Synthesis of a novel polyester-ether copolymer and its derivatives as antistatic additives for thermoplastic films

Journal Pre-proof Synthesis of a novel polyester-ether copolymer and its derivatives as antistatic additives for thermoplastic films Hüsnü Kemal Gürakin, Ahmet C. Turan, Hüseyin Deligöz PII:

S0142-9418(19)31384-4

DOI:

https://doi.org/10.1016/j.polymertesting.2019.106214

Reference:

POTE 106214

To appear in:

Polymer Testing

Received Date: 10 August 2019 Revised Date:

26 October 2019

Accepted Date: 7 November 2019

Please cite this article as: Hüü.Kemal. Gürakin, A.C. Turan, Hü. Deligöz, Synthesis of a novel polyesterether copolymer and its derivatives as antistatic additives for thermoplastic films, Polymer Testing (2019), doi: https://doi.org/10.1016/j.polymertesting.2019.106214. This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. © 2019 Published by Elsevier Ltd.

Synthesis of a Novel Polyester-ether Copolymer and its Derivatives as Antistatic Additives for Thermoplastic Films Hüsnü Kemal GÜRAKINa,b, Ahmet C. TURANb, Hüseyin DELİGÖZa,* a

Engineering Faculty, Chemical Engineering Department, Istanbul University Cerrahpaşa, Istanbul 34320, Turkey b

Setaş Kimya San A.Ş., Çerkezköy, Tekirdağ, Turkey

Abstract. Development of antistatic thermoplastic elastomer composites is gaining much interest in scientific and industrial aspects. In this contribution, a novel type of polyester-block-ether copolymer (PEBE), PEBE with ionic liquid (PEBE-IL) and quaternized PEBE (PEBE-Q) were synthesized, characterized and compounded with a commercial bottle grade polyester (PET) resin. It was found that the surface resistivity of the PET composite films was around 109-1010 ohm/sq. The addition of the PEBE copolymers as an antistatic agent into PET matrix resulted in almost 106 times enhancement in surface resistivity compared to neat PET film. Among the PET films with an antistatic agent, it was emphasized that PEBE-IL and ionic liquid doping to PET matrix led to a relatively lower crystallization degree, surface resistivity, contact angle and breaking force with a translucent appearance compared to neat PET film. Furthermore, it was illustrated that antistatic PET films with fine-tune physical, mechanical and morphological properties can be achieved by choosing appropriate antistatic agent type and amount.

Keywords: Polyester-block-ether copolymer, antistatic polyester film, ionic liquid

1.

Introduction

Static charges accumulated on the surface of the polymers can cause some problems, especially in the packaging applications. Sensitive electronic devices such as hard disks and motherboards can be severely damaged by a short circuit caused by electrostatic discharge [1]. Most of the polymers used in the packaging industry are inherently insulators. In particular, the relatively less polar molecular structure of the polyethylene terephthalate (PET) (which is one of the most common packaging polymers) makes the polymer itself hydrophobic and facilitates the accumulation of static charges. Many studies in the past 30 years have shown that combining the polar comonomers with the polyester chain resulted in an enhancement of the wetting and static dissipative properties of the neat PET. For example, the addition of poly(ethylene glycol) (PEG) [1-3], polytetramethylene ether glycol (PTMEG, pTHF) [4], diacids like adipic [3], isophthalic [2,3], and sulfoisophthalic acid [4] to the PET polymer allows faster absorption of the moisture and eases the drain of the static charges while disordering the crystalline structure. The ether groups existing at the polyether diol molecules are substantially polar to draw moisture and static charges are more easily distributed thanks to the moisture layer absorbed on the surface of the

1

polymer [5]. Furthermore, aliphatic diacids weaken the crystallinity of the polymer backbone and give an amorphous structure which leads to faster discharge of static electricity [3].

Another approach to gain the antistatic effect is to blend static dissipative copolymers with the insulative resin via melt blending. This theory is based on the formation of interpenetrating continuous conductive polymer networks. In the literature, polyether block amides were widely used for this application but the antistatic copolyesters based on polyester-ethers have been scarcely reported. In a study by Li et al. [2], the polyester copolymers were obtained from diacids, namely isophthalic and terephthalic acid and the different portions of PEGs having different molecular weights. Final polyester fibers containing 18 wt% of PEG 1,000 showed a volume resistivity of 5.8 x 1010 ohm/cm. In another study, polyester-ether copolymers having PEG and other hydrophilic segments were used to gain hydrophilicity to the polyester bulk materials. They reported that the introduction of 12 wt% of PEG comonomer into the PET matrix increased the moisture absorptivity value of the neat polyester from 0.56% to 0.96% [3]. In a work published by George, et al. [4], sulfoisophthalic acid was used as a comonomer in the production of the antistatic copolyester. The final films having 30 wt% of antistatic copolymer in a polyethylene terephthalate glycol (PETG) showed surface resistivity values ranging from 1011 ohm/sq to 109 ohm/sq.

Ionic liquids can be defined as salts that are liquid at room temperature and can be mainly used as conductive fillers [6]. They are also very promising antistatic agents for different thermoplastic and thermoset polymers. Melt blending of ionic liquids led to great improvement in the antistatic properties of some polymers such as polyurethanes [7-9], polycarbonate [10], polyamide [11] and other polymers [12-15]. For example; in a study published by Guo, et al. [16], 1,3-bis(2-hydroxyethyl) imidazolium chloride grafted PET copolymer was synthesized via polycondensation method and the changes in hydrophilicity and conductivity of this polymer were investigated as a function of the ionic liquid content. The conductivity values up to 15 µS/cm were reported.

As far as we know from the literature quaternization of polymer backbone resulted in more polarity and facilitated charge transfer due to the positive charge of the ammonium cation [17]. Also, it was found that quaternized compounds became more hydrophilic and hygroscopic due to the moisture adsorption of these polar sites [18]. In the literature, many studies were reported with the cationic surface treatment technique. For example, in a study published by Zaman, et al. [19], cationically modified cellulose was used as a surface finish chemical for polyester fabrics to gain the hydrophilicity and the water absorption of the treated fabrics significantly increased compared to untreated fabrics.

In this study, a novel type of thermoplastic polyester-ether block copolymer (PEBE) from PEG, PTMEG, isophthalic acid, adipic acid, sulfoisophthalic acid, and polyether 1,3 diol was successfully prepared and characterized. To the best of our knowledge, the use of polyether 1,3 diol as a comonomer in an antistatic polyester-ether copolymer composition and 2,3-epoxypropyltrimethyl ammonium chloride as a quaternization agent for this copolymer have not been reported formerly. Quaternary alkylammonium sulfonimide based ionic liquid and quaternized polyester-ether block copolymer were also used as antistatic discharge promoters in PEBEs and the effects of these antistatic agents on surface resistivity of PET composite films were comparatively

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investigated. As far as we know from the literature, this type of commercially available ionic liquid was not used as an antistatic agent for PET-based cast films before. Furthermore, physicochemical, thermal and morphological properties of the PEBE and PET composite films prepared using twin-screw and single-screw extruders respectively were also extensively characterized.

2. Experimental

2.1. Materials

Polyethylene glycol (PEG 4,000 g/mol), mono ethylene glycol and diethylene glycol were purchased from DOW Chemicals.

Isophthalic acid and adipic acid were purchased from Eastman Co. and Brenntag Turkey,

respectively. Poly(tetrahydrofuran) (2,000 g/mol) was purchased from BASF while 5-sulfoisophthalic acid was supplied from Yangtai Chemicals Co. Polyether 1,3 diol (Tegomer D3403, 1,200 g/mol) was supplied by EVONIK, quaternary alkylammonium sulfonamide based ionic liquid (FC 5000) was kindly supplied by 3M, 2,3 epoxypropyl trimethyl ammonium chloride (GTMAC) was supplied by SKW Quab Chemicals Inc. Bottle grade 0.82 IV polyester chip was purchased from Indorama Ventures and it was dried at 160°C for 6 hours in a dryer before use. In order to avoid hydrolysis reactions with the polyester end groups, the water content of 2,3 epoxypropyl trimethyl ammonium chloride was evaporated at 20 ºC with 1 mbar vacuum at 24 h. All other chemicals were used as received.

2.2. Methods

Synthesis of PEBE Copolymer A novel polyether block ester copolymer (PEBE) was synthesized in a two-stage process of transesterification and followed by polycondensation. The reaction was carried out in a two-liter stainless steel reactor (Amar Instruments) with a condenser, vacuum pump, and nitrogen inlet. Total glycol and total acid mole ratio was kept at 1.32 in the formulation. For synthesis of the copolymer (abbreviated as PEBE), reactor was loaded with 458 grams (~0.114 mole) of PEG 4,000, 212 grams (~1.276 mole) of isophthalic acid (IPA), 123 grams (~1.981 mole) of monoethylene glycol (MEG), 15 grams (~0.141 mole) of diethylene glycol (DEG), 40 grams (~0.149 mole) of sulfoisophthalic acid (SIPA), 35 grams (0.029 mole) of polyether 1,3 diol, 47 grams (~0.322 mole) of adipic acid and 70 grams (0.035 mole) of polyTHF 2,000. 300 ppm antimony trioxide (Sb2O3) was used as a catalyst. The flask was purged with nitrogen and stirred under nitrogen atmosphere at 232°C for 4 hours under 3 bar. After 4 hours of esterification, the pressure was gradually reduced from 3 bar to 1 bar and 10 mm Hg (~ 0.0133 bar) for 30 minutes. At the final stage, the polymer was kept at 245ºC for 1.5 hours to perform polycondensation. It was replaced with a nitrogen atmosphere and allowed to cool for 30 minutes before the removal of polymer from the reactor. The synthesis steps of the PEBE are presented in Figure 1. Furthermore, the intrinsic viscosity value of the PEBE copolymer was measured after each production by dissolving the polymer in phenol/1,2-

3

dichlorobenzene (50/50 by weight) solution and determined to be between 0.58–0.61 dL/g according to ASTM D4603-18.

Figure 1. Schematic representation of PEBE synthesis (a) comonomer structures (b) repeating units of the PEBE copolymer with possible formations.

Preparation of PEBE-IL and PEBE-Q In order to reduce the resistivity of PEBE, ionic liquid and quaternization agent were added to PEBE copolymer synthesized according to the method described above. After the last stage of the polymerization, the quaternary alkylammonium sulfonimide based ionic liquid and 2,3 epoxypropyl trimethyl ammonium chloride were added individually to PEBE at 100ºC and mixed for an additional 60 minutes to obtain PEBE-IL and PEBE-Q, respectively. PEBE-IL and PEBE-Q contain 10 wt% of ionic liquid or quaternization agent and 90 wt% of PEBE copolymer. After the synthesis of PEBE and its derivatives, they poured into a mold and the surface resistivity of

4

these products were measured with a two-point probe method according to ASTM D 257 at 20°C and 65% relative humidity (RH).

Preparation of Copolyester–PET Compounds PEBE, PEBE-IL, and PEBE-Q were melt-mixed and blended with a commercial bottle grade PET resin in a corotating intermeshing (Leistritz, L/D: 45) double-screw extruder. The barrel temperature profile of the extruder was 285°C-280°C-275°C-270°C-275°C-260°C-255°C from the feed throat to the die, and the melt temperature of the blends was 273°C. The employed screw speed was 350 rpm. The final product was obtained in the form of granules from a filament die. All compounds were prepared at 15% wt of antistatic agent (PEBE, PEBE-IL, and PEBE-Q separately) with bottle grade commercial PET.

Preparation of PET Composite Films Cast film samples were prepared by using a laboratory scale Dr. Collin single screw extruder equipped with a Maddock mixing screw. The employed screw speed was 160 rpm. The barrel temperature profile of the extruder was 250°C-255°C-260°C-270°C-275°C-285°C-290°C from the feed throat to the die, and the melt temperature of the blends was 271°C. All cast films were produced at 100-micrometer thickness. Compounds with 15 wt% PEBE, PEBE-IL and PEBE-Q loading which were pre-prepared with a twin-screw extruder were diluted to the final compositions of 1-2-3-4-5-6-8-10-15 wt% antistatic agent. The surface resistivity values of the films were measured by constant voltage two-point probe method at an applied voltage of 500 V according to ASTM D 257 at 20 °C and 65% RH. The films of PET and PEBE was donated as PET/PEBE while PET/(PEBE-IL) showed the composition of PET and PEBE-IL.

2.3 Characterization

Chemical and Thermal Analysis PEBE, PEBE-IL, PEBE-Q, and PET were characterized on a Shimadzu IR Prestige-21 FTIR spectrometer with attenuated total reflectance (ATR) unit on a resolution of 4 cm-1. The scanning range was altered from 600 to 4,000 cm-1. X-ray diffraction (XRD) measurements were conducted by a Bruker AXS advance powder diffractometer with a Cu Kα radiation source between 10 to 90 theta angles. X-ray Fluorescence Spectrometry (XRF) analyzes of the samples were conducted on EDX-8000 (Shimadzu) spectrometer.

Differential scanning calorimetry (DSC) measurements of the synthesized antistatic copolymers, PET composite films, and neat PET were carried out in a DSC 2.0 (METTLER TOLEDO) analyzer. To eliminate the thermal history, samples were heated in the first heating run (-70°C to 300°C), cooling (300°C to 70°C) and second heating (-70°C to 300°C) with a rate of 10°C/min. Glass transition (Tg) and melting temperature (Tm) peaks were determined from the second heating run. Approximately 10-20 mg of sample was placed into the aluminum pans and measurements were performed under 50 ml/min of nitrogen flow. Glass transition temperatures were calculated from the peak of the first derivative of the inflection in the second heating curve. Crystallinity degree (%) values of the PET composite films were calculated from the first heating cycle according to Equation 1. The

5

melting enthalpy (∆Hm) of 100% crystalline PET was taken as 140 J/g [20]. Since all antistatic PET films were semicrystalline, the cold crystallization enthalpy (∆Hcc) values were taken into account.

Crystallinity %:

∆Hm-∆Hcc ∆H(100% Crystalline PET)

x 100

Equation 1.

TG analysis of the copolymers, PET composite films, and neat PET were carried out using a Shimadzu DTG-60 series differential thermal-thermogravimetric analyzer at a heating rate of 10ºC/min from room temperature to 600°C. The onset of thermal decomposition was determined from the temperature at which 10% weight loss occurred.

Surface Resistivity Measurements A surface resistivity meter (Norma Instruments) was used to measure the surface resistivity of the copolymers and PET composite films. The surface resistivity values of all samples were measured by a constant voltage two-point probe method at an applied voltage of 500 V according to ASTM D 257. The surface resistivity of the samples was measured at 20 °C and 65% relative humidity (RH) conditions with a standard deviation of ± 1% for all the samples.

Surface and Optical Measurements Total transmittance and haziness measurements of the PET composite films were conducted with Hunterlab UltraScan Pro dual-beam spectrophotometer with a standard deviation of ± 0.5%. The surface morphology of neat PET and PET composite films were examined using a scanning electron microscope (FEI Quanta FEG 450). Before imaging, all the film samples were coated with a conductive layer of sputtered gold. Contact angle measurements of the samples were conducted by using an Attension Theta (Biolin Scientific) tensiometer. Contact angles were evaluated on both sides of the films with distilled water. The contact angle values reported here were calculated from the average of three measurements with a standard deviation of ± 2°.

Moisture Absorption Measurements Moisture absorption of the antistatic PET films was also determined. For this purpose, the prepared films were firstly weighted accurately. Subsequently, the films were kept under 65% relative humidity at 20°C for one week. Finally, the moisture uptake was obtained from Equation 2.

Moisture Uptake %:

×100

Equation 2.

where W0 is the mass of the dried film before moisture treatment and W is the mass of the film after moisture treatment.

Tensile Properties

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Elongation at break (%) and the breaking force (N/15mm) values of the 100-micron thick PET-based composite films prepared by cast film extruder were measured by using Zwick Roell Z2.5 with a tensile rate of 100 mm/min in the machine direction with a standard deviation of ± 1%. The dimensions of the films were 150 mm x 15mm and the crosshead distance was 60 mm. Before the tests, the composite films were stored at 20°C and 65% relative humidity for 24 hours. 3. Results and Discussion

3.1. Chemical and Thermal Properties of Copolymers Figure 2 shows the FTIR spectra of PEBE, PEBE-Q, PEBE-IL, and neat PET. It can be clearly seen that C=O stretching appeared in the range of 1750–1735 cm–1 for PEBE-based copolymers due to the formation of ester bonds. It was illustrated that the ester-exchange reaction occurred successfully for all compositions. In comparison with the neat PET, the C-H stretching bands of PEBE, PEBE-Q, and PEBE-IL copolyesters seen around 2875 cm-1 indicated the existence of long polyethylene oxide units and confirmed PEG presence in the copolyester chain [21]. The band at 872 cm-1 observed in all copolyesters has belonged to the C-H deformation of two adjacent coupled hydrogens on the aromatic ring [22]. Sharp bands at 1245-1 cm for PET and 1294-1 cm and 1240 cm-1 for other copolyesters were attributed to valance vibrations of the C-C bonds [23]. The C-H stretching vibration of GTMAC at 1482 cm−1 was overlapped with the intermolecular band of the PEBE copolymer (C–H stretching at 1464 cm-1), while the stretching vibration of C-O of oxirane group at 914 cm-1 in the FTIR spectrum of GTMAC was not observed at the PEBE-Q copolymer (Figure 2) [24,25]. In addition to FTIR graphs of PEBE based copolyesters, carboxyl end group equivalent values of the PEBE and PEBE-Q copolymers were also measured and a significant decrease in the carboxylic end groups was determined after quaternization reaction. This value was measured as 96.8 meq/kgs for the PEBE and 4.12 meq/kgs for PEBE-Q according to ASTM D7409-15. These results demonstrated that the reaction between PEBE copolymer and GTMAC was achieved and PEBE-Q was successfully synthesized.

Figure 2. FTIR spectra of the synthesized copolyesters.

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Concerning infrared spectra of ionic liquid, namely alkylammonium sulfonimide and 2,3 epoxypropyl trimethyl ammonium chloride (GTMAC), they are illustrated in Figure 3. In the FTIR spectrum of GTMAC, the broad band at 3300 cm-1 was assigned to the O-H stretching vibration of water. Also, a strong absorption band at 1482 cm-1 appeared in the IR spectrum of GTMAC due to C-H symmetric bending of methyl groups on the quaternary ammonium substituent while the absorption bands at around 950 cm-1 and 914 cm-1 showed the characteristics of the epoxide group [25,26].

Figure 3. FTIR spectra of ionic liquid and quaternization agent (GTMAC). In the FTIR spectrum of ionic liquid, -CF3 symmetric stretching was attributed to the bands at 1182 cm-1 and 1136 cm-1. The medium intense band located at 1473 cm-1 in the spectrum was assigned to the SO2 asymmetric stretching [27]. In the FTIR spectrum of PEBE-IL, the bands at 1136 cm-1 and 1473 cm-1 from the ionic liquid were overlapped with the intermolecular C-H stretching bands of the PEBE copolyester but -CF3 symmetric stretching vibration band at 1182 cm-1 was still visible in PEBE-IL [27].

X-ray diffraction (XRD) curves of the PEBE, PEBE-IL and PEBE-Q copolymers are shown in Figure 4. According to these results, PEBE and PEBE-Q copolymers showed similar diffraction patterns. Strong and sharp peaks at 19º, 22.8º, 25.8º and 44º (2θ) and relatively small peaks at 35.6º, 39º, 64º and 81.3º (2θ) were very similar in PEBE and PEBE-Q copolymer. The peaks at 19º, 22.8º and 25.8º (2θ) were probably due to the PEG presence in the copolymers [28]. On the other hand, the first three strong peaks observed for PEBE and PEBE-Q were shifted to the higher degrees and the intensities of these peaks reduced for PEBE-IL copolymer. Three main peaks of the PEBE-IL were at 20.4º, 24.2º, and 27º (2θ) and no small peaks were observed, unlike PEBE and PEBE-Q. This result demonstrated that the addition of ionic liquid clearly reduced the crystallinity and made the PEBE-IL copolymer more amorphous compared to other derivatives.

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Figure 4. XRD spectra of the PEBE, PEBE-IL and PEBE-Q copolymers.

X-ray Fluorescence Spectrometry (XRF) investigation was carried out to screen the expected elements in the PEBE, PEBE-IL and PEBE-Q copolymers and the related graphs are depicted in Figure 5. The ionic liquid was also analyzed to see the fluorine (F) and sulfur (S) arisen from bis(trifluoromethane sulfonyl) imide anion.

(a)

(b)

(c)

(d)

Figure 5. XRF spectra of the antistatic additives (a) IL, (b) PEBE, (c) PEBE-IL, (d) PEBE-Q. The peaks rhodium (Rh), copper (Cu) and iron (Fe) are due to the XRF sample holder and detector.

The sulfur peak of the PEBE (Figure 5b) has corresponded to sulfoisophthalic acid comonomer and the polycondensation catalyst was the reason for the antimony (Sb) peak. According to Figure 5a and 5c, it was seen

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that the PEBE-IL contained fluorine from the ionic liquid. The amount of the sulfur moiety was increased compared to PEBE because of the addition of the sulfonyl groups. In addition to the sulfur peak, the chlorine (Cl) and sodium (Na) peaks were clearly seen in the XRF spectra of PEBE-Q (Figure 5d) due to the presence of GTMAC.

DSC thermograms of the PEBE, PEBE-IL, and PEBE-Q obtained from first heating (-70°C to 300°C), cooling (300°C to -70°C) and second heating (-70°C to 300°C) cycles at 10°C/min rate are shown in Figure 6 and the different measurable quantities are shown in Table 1.

(a)

(b)

(c)

(d)

Figure 6. DSC thermograms of PEBE, PEBE-IL and PEBE-Q: (a) first heating from -70°C to 300°C, (b) cooling from 300°C to -70°C (c) second heating from -70°C to 300°C and (d) second heating after 15 minutes of cooling at -70°C (all cycles were run at a rate of 10°C/min).

Table 1. DSC results for copolymers. First Heating

Cooling

Second Heating

Second Heating after 15 min. of cooling at -70 °C

Tg (°C)

Tm (°C)

∆Hm(j/gr)

Tc (°C)

Tg (°C)

Tcc (°C)

∆Hcc(j/gr)

Tm (°C)

∆Hm(j/gr)

Tg (°C)

Tcc (°C)

∆Hcc(j/gr)

Tm (°C)

∆Hm(j/gr)

PEBE

-25.4

47.8

66.6

-35.4

-40.9

-5.2

51.5

40.5

52.2

-39.5

-7.0

50.9

43.5

53.1

PEBE-IL

-36.5

44.7

47.1

-27.4

-37.6

―

―

―

―

-38.1

18.2

30.5

38.7

22.1

PEBE-Q

-30.1

37.3

49.3

-37.9

-42.6

-12.7

53.8

42.5

54.1

-42.8

-16.2

53.9

43.7

53.7

Standard deviation of the DSC results: within ± 0.2° C for all the samples.

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In the first heating process (Figure 6a), no cold crystallization peaks were observed for any of the three copolymers which indicated that at the beginning all polymers were in crystalline structure but in the second heating run, PEBE and PEBE-Q copolymers showed the cold crystallization peaks. For PEBE-Q (Figure 6c), it was found that the cold crystallization (Tcc) peak was shifted to a lower temperature compared to PEBE and it reduced from -5.2°C to -12.7°C. From this finding, we can conclude that quaternization slightly accelerated the nucleation process of the copolyester similar to a nucleating agent. According to Figure 6b, broad exothermal peaks appeared between -27°C and -37°C, indicating the poor crystallization ability of all copolymers during the cooling crystallization process.

In the second heating run, PEBE and PEBE-Q polymers displayed a relatively sharp melting endotherm enthalpies (∆Hf) of 52.2 J/gr at 40.5°C and 54.1 J/gr at 42.51°C while PEBE-IL copolymer showed an amorphous curve without any melting or crystallization peak. From this observation, we can conclude that PEBE-IL copolyester was completely amorphous and ionic liquid had a plasticizing effect on the polymer [29]. On the other hand, the cooling crystallization (Tcc) and glass transition (Tg) temperatures of PEBE-IL calculated from the cooling run (Figure 6b) and second heating run (after 15 minutes of cooling at -70°C) (Figure 6d) respectively were slightly higher than those of PEBE and PEBE-Q. This can be explained by the plasticizing effect of ionic liquid improved the mobility of polyester chains and played a key role in accelerating the rate of crystallization [30,31]. An increase in Tg has been previously reported upon the addition of ionic liquids into sodium and lithium salts [32]. The increase in Tg with the addition of ionic liquid may be due to the enhancing ion-ion attractions between ionic liquid and sodium salt of sulfoisophthalic acid from PEBE polymer chain [33]. According to Figure 6d and the data from Table 2, after 15 minutes of cooling at -70°C, PEBE-IL had enough time to partially crystallize, so in the second heating run, the glass transition, melting and crystallization peaks have appeared for PEBE-IL copolymer.

Thermal stability and onset degradation (~10% weight loss) temperatures of the PEBE based copolymers were determined by TGA. The influences of ionic liquid and quaternization on the thermal stability of PEBE copolyester is shown in Figure 7. PEBE-IL and PEBE-Q exhibited lower thermal stability than that of neat PEBE. The onset degradation temperature for PEBE was 369.8°C and only 2% of its weight was lost at the extrusion melting temperature range (~273°C). On the other hand, PEBE-IL had an onset degradation temperature of 328°C while PEBE-Q showed the onset decomposition temperature of 292.2°C. Thus, the lowest thermal stability was observed for PEBE-Q among the prepared PEBE copolyesters. This is most probably due to the degradation of quaternary ammonium groups at ~285°C [34,35]. In short, it was concluded that all the copolyesters were thermally stable up to 270°C and they showed no thermal degradation during extrusion compounding and film preparation steps. Further, the addition of ionic liquid weakens the polymer chains and also the decomposition trigger temperature for the ionic liquid itself is expressed as 320 °C [36].

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Figure 7. Thermal stability of PEBE based copolymers and commercial neat PET.

3.2 Chemical and thermal properties of PET composite films FTIR analysis of some selected PET composite films containing 10 wt% PEBE, 10 wt% PEBE-IL, 10 wt% PEBE-Q and 5 wt% ionic liquid were conducted and the obtained spectra are shown in Figure 8. For comparison, the FTIR spectrum of neat PET is also given. According to these results, the neat PET had four main peaks, the absorption peak at 1720 cm-1 was attributed to carbonyl stretching vibration of C=O terephthalate units while the peaks at 1250 cm-1 and 1090 cm-1 were trans and gauche stretching of the ester C-O bonds. The peak at 729 cm-1 was corresponded to out of plane C-H bending of the aromatic nuclei [23,37]. Since the composite films consisted of 90 wt% of PET, all antistatic films had shown similar peaks compared to neat PET. The composite films with PEBE, PEBE-Q, and PEBE-IL showed slight peaks at 2880 cm-1 attributed to the C-H stretching of the PEG moiety in copolymer compositions [28].

Figure 8. FTIR spectra of the PET composite films with PEBE and its derivatives.

To investigate the thermal transition temperatures of PET composite films, DSC analysis of the selected antistatic PET films were measured and the obtained results are given in Figure 9 and Table 2 in detail. Three of the

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selected films comprising 10 wt% PEBE, PEBE-Q, and PEBE-IL, while one film was with 5 wt% ionic liquid. Neat PET reference film was also measured as a reference.

a)

b)

c) Figure 9. DSC thermograms of PET composite films with PEBE and its derivatives: (a) first heating from -70° C to 300 °C, (b) cooling from 300 °C to -70° C and (c) second heating from -70° C to 300° C (all cycles were run at a rate of 10 °C/min).

In the first heating and cooling cycles (Figure 9a and 9b), DSC curves of the PET composite films showed that the cold crystallization and cooling crystallization temperature of all antistatic PET films decreased to lower temperatures compared to the neat PET film. For example, the cooling crystallization temperature of the neat PET film was measured as 181.1 °C while the composite films containing 10 wt% PEBE-Q and 5 wt% IL had crystallization points of 207.3 °C and 203.6 °C, respectively. Probably, it can be explained by the improved mobility and re-arrangement of the PET chains due to the soft segments of antistatic copolymer structured agents [38]. Furthermore, from Figure 9a and Table 2, the crystallinity degree (%) of the PET composite films and neat PET film were determined according to Equation 1 as a function of antistatic agent type comparatively. The crystallinities of the PET films with 10 wt% PEBE copolyester and its derivatives were determined as in the range of 4.3% and 8.6% while the crystallinity of neat PET film was 13.1%. Therefore, it can be clearly said that crystallinity % of antistatic agent containing PET films was lower compared to neat PET film and the introduction

13

of antistatic agents significantly reduced the crystallinity level. Moreover, the PET composite film with 5 wt% ionic liquid showed the lowest crystallinity degree (3%) among the all prepared antistatic agent containing films. These results revealed that the use of copolyester based antistatic agents declined the crystallinity level and led to a more amorphous structure. Please note that the obtained crystallinity degrees can be acceptable for cast PET films although some oriented polymeric films had a higher crystallinity degree.

Table 2. DSC values of the antistatic PET films* Cooling (300 ºC to 70 ºC)

First Heating (-70 ºC to 300 ºC)

Second Heating (-70 ºC to 300 ºC)

Neat PET

Tg (°C) 75.1

137.6

23.0

Tm (°C) 252.3

41.4

Crystalinity (%) 13.1

181.1

85,1

249.3

PET/PEBE

73.9

121.0

31.5

257.3

41.6

7.2

195.6

76,1

249.1

PET/IL

73.0

123.2

34.2

254.4

38.3

3.0

203.6

73.0

249.2

PET/(PEBE-Q)

74.8

121.3

29.4

253.9

41.4

8.6

207.3

81.0

248.7

PET/(PEBE-IL)

73.4

122.2

34.1

253.1

40.1

4.3

187.9

75.0

249.4

Tcc (°C)

∆Hcc(j/gr)

∆Hm(j/gr)

Tc (°C)

Tg (°C)

Tm (°C)

* All films except neat PET and PET/IL, contain 10 wt% of additive. PET/IL contains 5 wt% IL. The standard deviation of the DSC results: within ± 0.2° C for all the samples.

In addition to the influence of antistatic agent addition on the crystallization degree of PET matrix, the glass transition temperatures of the antistatic PET composite films were determined from the second heating run. The results indicated that the addition of antistatic additive caused to lower Tg values compared to the neat PET (85.1 ºC). The highest Tg value of pristine PET film can be attributed to the relatively larger crystallinity degree compared to PET composite films with antistatic agents. On the other hand, glass transition temperatures of PET/PEBE, PET/(PEBE-Q), and PET/(PEBE-IL) were found to be almost 76.1ºC, 81ºC and 75ºC respectively (see in Table 2). The relatively higher Tg value of PET/(PEBE-Q) can be explained by the formation of more crystalline and rigid structure compared to other antistatic agent containing PET composite films. By the way, it was found that the use of only ionic liquid as a conductive agent resulted in a more flexible structure due to its lower crystallinity as shown in Table 2. As it was discussed in the section of the mechanical properties, ionic liquid addition into the PET matrix caused less rigidity due to its function as a plasticizer. Hence, Tg of PET/IL was found to be the lowest one (73 ºC). This decrease in Tg is quite consistent with the results of previous studies [39]. According to Figure 9c, all-composite films were showed almost similar melting points around ~249 ºC and no cooling crystallization peak was observed because all films were crystallized during the previous cooling cycle.

14

Figure 10. TGA curves PET composite films with PEBE and its derivatives.

Thermogravimetric investigation of the selected antistatic films was carried out to understand the effect of these additives on the thermal properties of the composite films. TGA curves of the four selected PET composite films (10 wt% PEBE, 10 wt% PEBE-IL, 10 wt% PEBE-Q, 5 wt% IL) and neat PET reference film are presented in Figure 10. Generally speaking, the thermal degradation behavior of these selected films were quite consistent with the TGA values of the copolymers explained in the previous section. For example, the onset degradation temperature (~10 % weight loss) of the 10 wt% PEBE-Q containing antistatic PET film was found to be 348ºC while the neat PET film was measured as 415ºC. This lower thermal stability of 10 wt% PEBE-Q containing PET composite film (PET/PEBE-Q) was due to the less thermal durability of ammonium moiety [34,35]. PEBE, PEBE-IL, and IL bearing PET composite films had thermal decomposition values of 401ºC, 396ºC, and 381ºC, respectively.

3.3 Surface Characteristics of Antistatic Films

Influence of the Copolymer Content In order to study the influence of quaternization and ionic liquid doping on surface resistivity (Rs) of PEBE copolymer, firstly the electrical resistivities of bulk form antistatic copolymers were measured. It was pointed out that the surface resistivities of the copolyesters with both ionic liquid (PEBE-IL) and quaternization agent (PEBEQ) were lower than that of PEBE. While PEBE had an Rs value of 9 x 109 ohm/sq, PEBE-IL and PEBE-Q exhibited the surface resistivities of 4 x 108 ohm/sq and 1 x 109 ohm/sq, respectively.

Figure 11 demonstrates the effect of different concentrations of PEBE, PEBE-IL and PEBE-Q copolymers on the surface resistivity of PET composite film at 20°C and 65% RH. It was observed from Figure 11 that the surface resistivity of PET composite films significantly dropped depending on the amount of antistatic agents (PEBE and its derivatives). This lowering in surface resistivity was more obvious for PET/(PEBE-Q) and PET/(PEBE-IL) and it showed that the quaternization and ionic liquid doping had a positive effect on the increment of the surface conductivity of the PET composite films.

15

Figure 11. Surface resistivity changes of PET composite films as a function of the antistatic agent type and content (wt%) (measured at 20°C and %65 RH).

As one can see from Figure 11, the surface resistance of the composite films dramatically decreased with the addition of copolymers (PEBE, PEBE-IL and, PEBE-Q) to the neat PET until the percolation threshold. Beyond this point, the decrease in surface resistivity was very slight and resistivity values stayed nearly constant with further addition of PEBE and its derivatives. The surface resistivity of the PET film without any additive was found to be 7x1015 ohm/sq while antistatic additive including PET films exhibited the resistivity of 1011 ohm/sq in the case of 1 wt% loading into the matrix. Furthermore, the surface resistivity of PET composite films containing 15 wt% of antistatic agent lowered to 109 ohm/sq. It meant that the addition of antistatic agents into the PET led to lower surface resistivity, in which turn caused a higher surface conductivity around 104-106 times compared to neat PET film. Another important result can be drawn from the figure that pure ionic liquid insertion to the PET matrix caused a better impact on lowering surface resistivity of the corresponding film. It can be clearly shown that 4 wt% of IL addition resulted in 1.1 x 1010 ohm/sq of surface resistivity while the other antistatic agents yielded the surface resistivity of 7.4 x 1010 and 1.1 x 1011 ohm/sq at the same concentration. Probably, this higher conductivity can correspond to the use of pure ionic liquid which can facilitate the mobility of the electric charges along the polymer matrix due to the existence of more amorphous sites. On the other hand, percolation threshold points of the PET composite films were determined from Figure 11 and it was emphasized that the percolation threshold in respect of surface resistivity was about 4 wt% for ionic liquid and in the range of 6-10 wt% for other PEBEs.

Among all antistatic additives prepared in this study, PEBE had a lower impact on the improving surface conductivity of PET composite films compared to other antistatic agents. Nevertheless, 1 wt% of PEBE addition to the PET matrix caused roughly 104 times decay in surface resistivity compared to the neat PET film. This can be interpreted as PEG, other alcohols and aliphatic acid segments from the PEBE chain increased the content of ether bonds and the irregularity of molecular chain arrangement thus resulted in more amorphous and hydrophilic regions in the film. Therefore, the mobility of the electrical charges in these amorphous structures of PEBE

16

containing PET film was much easier. Comparing copolyester based antistatic additives, it can be briefly said that PEBE-IL containing film had lower surface resistivity than those of PEBE and PEBE-Q based corresponding composite films. For example; the surface resistivity of 8 wt% of PEBE-IL consisting PET film was found to be 1.1 x 1010 ohm/sq while the film comprising the same amount of PEBE showed the surface resistivity of 2 x 1010 ohm/sq. To fully understand the difference, the surface resistivity of two films containing 1 wt% of the ionic liquid in the final composition was compared. 1 wt% IL and 10 wt% PEBE-IL containing PET composite films showed the surface resistivity of 2x1011 ohm/sq and 9,7x109 ohm/sq respectively. Thus 10 wt% PEBE-IL PET composite films had 20 times lower surface resistivity than that of corresponding on the basis of 1 wt% IL presence in the film composition. This result illustrated that the presence of PEBE and ionic liquid had a synergistic effect on the antistatic properties of PET composite films.

Unlike classical antistatic additives, the synthesized inherently dissipative copolymers are not migratory. The homogenous distribution of conductive copolymers into an insulating matrix (PET) to form conductive paths is the main reason for the formation of the antistatic effect. Although the dissipation mechanism on the polyetherbased antistatic agents without any salt has not been clearly understood, the proposed conductivity mechanism of the prepared composite films is based on the ionic conductivity of polyoxyethylene repeated units with the formation of conductive three-dimensional networks [40,41]. These ion conductive pathways are mainly responsible for electrostatic dissipative behavior while maintaining the immediate, permanent and low humidity dependent antistatic effect. Unlike classical polyether block amide copolymers, synthesized polyether block ester antistatic copolymer contains sulfoisophthalic acid segments that could ease and support the ion transport via SO3sites on the polymer backbone. In addition, the hygroscopic and hydrophilic character of the antistatic additives facilitates the moisture adsorption from the air and supports the antistatic behavior of the composite films [42].

In addition to polar ethylene oxide sites, the quaternization of PEBE leads to improve the ionic conductivity of copolymer by dissociation of ionic groups. As far as we know from the literature, ionic conduction can occur in two different mechanisms, namely hopping and vehicle for ionic group-containing polymers. In PEBE-Q, the ionic conduction can take place by hopping mechanism due to the absence of any vehicle (such as water, etc.) to support ion transfer [43,44].

Besides the self-assembly static dissipation of the block copolymers, the conductivity can be enhanced with the addition of ionic moieties like ionic liquids and other salts. In our case, the doping of the commercially available ionic liquid into the PEBE copolymers resulted in a significant increase in the conductivity. Even cation-anion based ionic conductivity is not fully understood yet, it is believed that the mechanism is based on the incorporation of the cations with the polar groups of the host polymer [45]. This type of ionic conductivity was also assisted with the amorphous segments, low glass transition temperature and low crystallinity of the polymer backbone [46]. As one can see from the thermal analysis results from the previous chapters, PEBE based copolymers and films produced thereof have lower crystallinity and the glass transition points of all PEBE derivatives are below 0 ºC.

17

From a commercial point of view, there are many inherently dissipative polymers (IDP) that were available in the market. But few of them were reported in the PET film application. For example, polyether amides (PEBA), polyether ester amides (PEEA) and polyether urethanes were sold for different applications such as antistatic injection molding and packaging. For polyether block amide in PET, it was reported that it is possible to achieve 1011-1012 ohm/sq surface resistivity with 10-20 wt% standard grade (without any salt) PEBA loading [47]. In another work, the ternary blends of LDPE/PEBA/PET with 25 wt% PEBA showed surface resistivity values between 1011-1012 ohm/sq [41]. For PBT and PETG polymer matrices, it was reported that required polyether ester amide dosage to achieve 1 x 1011 ohms/sq surface resistivity was 15 wt% [48]. In another work, with the addition of 12 wt% polyether ester amide into PTT based plaques resulted in surface resistivity of 1.7 x 1012 ohm/sq [49]. In this work, our standard grade inherently dissipative copolyester without ionic liquid and quaternization (PEBE) showed a surface resistivity of 1.6 x 1010 ohm/sq with 10 wt% loading. For example, the surface resistivity values of PET composite films containing 15 wt% PEBE-IL and PEBE-Q were measured as 6.9x109 ohm/sq and 9.9x109 ohm/sq respectively which was very sufficient for an antistatic flexible packaging application and it was also competitive with current IDP grades in terms of obtained surface resistivity.

Hydrophilicity In order to investigate the hydrophilicity of the prepared PET composite films consisting of different antistatic additives, both contact angle and moisture uptake of the PET films were determined as a function of antistatic agent type and content. The obtained results are given in Figures 12 and 13 respectively. Figure 12 displayed that the neat PET film had a contact angle (theta) of 76° while this value descanted down to 63° with the increasing PEBE and IL amount. A sharp decrease in the contact angle of the PET composite films was observed in the case of using pure IL as an antistatic agent and theta value reached 63.7º if 6 wt% of IL was introduced to the PET matrix. Furthermore, it was pointed out that the contact angle of PEBE-IL including PET films dropped to 62.1º with 15 wt% PEBE-IL addition. Generally speaking, the contact angle of all prepared PET-based composite films was around at 73.6º and 62.1º. This result can be explained by the superior hydrophilicity of synthesized copolyesters and the ionic liquid owing to their polarity compared to neat PET.

18

Figure 12. Contact angle values of the PET composite films as a function of the antistatic agent type and content (wt%). Besides, moisture uptakes of the antistatic additive containing PET films were measured at 20 oC and 65% RH for one week and the obtained results are given in Figure 13. The neat PET film absorbed 0.42% moisture after seven days of conditioning. Concerning the moisture uptake (%) of PET composite films with antistatic additives, IL and PEBE-IL containing films displayed higher moisture uptake values than those of PEBE and PEBE-Q based composite films. Moisture uptake values of all films obviously increased until 8 wt% of PEBE, PEBE-IL and PEBE-Q addition into PET matrix and reached to 1.9% for PEBE-IL containing films. Beyond 10 wt% of antistatic agent addition, moisture uptake values remained nearly unchanged regardless of the used antistatic agent type. These results also showed a similar trend with the contact angle behavior of all PET composite films regardless of the antistatic agent. Thus, IL containing PET composite films showed the most hygroscopic character due to lower contact angle value while this film exhibited higher moisture uptake value at the same time.

Figure 13. Moisture uptake of the PET composite films as a function of the antistatic agent type and content (wt%).

In conclusion, these results demonstrated that the addition of synthesized PEBEs into the PET matrix increased the hydrophilicity, wettability, and conductivity of the composite films. The hydrophilicity of PEBE derivatives and the ionic liquid containing composite films are superior to neat PET owing to the incorporation of water with their polar moieties [50,51].

Surface Morphology To investigate the morphology of the antistatic PET composite films, SEM analysis of the selected films were performed and the photos are presented in Figure 14. It can be observed from Figure 14 that surface views of all films were homogeneous, dense and defect-free. Apart from neat PET, the IL and PEBE-IL containing PET composite films, some slightly straight lines were observed for the composite films with PEBE and PEBE-Q. Probably, this can be explained by the slight incompatibility between neat PET and these copolyester structures.

19

Whereas, it was seen that the addition of IL and PEBE-IL resulted in more smooth surfaces of antistatic PET films. Therefore, it may be concluded that IL acts as a compatibility enhancer between neat PET and copolyester. This finding can also be supported by the optical properties of the antistatic films that will be explained in the following part.

(a)

(b)

(c)

(d)

(e)

20

Figure 14. SEM photos of (a) neat PET, (b) PET with 10 wt% PEBE, (c) PET with 10 wt% PEBE-Q, (d) PET with 10 wt% PEBE-IL, (e) PET with 5 wt% ionic liquid.

Optical and Mechanical Characteristics From the industrial point of view, adequate surface resistance, lower haziness, and sufficient mechanical properties are the major requirements for an antistatic packaging film. Blending the inherently dissipative copolymers into a transparent polymer matrix creates haziness to the final film. For this purpose, the haziness and the total light transmittance of the films were measured and the obtained results are given in Figures 15 and 16. As one can see from Figure 15a that the haziness of the PET composite films was almost linearly increased with the addition of antistatic agent and no significant transparency change was observed until 5 wt% of antistatic agent loading. Beyond this point, the haziness values of the PET composite films were gradually rose depending on the type of antistatic agent. Among PET composite films, PEBE-Q containing PET film had higher haziness values than those of PEBE and PEBE-IL containing films. For example; it was found that the haziness value of 15 wt% PEBE comprising PET film was found to be 10.5% while the film including the same amount of PEBE-Q exhibited the haziness of 11.1%. This result can be explained by the more crystalline structure of PEBE-Q compared to PEBE. Unlike PEBEs, the use of only ionic liquid had no obvious negative effect on the optical properties of the PET composite film. Haziness values of the ionic liquid doped films (PET/IL) slightly increased up to 2.3% with the increasing amount of ionic liquid. This result may be explained by its relatively amorphous structure. This finding was also confirmed by DSC and XRD analysis given in the former sections.

In addition to haziness values, total light transmission % of the PET composite films is given Figure 15b. Similarly, it was found that the transmission values of the composite films linearly dropped with the antistatic agent addition regardless of its type and reached to 75-78% for composite films with 15 wt% of antistatic agent. The explanations given as above are also valid for the relationship between total transmission and additive agent’s type and content.

a)

b)

Figure 15. (a) Haziness and (b) total transmission values of the PET composite films as a function of the antistatic agent type and content (wt%).

21

In addition, the appearances of the selected composite films are presented in Figure 16. It was seen from the figure that there is no obvious change in transparency of PET and PET/IL composite films (Figure 16b and 16c) however, a translucent appearance was observed with the addition of PEBE and its derivatives as an antistatic agent to the PET film structure. This can probably be explained by the incompatibility between long ether chains of PEG and the hard segments of commercial PET which mainly caused by the incompatibility of the polyether segments of the copolymer structure.

Another important issue in the PET sheet manufacturing process is the recycling of post-consumer products. In this recycling process, the transparency of the recycled product is very critical and has to be maintained. For this reason, the PET film producers always tend to use additives with lower haziness impact to the final article.

In this study, we prefer a polyether-ester structure rather than a polyether-amide structure because the ester bonds are more compatible with the PET matrix rather than the amide structure. This makes prepared antistatic copolyester more similar, compatible and easier to recycle with the virgin PET polymer. Despite these low haziness values provided with PEBE and its derivatives, there is still a need to develop inherently dissipative copolymers that have a much lower impact on the visual properties of the polymer matrix to which they are incorporated.

a)

b)

c)

d)

e)

f)

Figure 16. Photos of the films with a black background (computer keyboard) (a) no film, (b) PET reference, (c) PET with 5 wt% IL, (d)PET with 10 wt% PEBE, (e) PET with 10 wt% PEBE-Q, (f) PET with 10 wt% PEBE-IL.

Breaking force and elongation at break of the PET composite films including copolyester ether (PEBE) and its derivatives as an antistatic agent were measured to understand the effect of these additives on the mechanical properties. Figure 17 shows the breaking force and elongation at break of PET films in terms of the type and content of the antistatic agent. In general, increasing the contents of additives in the PET film resulted in an improvement in elongation at break and a substantial reduction of breaking force. Among PET composite films, PEBE-Q containing PET film had higher breaking force than those of other PEBE and derivatives containing PET films whereas the film with PEBE-IL and only ionic liquid showed the highest elongation at break. The elongation at break of the neat PET film was measured 95.5% while 10 wt% PEBE-IL had a value of 144%. In the case of using only ionic liquid to improve surface resistivity of PET films, it was found that the elongation at break became larger and larger with the amount of ionic liquid added into the polymer matrix and it reached

22

183% with 6 wt% of ionic liquid loading. This result showed that the introduction of ionic liquid to the polymer matrix resulted in a more amorphous and flexible structure. As we know from the literature, the ionic liquids as conductive filler in polymer composite systems generally act as plasticizers and the flexibility of polymer backbone improves with the ionic liquid content [52]. Therefore, both literature and our findings confirmed the effect of ionic liquid in the physical and mechanical properties of PET composite films. On the other hand, elongation at break of 10 wt% PEBE containing PET film was around 139% while the film including the same amount of PEBE-Q showed the elongation at break of 132%. This indicated that the quaternization of PEBE copolyester led to a slight increase in the rigidity of PET composite film. Similarly, our findings on the crystallinity degree of PEBE and PEBE derivatives were a very good agreement with these obtained results.

a)

b)

Figure 17. (a) Elongation at break and (b) breaking force of the PET composite films as a function of the antistatic agent type and content (wt%).

Besides, as one can see from Figure 17b that the breaking forces of PET composite films with 10 wt% PEBE, PEBE-Q, and PEBE-IL antistatic additives were found to be 63, 66 and 59 N/15 mm respectively. This result can be explained by the more crystalline structure of PEBE-Q and the relatively amorphous structure of PEBE-IL compared to PEBE copolymer. By the way, if we compare the breaking force of PET composite films with neat PET, we can conclude that the pristine PET film showed significantly higher breaking force (110 N/15mm) compared to antistatic agent containing PET composite films. Most probably the reason is the larger crystallinity of the neat PET film than those of other composite films shown in Table 2. In contrast to the highest elongation at break value of PET/IL based composite film, the breaking force of that film showed the lowest value. This is an expectedly result considering the plasticizer effect of the ionic liquid.

4. Conclusion

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In this study, three novel antistatic polyether block esters (PEBE) were successfully synthesized and characterized. Two different approaches were applied to improve conductivity. Firstly, the quaternization of PEBE with 2,3-epoxypropyl trimethyl ammonium chloride (PEBE-Q) and secondly doping the copolymer matrix with ionic liquid, namely quaternary alkylammonium sulfonamide type (PEBE-IL), were carried out. From FTIR measurements of the PEBE copolymers, it was observed that the transesterification, quaternization and ionic liquid doping of the copolyesters were successful. It was found that the quaternization of PEBE improved the crystallinity with a decrease in thermal decomposition temperature. Whereas it was detected that the presence of ionic liquid and other PEBE derivatives decreased the glass transition temperature and the crystallization temperature as well as the degree of crystallinity compared to neat PET film. XRF measurements of the PEBE copolymers confirmed the presence of the fluorine in the ionic liquid structure. Concerning the crystallinity of PEBE and its derivatives, XRD results indicated that the PEBE-IL had a more amorphous structure while the PEBE-Q relatively larger crystalline regions.

It was illustrated that the antistatic PET films can be achieved by choosing appropriate antistatic agent type and content. Also, it was pointed out that the controlling of the crystallization degree was a major factor to adjust electrical resistivity as well as optical properties. The antistatic performance of the ionic liquid alone is better than PEBE compositions at the same concentration but blending ionic liquid with a copolymer (PEBE-IL) had a synergist effect and improved the antistatic performance of the ionic liquid and copolyester.

SEM investigation indicates that antistatic agents showed good compatibility with the PET matrix without the addition of compatibilizer. Among PET composite films, PEBE-Q containing PET film had higher breaking force than those of other PEBE derivatives containing PET films whereas the film with PEBE-IL and only ionic liquid showed the highest elongation at break. In conclusion, the addition of synthesized PEBEs into the PET matrix increased the hydrophilicity, wettability, and conductivity of the composite films. The hydrophilicity of PEBE and the ionic liquid containing composite films are superior to neat PET owing to the incorporation of water with the polar moieties of the antistatic agent [50,51]. From these observations, we conclude that PET composite films with fine-tune physical, mechanical and morphological properties can be developed depending on the application area where it may need some special features.

Acknowledgement The authors gratefully acknowledge the Setaş Kimya Sanayi A.Ş. and Istanbul University-Cerrahpaşa, Chemical Engineering Department for providing technical support in characterization and extrusion trials.

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Highlights Novel types of polyether block esters (PEBE) as antistatic agents were synthesized The surface resistivity of PET composite film dropped to ~109 Ω/sq The conductivity of PET composite film improved ~106 times compared to the neat PET film Antistatic PET composite films had good mechanical and optical properties The percolation threshold was 6-10 wt% PEBE based antistatic agents

Conflict of Interest and Authorship Conformation Form

All authors have participated in (a) conception and design, or analysis and interpretation of the data; (b) drafting the article or revising it critically for important intellectual content; and (c) approval of the final version. This manuscript has not been submitted to, nor is under review at, another journal or other publishing venue. The authors have no affiliation with any organization with a direct or indirect financial interest in the subject matter discussed in the manuscript

Author’s name Hüsnü Kemal Gürakın Ahmet TURAN Hüseyin DELİGÖZ

Affiliation Istanbul University Cerrahpaşa and Setaş Kimya San A.Ş. Setaş Kimya San A.Ş. Istanbul University Cerrahpaşa