Electroconductive Composites from Polystyrene Block Copolymers

materials Article

Electroconductive Composites from Polystyrene Block Copolymers and Cu–Alumina Filler QuratulAin Nadeem 1 , Tasneem Fatima 1 , Pepijn Prinsen 2 , Aziz ur Rehman 3 , Rohama Gill 1, *, Rashid Mahmood 4 and Rafael Luque 2 1 2 3 4

*

Department of Environmental Sciences, Fatima Jinnah Women University, Rawalpindi 46000, Pakistan; [email protected] (Q.N.); [email protected] (T.F.) Departamento de Universidad de Córdoba, Edificio Marie Curie, Ctra Nnal IV-A, Km396, E14014 Córdoba, Spain; [email protected] (P.P.); [email protected] (R.L.) Department of Chemistry, the Islamia University of Bahawalpur, Bahawalpur 63000, Pakistan; [email protected] Department of Chemistry, University of Azad Jammu and Kashmir Chehla Campus Muzaffarabad, Muzaffarabad 13100, Pakistan; [email protected] Correspondence: [email protected] or [email protected]; Tel.: +92-51-9292-900 (ext. 101)

Academic Editor: Reza Montazami Received: 20 October 2016; Accepted: 1 December 2016; Published: 7 December 2016

Abstract: Technological advancements and development of new materials may lead to the manufacture of sustainable energy-conducting devices used in the energy sector. This research attempts to fabricate novel electroconductive and mechanically stable nanocomposites via an electroless deposition (ELD) technique using electrically insulating materials. Metallic Cu is coated onto Al2 O3 by ELD, and the prepared filler is then integrated (2–14 wt %) into a matrix of polystyrene-block-poly(ethylene-ran-butylene)-block-polystyrene-graft-maleic anhydride (PS-b(PE-r-B)-b-PS-g-MA). Considerable variations in composite phases with filler inclusion exist. The Cu crystallite growth onto Al2 O3 was evaluated by X-ray diffraction (XRD) analysis and energy dispersive spectrometry (EDS). Scanning electron microscopy (SEM) depicts a uniform Cu coating on Al2 O3 , while homogeneous filler dispersion is exhibited in the case of composites. The electrical behavior of composites is enhanced drastically (7.7 × 10−5 S/cm) upon incorporation of Cu–Al2 O3 into an insulating polymer matrix (4.4 × 10−16 S/cm). Moreover, mechanical (Young’s modulus, tensile strength and % elongation at break) and thermal (thermogravimetric analysis (TGA), derivative thermogravimetry (DTG), and differential scanning calorimetry (DSC)) properties of the nanocomposites also improve substantially. These composites are likely to meet the demands of modern high-strength electroconductive devices. Keywords: copolymers; composites; morphology; mechanical properties; thermal properties

1. Introduction Technological advances highly depend on the development of a wide diversity of new materials. Conductive polymer composites (CPCs) have an array of applications in various industries, among them the electronic industry, which made revolutionary developments both in manufacturing and recycling. Electrostatic discharge (ESD) and electromagnetic interference (EMI) are phenomena that affect the economy of the electronic industry. They can arise during manufacturing, packing, conveyance, and working. Thus, the use of appropriate EMI-shielding materials to reduce electric energy losses is essential [1]. The ever-growing electronic waste (e-waste) is now posing devastating impact on the environment due to its accumulation. One way to reduce this accumulation is to increase the life span of electronics to protect them from the detrimental effects of EMI and ESD. Design and

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application of CPCs as advanced materials have been shown to expand the shelf life of electronics, which may ultimately reduce the production of e-waste [2]. Although, production of various classes of conducting polymer nanocomposites on a commercial scale is growing at a rapid pace, yet metal-filled CPCs exhibit poor mechanical properties and are no longer preferred by modern industries due to their high cost. To provide exceptional electrical properties without compromising the mechanical behavior, researchers switched their focus towards metal-coating techniques such as electrodeposition, chemical vapor deposition, physical vapor deposition, electrospinning, and others. Among them, electroless deposition (ELD) is a novel metal deposition technique. The ELD-plating technique is able to incorporate desired properties of a metallic coating irrespective of the substrate geometry and at low temperature. This coating technique is redox-sensitive, as the internal current is supplied by the oxidation of a reducing agent [3,4], thus uniform plating can also be carried out inside the holes, recesses, and non-line-of-sight surfaces [5–7]. A variety of metals—such as Ag, Cu, Au, and Ni (in order of decreasing conductivity)—have been coated on different substrates via ELD to fabricate electrically conductive materials like conductive plates, wires, rods, and powders for various electronic applications [8–10]. The novelty of the present research work lies in the preparation of electrically conductive Cu-coated alumina powder via ELD, which was then used, for the first time, as filler in a matrix of polystyrene-block-poly(ethylene-ran-butylene)-block-polystyrene-graft-maleic anhydride (PS-b(PE-r-B)-b-PS-g-MA). The selected polymer matrix is electrically insulating and offers the characteristics of vulcanized rubber without going through the process of vulcanization. Also, the presence of styrene maleic anhydride (SMA) segments in the copolymer elevates the glass transition temperature (Tg ). The appropriate interfacial properties of the matrix [11,12] makes it suitable for the preparation of blends and composites. The limitations of the selected copolymer are its low strength and stiffness [13]. Alumina is used in numerous applications in various fields due to its excellent mechanical properties, anticorrosivity, wear resistance, and hardness. The presence of Cu in the ELD-deposited metal-ceramic filler enhances the electrical conductivity and the incorporation of Al2 O3 increases the mechanical strength, compensating for the low strength and stiffness of the copolymer. The resultant concoction may improve the durability of advanced material applications, such as EMI- and ESD-shielding materials [8], heat sinks for microelectronics [14], sensors for biomedical usage [9], and so on. 2. Experimental Section This research work focused on the synthesis and characterization of conductive composites by adding a conductive ceramic filler, coated with a metal through ELD technique, in a nonconducting polymer. 2.1. Materials The following analytical-grade chemicals were used: Fluka Chemika (Buchs, Switzerland, aluminium oxide (Al2 O3 )), Riedel-de Haen (Seelze, Germany, nitric acid (HNO3 37%), copper sulphate pentahydrate (CuSO4 ·5H2 O), and potassium sodium tartrate (KNaC4 H4 O6 ·4H2 O)), Merck (Darmstadt, Germany, hydrofluoric acid (HF)), Scharlau (Barcelona, Spain, sodium hydroxide (NaOH)), Sigma Aldrich (Buchs, Switzerland, polyethylene glycol (C2n H4n+2 On+1 ), thiourea (CH4 N2 S), palladium chloride (PdCl2 ), stannous chloride (SnCl2 ·2H2 O), ethylenediaminetetraacetic acid disodium salt (C10 H14 N2 Na2 O8 ), formaldehyde solution (HCHO), dimethylamine borane (C4 H10 BN), boric acid (H3 BO3 ), chloroform (CHCl3 ), and polystyrene-block-poly(ethylene-ran-butylene)-blockpolystyrene-graft-maleic anhydride (PS-b-(PE-r-B)-b-PS-g-MA)). 2.2. Preparation of Conductive Filler Electroless deposition (ELD) method was employed for the preparation of conductive filler. Copper (Cu) deposition onto Al2 O3 substrate was accomplished after successive substrate pretreatment steps.


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2.2.1. Pretreatment of Al2 O3 Pretreatment of Al2 O3 was done before the deposition step, followed by surface cleaning and surface activation. To avoid tedious filtration steps, Al2 O3 was packed in commercially available silk cloth (160 mesh) and was dipped in subsequent solutions rather than dispersion in solution, which may also increase the reaction time. First, the Al2 O3 substrate was dipped in concentrated HNO3 (2 min) to remove oil and dirt. Acid-cleaned Al2 O3 was dipped in catalytic activator solution containing 0.03 mmol of PdCl2 and 0.246 mmol of SnCl2 in 40 mL of concentrated HCl (14 min). After activation, the substrate was introduced to a reduction bath made of 4.74 mmol of (C4 H10 BN) and 4.52 mmol of (H3 BO3 ) in a sufficient quantity of distilled water (7 min). Each step of pretreatment was followed by 1 min rinsing in distilled water. Pretreated Al2 O3 was then used for ELD of Cu. 2.2.2. Cu Coating on Pretreated Al2 O3 Pretreated Al2 O3 was dipped in an electroless plating bath (Table 1). After deposition, Cu-deposited Al2 O3 was rinsed with distilled water and oven-dried for 3–4 h at 40 ◦ C. The prepared Cu–Al2 O3 powder was used further as conductive filler for insulating polymer matrix. Table 1. Composition of electroless (EL) bath and conditions used for Cu plating. Constituents of EL Bath

Chemicals

Amount (mmol)

Metal Salt

CuSO4 ·5H2 O

64

Complexing Agent

KNaC4 H4 O6 ·4H2 O Na2 EDTA NaOH

106 54 350

Reducing Agent

HCHO

170

Stabilizer

CH4 N2 S C2n H4n+2 On+1

0.013 50 mL

Conditions in EL bath

Temperature Time pH

45–50 ◦ C 30 min 12.0–12.5

2.3. Synthesis of Conductive Composites Conductive polymer composites (CPCs) were prepared by incorporating Cu–Al2 O3 filler with varied content (2, 4, 6, 8, 10, 12, and 14 wt %) in PS-b-(PE-r-B)-b-PS-g-MA polymer matrix. PS-b-(PE-r-B)-b-PS-g-MA was dissolved in 30 mL chloroform followed by addition of the filler. The polymer–filler solution was stirred for 1–2 h at 750 rpm, poured into a Petri dish for film casting, and then detached from the mold after solvent evaporation. The prepared composite films were utilized for characterization. To attain accuracy in performance and results, samples were prepared in triplicates and the mean values were reported after characterization. 2.4. Instrumentation and Characterization 2.4.1. X-ray Diffraction (XRD) Analysis PANalytical X-ray diffractometer (XPERT-PRO) (Düsseldorf, Germany) was used for XRD analysis of pristine Al2 O3 , Cu–Al2 O3 , PS-b-(PE-r-B)-b-PS-g-MA, and Cu–Al2 O3 /PS-b-(PE-r-B)-b-PS-g-MA composites. As Cu is the anodic material, X-rays of wavelength 1.540598 Å (Cu-Kα) were used for analysis. The 2θ data were analyzed with 0.05◦ scan step size, scan range 5◦ –70◦ (1 s) at 40 kV voltage and 30 mA beam current. The d-spacing and average crystallite size of Cu and Cu–Al2 O3 particles were calculated by Bragg’s and Scherrer’s equation, respectively.


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2.4.2. Morphological Analysis The surface morphologies of pristine Al2 O3 , Cu-coated Al2 O3 , host polymer, and its respective composites were analyzed with SEM, obtained by a HT-Phys-UAJK microscope equipped with a secondary electron (SE) detector at 25 kV accelerating voltage. Fractured surfaces of composites were also examined by MIRA3 TESCAN (Nova 400 Nano, Salem, OR, USA) (SE detector at an accelerating voltage of 10 kV) to analyze the dispersion of filler in polymer matrix. 2.4.3. Energy Dispersive Spectrometry (EDS) Analysis Elemental composition and atomic weight % of Cu coated Al2 O3 , host polymer and its respective composites were investigated by using a JSM6490LV (JEOL) microscope (Tokyo, Japan). The instrument was equipped with QUANTAX EDS XFlash detector 4010-Bruker (Billerica, MA, USA) at an accelerating voltage of 20 kV. 2.4.4. Analysis of Surface/Volume Resistivity and Electrical Conductivity The surface resistivity (Ω/) and volume resistivity (Ω·cm) of composites were measured by the 4-probe method using a high-resistance meter by applying the ASTM D-257 test method [15] at room temperature. A 500 V direct current field was applied through electrodes made up of tungsten carbide. Since electrical conductivity is inversely proportional to volume resistivity, electrical conductivities (S/cm) were calculated as the inverse of the volume resistivities (Ω·cm). 2.4.5. Analysis of Mechanical Properties The mechanical features of composites were examined by calculating the Young’s modulus (MPa), tensile strength (MPa), and % elongation at break according to the ASTM D638-02 [16] and ASTM D638-03 [17] test procedures for mechanical analysis. An Instron tester (4465UK, Norwood, MA, USA) was used at 20 ± 2 ◦ C by subjecting samples with dimensions of 0.8–1.0 mm thickness and 6 mm× 70 mm (width × gauze length). 2.4.6. Analysis of Thermal Properties Thermogravimetric analysis (TGA) was carried out with a Perkin Elmer TGA-7 (Waltham, MA, USA) in the 50–550 ◦ C temperature range at 20 ◦ C/min in dynamic atmosphere (20 mL/min N2 flow) using a 2 mg sample. Non-isothermal conditions were used for recording thermal analytical results. A DSC 404-NETZSCH instrument was used for differential scanning calorimetry (DSC) analysis in the 20–500 ◦ C range at 20 ◦ C/min. 3. Results and Discussion 3.1. XRD Analysis of Pristine and Cu-Coated Al2 O3 Powder and Composite Films The prepared filler was analyzed with XRD for the determination of phase change and particle size. Scherrer’s equation is used to calculate the particle size of pristine and Cu-coated Al2 O3 as expressed in Equation (1) [18]: Kλ D= (1) β cosθ where D = crystallite size (nm); λ = wavelength; K = Scherrer’s constant; β = angular width (radians); and θ = Bragg’s angle. Interplanar spacing between atoms within the crystallite structure is denoted by d-spacing. Bragg’s equation used for the determination of d-spacing of pristine and Cu-coated Al2 O3 is given in Equation (2). 2dsinθ = n λ (n − 1)

(2)

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The XRD spectrum of pristine Al2O3 powder is presented in Figure 1. The three peaks at 13.13°, 46.04°, and 67.28° (2θ values), correspond to the Al2O3 phase. The strongest diffraction is ◦ The XRD spectrum pristine AlO 2O3 powder is presented in Figure 1. The three peaks atpeak 13.13°, The XRD spectrum ofofpristine Al 2 3 powder is presented in Figure 1. The three peaks at 13.13 , observed at 67.28° with minimum d-spacing to 0.139 At3 46.04°, peak exists corresponding 46.04°, and (2θ values), correspond thenm. Al2O phase. another The strongest diffraction peak is ◦ ◦ 46.04 , and 67.28 (2θ values), correspond to the Al2 O3 phase. The strongest diffraction peak is to Al2O3 with d-spacing 0.197 nm. d-spacing The average sizenm. of the cubic lattice of Al 2O3exists is approximately 8.8 observed at 67.28° with minimum 0.139 At 46.04°, another peak corresponding observed at 67.28◦ with minimum d-spacing 0.139 nm. At 46.04◦ , another peak exists corresponding to nm. to Al2O3 with d-spacing 0.197 nm. The average size of the cubic lattice of Al2O3 is approximately 8.8 Al2 O3 with d-spacing 0.197 nm. The average size of the cubic lattice of Al2 O3 is approximately 8.8 nm. nm.

Figure X-ray diffraction(XRD) (XRD)pattern patternof of pristine pristine Al Figure 1. 1. X-ray diffraction Al22O O33nanopowder. nanopowder. Figure 1. X-ray diffraction (XRD) pattern of pristine Al2O3 nanopowder.

The XRD spectrum of Cu–Al2O3 (Figure 2) depicts the strongest peak at 43.5° and a relatively The XRD spectrum of Cu–Al2 O3 (Figure 2) depicts the strongest peak at 43.5◦ and a relatively less intense peak at 50.6°of corresponding to the2)(111) andthe (200) lattice planes of43.5° Cu, respectively. The The XRD spectrum Cu–Al2O3 (Figure depicts strongest peak at and a relatively less intense peak at 50.6◦ corresponding to the (111) and (200) lattice planes of Cu, respectively. strongest diffraction peak at 43.5° is characteristic of a face-centered cubic structure with d-spacing of less intense peak at 50.6° corresponding to the (111) and (200) lattice planes of Cu, respectively. The ◦ is characteristic of a face-centered cubic structure with d-spacing Thestrongest strongest diffraction peak at 43.5 0.21 nm; diffraction this confirms of crystal-structured metallic Cu on structure the substrate [18,19]. The peakdeposition at 43.5° is characteristic of a face-centered cubic with d-spacing of of 0.21 0.21 nm; nm; thisintensity confirms deposition of crystal-structured metallic onsubstrate the Al substrate [18,19]. relative peak at 2θ = 67.3°ofclearly represents themetallic XRD pattern ofthe pristine 2O[18,19]. 3 (Figure 1), this confirms deposition crystal-structured Cu onCu The ◦ clearly represents the XRD pattern of pristine Al O Therelative relative peak intensity 2θthe = clearly 67.3 2 3 whose amount was lower composite material. The disturbance observed the peak peak intensity at 2θat=in67.3° represents the XRD pattern of pristine Al2Oin 3 (Figure 1), (Figure 1),amount whosetoamount lower indue thetocomposite material. The disturbance observed inthe the corresponding the lower Al2was O3 in phase thematerial. change in thedisturbance nature of original 2O3 the afterpeak whose was the iscomposite The observedAl in peak corresponding to the Al O phase is due to the change in the nature of original Al O after deposition of Cu. The average crystallite size of Cu–Al 2 O 3 was calculated as approximately 26.2 nm. 3 3 corresponding to the Al2O32 phase is due to the change in the nature of original Al2O23 after thethe deposition of Cu. The average crystallite size of Cu–Al O was calculated as approximately 26.2 nm. XRD analysis alsoThe revealed that average size crystallite size Al2O 3 increased 8.8 nm to 26.2 nm. nm, deposition of Cu. average crystallite of Cu–Al 33was calculated as from approximately 22Oof XRD analysis also revealed that average crystallite size Al22OO3 3increased increased from nm to 26.2 nm, which confirms the deposition Cu crystallites, with anofincrease in the mean thickness to nm. XRD analysis also revealed thatof average crystallite Al from 8.88.8 nm to~17.4 26.2 nm, A similar XRD pattern was reported in literature [20,21], wherein the strongest peak oftoto electroless which confirms the deposition Cucrystallites, crystallites, with an increase the mean ~17.4 nm. which confirms the deposition ofofCu with increase in the meanthickness thickness ~17.4 nm. deposited-Cu appeared at 2θ = 43°. A similar XRD pattern was reported in literature [20,21], where the strongest peak of electroless A similar XRD pattern was reported in literature [20,21], where the strongest peak of electroless ◦. deposited-Cu appeared deposited-Cu appeared atat2θ2θ= =4343°.

Figure 2. XRD pattern of Cu-coated Al2O3 nanopowder. Figure 2. XRD pattern of Cu-coated Al2O3 nanopowder. Figure 2. XRD pattern of Cu-coated Al2 O3 nanopowder.

For determining the effect of Cu–Al2O3 filler in the host polymer matrix, XRD spectra of the polymer with 2 wt % the and effect 14 wt of % Cu–Al of Cu–Al 3-loading Thespectra XRD pattern For determining 2O32O filler in thewere host recorded polymer (Figure matrix, 3). XRD of the For determining the effect of Cu–Al O filler in the host polymer matrix, XRD spectra 2 3 of neat PS-b-(PE-r-B)-b-PS-g-MA shows a broad peak at 10°–27° and one(Figure relatively less XRD intense peakof polymer with 2 wt % and 14 wt % of Cu–Al 2O3-loading were recorded 3). The pattern theof polymer with 2 wt % and 14 wt % of Cu–Al O -loading were recorded (Figure 3). The XRD at neat 48.9°,PS-b-(PE-r-B)-b-PS-g-MA which confirms its amorphous 2 wt % Cu–Al 2O3relatively loading inless PS-b-(PE-r-B)-b2Upon 3at 10°–27° shows astructure. broad peak and one intense peak ◦ ◦ pattern of which neat shows aUpon broad peak at 102is and inone relatively less PS-g-MA, twoPS-b-(PE-r-B)-b-PS-g-MA peaks at 42.6°and 49.9° are observed. The2peak 42.6° to the crystalline at 48.9°, confirms its amorphous structure. wt %atCu–Al O–27 3attributed loading PS-b-(PE-r-B)-b◦ , which confirms its amorphous structure. Upon 2 wt % Cu–Al O loading intense peaktwo at 48.9 PS-g-MA, peaks at 42.6°and 49.9° are observed. The peak at 42.6° is attributed to the 2crystalline 3 in PS-b-(PE-r-B)-b-PS-g-MA, two peaks at 42.6◦ and 49.9◦ are observed. The peak at 42.6◦ is attributed

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◦ might represent nature of Cu, while peak another at 49.9°peak might represent a slight peak shift from to the crystalline natureanother of Cu, while at 49.9 a slight peak shift48.92° from nature of Cu, while another peak at 49.9° might represent a slight peak shift from 48.92° ◦ corresponding to amorphous phase phase of the of polymer. At 14 At wt14 % wt Cu-Al 2O3 loading, three peaks at 2θ 48.92 corresponding to amorphous the polymer. % Cu-Al O loading, three peaks 2 3 corresponding to amorphous phase of peak the polymer. At 14 wtis%characteristic Cu-Al2O3 loading, threeCu peaks at 2θ ◦ and ◦ arise. = 36.2°, arise. sharp observed 42.9° of metallic at 2θ = 42.9° 36.2◦ ,and 42.950.1° 50.1The The sharp peak at observed at 42.9◦ is characteristic ofinclusion metallic =supported 36.2°, 42.9°by andanother 50.1° arise. The sharp peak observed at 42.9° is characteristic of metallic Cu inclusion at 50.1°peak andatthus crystalline phase of the prepared Cu inclusion supportedpeak by another 50.1◦confirms and thusthe confirms the crystalline phase of the supported by another peak at 50.1° and thus confirms the crystalline phase of the prepared composites. prepared composites. composites.

Figure 3. of neat polystyrene-block-poly(ethylene-ran-butylene)-block-polystyrene-graft-maleic Figure 3. XRD XRDpatterns patterns of neat polystyrene-block-poly(ethylene-ran-butylene)-block-polystyreneFigure 3. XRD patterns of neat polystyrene-block-poly(ethylene-ran-butylene)-block-polystyrene-graft-maleic anhydride (PS-b-(PE-r-B)-b-PS-g-MA) (0 wt % Cu-Al and composites with 2 wt % and 14 wt % Cu– graft-maleic anhydride (PS-b-(PE-r-B)-b-PS-g-MA) (02O wt3)% Cu-Al 2 O3 ) and composites with 2 wt % and anhydride (PS-b-(PE-r-B)-b-PS-g-MA) (0 wt % Cu-Al 2O3) and composites with 2 wt % and 14 wt % Cu– 2O3. Alwt 14 % Cu–Al2 O3 . Al2O3.

3.2. Morphological Morphological Study Study of Cu–Al Cu–Al2O Filler and Block Copolymer Composites 3.2. O333 Filler Filler and and Block Block Copolymer Copolymer Composites Composites 3.2. Morphological Study of of Cu–Al22O SEM analysis was was used used to determine determine the the surface surface morphology and and crystalline structure structure of the the SEM SEM analysis analysis was used to to determine the surface morphology morphology and crystalline crystalline structure of of the materials. An SEM micrograph of pristine Al 2O3 and Cu–Al2O3 powder are shown in Figure 4a,b, materials. An SEM of pristine Al and Cu–Al Cu–Al22O O33powder powderare are shown shown in in Figure Figure 4a,b, 4a,b, 22O materials. An SEM micrograph micrograph ofCu pristine Alon O33the and respectively, showing a uniform coating alumina surface. The dispersion of the filler is respectively, showing aa uniform Cu coating on the alumina surface. The dispersion of the filler is respectively, showing uniform Cu coating on the alumina surface. The dispersion of the filler is improved as as compared compared to pristine pristine alumina aluminapowder. powder.The The Cu-coatedAl Al2O3 particles particles exhibit exhibit fine-scale improved improved ascharacteristic compared to to of pristine alumina powder. The Cu-coated Cu-coated Al22O O33 particles exhibit fine-scale fine-scale roughness, metal coating [22,23]. Silvain and co-workers also deposited Cu onto onto roughness, characteristic of metal coating [22,23]. Silvain and and co-workers also deposited Cu roughness, characteristic of metal coating [22,23]. Silvain co-workers also deposited Cu onto submicron-sized Al2O3 particles [24]. Their work revealed uniform and fine coating of metallic Cu submicron-sized Al [24]. Their work revealed uniform and finefine coating of metallic Cu and submicron-sized Al22O O33 particles particles [24].of Their revealed uniform and coating of metallic Cu and increased average particle size Al2Owork 3 particles after Cu deposition. The SEM image of Cu– increased average particle size of Al O particles after Cu deposition. The SEM image of Cu–Al 2of 3Al2O3 particles after Cu deposition. The SEM image of Cu– 2 O3 and increased average particle size Al2O3 from Wang and co-workers [25] showed good similarity (Figure 4c). In comparison, Krupa and from Wang and co-workers [25] showed good similarity (Figure 4c). In comparison, Krupa and Al 2O3 from Wang and co-workers [25] showed good similarity (Figure 4c). In comparison, Krupa and co-workers deposited Ag on polyimide particles (Figure 4d) [26]. In all these cases, the ELD-plating co-workers deposited Ag on (Figure 4d) [26]. all these the co-workers deposited Agmorphological on polyimide polyimide particles particles (Figure [26]. In In allseem thesetocases, cases, the ELD-plating ELD-plating technique was used. The properties looked4d) similar and be rather irrespective technique was used. The morphological properties looked similar and seem to be rather irrespective technique was used. The morphological properties looked similar and seem to be rather irrespective of the type of substrate. of of the the type type of of substrate. substrate.

Figure 4. Cont.


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Figure 4. SEM micrographs of (a) pristine Al2O3 powder and Cu-coated Al2O3 (b) in this work; (c) in Figure 4. SEM micrographs of (a) pristine Al2 O3 powder and Cu-coated Al2 O3 (b) in this work; Wang et al. [25]; Ag coated onto polyimide [26]. [26]. (c) in Wang et al. and [25];(d) and (d) Ag coated onto polyimide Figure 4. SEM micrographs of (a) pristine Al2O3 powder and Cu-coated Al2O3 (b) in this work; (c) in Wang et al. morphology [25]; and (d) Agofcoated ontopolymer polyimidePS-b-(PE-r-B)-b-PS-g-MA [26]. The surface the host and the composite films

of the host polymer PS-b-(PE-r-B)-b-PS-g-MA and the composite films with The 2, 6, surface 10, and morphology 14 wt % of Cu–Al 2O3 are shown in Figure 5a–d. The incorporation of filler played a with 2,The 6, 10, and morphology 14 wt % ofofCu–Al are shown in Figure 5a–d. The incorporation filler surface the host PS-b-(PE-r-B)-b-PS-g-MA the composite films 3polymer remarkable role on the morphology of2 O the resultant composites. With theand incorporation ofof lowest played a remarkable role on the morphology of the resultant composites. With the incorporation with 2, 6, 10, 14 wt % of Cu–Al2dispersion O3 are shown in Figure 5a–d. The of filler played a of filler content (2and wt %), homogenous of filler is observed inincorporation both the composites predicting lowest filler content wtmorphology %), homogenous of filler isto observed in both the composites remarkable role on(2 the of the resultant With the incorporation of lowest good filler–polymer interaction. At least 10 wtdispersion % filler composites. is required observe the initiation of particlefiller content (2filler–polymer wt %), homogenous dispersion of filler is observed inrequired both the to composites predicting predicting good interaction. At least 10 wt % filler is observe the to-particle connectivities, which improve throughout the matrix when the filler content isinitiation further good filler–polymer interaction. At least 10 wt % filler throughout is required tothe observe thewhen initiation of particleof particle-to-particle connectivities, which improve matrix the filler content increased to 14 wt %. The comparison of Figure 5b,e illustrates the decreased interparticle distance. to-particle connectivities, improve throughout the 5b,e matrix when the contentinterparticle is further is further toin 14the wtwhich %. The comparison of the Figure illustrates thefiller decreased The shinyincreased small areas SEM images resemble presence of the metal coated on ceramic filler. increased 14 wtsmall %. The comparison ofimages Figure 5b,e illustrates the decreased interparticle distance. distance. Thetoshiny areas in thecould SEM resemble presence of the metal coated Even smaller interparticle distance be achieved withthe filler loadings higher than 14 on wtceramic %, but The shiny small areas in the SEM images resemble the presence of the metal coated on ceramic filler. filler.compromises Even smaller the interparticle distance could be considering achieved with filler loadingsofhigher than 14 wt %, this mechanical performance the properties ceramics. A clear Even smaller interparticle distance could be achieved with filler loadings higherof than 14 wt %,Abut but this compromises the mechanical performance considering the properties ceramics. clear transition in the particle and surface roughness takes place upon Cu metallization. TheAuniform this compromises theshape mechanical performance considering the properties of ceramics. clear transition in the particle shape and surface roughness takes place upon Cu metallization. The uniform growth of Cuincrystallites Al2O 3 explains the change in morphology regarding particle distribution, transition the particleon shape and surface roughness takes place upon Cu metallization. The uniform growthultimately of Cu crystallites on Al the change morphology regarding particle distribution, 2 O3 explains which affects the Atinin higher filler loading, agglomerates or islands growth of Cu crystallites onmean Al2O3coating explainsthickness. the change morphology regarding particle distribution, which ultimately affects the mean coating thickness. At higher filler loading, agglomerates ortransfer islands of of which the filler particles are formed within the matrix material, which helps the smooth ultimately affects the mean coating thickness. At higher filler loading, agglomerates or islands of the filler particles are nanosized formed within the matrixare material, which helps theinsmooth transfer of electrons. electrons. Individual filler particles not material, distinctly visible SEM because of the filler particles are formed within the matrix which helps the micrographs smooth transfer of Individual nanosized filler particles are not distinctly visible in SEM micrographs because of this of this phenomenon [27]. electrons. Individual nanosized filler particles are not distinctly visible in SEM micrographs because phenomenon [27]. of this phenomenon [27].

Figure 5. Cont.


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Figure 5. SEM micrographs of (a) PS-b-(PE-r-B)-b-PS-g-MA and composites with (b) 2; (c) 6; (d) 10; Figure 5. SEM micrographs of (a) PS-b-(PE-r-B)-b-PS-g-MA and composites with (b) 2; (c) 6; (d) 10; and (e) 14 wt % Cu–Al2O3. and (e) 14 wt % Cu–Al2 O3 .

3.3. EDS Analysis of Cu–Al2O3 Filler and Block Copolymer Composites 3.3. EDS Analysis of Cu–Al2 O3 Filler and Block Copolymer Composites EDS was used to study the elemental composition of Cu–Al2O3 filler and Cu–Al2O3/PS-b-(PE-rEDS was used to study the elemental Cu–Al andfiller Cu–Al 2 O3 filler 2 O3 /PS-b-(PE-r-B)B)-b-PS-g-MA composites (Table 2). Cu,composition Al, and Pd of were detected in the material. The high b-PS-g-MA composites (Table 2). Cu, Al, and Pd were detected in the filler material. The highofcontent content of Cu (67.7%) followed by Al (30.4%) and Pd (1.9%) confirms the effective deposition Cu– of Al Cu2O(67.7%) by Al and in Pdsmall (1.9%) confirmsasthe effective of Cu–Al2 O3 3 via thefollowed ELD process. Pd(30.4%) was present quantities, it was used atdeposition a minor concentration viafor thesurface ELD process. Pdofwas present in small quantities, as it was used at a minor concentration for activation the Al 2O3 substrate. surface activation of the Al2 O3 substrate. Table 2. Elemental composition of Cu–Al2O3/PS-b-(PE-r-B)-b-PS-g-MA composites. Table 2. Elemental composition of Cu–Al2 O3 /PS-b-(PE-r-B)-b-PS-g-MA composites. Atomic wt % of Elements Cu–Al2O3 (wt %) C O Al Cu Atomic wt % of Elements 95.3 4.7 – – Cu–Al20O3 (wt %) C O4.3 Al1.3 Cu9.3 2 85.1 95.3 4.73.5 – 0.4 –16.9 140 79.2 2 14

85.1 79.2

4.3 3.5

1.3 0.4

9.3 16.9

3.4. Surface/Volume Resistivity and Electrical Conductivity of Block Copolymer Composites The volumeResistivity resistivityand is Electrical the reciprocal of the of electric conductivity. Measurement of the 3.4. Surface/Volume Conductivity Block Copolymer Composites resistance across the materials’ surface, which is in contact with the electrodes, is termed surface The volume is the reciprocal the electric conductivity. Measurement of isthe resistivity (Ω/sq resistivity or Ω/□) [28,29], while electricalofresistance through a cube of insulating material resistance across the materials’ surface, is inmatrix contact with the is termed surface considered as volume resistivity (Ω·cm).which The host polymers areelectrodes, usually non-conducting in resistivity (Ω/sq or Ω/ [28,29], while electrical resistance through a cube of insulating material nature and contain an)insignificant number of charge carriers in free-state. Thus, the electrical properties ofas such matrixresistivity polymer composites almost depend on selection of filler and is considered volume (Ω·cm). The hostexclusively matrix polymers arethe usually non-conducting ability to form smooth conductive networks the matrix The Thus, surfacethe resistivity in its nature and contain an insignificant numberthroughout of charge carriers in [30–35]. free-state. electrical of Cu–Alof 2O3such /PS-b-(PE-r-B)-b-PS-g-MA matrix composites with increasing filleronloadings (2–14 wt properties matrix polymer composites almost exclusively depend the selection of %) filler were studied. The surface and volume resistivity of neat polymer was also analyzed to determine its and its ability to form smooth conductive networks throughout the matrix [30–35]. The surface electricalofbehavior as3 /PS-b-(PE-r-B)-b-PS-g-MA intrinsic or extrinsic conducting polymer matrix. Table 3 showsfiller the surface resistivity Cu–Al2 O matrix composites with increasing loadings resistivity, the volume resistivity, and the electrical conductivity. The values for PS-b-(PE-r-B)-b-PS(2–14 wt %) were studied. The surface and volume resistivity of neat polymer was also analyzed are 2.30 1014 Ω/□, 2.3 × 1015 Ω·cm, and 4.348 10−16 S/cm, respectively, which confirms it 3 to g-MA determine its×electrical behavior as intrinsic or ×extrinsic conducting polymer matrix. that Table cannot act as intrinsic conducting polymer; although bulky aromatic rings are present as pendants, shows the surface resistivity, the volume resistivity, and the electrical conductivity. The values for the main chain is saturated, rendering an insulation material. PS-b-(PE-r-B)-b-PS-g-MA are 2.30 × 1014 Ω/, 2.3 × 1015 Ω·cm, and 4.348 × 10−16 S/cm, respectively, which confirms that it cannot act as intrinsic conducting polymer; although bulky aromatic rings are Table 3. Surface/volume resistivity and electrical conductivity of Cu–Al2O3/PS-b-(PE-r-B)-b-PS-g-MA presentcomposites. as pendants, the main chain is saturated, rendering an insulation material. With the inclusion of small amounts of filler (2 wt %), the surface resistivity of the corresponding Cu–Al2O3 (wt %) Surface Resistivity (Ω/□) Volume Resistivity (Ω·cm) Electrical Conductivity (S/cm) composite readily drops from insulating to antistatic region. The corresponding electrical conductivity 0 2.3 × 1014 2.3 × 1015 4.35 × 10−16 14 Ω ·cm. This 10 13 increases to 2.381 × 10 immediate shift from insulating to antistatic 2 4.2 × 10 4.2 × 10 2.38 × 10−14region might be 9 12 5.8 × 10 × 10−13 anhydride and 4 5.8 × 10 attributed to the connection with unsaturated side chain substitutions like1.72 maleic 5.1 × 1010 1.96 × 10−11 6 5.1 × 109 benzene groups, which essentially help to enhance particle-to-particle interaction [36]. By increasing 2.3 × 107 4.35 × 10−8 8 2.3 × 108 the loading of10Cu–Al2 O3 filler2.1in× 10 the polymer matrix from 4 to 12 wt %, the surface and volume 8 6 −7 2.1 × 10 4.76 × 10 9 8 13 4 8 4 −5 × 10 4.2 × 10 to 4.5 ×2.22 12 from 5.8 × 10 1.3 10 × 10 Ω/ and4.5 resistivity drop to×1.3 from 10× 10 Ω·cm, respectively. 1.3 × 104 × 10−5 14 × 104 This drop shifts the conductive4.0properties of the material from the antistatic7.69 to the static dissipative


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region [37]. Upon further incorporation of filler (14 wt %), the surface resistivity drops drastically to 4.0 × 104 Ω/, while the volume resistivity and electric conductivity changed only substantially compared to 12 wt % filler loading. The gradual increment in conductivity with addition of 2–14 wt % filler is shown in Figure 6. It confirms network formation as suggested by the SEM results, showing the transition from insulating to a semiconducting region. Materials 2016, an 9, 989 9 of 17 the inclusion ofresistivity small amounts filler (2 wtconductivity %), the surface of resistivity the corresponding Table 3. With Surface/volume andofelectrical Cu–Alof 2 O3 /PS-b-(PE-r-B)-b-PScomposite readily drops from insulating to antistatic region. The corresponding electrical Materials 2016, 9, 989 9 of 17 g-MA composites. 14

conductivity increases to 2.381 × 10 Ω·cm. This immediate shift from insulating to antistatic region might be attributed to the connection withofunsaturated side chain substitutions maleic anhydride With the inclusion of small amounts filler (2 wt %), the surface resistivitylike of the corresponding Cu–Al2and O3 (wt %) Surface which Resistivity (Ω/ ) help Volume Resistivity (Ω·cm) Electrical Conductivity benzene groups, essentially enhance particle-to-particle interaction [36]. By (S/cm) composite readily drops from insulating toto antistatic region. The corresponding electrical 15 from 4 to 12 wt %, the −and 16 increasing the loading to of2.381 Cu–Al O314filler inThis the polymer matrix surface 0 2.3 × 10×14210 2.3 × 10 4.35 × 10 conductivity increases Ω·cm. immediate shift insulating to antistatic region −14 13 to 4.5 2 4.2connection × 1010 ×chain 1013 from 2.38 ×4 10 volume drop from 5.8 × with 109 to 1.3 × 108 4.2 Ω/□ and 4.2 × 10like × anhydride 10 Ω·cm, might be resistivity attributed to the unsaturated side substitutions maleic 9 12 −13 4 benzene This 5.8 × the 10 5.8 1.72 10static respectively. drop which shifts conductive properties of × the10 material from the antistatic to× the and groups, essentially help to enhance particle-to-particle interaction [36]. By 9 10 −11 6 5.1 × 10 × 10 1.96 × 10 dissipative region [37].of Upon further incorporation of5.1 filler (14 wt %),4 the surface drops increasing the loading Cu–Al 2O3 filler in the polymer matrix from to 12 wt %, resistivity the surface and 8 −8 8 × 10 2.3 ×and 107 from 4.35 drastically to 4.0 ×drop 104 2.3 Ω/□, while and electric only volume resistivity from 5.8 ×the 109 volume to 1.3 ×resistivity 108 Ω/□ 4.2conductivity × 1013 to 4.5changed × 10×4 10 Ω·cm, 8 6 −7 10 2.1 × 10 2.1 × 10 4.76 × 10 substantiallyThis compared to 12 wt filler loading. The gradual in conductivity with addition respectively. drop shifts the% conductive properties of theincrement material from the antistatic to the static 8 4 −5 122–14 wt region 1.3 × 10 × 10 2.22 of % filler[37]. is shown in Figure 6. It confirms network suggested by × the10 SEM dissipative Upon further incorporation of4.5 filler (144 formation wt %), theassurface resistivity drops 4 −5 14 4.0 × 10 1.3 × 10 7.69 × 10 4 Ω/□, while results, showing transition from the an insulating to a semiconducting drastically to 4.0the × 10 volume resistivity and electricregion. conductivity changed only substantially compared to 12 wt % filler loading. The gradual increment in conductivity with addition of 2–14 wt % filler is shown in Figure 6. It confirms network formation as suggested by the SEM results, showing the transition from an insulating to a semiconducting region.

6. Electrical conductivity of Cu–Al2O3/PS-b-(PE-r-B)-b-PS-g-MA composites. Figure 6.Figure Electrical conductivity of Cu–Al2 O3 /PS-b-(PE-r-B)-b-PS-g-MA composites.

The electron transfer responsible for conductivity throughout the Cu–Al2O3/PS-b-(PE-r-B)-b-PS-g-MA matrix takes placeresponsible interaction zones between filler and matrix find composites. connections (Figure 7), The electron transfer for conductivity the Cu–Al Figure 6.when Electrical conductivity of Cu–Al 2Othroughout 3/PS-b-(PE-r-B)-b-PS-g-MA 2 O3 /PS-b-(PE-r-B)-b-PS-g-MA establishing a web [38–41]. Cu–Al2O3/PS-b-(PE-r-B)-b-PS-g-MA composites are cost-effective matrix takes place when interaction zones between filler and matrix find connections (Figure 7), materials, as theytransfer showedresponsible enhanced for electrical conductivity and the theyCu–Al are easy to prepare compared to The electron conductivity throughout 2O3/PS-b-(PE-r-B)-b-PS-g-MA establishing a web [38–41]. Cu–Al /PS-b-(PE-r-B)-b-PS-g-MA composites arelimit, cost-effective 2 O3Beyond previously [42]. thebetween critical concentration or percolation there is 7), no materials, matrix takescited placeliterature when interaction zones filler and matrix find connections (Figure as they showed enhanced electrical conductivity and they are easy to prepare compared to further significant increase in electrical even though more filler isare contained in thepreviously establishing a web [38–41]. Cu–Al2O3conductivity /PS-b-(PE-r-B)-b-PS-g-MA composites cost-effective composite material. Once the saturation point is attained, further increase in filler loading may only materials, as they showed enhanced electrical conductivity and they are easy to prepare compared to significant cited literature [42]. Beyond the critical concentration or percolation limit, there is no further increase thecited sum of conductive networks and critical does not contribute in or further conductivity increments. previously literature [42]. Beyond the concentration percolation limit, there is no increase in electrical conductivity even though more filler is contained in the composite material. In contrast, shielding effectiveness may increase when even higherthough filler loadings are used [43–45]. in the further significant increase in electrical conductivity more filler is contained Once the saturation point is attained, further increase in filler loading may only increase the sum of composite material. Once the saturation point is attained, further increase in filler loading may only conductive networks and does not contribute further conductivity increments. contrast, shielding increase the sum of conductive networks andindoes not contribute in further conductivityIn increments. In contrast, shielding when effectiveness may increase when higher filler [43–45]. loadings are used [43–45]. effectiveness may increase higher filler loadings are used

Figure 7. Schematic illustration of interaction between Cu–Al2O3 conductive filler and PS-b-(PE-r-B)b-PS-g-MA polymer matrix responsible for electron transfer. 7. Schematic illustration of interactionbetween between Cu–Al 2O3 conductive filler and PS-b-(PE-r-B)Figure 7. Figure Schematic illustration of interaction Cu–Al filler and PS-b-(PE-r-B)2 O3 conductive b-PS-g-MA polymer responsible electron transfer. b-PS-g-MA polymer matrixmatrix responsible forforelectron transfer.

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3.5. Mechanical Mechanical Properties Properties of of Cu–Al Cu–Al2O O3/PS-b-(PE-r-B)-b-PS-g-MA Composites 3.5. 2 3 /PS-b-(PE-r-B)-b-PS-g-MA Composites Mechanical performance performance of of aa polymer polymer matrix matrix composite composite can can be be influenced influenced by by the the composition composition Mechanical and interaction of filler and matrix materials used. Geometrical aspects, such as structure shape and and interaction of filler and matrix materials used. Geometrical aspects, such as structure shape size of reinforcement material, considerably affect the mechanical behavior of composites [46]. For and size of reinforcement material, considerably affect the mechanical behavior of composites [46]. the the synthesis of structurally resilient composites, filler For synthesis of structurally resilient composites, fillerdispersion dispersionand anddeclustering declusteringisisaa prerequisite. prerequisite. Thus, by critically controlling the volume fraction of filler, mechanical properties were measured to Thus, by critically controlling the volume fraction of filler, mechanical properties were measured analyze thethe effect of of filler inclusion and to to prevent any deterioration in in mechanical properties of to analyze effect filler inclusion and prevent any deterioration mechanical properties composites [45]. The mechanical behavior of Cu–Al 2O3/polymer composites was examined by of composites [45]. The mechanical behavior of Cu–Al2 O3 /polymer composites was examined by calculating Young’s Young’s modulus, modulus, tensile tensile strength, strength, and and % % elongation elongation at at break break of of the the composites composites with with calculating increasingfiller fillerloading loading(0–14 (0–14wt wt%). %). increasing 3.5.1. Young’s Young’sModulus Modulus 3.5.1. Young’smodulus modulusis is aa quantitative quantitative parameter parameter for for the the stiffness stiffness determination determination of of elastic elastic materials. materials. Young’s It is defined as the ratio of applied stress to the strain along the same axis. The applied stress should It is defined as the ratio of applied stress to the strain along the same axis. The applied stress should be bethe in the range in which Hook’s holds properly [47]. Young’s modulus of neat block copolymer in range in which Hook’s lawlaw holds properly [47]. Young’s modulus of neat block copolymer is is 50 ± 3 MPa, which increased to 150 ± 3 MPa (Figure 8) with the gradual addition of reinforcement 50 ± 3 MPa, which increased to 150 ± 3 MPa (Figure 8) with the gradual addition of reinforcement material. This This gradual gradual and and constant constant increase increase in in Young’s Young’s modulus modulus of of composites composites with with increased increased filler filler material. loading indicates indicates enhancement enhancementin instiffness stiffnessimparted impartedby byAl Al22O O33.. loading

Figure8.8.Young’s Young’smodulus modulusofofCu–Al Cu–AlO 2O3/PS-b-(PE-r-B)-b-PS-g-MA composites. Figure 2 3 /PS-b-(PE-r-B)-b-PS-g-MA composites.

3.5.2. Tensile Strength 3.5.2. Tensile Strength The maximum stress that a material can endure before failing or breaking is known as tensile The maximum stress that a material can endure before failing or breaking is known as tensile strength [48]. The incorporation of Cu–Al2O3 in the polymer matrix increases the tensile strength of strength [48]. The incorporation of Cu–Al2 O3 in the polymer matrix increases the tensile strength the resultant composites. At 14 wt % Cu–Al2O3 loading, the tensile strength of the composite reached of the resultant composites. At 14 wt % Cu–Al2 O3 loading, the tensile strength of the composite 82 ± 3 MPa, as compared to 15 ± 3 MPa of the neat polymer. Figure 9 shows the gradual increase of reached 82 ± 3 MPa, as compared to 15 ± 3 MPa of the neat polymer. Figure 9 shows the gradual tensile strength with filler loading. Tensile strength is strongly dependent upon interfacial increase of tensile strength with filler loading. Tensile strength is strongly dependent upon interfacial adhesion/bonding between filler and matrix and is aided by uniform filler dispersion. Interfacial adhesion/bonding between filler and matrix and is aided by uniform filler dispersion. Interfacial adhesion determines the strength of such composites. The results suggest good compatibility adhesion determines the strength of such composites. The results suggest good compatibility between particulate filler and polymer matrix and confirms active transfer of stress from matrix to between particulate filler and polymer matrix and confirms active transfer of stress from matrix particulate filler [49–51]. The PS-b-(PE-r-B)-b-PS-g-MA/Cu-Al2O3 composites offer good strength and to particulate filler [49–51]. The PS-b-(PE-r-B)-b-PS-g-MA/Cu-Al2 O3 composites offer good strength mechanical resistance, compared to previously reported polymer/metal-coated polymers [26], and mechanical resistance, compared to previously reported polymer/metal-coated polymers [26], polymer/carbon [42], polymer/ceramic [52], polymer/mineral ([53,54], ethylene–propylene–diene polymer/carbon [42], polymer/ceramic [52], polymer/mineral ([53,54], ethylene–propylene–diene monomer rubber/Mg(OH)2) [55] and polymer/polymer composites [53], as illustrated in Table 4. monomer rubber/Mg(OH)2 ) [55] and polymer/polymer composites [53], as illustrated in Table 4.

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Figure9.9.Tensile Tensilestrength strengthof ofCu–Al Cu–Al22O O33/PS-b-(PE-r-B)-b-PS-g-MA /PS-b-(PE-r-B)-b-PS-g-MA composites. Figure composites. Table4.4.Comparison Comparisonofofthe thetensile tensilestrength strengthofofPS-b-(PE-r-B)-b-PS-g-MA/Cu-Al PS-b-(PE-r-B)-b-PS-g-MA/Cu-Al22O O33 composites composites with with Table previously reported data. previously reported data. Composite Type Composite Type PS-b-(PE-r-B)-b-PS-g-MA/Cu-Al 2O3 PS-b-(PE-r-B)-b-PS-g-MA/Cu-Al Polyethylene/Ag-coated polyamide 2 O3 Polyethylene/Ag-coated polyamide Waterborne polyurethane/graphene Waterborne polyurethane/graphene Polyurethane/silica Polyurethane/silica Polypropylene/CaCO3 Polypropylene/CaCO3 Polypropylene/BaSO4 Polypropylene/BaSO4 Ethylene–propylene–diene monomer rubber/MgOH2 Ethylene–propylene–diene monomer rubber/MgOH2 Polypropylene/poly(methylmethacrylate) Polypropylene/poly(methylmethacrylate)

Tensile Strength (MPa) Tensile Strength (MPa) 82.9 82.9 2.7 2.7 9.6 9.6 6.80 6.80 29.7 29.7 30.0 30.0 9.6 9.6 29.5 29.5

Reference Reference Present research Present research [26] [26] [42] [42] [52] [52] [53] [53] [54] [54] [55] [55] [53] [53]

3.5.3. Elongation at Break 3.5.3. Elongation at Break Elongation at break is a quantitative parameter for the ductility of the material. It is defined as Elongation at break is a quantitative parameter for the ductility of the material. It is defined the percentage of elongation of a material from zero stress to the breaking point of that material [56]. as the percentage of elongation of a material from zero stress to the breaking point of that The elongation at break is also an indicator for determining the toughness of two phase materials material [56]. The elongation at break is also an indicator for determining the toughness of two [57]. The elongation at break calculated for PS-b-(PE-r-B)-b-PS-g-MA polymer was 16.9% ± 0.4%. Cu– phase materials [57]. The elongation at break calculated for PS-b-(PE-r-B)-b-PS-g-MA polymer Al2O3/PS-b-(PE-r-B)-b-PS-g-MA composites with increasing filler loadings (0%–14%) showed a was 16.9% ± 0.4%. Cu–Al2 O3 /PS-b-(PE-r-B)-b-PS-g-MA composites with increasing filler loadings gradual decrease from 16.9% to 10.1% (Figure 10). Polymers are ductile in nature while ceramics (0%–14%) showed a gradual decrease from 16.9% to 10.1% (Figure 10). Polymers are ductile in nature exhibit brittle behavior. Thus, the gradual increase in brittle behavior is due to the incorporation of while ceramics exhibit brittle behavior. Thus, the gradual increase in brittle behavior is due to the the reinforcement material [58], and may arise from interstructural progression in which filler incorporation of the reinforcement material [58], and may arise from interstructural progression in particles are dispersed in the interaggregate space [48]. At low filler loading, the matrix is not which filler particles are dispersed in the interaggregate space [48]. At low filler loading, the matrix adequately reinforced. So, it could not withstand high load, and eventually failure happens at lower is not adequately reinforced. So, it could not withstand high load, and eventually failure happens at elongation. However, at higher filler loading, the matrix is increasingly reinforced and endures high lower elongation. However, at higher filler loading, the matrix is increasingly reinforced and endures load before the breaking point is reached. The reinforcement mechanism preludes that, at higher filler high load before the breaking point is reached. The reinforcement mechanism preludes that, at higher loading, the molecular mobility drops because of the formation of physical bonds among particles of filler loading, the molecular mobility drops because of the formation of physical bonds among particles filler and polymer molecule chains [43]. of filler and polymer molecule chains [43].


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Figure 10. Elongation at break of Cu–Al2O3/PS-b-(PE-r-B)-b-PS-g-MA composites.

Figure 10. Elongation at break of Cu–Al2 O3 /PS-b-(PE-r-B)-b-PS-g-MA composites.

3.6. Thermal Characteristics of Block Copolymer Composites

3.6. Thermal Characteristics of Block Copolymer Composites Figure 10. Elongation at break of Cu–Al 2O3/PS-b-(PE-r-B)-b-PS-g-MA composites. 3.6.1. Thermogravimetric Analysis (TGA)

3.6.1.3.6. Thermogravimetric Analysis Thermal Characteristics of Block(TGA) Copolymer Composites

TGA examines the thermal properties as the weight alteration upon heating during the phases

TGA examines the thermal properties as the weight alteration heating during the phases of thermal breakdown. The thermal behavior determines the possibleupon specific application fields of 3.6.1. Thermogravimetric Analysis (TGA) nanocomposites [59].The TGAthermal thermograms of neat PS-b-(PE-r-B)-b-PS-g-MA and Cu–Al 2O3 loaded of thermal breakdown. behavior determines the possible specific application fields of TGA examines the thermal as neat the weight alteration upondecomposition heatingand during phases composites from and 14 wt properties % are shown in Figure 11. A two-phase isthe observed nanocomposites [59].0, 2, TGA thermograms of PS-b-(PE-r-B)-b-PS-g-MA Cu–Al 2 O3 loaded of thermal breakdown. Theslight thermal behavior determines the possible specific application fields of for neatfrom block dipshown at 250 °C theA presence of some residual low is molecular composites 0,copolymer. 2, and 14 A wt % are in indicates Figure 11. two-phase decomposition observed for nanocomposites [59]. TGApolymer. thermograms of neat conditions, PS-b-(PE-r-B)-b-PS-g-MA and Cu–Al 3 loaded weight compounds in the In the◦ present the polymer remains stable2Oup 397 neat block copolymer. A slight dip at 250 C indicates the presence of some residual low to molecular composites from 0, 2,The andsecond 14 wt phase % are of shown in Figure 11. A two-phase decomposition is observed °C (8% weight loss). decomposition starts at 397 °C (T max) and continues up to a ◦ weight in the polymer. In the present conditions, the polymer up to 397 C forcompounds neat block copolymer. A slight °C indicates theat presence of someremains residualstable low molecular final degradation temperature of dip 480 at °C250 (99% weight loss Tf). With of 2 wt % Cu– ◦ C (Tthe inclusion (8% weight loss). The second phase of decomposition starts at 397 ) and continues up a final max weight compounds in the polymer. In the present conditions, polymer remains to to 397 Al 2O3, the thermal stability of the composite is improved, wherethe Tmax raises from 397 stable to 405 up °C and Tf ◦ C (99% weight loss at T ). With the inclusion of 2 wt % Cu–Al O , degradation temperature of 480 °C (8% weight loss). second decomposition 397 °C (Tmax30 ) and to a 2 3 from 480 to 492 °C. The At 14 wt %phase filler of loading, Tmax and starts Tff areatrespectively °C continues and 9 °C up higher final degradation temperature of (99%(Tweight loss67% at Tresidue fmax ). With inclusion ofto2heating wt %◦ C Cu– the thermal stability of the composite ispoint improved, where raises from 405 and Tf compared to the neat polymer. At480 this°C f 489 °C), isthe still left. 397 Upon the ◦ C. At ◦C T Al 2O3to , the thermal of%the composite is improved, raiseshave frominteracted 397◦to °C9and f frompolymer, 480 492 14 wt filler loading, Tmax andwhere Tfwhich areTmax respectively 30 C 405 andwith higher the long stability chains break down into small fragments might Cu– ◦ C),Tto from to 492 °C.got Attrapped 14 wt At % filler loading, max and f are respectively 30 °C and 9improving °C heating higher the Al 2O3 480 particles and into filler particles difficult be decomposed further, thus compared to the neat polymer. this point (TfT489 67% residue is still left. Upon compared tostability the neatof polymer. At into this small point (T f 489composites °C), which 67% residue ishave stillbehavior left. Upon heating the O the thermal the PS-b-(PE-r-B)-b-PS-g-MA [56]. Similar was observed polymer, the long chains break down fragments might interacted with Cu–Al 2 3 polymer, thewhere long chains break down into small fragments which might have which interacted with Cu– previously, thermal stability was enhanced due to filler incorporation hindered the particles and got trapped into filler particles difficult to be decomposed further, thus improving the Al2O3 particles and gotof trapped into fillerintermingled particles difficult be decomposed further,polymer thus improving segmental movement polymer when withtosmall chains of the [27,48]. thermal stability of the PS-b-(PE-r-B)-b-PS-g-MA composites [56]. Similar host behavior was observed the thermaldegradation stability of the PS-b-(PE-r-B)-b-PS-g-MA composites [56]. Similar behavior was observed Analogous patterns are seen in the derivative thermogravimetry (DTG) curves of host previously, where thermal stability was enhanced due to filler incorporation which hindered previously, thermal stability was enhanced due to filler incorporation which hindered the the polymer andwhere its composites (Figure 12). segmental movement of polymer when withsmall small chains of the polymer [27,48]. segmental movement of polymer whenintermingled intermingled with chains of the hosthost polymer [27,48]. Analogous degradation patterns thermogravimetry (DTG) curves of host Analogous degradation patternsare areseen seenin inthe the derivative derivative thermogravimetry (DTG) curves of host polymer its composites (Figure 12). polymer and and its composites (Figure 12).

Figure 11. Thermogravimetric analysis (TGA) thermograms of neat PS-b-(PE-r-B)-b-PS-g-MA and composites with 2 wt % and 14 wt % Cu–Al2O3 loading. Figure 11. Thermogravimetric analysis (TGA) thermograms of neat PS-b-(PE-r-B)-b-PS-g-MA and

Figure 11. Thermogravimetric analysis (TGA) thermograms of neat PS-b-(PE-r-B)-b-PS-g-MA and composites with 2 wt % and 14 wt % Cu–Al2O3 loading. composites with 2 wt % and 14 wt % Cu–Al2 O3 loading.


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Figure Figure 12. Derivative thermogravimetry (DTG) of neat PS-b-(PE-r-B)-b-PS-g-MA and composites with Figure12. 12.Derivative Derivativethermogravimetry thermogravimetry(DTG) (DTG)of ofneat neatPS-b-(PE-r-B)-b-PS-g-MA PS-b-(PE-r-B)-b-PS-g-MAand andcomposites compositeswith with 222wt % and 14 wt % Cu–Al 2 O 3 loading. wt % and 14 wt % Cu–Al 2 O 3 loading. wt % and 14 wt % Cu–Al2 O3 loading.

3.6.2. 3.6.2. Differential Scanning Calorimetry (DSC) 3.6.2.Differential DifferentialScanning ScanningCalorimetry Calorimetry (DSC) (DSC) DSC provides the determination the glass transition temperature gg)) of DSC analysis provides providesthe thedetermination determinationofof ofthe the glass transition temperature of materials, materials, DSC analysis analysis glass transition temperature (Tg(T )(Tof materials, the the temperature at which a polymer transforms from a glassy to a rubbery state [60]. The DSC the temperature at which a polymer transforms from a glassy to a rubbery state [60]. The DSC temperature at which a polymer transforms from a glassy to a rubbery state [60]. The DSC thermograms thermograms of and corresponding with 0, and thermograms of neat neat PS-b-(PE-r-B)-b-PS-g-MA PS-b-(PE-r-B)-b-PS-g-MA and the thecomposites corresponding composites with 0, 2, 2, loading and 14 14 of neat PS-b-(PE-r-B)-b-PS-g-MA and the corresponding with composites 0, 2, and 14 wt % filler wt % filler loading are shown in Figure 13. The stiffness of polymers is usually studied by T gganalysis. wt % filler loading are shown in Figure 13. The stiffness of polymers is usually studied by T analysis. are shown in Figure 13. The stiffness of polymers is usually studied by Tg analysis. Stiff polymer Stiff polymer chains with bulky, rigid side to main high gg.. It Stiff polymer chains withside bulky, rigid side groups groups attached to the the main chain imparts high TTthat It is is chains with bulky, rigid groups attached to theattached main chain imparts achain highimparts Tg . It isaaknown at known that at T gg,, polymer chains start to move. The results show that the incorporation of Cu–Al 22O 33 known that at T polymer chains start to move. The results show that the incorporation of Cu–Al O Tg , polymer chains start to move. The results show that the incorporation of Cu–Al2 O3 in the polymer in the matrix in the polymer polymer matrix increases the the TTgg as as the the chains chains of of PS-b-(PE-r-B)-b-PS-g-MA PS-b-(PE-r-B)-b-PS-g-MA strongly strongly adhere adhere to to matrix increases the Tincreases g as the chains of PS-b-(PE-r-B)-b-PS-g-MA strongly adhere to the Cu–Al2 O3 the Cu–Al 22O 33 particles, which prevents free motion of polymer chains and hinders the segmental the Cu–Al O particles, which prevents free motion of polymer chains and hinders the segmental particles, which prevents free motion of polymer chains and hinders the segmental movement of movement of movement of chains chains [61,62]. [61,62]. chains [61,62].

Figure Figure 13. Differential Differential scanning scanning calorimetry calorimetry (DSC) (DSC) of neat neat PS-b-(PE-r-B)-b-PS-g-MA PS-b-(PE-r-B)-b-PS-g-MA and and composites Figure13. 13. Differential scanning calorimetry (DSC) of of neat PS-b-(PE-r-B)-b-PS-g-MA andcomposites composites with 2 wt % and 14 wt % Cu-Al 22O 33 loading. with 2 wt % and 14 wt % Cu-Al O loading. with 2 wt % and 14 wt % Cu-Al2 O3 loading.

4. 4. Conclusions 4.Conclusions Conclusions In In this study, nanocomposites were were synthesized from the block copolymer polystyrene-blockIn this this study, study, nanocomposites nanocomposites were synthesized synthesized from from the the block block copolymer copolymerpolystyrene-blockpolystyrene-blockpoly(ethylene-ran-butylene)-block-polystyrene-graft-maleic anhydride (PS-b-(PE-r-B)-b-PS-g-MA) poly(ethylene-ran-butylene)-block-polystyrene-graft-maleic anhydride (PS-b-(PE-r-B)-b-PS-g-MA) as poly(ethylene-ran-butylene)-block-polystyrene-graft-maleic anhydride (PS-b-(PE-r-B)-b-PS-g-MA)as as the the matrix matrix and and from from aa filler filler material, material, prepared prepared by by the the electroless electroless deposition deposition (ELD) (ELD) of of Cu Cu particles particles on on alumina aluminapowder. powder.The Thenanocomposite nanocompositebelongs belongsto tothe theclass classof ofinorganic–organic inorganic–organiccomposites compositescontaining containing


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the matrix and from a filler material, prepared by the electroless deposition (ELD) of Cu particles on alumina powder. The nanocomposite belongs to the class of inorganic–organic composites containing metal-coated ceramic reinforcement agent embedded in a thermoplastic polymer insulation, categorized as conductive polymer nanocomposites. The nanocomposites are easy to prepare, show enhanced electrical conductivity, improved thermal stability, and mechanical properties. The pronounced increment in electrical conductivity with increased filler ratio, up to 7.692 × 10−5 S/cm in the case of 14 wt % filler loading, indicates the formation of conductive networks within the prepared composites. A good interfacial adhesion between filler and matrix permits to improve the Young’s modulus and tensile strength at 14 wt % filler loading up to 159.475 MPa and 82.889 MPa, respectively. The composites also show improved thermal stability, while heat flow measurements via DSC show a higher glass transition temperature range with higher filler inclusion. XRD patterns indicate a more crystalline phase of the composites due to addition of metallic filler. SEM micrographs of the composites illustrate a uniform Cu deposition on Al2 O3 and its homogeneous dispersion throughout polymer matrix when using the ELD technique. These results support the potential application of the prepared composites in electronic applications that require a prolonged shelf life, both in electronic semiconductors as in microelectronic packaging, EMI- and EDS-shielding materials, antistatic coatings for electronic, flexible IT devices, and others. Depending on the requirements of the applications, these materials may be used either in coatings or for standalone components. Acknowledgments: Rohama Gill gratefully acknowledges the assistance of Muhammad Rafique (QAU) for mechanical analysis. Author Contributions: Rohama Gill conceived and designed the experiments; QuratulAin Nadeem and Tasneem Fatima performed the experiments; Pepijn Prinsen and Rafael Luque analyzed the data; Aziz ur Rehman and Rashid Mahmood contributed reagents/materials/analysis tools; Rohama Gill, QuratulAin Nadeem and Tasneem Fatima wrote the paper. Conflicts of Interest: The authors declare no conflict of interest.

References 1. 2. 3. 4. 5. 6.

7.

8. 9. 10.

Rimdusit, S.; Jubsilp, C.; Tiptipakorn, S. Alloys and Composites of Polybenzoxazines: Properties and Applications; Springer: Singapore, 2013; pp. 139–141. Robinson, B.H. E-waste: An assessment of global production and environmental impacts. Sci. Total Environ. 2009, 408, 183–191. [CrossRef] [PubMed] Shacham-Diamand, Y.; Osaka, T.; Okinaka, Y.; Sugiyama, A.; Dubin, V. 30 years of electroless plating for semiconductor and polymer micro-systems. Microelectron. Eng. 2015, 132, 35–45. [CrossRef] Sudagar, J.; Lian, J.; Sha, W. Electroless nickel alloy composite and nano coatings—A critical review. J. Alloys Compd. 2013, 571, 183–204. [CrossRef] Agarwala, R.C.; Agarwala, V. Electroless alloy composite coatings: A review. Sadhana 2003, 28, 475–493. [CrossRef] Zhai, T.; Ding, C.; Lu, L.; Zhang, C. Autocatalytic deposition of copper coating on poly (ether ether ketone)/multiwalled carbon nanotubes composites via a palladium-free and simplified electroless process. Mater. Lett. 2015, 147, 46–49. [CrossRef] Reddy, E.L.; Lee, H.C.; Kim, D.H. Steam reforming of methanol over structured catalysts prepared by electroless deposition of Cu and Zn on anodically oxidized alumina. Int. J. Hydrogen Energy 2015, 40, 2509–2517. [CrossRef] Moon, J.H.; Kim, K.H.; Choi, H.W.; Lee, S.W.; Park, S.J. Electroless silver coating of rod-like glass particles. Ultramicroscopy 2008, 108, 1307–1310. [CrossRef] [PubMed] Liu, S.; Liu, J.; Wang, L.; Zhao, F. Development of electrochemical DNA biosensor based on gold nanoparticle modified electrode by electroless deposition. Bioelectrochemistry 2010, 79, 37–42. [CrossRef] [PubMed] Kretz, F.; Gacsi, Z.; Kovacs, J.; Pieczonka, T. The electroless deposition of nickel on SiC particles for aluminum matrix composites. Surf. Coat. Technol. 2004, 180, 575–579. [CrossRef]


11.

12.

13. 14. 15. 16. 17. 18. 19.

20.

21. 22. 23. 24. 25. 26.

27. 28.

29. 30. 31. 32.

15 of 17

Kuester, S.; Merlini, C.; Barra, G.M.; Ferreira, J.C.; Lucas, A.; de Souza, A.C.; Soares, B.G. Processing and characterization of conductive composites based on poly (styrene-b-ethylene-ran-butylene-b-styrene)(SEBS) and carbon additives: A comparative study of expanded graphite and carbon black. Compos. Part B 2016, 84, 236–247. [CrossRef] Sarı, A.; Alkan, C.; Karaipekli, A.; Onal, A. Preparation, characterization and thermal properties of styrene maleic anhydride copolymer (SMA)/fatty acid composites as form stable phase change materials. Energy Convers. Manag. 2008, 49, 373–380. [CrossRef] Araby, S.; Meng, Q.; Zhang, L.; Kang, H.; Majewski, P.; Tang, Y. Electrically and thermally conductive elastomer/graphene nanocomposites by solution mixing. J. Polym. 2014, 55, 201–210. [CrossRef] Tian, Q.H.; Guo, X.Y. Simulation of electromagnetic-flow fields in Mg melt under pulsed magnetic field. Trans. Nonferrous Met. Soc. China 2010, 20, 283–287. [CrossRef] Standard Test Methods for DC Resistance or Conductance of Insulating Materials; ASTM D257-07; ASTM International: West Conshohocken, PA, USA, 2007. Standard Test Method for Tensile Properties of Plastics; ASTM D638-02; ASTM International: West Conshohocken, PA, USA, 2002. Standard Test Method for Tensile Properties of Plastics; ASTM D638-03; ASTM International: West Conshohocken, PA, USA, 2003. Ma, H.; Liu, Z.; Wu, L.; Wang, Y.; Wang, X. Study of a pre-treatment process for electroless copper plating on ceramics. Thin Solid Films 2011, 519, 7860–7863. [CrossRef] Mondin, G.; Lohe, M.R.; Wisser, F.M.; Grothe, J.; Mohamed-Noriega, N.; Leifert, A.; Dorfler, S.; Bachmatiuk, A.; Rummelib, M.H.; Kaskel, S. Electroless copper deposition on (3-mercaptopropyl) triethoxysilane-coated silica and alumina nanoparticles. Electrochim. Acta 2013, 114, 521–526. [CrossRef] Reddy, K.R.; Sin, B.C.; Yoo, C.H.; Park, W.; Ryu, K.S.; Lee, J.S.; Shon, D.; Lee, Y. A new one-step synthesis method for coating multi-walled carbon nanotubes with cuprous oxide nanoparticles. Scr. Mater. 2008, 58, 1010–1013. [CrossRef] Chang, H.F.; Saleque, M.A.; Hsu, W.S.; Lin, W.H. Characterization and dehydrogenation activity of CuAl2 O3 catalysts prepared by electroless plating technique. J. Mol. Catal. A Chem. 1996, 109, 249–260. [CrossRef] Sharma, R.; Agarwala, R.C.; Agarwala, V. Development of copper coatings on ceramic powder by electroless technique. Appl. Surf. Sci. 2006, 252, 8487–8493. [CrossRef] Leon, C.A.; Rodriguez-Ortiz, G.; Nanko, M.; Aguilar, E.A. Pulsed electric current sintering of Cu matrix composites reinforced with plain and coated alumina powders. Powder Technol. 2014, 252, 1–7. [CrossRef] Silvain, J.F.; Bobet, J.L.; Heintz, J.M. Electroless deposition of copper onto alumina sub-micronic powders and sintering. Compos. Part A Appl. Sci. Manuf. 2002, 33, 1387–1390. [CrossRef] Wang, H.; Jia, J.; Song, H.; Hu, X.; Sun, H.; Yang, D. The preparation of Cu-coated Al2 O3 composite powders by electroless plating. Ceram. Int. 2011, 37, 2181–2184. [CrossRef] Krupa, I.; Miková, G.; Novák, I.; Janigová, I.; Nógellova, Z.; Lednický, F.; Prokes, J. Electrically conductive composites of polyethylene filled with polyamide particles coated with silver. Eur. Polym. J. 2007, 43, 2401–2413. [CrossRef] Goyal, R.K.; Tiwari, A.N.; Mulik, U.P.; Negi, Y.S. Novel high performance Al2 O3 /poly (ether ether ketone) nanocomposites for electronics applications. Compos. Sci. Technol. 2007, 67, 1802–1812. [CrossRef] Choi, S.; Kim, K.; Nam, J.; Shim, S.E. Synthesis of silica-coated graphite by enolization of polyvinylpyrrolidone and its thermal and electrical conductivity in polymer composites. Carbon 2013, 60, 254–265. [CrossRef] Al-Saleh, M.H.; Saadeh, W.H.; Sundararaj, U. EMI shielding effectiveness of carbon based nanostructured polymeric materials: A comparative study. Carbon 2013, 60, 146–156. [CrossRef] Chu, B.; Zhou, X.; Ren, K.; Neese, B.; Lin, M.; Wang, Q.; Bauer, F.; Zhang, Q.M. A dielectric polymer with high electric energy density and fast discharge speed. Science 2006, 313, 334–336. [CrossRef] [PubMed] Rahaman, M.; Chaki, T.K.; Khastgir, D. Development of high performance EMI shielding material from EVA, NBR, and their blends: effect of carbon black structure. J. Mater. Sci. 2011, 46, 3989–3999. [CrossRef] Dang, Z.M.; Yuan, J.K.; Zha, J.W.; Zhou, T.; Li, S.T.; Hu, G.H. Fundamentals, processes and applications of high-permittivity polymer–matrix composites. Prog. Mater. Sci. 2012, 57, 660–723. [CrossRef]


33.

34. 35.

36.

37.

38. 39. 40. 41. 42.

43. 44.

45.

46.

47. 48. 49. 50.

51. 52. 53. 54.

16 of 17

Xu, S.; Rezvanian, O.; Peters, K.; Zikry, M.A. The viability and limitations of percolation theory in modeling the electrical behavior of carbon nanotube–polymer composites. Nanotechnology 2013, 24, 155706. [CrossRef] [PubMed] Pang, H.; Xu, L.; Yan, D.X.; Li, Z.M. Conductive polymer composites with segregated structures. Prog. Polym. Sci. 2014, 39, 1908–1933. [CrossRef] Deng, H.; Lin, L.; Ji, M.; Zhang, S.; Yang, M.; Fu, Q. Progress on the morphological control of conductive network in conductive polymer composites and the use as electroactive multifunctional materials. Prog. Polym. Sci. 2014, 39, 627–655. [CrossRef] Hu, J.; Zhang, H.B.; Hong, S.; Jiang, Z.G.; Gui, C.; Li, X.; Yu, Z.Z. Simultaneous improvement in both electrical conductivity and toughness of polyamide 6 nanocomposites filled with elastomer and carbon black particles. Ind. Eng. Chem. Res. 2014, 53, 2270–2276. [CrossRef] Arjmand, M.; Mahmoodi, M.; Gelves, G.A.; Park, S.; Sundararaj, U. Electrical and electromagnetic interference shielding properties of flow-induced oriented carbon nanotubes in polycarbonate. Carbon 2011, 49, 3430–3440. [CrossRef] Zheng, W.; Wong, S.C. Electrical conductivity and dielectric properties of PMMA/expanded graphite composites. Compos. Sci. Technol. 2003, 63, 225–235. [CrossRef] Wei, Y.F.; Li, Z.Q. Measurement of specific contact resistivity using scanning voltage probes. Appl. Phys. Lett. 2013, 102, 131605. Al-Saleh, M.H. Influence of conductive network structure on the EMI shielding and electrical percolation of carbon nanotube/polymer nanocomposites. Synth. Met. 2015, 205, 78–84. [CrossRef] Nadeem, Q.; Rizwan, M.; Gill, R.; Rafique, M.; Shahid, M. Fabrication of alumina based electrically conductive polymer composites. J. Appl. Polym. Sci. 2016, 133. [CrossRef] Choi, S.H.; Kim, D.H.; Raghu, A.V.; Reddy, K.R.; Lee, H.I.; Yoon, K.S.; Jeong, H.M.; Kim, B.K. Properties of graphene/waterborne polyurethane nanocomposites cast from colloidal dispersion mixtures. J. Macromol. Sci. Part B Phys. 2012, 51, 197–207. [CrossRef] Sau, K. Acetylene black filled Elastomeric conductive composites based on EPDM, NBR and Silicone rubber. History 2015, 15, 13–19. Sohi, N.J.S.; Rahaman, M.; Khastgir, D. Dielectric property and electromagnetic interference shielding effectiveness of ethylene vinyl acetate-based conductive composites: Effect of different type of carbon fillers. Polym. Compos. 2011, 32, 1148–1154. [CrossRef] Verma, P.; Saini, P.; Malik, R.S.; Choudhary, V. Excellent electromagnetic interference shielding and mechanical properties of high loading carbon-nanotubes/polymer composites designed using melt recirculation equipped twin-screw extruder. Carbon 2015, 89, 308–317. [CrossRef] Kwon, S.C.; Adachi, T.; Araki, W.; Yamaji, A. Effect of composing particles of two sizes on mechanical properties of spherical silica-particulate-reinforced epoxy composites. Compos. Part B Eng. 2008, 39, 740–746. [CrossRef] Fletcher, A.; Gupta, M.C. Mechanical properties of elastomer nanocomposites for electromagnetic interference shielding applications. J. Compos. Mater. 2014, 48, 1261–1276. [CrossRef] Bishay, I.K.; Abd-El-Messieh, S.L.; Mansour, S.H. Electrical, mechanical and thermal properties of polyvinyl chloride composites filled with aluminum powder. Mater. Des. 2011, 32, 62–68. [CrossRef] Gao, H.; Ji, B.; Jäger, I.L.; Arzt, E.; Fratzl, P. Materials become insensitive to flaws at nanoscale: Lessons from nature. Proc. Natl. Acad. Sci. USA 2003, 100, 5597–5600. [CrossRef] [PubMed] Tang, L.S.; Mariatti, M. Comparison on the properties of nickel-coated graphite (NCG) and graphite particles as conductive fillers in polypropylene (PP) composites. Polym. Plast. Technol. Eng. 2009, 48, 614–620. [CrossRef] Kuo, M.C.; Tsai, C.M.; Huang, J.C.; Chen, M. PEEK composites reinforced by nano-sized SiO2 and Al2 O3 particulates. Mater. Chem. Phys. 2005, 90, 185–195. [CrossRef] Chen, Y.; Zhou, S.; Yang, H.; Wu, L. Structure and properties of polyurethane/nanosilica composites. J. Appl. Polym. Sci. 2005, 95, 1032–1039. [CrossRef] Renner, K.; Yang, M.S.; Móczó, J.; Choi, H.J.; Pukánszky, B. Analysis of the debonding process in polypropylene model composites. Eur. Polym. J. 2005, 41, 2520–2529. [CrossRef] Wang, K.; Wu, J.; Ye, L.; Zeng, H. Mechanical properties and toughening mechanisms of polypropylene/barium sulfate composites. Compos. Part A Appl. Sci. Manuf. 2003, 34, 1199–1205. [CrossRef]


55. 56. 57. 58.

59. 60.

61. 62.

17 of 17

Zhang, Q.; Tian, M.; Wu, Y.; Lin, G.; Zhang, L. Effect of particle size on the properties of Mg(OH)2 -filled rubber composites. J. Appl. Polym. Sci. 2004, 94, 2341–2346. [CrossRef] Ku, H.; Wang, H.; Pattarachaiyakoop, N.; Trada, M. A review on the tensile properties of natural fiber reinforced polymer composites. Compos. Part B Eng. 2011, 42, 856–873. [CrossRef] Zhou, W.; Qi, S.; Li, H.; Shao, S. Study on insulating thermal conductive BN/HDPE composites. Thermochim. Acta 2007, 452, 36–42. [CrossRef] Meincke, O.; Kaempfer, D.; Weickmann, H.; Friedrich, C.; Vathauer, M.; Warth, H. Mechanical properties and electrical conductivity of carbon-nanotube filled polyamide-6 and its blends with acrylonitrile/butadiene/ styrene. Polymer 2004, 45, 739–748. [CrossRef] Shafiq, M.; Yasin, T.; Saeed, S. Synthesis and characterization of linear low-density polyethylene/sepiolite nanocomposites. J. Appl. Polym. Sci. 2012, 123, 1718–1723. [CrossRef] Vilaplana, F.; Ribes-Greus, A.; Karlsson, S. Analytical strategies for the quality assessment of recycled high-impact polystyrene: A combination of thermal analysis, vibrational spectroscopy, and chromatography. Anal. Chim. Acta 2007, 604, 18–28. [CrossRef] [PubMed] Lee, J.G.; Kim, S.H.; Kang, H.C.; Park, S.H. Effect of TiO2 on PVDF/PMMA composite films prepared by thermal casting. Macromol. Res. 2013, 21, 349–355. [CrossRef] Xie, S.H.; Zhu, B.K.; Wei, X.Z.; Xu, Z.K.; Xu, Y.Y. Polyimide/BaTiO3 composites with controllable dielectric properties. Compos. Part A Appl. Sci. Manuf. 2005, 36, 1152–1157. [CrossRef] © 2016 by the authors; licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC-BY) license (http://creativecommons.org/licenses/by/4.0/).