respectively. Besides, the firstmaximum decomposition temperatures for Poly, Poly-0.1EIL, Poly-0.25EIL and Poly-0.5EIL were obtained tobe 335, 340, 338 and 333°C, respectively. It is probablethat the mass loss in this step also involves the decompo-sition of imidazolium ring.19 The second maximumdecomposition temperatures for Poly, Poly-0.1EIL,Poly-0.25EIL and Poly-0.5EIL were obtained to be 445,448, 450 and 447°C, respectively. The slightly increasedthermal stability may be attributed to the difference inthe tethering point of the imidazolium ring to the acrylicpolymer backbone.20,21 The mass losses in the tempera-ture range 25–600°C for Poly, Poly-0.1EIL, Poly-0.25EIL and Poly-0.5EIL are 92, 95, 96 and 96%,



Table 1 TGA data for EIL-based polymers

SampleMass lossto 110°C Ti/°C Tmax1 Tmax2

Mass lossto 600°C

Poly 1.2 255 335 445 92Poly-0.1EIL 0.4 236 340 448 95Poly-0.25EIL 0.4 250 338 450 96Poly-0.5EIL 0.6 256 333 447 96

5 TGA curves of EIL-based acrylic polymer


Plastics, Rubber and Composites 2016 3

respectively. The total mass losses of Poly-0.1EIL, Poly-0.25EIL and Poly-0.5EIL are higher than that of Poly.From TGA analyses, it can be noted that acrylic polymercontaining EIL as an antistatic agent does not decomposeif the working temperature is below the temperature of235°C.

Thermal conductivity analysisThe effect of EIL loading on thermal conductivity andeffusivity values of acrylic polymer is shown in Fig. 6.Thermal conductivity value of acrylic polymer wasobtained to be 0.68 W mK−1. Additions of 0.1, 0.25 and0.5 g of EIL decreased the thermal conductivity of acrylicpolymer by about 40, 47 and 51%, respectively. Besides,EIL addition decreased the thermal effusivity of acrylicpolymer. This indicates that with the addition of EILthe amount of thermal energy, which can be absorbedby acrylic polymer, is reduced.22 It is interesting to notethat EIL loading made the acrylic polymer electricallyconductor but thermally insulator.

Mechanical analysisTensile test and three point bending test results are shownin Fig. 7. Tensile strength of polymer was obtained to be6.24 MPa. 0.1, 0.25 and 0.5 EIL loadings into acrylicresin decreased the tensile strength to 3.26, 3.29 and3.10 MPa, respectively. It is seen that the decrements intensile strength is irrespective of the amount of loadedEIL. Young’s modulus of unloaded polymer is40.23 MPa. However EIL loading decreased the Young’smodulus of unloaded polymer. It can be also noted that0.1 EIL loading led to less decrement in Young’s modulus.It is known that the ILs are generally used as lubricant

6 Thermal conductivity and effusivity values of EIL-basedacrylic polymer

7 Tensile test and three point bonding test results



and plasticiser. Besides it was also reported that theaddition of plasticisers decreases the tensile strength andYoung’s modulus.23 Similar decreases were observed forpermanently antistatic polyurethanes containing ILs.17

Flexural strength of unloaded polymer was determinedto be 5.25 MPa and decreased to 2.53, 1.12 and1.20 MPa after 0.1 EIL, 0.25 EIL and 0.5 EIL loadinginto polymer, respectively. As can be seen from Fig. 7,flexural modulus of polymer is 111.03 MPa. EIL loadingled to considerable decrease in the flexural modulus.These decrements can be explained by taking poor dis-persion of EIL in polymer into consideration. Poor dis-persion of IL, EIL in acrylic polymer, causes aggregateswhich could act as stress concentrators. Probably, thesedecrease the mechanical properties of polymers. Besides,SEM images confirm poor dispersion of EIL in polymermatrix.

SEM observationSEM micrographs of Poly, Poly-0.1EIL, Poly-0.25EILand Poly-0.5EIL are presented in Fig. 8a–d, respectively.As can be seen from Fig. 8b, EIL particles in Poly-0.1EIL cannot be seen clearly. However, EIL particlesin Poly-0.25EIL can be seen clearly in nano-size range.The particles range about from 100 to 250 nm. Asshown in Fig. 8c, the particles were sparsely distributed

in the surface of Poly-0.25EIL. When the amount ofEIL is increased by two times, more particles can beseen in SEM micrographs, as presented in Fig. 8d.Although nanoparticles can be seen in SEM images ofPoly-0.5EIL, particle aggregation also took place. FromSEM images it can be reported that interconnected EILparticles in Poly-0.5EIL may improve electrical connec-tivity of polymer. This interconnection may provide apath for current flow.

Contact angle measurementsThe effect of EIL addition on hydrophilicity of the acrylicpolymers was determined by measuring the contact anglevalues of films. Contact angle measurement of films is

8 SEM images of film samples. a Poly, b Poly-0.1EIL, c Poly-0.25EIL, d Poly-0.5EIL

9 Contact angle values of film samples


Plastics, Rubber and Composites 2016 5

shown in Fig. 9. Contact angle values for Pol, Poly-0.1EIL, Poly-0.25EIL and Poly-0.5EIL are 71°, 82°, 77°and 55°, respectively. 0.5 EIL addition into Polymerdecreased the contact angle of polymer significantly.Besides 0.1 EIL addition slightly increased the contactangle of acrylic polymer. However, 0.25 EIL did notlead to significant difference in contact angle value ofpolymer. 0.5 EIL addition made the surface of acrylicpolymer more hydrophilic. Therefore it can be said that0.25 EIL addition into acrylic polymer did not consider-ably affect the hydrophilicity of the acrylic polymer sur-face. However it can be noted that 0.5 EIL has anapparent influence on the hydrophilicity of acrylic poly-mer surface. The greatest EIL content (0.5 EIL) led to amore hydrophilic polymer surface. This increase in hydro-philicity may be mostly attributed to sulphate group ofEIL. It was reported that contact angles for imidazoliumcations enhance with the alkyl chain length in the ILcation structure. However the type of anion should betaken into account in wetting studies as well as water con-tent of IL.24 It is probable that water forms hydrogenbonds with –SO(3) in the ethyl sulphate anion and withthe imidazolium ring in the 1-ethyl-2,3-dimethylimidazo-lium cation.25

ConclusionEIL, as an IL, addition into acrylic polymer lowers the sur-face resistivity of the acrylic polymer and forms a long-term antistatic acrylic polymer. With the addition of 0.1EIL, 0.25 EIL and 0.5 EIL, surface resistivity of acrylicpolymer increased from 3.03 × 1014 Ω sq−1 to 2.83 ×1013, 3.73 × 1013 and 6.87 × 1010, respectively, on 90thday. Thebest performances in terms of long-termantistaticproperty were achieved by loading with 0.5 EIL intoacrylic polymer. 0.5 EIL addition has an apparent influ-ence on the hydrophilicity of acrylic polymer surface.The dispersion of EILparticles on the surface of the acrylicpolymer matrix took place in nano-size range. EILaddition into acrylic polymer decreased the tensilestrength, Young’s modulus, flexural strength and flexuralmodulus of acrylic polymer. Besides, EIL addition signifi-cantly decreased the thermal conductivity and effusivityvalues of polymer. With the addition of EIL at differentratios decreased the thermal conductivity of acrylic poly-mer by about 40, 47 and 51%, respectively. However, EILaddition slightly increased the thermal stability of acrylicpolymer. From the results it can be reported that EILaddition made the acrylic polymer electrically conductorbut thermally insulator. It can be concluded that EILincorporation can be used as an efficient way to improvethe long-term antistatic property of acrylic-based polymerfilm.

AcknowledgementsThis study was supported byMinistry of Science, Industryand Technology (Turkey), Project Number:0016.STZ.2013-1. We also would like to thank to OkanErgül and Merve Dilaver from DYO Boya FabrikalarıSan.ve Tic. A.S., Izmir.

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