Maleic Anhydride Grafted

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Materials and Interfaces

Effect of Graphene on Polypropylene/Maleic Anhydride Grafted Ethylene Vinyl Acetate (PP/EVA-g-MA) blend: Mechanical, Thermal, Morphological and Rheological Properties Anish Mathai Varghese, Vengatesan Muthukumaraswamy Rangaraj, Sung Cik Mun, Christopher W. Macosko, and Vikas Mittal Ind. Eng. Chem. Res., Just Accepted Manuscript • DOI: 10.1021/acs.iecr.7b04932 • Publication Date (Web): 30 Apr 2018 Downloaded from http://pubs.acs.org on May 1, 2018

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Industrial & Engineering Chemistry Research

Effect of Graphene on Polypropylene/Maleic Anhydride Grafted Ethylene Vinyl Acetate (PP/EVA-g-MA) blend: Mechanical, Thermal, Morphological and Rheological Properties Anish Mathai Varghesea, Vengatesan Muthukumaraswamy Rangaraja, Sung Cik Munb, Christopher W. Macoskob, Vikas Mittala*

a

Department of Chemical Engineering, Khalifa University of Science and Technology (KUST),

Sas Al Nakhl campus, Abu Dhabi, P.O 2533, U.A.E. b

Department of Chemical Engineering and Materials Science, University of Minnesota, 421

Washington Ave. SE, Minneapolis, MN 55455, U.S.A.

*Author to whom correspondence should be addressed. Dr. Vikas Mittal, Email: [email protected]; Phone: +971-26075491. 1

ACS Paragon Plus Environment

Industrial & Engineering Chemistry Research 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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Abstract We have studied the effect of thermally reduced graphene oxide (TRG) on the properties of polypropylene/maleic anhydride-grafted-ethylene vinyl acetate (PP/EVA-g-MA) blends. In blends without TRG, EVA-g-MA was dispersed as droplets in PP. At low TRG content, the sheets located in the EVA-g-MA phase. At 5 wt. %, the morphology was co-continuous and the domain sizes of EVA-g-MA were small, while TRG sheets were randomly distributed in the blend. The electrical percolation threshold was between 3 and 5 wt. %. Melt rheological analysis revealed that PP/EVA-g-MA/TRG nanocomposites exhibited a viscous behavior of up to 3 wt. %, but showed a solid-like behavior at 5 wt. %. The addition of TRG into PP/EVA-g-MA blend up to 3 wt. % enhanced the tensile strength and modulus of PP/EVA-g-MA blend, while not adversely affecting its impact strength. PP/EVA-g-MA/TRG nanocomposites exhibited higher electrical and thermal conductivities compared to PP or PP/EVA-g-MA blends.

Keywords:

Graphene,

polypropylene,

toughness,

stiffness,

conductivity.

2


nanocomposites,

thermal

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1. Introduction Carbon-based nanomaterials such as carbon black, carbon nanotubes, carbon nanofibers, and graphene have been used as nanofillers to create conductive polymers.1-3 Among the carbonbased nanomaterials, graphene has been recognized as a promising alternative to others due to its superior mechanical, thermal, and electrical properties along with high aspect ratio.4 Graphene is composed of sp2-hybridized carbon atoms with unique structural properties including large surface area, high stiffness, efficient charge carrier mobility, and excellent thermal conductivity.5-7 However, the physical properties of polymer/graphene nanocomposites highly depend on the dispersion of graphene.6,8 The polarity of polymer, the nature of graphene and dispersion methods are the key factors for the better dispersion of graphene in the polymer matrix. The dispersion of graphene is quite challenging in non-polar polymers like polyolefins due to the mismatch of polarity.8 Polypropylene (PP) is widely used because of its outstanding physical and mechanical properties, ease of processability, thermal stability, low cost and recyclability.9-12 PP/graphene nanocomposites have been fabricated by melt blending,13,

14

in situ polymerization,15,

16

and

solution blending.17-19 Most of the studies revealed that the solution blending method provides good dispersion of graphene in the polymer matrix without sacrificing the electrical properties.18, 19

The uniform dispersion of graphene into PP matrix has been achieved by (i) covalent

interaction using surface-functionalized graphene or graphene oxide (GO)

20, 21

(ii) non-covalent

interaction via compatibilizer/elastomers.22-25 Yun et al developed alkylated GO/PP nanocomposites in which the alkylated groups improved the interfacial interaction of graphene and PP, thereby increasing the Young's modulus of PP by more than 70% with 0.1 wt. %.19 Rhu et al prepared amine-functionalized GO and dispersed it in PP in the presence of PP–grafted3



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maleic anhydride (PP-g-MA). They found that the addition of 2 wt. % modified GO improved the modulus of PP by about 35%.26 Cao et al successfully grafted PP chain on the surface of graphene, thereby improving the compatibility and interfacial interaction of graphene with an isotactic PP matrix.27 Also, the dispersion of graphene/GO was improved by covalent functionalization, the formation of defects on the crystal lattice of graphene deteriorated the electrical properties of nanocomposites.28 Non-covalent interactions like CH-π or π-π interactions could be an alternative approach to promoting the interfacial interaction without loss of electrical properties.29,

30

Vasileiou et al

developed polyethylene/graphene nanocomposites through non-covalent compatibilization with improved graphene dispersion.31 Generally, maleic anhydride (MA) grafted copolymers have been used as the compatibilizer for polyolefin, which significantly improves the interfacial adhesion.32 Schniepp et al reported that MA acted as a polarity bridge and enhanced the dispersion of graphene in polyethylene.33 But still, only limited studies have been conducted on PP/elastomer/graphene

nanocomposites

through

non-covalent

interaction.23-25

Parameswaranpillai et al developed PP/styrene ethylene butylene styrene block copolymer (SEBS)/graphene nanocomposite and found that the elastomer layered over on the graphene sheets and thus improved the interaction between the graphene and PP matrix.25 In rubbertoughened polymer/conductive filler nanocomposites, the location of conductive fillers played a crucial role in improving both conductivity and toughness.34, 35 From the best of our knowledge, no reports are available in PP/EVA-g-MA/graphene nanocomposites. EVA-g-MA has been chosen as the compatibilizer in the present work, which significantly improves the interfacial interaction and dispersion of graphene in the PP matrix. Herein, we studied the effect of TRG on the mechanical, thermal, electrical, rheological and morphological properties of PP/EVA-g-MA 4


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blend. The phase morphology and the localization of TRG in the nanocomposites have been studied and the results were correlated with electrical and thermal conductivities of the nanocomposites.

2. Experimental 2.1. Materials PP homopolymer (HD915CF) was obtained from Abu Dhabi Polymers Company Limited (Borouge), UAE with a melt flow rate of 8 g/10 min (230 °C/2.16 kg) and a density of 0.90-0.91 g/cm³. EVA-g-MA (Fusabond C250) with a melt flow rate of 1.4 g/10 min (190 °C/2.16 kg) and a density of 0.962 g/cm³ was purchased from DuPont, USA. 2.2. Preparation of TRG GO was prepared by liquid phase oxidation of graphite using improved Tour’s method.36 Then TRG was obtained by rapid thermal exfoliation of GO at 1000 °C for 30 s under nitrogen environment in a tube furnace (Model 21100 Barnstead thermolyne). Concurrent thermal exfoliation and reduction of oxygen-containing groups such as hydroxyl, epoxy, carbonyl and carboxyl8 in GO generated CO, CO2 and the small amount of steam produced a highly mesoporous structure of TRG with large surface area (385 m2/g).37 The BET isotherm of TRG exhibited a type IV isotherm with well-defined hysteresis loop which indicates mesoporous nature of the material (Figure S1). Also, as-synthesized TRG showing C/O ratio of 6.8 which was measured by X-ray Photo electron spectroscopy (XPS) analysis (Figure S2).

5



2.3. Preparation of PP/EVA-g-MA/TRG nanocomposites PP/EVA-g-MA/TRG nanocomposites were prepared by solution mixing method using xylene as the solvent. Initially, 100 mg of TRG (1 wt.%) was dispersed in 400 mL of xylene for 2 h at room temperature using pulse sonicator. It was then placed in an ultra-sonicator for complete dispersion of graphene sheets. Subsequently, desired amount of PP (8 g) (80 wt. %) and EVA-gMA (2 g) (20wt. %) were added into the TRG dispersion. The mixture was vigorously stirred (900 rpm) at 130 ˚C with a refluxing condenser for 2 h. The solvent was removed at 100˚C for 24 h using vacuum oven. The dried nanocomposite was named as PP/EVA-g-MA/1wt.%TRG. The nanocomposites with 3 and 5 wt. % TRG were prepared using the same procedure and the nanocomposites were termed as PP/EVA-g-MA/3 wt. %TRG and PP/EVA-g-MA/5 wt. %TRG respectively. Dumbbell, rectangular bar and disc-shaped specimens for mechanical and rheological analysis were molded using mini injection molding machine (HAAKE MiniJet PRO, Thermo scientific) at a cylinder temperature of 180 ⁰C, mold temperature of 125 ⁰C, along with an injection pressure of 430 bar for 10 s and post pressure of 500 bar for 6 s. 2.4. Characterization Differential scanning calorimetry (DSC) analysis of pure PP, EVA-g-MA, PP/EVA-g-MA blend and PP/EVA-g-MA/TRG nanocomposites was studied using Discovery DSC from TA Instruments in nitrogen atmosphere. The melting and crystallization behaviors and percentage crystallinity were determined by scanning ~5 mg of the sample from -60 to 200 ˚C and then 200 to 25 ˚C at a rate of 10 ˚C/min. The second heating and cooling cycles were used for the analysis. The thermal degradation behavior of pure PP, blend, and the composites was analyzed using

6


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thermogravimetric analysis (TGA). ~5 mg of the sample was heated from 25 to 700 ˚C at a rate of 10 ˚C/min on the Discovery TGA from TA Instruments under the nitrogen atmosphere. The tensile analysis was carried out using a universal testing machine Instron 3345 at ambient temperature according to ASTM D638. The dumbbell-shaped test specimens were used for the test with a loading rate of 10 mm/min. The results represented an average of five measurements. Resil Impactor of Ceast with hammer energy of 4 J and speed 3.46 m/s was used to measure the un-notched Izod impact strength of the PP/EVA-g-MA/TRG nanocomposites at room temperature (ASTM D256). The rectangular bar-shaped specimens were used and an average of five measurements is reported. Wide angle X-ray diffraction analysis of the PP/EVA-g-MA/TRG nanocomposites was performed on a PANalytical Powder Diffractometer (X’Pert PRO) (45 kV, 40 mA) with Cu-Kα radiation (wavelength (λ) = 1.5406 A°). The X-ray diffraction data was collected using 2θ range from 5 to 60° with a step width of 0.0170°/s. The inter-planar distances of diffraction peaks were measured using the Bragg’s relationship, d = λ/ (2sinθmax), where λ is the wavelength of X-ray (1.5406 Å). The melt rheological properties such as storage modulus (Gꞌ), loss modulus (Gꞌꞌ), and complex viscosity (η*) as a function of angular frequency (ω) were analyzed using AR 2000ex shear Rheometer from TA Instruments (ASTM D4440). Injection molded disc-shaped samples of 25 mm diameter and 1.5 mm thickness were used and the analysis was carried out at 180 °C in parallel plate geometry with a geometric gap of 1.4 mm. Dynamic frequency scans were performed from 0.1 to 100 rad/s at 2 % strain.

7



Laser flash method using Netzsch LFA 447 was employed to measure the thermal conductivity of the samples at varying temperatures (25, 50, 75 and 100 °C). The thermal conductivity was measured according to ASTM E1461, using the measured heat capacity and thermal diffusivity, with separately entered density data. The disc-shaped samples of 12 mm diameter and 2 mm thickness were used for the analysis and Vespel was used as the standard. The electrical conductivity of the nanocomposite was measured using two-probe method (Keithley 2611B source meter) in voltage sweep mode from -20 to 20 V with intervals of 1 V. Conductive copper electrode (Copper Foil Tape 1181, 3M) was attached on either side of the compression-molded samples. The current was recorded by a manual probe station. The slope of the current-voltage curve was then converted to electrical conductivity. The microstructure of the un-notched impact fractured surface of the PP/EVA-g-MA/TRG nanocomposites was analyzed using scanning electron microscope (SEM) (FEI Quanta, FEG250, USA) at accelerating voltages of 10-20 kV. Before scanning, the surface of the samples was sputter coated with carbon. Transmission electron microscopy images were obtained on FEI Technai T12 microscope at an accelerating voltage of 120 kV. Nanocomposites blocks were embedded in epoxy and cured overnight at 60 °C. The samples were cryo-microtomed with a diamond knife at -160 °C into ~ 80 nm sections using a Leica EM UC6 ultra microtome. The sections were then placed on 300-mesh copper grids.

8


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3. Results and Discussion 3.1. Phase morphology and dispersion of TRG in PP/EVA-g-MA blend

Figure 1: TEM images of a) PP/EVA-g-MA blend, b) PP/EVA-g-MA/0.5wt.%TRG, c-d) PP/EVA-g-MA/1 wt. %TRG, e-f) PP/EVA-g-MA/3 wt. %TRG and g-h) PP/EVA-g-MA/5 wt.%TRG nanocomposites 9



The phase morphology and dispersion of TRG in the PP/EVA-g-MA blend were observed using TEM analysis. As PP and EVA are immiscible, the morphology of PP/EVA blend is known to be unstable.38 MA-grafted resins are often used as compatibilizers to decrease the interfacial tension of immiscible polymer blends.39 Goodarzi et al studied the morphology of PP/EVA/clay nanocomposites and found that the incorporation of PP-g-MA reduced the dispersed droplets size of EVA phase from 1.19 to 0.69 µm2 in the PP/EVA (75:25) blend.40 Figure.1a shows the TEM image of PP/EVA-g-MA blend without TRG sheets. The EVA-g-MA phase appeared as spherical droplets and was uniformly dispersed in the PP phase with an average domain size (A) of about 0.43 µm^2, which is considerably smaller as compared to the dispersed droplet size of EVA in PP/EVA blend reported previously.40 Also, the equivalent diameter of the of droplet size is 0.74µm, which has calculated from the average domain size of the dispersed phase (A) using the following equation, 41 Equivalent diameter (d) = (4A/π) ^0.5………………………………. (1) Figure1b and Figure.S5a-b show the TEM image of PP/EVA-g-MA/0.5wt.%TRG. Most TRG sheets were encapsulated by EVA-g-MA phase and a few sheets were located at the interface of PP/EVA-g-MA blend, which is similar to a morphology of PLA/EVA/functionalized GO composites reported previously.42 On the other hand, in PP/EVA-g-MA/1wt.%TRG (Figure1c-d & Figure S5c-d) and PP/EVA-g-MA/3wt.%TRG (Figure 1e-f & Figure S5e-f), the dispersed EVA-g-MA phase started to be more continuous in the PP matrix and the TRG sheets were preferentially dispersed in EVA-g-MA phase. At higher TRG content (PP/EVA-gMA/5wt.%TRG), the size of co-continuous phases became small so that TRG seemed to lose its preference to the EVA-g-MA phase (Figure1g-h & Figure S5g-h). This is due to the higher content of TRG, which might increase the viscosity of EVA-g-MA phase and allow to saturating 10


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the dispersed EVA-g-MA phase. Therefore, the TRG sheets were evenly distributed and formed a percolating network throughout the matrix. In addition, the localization of TRG in EVA-g-MA phase can be explained by wetting coefficient at 180 oC (the temperature of cylinder in the injection molding machine) from surface energy of each material as listed in Table 1. Table 1. Surface energy (γ), its dispersive (γd) and polar component (γp) of graphene, polyethylene (PE), polyvinyl acetate (PVAc), ethylene vinyl acetate copolymer (EVA), and polypropylene (PP) at 180 oC (γ, γd, and γp in mN/m) Material

γp/γ

γ

γd

γp

Graphene

0.104

32.1

28.8[43]

3.3

PE

0[44]

26.5[44]

26.5

0

PVAc

0.329[44]

25.9[44]

17.4

8.5

EVA*

0.011~0.057

26.4~26.5

24.9~26.2

0.3~1.5

PP

0.020[44]

20.8[44]

20.4

0.4

*Provided that vinyl acetate content ranges from 3.5~17.8 mol %

The surface tension of graphene was estimated as suggested by Bai et al 43. γd of graphene at 180 o

C is 28.80 mN/m. The ratio of dispersive component and polar component (γd/γp) of the surface

energy of graphene is linearly proportional to its C/O ratio. Then, γd/γp is calculated to be 0.104 with the C/O ratio of 6.8, thereby resulting in the polarity (γp/γ) of 0.104. The surface energy and its dispersive and polar component of EVA was estimated by the following linear relation (2) 44, 45 ………………………………………. (2) 11



where γ is the surface energy and x is the mole fraction (the subscripts PE and PVAc refer to the ethylene and vinyl acetate component, respectively). The typical weight fraction of vinyl acetate in commercial EVA copolymers ranges from 10 to 40 wt. %, which correspond to 3.5 and 17.8 mol %, respectively. The interfacial energy between materials was calculated by the following harmonic-mean equation (3) and presented in Table 2.

………………………………………………….. (3)

where γij is the interfacial energy between two materials, γi and γi are the surface energy of each component, the superscripts d and p refer to the dispersive and polar components of the surface energy, respectively. Table 2. Interfacial energy (γij) between materials at 180 oC (in mN/m) Pairs

γij

Note

EVA/PP

0.68~1.07

VA content (3.5 ~ 17.8 mol %)

EVA/graphene

0.97~2.67

VA content (3.5 ~ 17.8 mol %)

PP/graphene

3.72

Applying the interfacial energy to the following equation (4) gives the wetting coefficient of the nanocomposite.

………………………………………………………. (4)

12


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where γPP/G or γEVA/G are the interfacial energy between graphene and PP or EVA, and γEVA/PP is the interfacial energy between EVA and PP. When ωa > 1 or ωa < -1, graphene is localized in the EVA phase or the PP phase, respectively. When -1 < ωa < 1, graphene is localized at the interface of PP/EVA blend.

3

Wetting Coeffiecient

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


2 Localized in EVA

1 0 Localized at the interface

-1 -2 Localized in PP

-3

0

5 10 15 20 Vinyl acetate content (mol%)

Figure 2: Wetting coefficient as a function of vinyl acetate content. As shown in Figure 2, the wetting coefficient is higher than 1, regardless of the vinyl acetate content. The effect of maleic anhydride on the surface tension of EVA was not taken into account because the mole fraction of maleic anhydride is low. Therefore, we conclude that TRG was preferentially localized in the EVA-g-MA phase, which agrees well with the morphology of nanocomposites.

13



3.2. Rheological studies of PP/EVA-g-MA/TRG nanocomposites

Complex viscosity, η∗ (Pa.s)

106

Pure PP

Storage modulus, G' (Pa)

Pure EVA-g-MA PP+EVA-MA PP+EVA-MA+1wt.% TRG

105

PP+EVA-MA+3wt.% TRG PP+EVA-MA+5wt.% TRG

104

103 0.1

1 10 100 Angular frequency, ω (rad/s)

105

104

103

PP+EVA-MA PP+EVA-MA+1wt.% TRG PP+EVA-MA+3wt.% TRG

10 0.1

104

G',G" (Pa)

Loss modulus, G" (Pa)

PP+EVA-MA+5wt.% TRG

2

105

104

Pure PP Pure EVA-g-MA

1 10 100 Angular frequency, ω (rad/s) G'@0.1Hz G"@0.1Hz

103

Pure PP Pure EVA-g-MA

10

3

PP+EVA-MA PP+EVA-MA+1wt.% TRG PP+EVA-MA+3wt.% TRG

5555

4444

102

3333

1 10 100 Angular frequency, ω (rad/s)

2222

0.1

1111

PP+EVA-MA+5wt.% TRG

0000

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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TRG content (wt.%)

Figure 3: Rheological analysis of PP/EVA-g-MA/TRG nanocomposites; a) Log-log plot of complex viscosity with function of angular frequency, b) Log-log plot of storage modulus with function of angular frequency, c) Log-log plot of loss modulus with function of angular frequency and d) Gꞌ and G′′ vs TRG content at 0.1 Hz

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When three-dimensional, percolating network structure is achieved by incorporated fillers, it restricts the long-range molecular motion of polymer matrix so that the nanocomposites display the transition from liquid-like to viscoelastic solid-like behavior.46,

47

This percolation

phenomenon can be identified by a sudden change in the storage modulus in the low frequency region.

48, 49

In this study, the formation of network structure of TRG in the blend was

investigated using melt rheological analysis. Frequency sweep tests of complex viscosity, storage modulus and loss modulus of PP/EVA-g-MA/TRG nanocomposites were carried out using a shear rheometer at 180°C. Figure 3a shows the log-log plot of complex viscosity (η*) as a function of angular frequency (ω) of pure PP, PP/EVA-g-MA blend and PP/EVA-g-MA/TRG nanocomposites. Pure PP, EVA-g-MA, PP/EVA-g-MA blend and nanocomposites were exhibited non-Newtonian shear thinning behavior. Figure 3b and 3c show the variation of storage modulus (Gꞌ) and loss modulus (Gꞌꞌ) of pure pp, EVA-g-MA, PP/EVA-g-MA blend and PP/EVA-g-MA/TRG nanocomposites with the function of ω. Both the Gꞌ and Gꞌꞌ values increased with increase in TRG content up to 3 wt. % because of the interaction between the TRG and PP/EVA-g-MA blend. Figure 3d represents the Gꞌ and Gꞌꞌ vs the TRG content at a frequency of 0.1 Hz. The incorporation of TRG into the PP/EVA-g-MA blend exhibited a viscous behavior (G′ < G′′) up to the TRG content of 3 wt. %. On the other hand, the elastic behavior was dominant (G′ > G′′) at the TRG content of 5 wt. %. The crossover of G′ and G′′ occurred between 3 and 5 wt. % due to sudden increase in G′, which is referred as percolation threshold.

15



3.3. Electrical conductivity of PP/EVA-g-TRG nanocomposites

Log (DC conductivity) (S/cm)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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-8 PP/EVA-g-MA/TRG nanocomposites

-9 -10 -11 -12 -13 -14

0

1 2 3 4 TRG content (wt.%)

5

Figure 4: DC electrical conductivity of PP/EVA-g-MA/TRG nanocomposites The incorporation of graphene into the polymer matrix could enhance the electrical conductivity of the resultant nanocomposites. The electrical conduction in the nanocomposites can be explained by either “contact” or “tunneling” mechanism.50 In the contact mechanism, the conductive fillers are physically in contact with each other and form a conducting network. On the other hand, in the tunneling mechanism, the mobility of electron has tunneled in between the neighboring conductive fillers which are separated by the polymeric layers.50 In most cases, conductive filler reinforced polymer nanocomposites follow the tunneling mechanism. Figure 4 shows the electrical conductivity of the PP/EVA-g-MA/TRG nanocomposites. The conductivity gradually increased up to 3 wt. % TRG and suddenly increased at 5 wt. %. At this point, the contact mechanism was dominant over by the tunneling mechanism, because individual TRG sheets are interconnected. As predicted from melt rheological analysis, the percolation threshold was between 3 and 5 wt. %. The electrical properties of nanocomposites depend on not only the content of conductive fillers but also the phase morphology. TEM images support that TRG 16


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sheets were trapped in EVA-g-MA phase at TRG contents up to 3 wt. % (Figure 1b-f). On the other hand, the higher content of TRG (5 wt.%) was not preferentially localized in EVA-g-MA phase but evenly distributed through the whole matrix, so that they could be in contact with each other to form a percolating network which evidenced by high electrical conductivity.

a)

b)

Thermal conductivity (W/m.K)

3.4. Thermal conductivity 0.32

Thermal conductivity (W/m.K)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


0.30

Pure PP PP/EVA-g-MA PP/EVA-g-MA/1wt.% TRG PP/EVA-g-MA/3wt.% TRG PP/EVA-g-MA/5wt.% TRG

0.28 0.24 0.20 0.16 25

50 75 Temperature (oC)

100

PP/EVA-g-MA/TRG nanocomposites

0.28 0.26 0.24 0.22 0.20 0


5

Figure 5: a) Variation of thermal conductivity of PP, PP/EVA-g-MA blend, and PP/EVA-gMA/TRG nanocomposites with temperature and b) Variation of thermal conductivity of PP/EVA-g-MA/TRG nanocomposites with TRG content at 25oC.

17



Thermal conductivity of polymer nanocomposites is strongly influenced by the nature of fillers, the structure of the fillers in the matrix, loading amount, dispersion and thermal resistance at the interface between fillers and the matrix. Due to its high surface area and sheet morphology, graphene improves thermal conductivity of polymer by reducing the barriers to phonon transport.51 It is also worth noting that graphene suspended in polymer possesses excellent thermal conductivity of about 5000 W/m K, whereas the thermal conductivity of PP is as low as 0.2 W/m K.52 The thermal conductivity of pure PP, PP/EVA-g-MA blend and PP/EVA-gMA/TRG nanocomposites as a function of temperature is presented in Figure 5a. In addition, the variations in the thermal conductivity of nanocomposites with TRG loading at room temperature are shown in Figure 5b. PP shows a thermal conductivity of about 0.203 W/m K which is in good agreement with a previous study.52 PP/EVA-g-MA blend shows the thermal conductivity similar to PP. Subsequent incorporation of TRG into PP/EVA-g-MA blend improved thermal conductivity and it reached ~ 0.30 W/m K with 5 wt. % TRG. The interconnected network consisting of thermally conductive fillers reduces the scattering of phonon transfer and improves the diffusion of phonon transfer in the resultant nanocomposite. However, even below the percolation threshold (< 5 wt. %), the thermal conductivity was gradually improved with small amounts of TRG. These results are consistent with other graphene filled polymer nanocomposite.51, 52 Figure 5 a shows the temperature dependence of the thermal conductivity of the PP/EVA-g-MA/TRG nanocomposites. From the figure, we observed that a small decrease in thermal conductivity with the increase in temperature. In general, the thermal conductivity of semi- crystalline and amorphous polymers has been varied with increase in temperature.53 Phonons are usually considered to be thermal carriers in polymers because there is a mere free electron. Li et al stated that the polymer contacted with the surface of the heat source possessed a 18


Page 18 of 43

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heat transfer in between the molecular chain which might alter the perfection of the crystal structure. The heat transfer could result a disordered vibration and rotation of atoms in the polymer chain, which significantly reduces the thermal conductivity of the polymer with the increase in temperature.54 A similar effect was also observed in the PP/EVA-g-MA/TRG nanocomposites.

3.5. Mechanical properties The tensile properties of PP, PP/EVA-g-MA blend, and PP/EVA-g-MA/TRG nanocomposites are summarized in Table 3. The PP/EVA-g-MA blend possessed slightly higher tensile modulus as compared to PP (~ 13 %), which is contradictory to the expected decrease based on elastomer toughening mechanism. It should be noted that the stiffness of polymer matrix is also influenced by its crystallinity. The incorporation of EVA-g-MA increased the crystallinity of PP (Table 3), mainly attributed to the nucleating ability of EVA-g-MA copolymer. Thus, the reduction in tensile modulus by elastomer was offset by the increase in PP crystallinity, thereby leading to a marginal increase as consistent with earlier reported results.55 The EVA-g-MA phase weakened the load-bearing area of the PP matrix, thus deteriorated the tensile strength of PP. On the other hand, the intrinsic chain flexibility of EVA-g-MA increased the elongation at break of PP.55 The tensile modulus of PP/EVA-g-MA increased with TRG content and reached a highest value of 1430 MPa for PP/EVA-g-MA/3wt.%TRG, which is 22% increment from pure PP. It was previously observed from TEM images that TRG sheets were localized in the EVA-g-MA phase only. Highly stiff TRG sheets could not only restrict the chain mobility of EVA-g-MA but also sustain effective transfer mechanism in EVA-g-MA phase. As a result, PP/EVA-g-MA/TRG 19



Page 20 of 43

nanocomposites exhibit enhanced tensile modulus and strength by incorporating TRG up to 3 wt. %. This is in good agreement with results from exfoliated graphene/PP nanocomposites.54 However, at a higher TRG loading (5 wt. %), TRG sheets were stacked with each other to form a percolating network or agglomerates in the PP matrix, adversely affecting the tensile strength and modulus.56 In addition, the increase in TRG content hindered the molecular elongation of EVA-g-MA, thus decreased the elongation at break of the nanocomposites.57 It is also seen that the addition of TRG might reduce the droplet size of the EVA phase and the “sea-island” morphology of the blend becomes more co-continuous (Fig1a-h). The lesser the droplet of EVA phase promotes TRG distribution more in PP phase, thereby yielding lower elongation at break value. Table 3: Mechanical properties of PP, PP/EVA-g-MA blend, and PP/EVA-g-MA/TRG nanocomposites Sample

Impact strengtha

Tensile

Tensile

Extension at

(kJ/m2)

strengthb

modulusc

breakd

(MPa)

(MPa)

(%)

PP

7

39

1011

24

PP/EVA-g-MA

42

30

1143

43

PP/EVA-g-MA/1wt.%TRG

41

33

1315

20


41

38

1412

19


31

37

1030

15

a

Maximum relative probable error 2%; b Maximum relative probable error 2%;

c

Maximum relative probable error 5%; d Maximum relative probable error 5%. 20


Page 21 of 43 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


The un-notched Izod impact strength of pure PP, PP/EVA-g-MA blend and PP/EVA-g-MA/TRG nanocomposites are presented in Table 3. PP/EVA-g-MA blend possessed 6 folds higher impact strength as compared to pure PP. The EVA-g-MA phase might induce the formation of microvoids in the PP/EVA-g-MA blend which prevented the crack growth (Figure 6a). The EVA-g-MA phase in the nanocomposites absorbed the sudden force which initiated the crazing and produced the shear yielding in the surroundings. The formation of cavitation and de-bonding at the interface of PP and EVA-g-MA could lead to higher plastic deformation and show higher toughness in the PP/EVA-g-MA blend.58, 59 It was found that the addition of TRG did not alter the impact strength of PP/EVA-g-MA blend and possessed an impact strength almost as same as that of the blend (42 kJ/m2) up to a content of 3 wt. %. It is well known that graphene dimensions are near several tens of micrometers and the thickness is in angstrom level.60 The influence of 1-3 wt. % of TRG had no detrimental effects on the formation of EVA-g-MA induced microvoids in the PP blend nanocomposite system and favorable dissipation of impact energy. Therefore, the impact strength values of 1-3 wt.% TRG filled nanocomposites exhibited good consistency with the impact strength of PP blend with 20 wt.% EVA-g-MA (Table 3).58,

61

Although, a large

amount of TRG (5 wt. %) decreased the impact strength of PP/EVA-g-MA to 31 kJ/m2, it was still higher than that of pure PP. This was probably due to the agglomeration of TRG sheets, which initiated the crack propagation resulting in a lower impact strength.

21



Page 22 of 43

3.6. Fractography SEM analysis used to examine the morphological features as well as the fracture behavior of PP/EVA-g-MA blend and PP/EVA-g-MA/TRG nanocomposites. The fractured surfaces of PP/EVA-g-MA

blend,

PP/EVA-g-MA/1wt.%TRG,

and


nanocomposites are represented in Figure 6a-c. The fracture surface of the blend shows scrubber like structure with many spherical microvoids and EVA-g-MA particles. The dispersed EVA-gMA phases served as an efficient stress concentrator and produced both crazing and shear yielding in the PP matrix, thus producing more number of spherical microvoids.62 The smaller particle size (0.43 µm2) (Figure 1a) and the uniform dispersion of the EVA-g-MA phase in the blend allows to dissipate the energy in a larger volume. Therefore, the formation of microvoids in the PP/EVA-g-MA blend assisted the dissipation of the sudden impact force in a ductile manner (Figure 6a). The fractograph of 1 and 3 wt. %TRG filled PP/EVA-g-MA blend nanocomposites reveals the existence of rough surface behavior as shown in Figure 6b&C. The addition of TRG into PP/EVA-g-MA blend did not show any significant variation in the impact strength of the resultant nanocomposite up to the content of 3wt. %. Some TRG sheets located on the interface could bridge over the crack concealment which minimizes the crack propagation.63 However, a major crack on the fractured material was observed in the fractography of PP/EVA-g-MA/5 wt. %TRG (Figure 6d). The percolating network in the nanocomposite at high TRG content could release stress from the crack tip, thereby inducing the crack propagation in the system and resulting in a decrease in impact strength.60

22


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a)

Spherical voids

b) TRG

Spherical void

c) TRG

Spherical void

d) TRG

Crack

Figure 6: SEM fractograph of MA/1wt.%TRG,

c)

a) PP/EVA-g-MA blend (80:20), b) PP/EVA-g-


and

nanocomposites.

23


d)



3.7. Thermal properties

Heat flow (mg/mw) Exo →

←

P P+EVA -g -MA+ 5w t.% T RG

Heat flow(mg/mw) Endo

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 24 of 43

PP+ EVA -MA+ 3w t.% T RG PP+ EVA-MA +1 w t.% TR G PP+ EVA -g- MA Pu r e PP

PP+E VA-g -MA +5 wt .% T R G PP+ EVA-g -M A+ 3w t.% T RG PP+ EVA-g -M A +1 w t.% T RG PP+ EVA-g -M A

Pu re PP

Pu re EVA-g -MA Pu re EVA-g -MA

50 10 0 o Tem pera tur e ( C)

40

150

60

80 10 0 12 0 o Tem pera tur e ( C)

1 40

Figure 7: DSC plots of PP, EVA-g-MA, PP/EVA-g-MA blend, and PP/EVA-g-MA/TRG nanocomposites The effect of TRG loading on the % crystallinity, melting and crystallization of PP/EVA-g-MA blend is summarized in Table 4. Second heating and cooling curves of composites are also represented in Figure 7. The melting and crystallization temperatures of pure PP were 169 and 128 °C, respectively. While weak melting and crystallization peaks from EVA-g-MA were not strong enough to be seen clearly, the melting and crystallization peaks of PP were present in PP/EVA-g-MA blend and PP/EVA-g-MA/TRG nanocomposites. This indicates that the addition of EVA-g-MA or TRG did not disturb the crystal structure of PP. The enthalpy of fusion and crystallization of both PP/EVA-g-MA blend and PP/EVA-g-MA/TRG nanocomposites were lower than those of pure PP. The ∆Hf and ∆Hc decreased from 91 and 99 J/g of pure PP to 77 and 73 J/g of PP/EVA-g-MA/5wt.%TRG nanocomposite, respectively. Percentage crystallinity (Xc)

24


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of pure PP, PP/EVA-g-MA blend, and PP/EVA-g-MA/TRG nanocomposites was measured by applying the below equation (5): …………………………. (5) where ∆H100 is the enthalpy of melting for 100 % crystalline isotactic PP (207.1 J/ g,), 26, 64 ∆H is the melt enthalpy of the samples and w is the fraction of PP in the blend or composite. The crystallinity of PP in PP/EVA-g-MA blend increased to 49% from 44% of pure PP due to the nucleating effect of EVA-g-MA. The higher content of TRG reduces the droplet size of EVA-gMA phase and possessed a random distribution. Even TRG already presented in PP phase at 5 wt. %, but it still didn’t promote the nucleation of PP due to some agglomeration of the TRG. 65

Table 4: DSC analysis data of PP/EVA-g-MA/TRG nanocomposites Sample

Tc (⁰C) ∆Hc (J/g)

Tm(⁰C)

∆Hf (J/g)

Xc (%)

PP

128

99

169

91

44

PP/EVA-g-MA

128

81

168

81

49


127

80

168

81

50


126

76

168

80

50


126

73

167

77

50

25



100 Weight loss (%)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 26 of 43

Pure PP Pure EVA-g-MA PP+EVA-g-MA PP+ EVA-g-MA+ 1 wt.%TRG PP+ EVA-g-MA+ 3 wt.%TRG PP+ EVA-g-MA+ 5 wt.%TRG

80 60 40 20 0 300

400 500 600 o Temperature ( C)

700

Figure 8: TGA graph of PP, EVA-g-MA, PP/EVA-g-MA blend, and PP/EVA-g-MA/TRG nanocomposites

Table 5: TGA data of PP, EVA-g-MA, PP/EVA-g-MA blend, and PP/EVA-g-MA/TRG nanocomposites Sample

T10% (⁰C)

T50% (⁰C)

Char yield at 700oC (%)

PP

404

448

0

EVA-g-MA

351

458

0

PP/EVA-g-MA

428

459

0


431

460

3.8


436

462

5.4


443

470

7.9

26


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Figure 8 shows the TGA thermograms of PP, PP/EVA-g-MA blend, and PP/EVA-g-MA/TRG nanocomposites as a function of temperature under nitrogen atmosphere. The thermal stability (T10% and T50%) and char yield are listed in Table 5. The initial degradation (T10%) of PP/EVA-gMA blend shows a higher value than pure PP and EVA-g-MA. On the other hand, T50% of the PP/EVA-g-MA blend is almost the same as pure EVA-g-MA. Goodarzi et al reported that activation energy of PP degradation was increased by adding EVA (25 wt. %). This improved thermal stability is in agreement with our results with PP/EVA-g-MA blend (80/20 w/w). 66 It should be noted that thermal stability of polymer blends does not always follow the rule of mixtures. For example, Lizymol et al reported that several EVA blends exhibit strong deviations from the rule of mixtures.67 In addition, the thermal stability of nanocomposites was further enhanced by adding more TRG. The nanocomposites exhibited higher thermal stability (T10% and T50%) than those of pure PP, EVA-g-MA and PP/EVA-g-MA blend. The heat transfer from PP to TRG nanosheets were promoted in the nanocomposites. The char yield of the nanocomposites increased with increase in content of TRG. The char yield of composites at 700 °C was 3.8, 5.4 and 7.9%, corresponding to 1, 3 and 5 wt. % TRG, respectively. This indicates that the surface of TRG would absorb the free radicals which were produced from the degradation of PP/EVA-gMA, thereby delaying the molecular breakdown of nanocomposites. This suggests that TRG acted as a thermal shield and thus retarded the thermal degradation during heating.68

3.8. XRD analysis Figure 9 shows the wide-angle XRD patterns of pure PP, PP/EVA-g-MA blend, and PP/EVA-gMA/TRG nanocomposites. Pure PP has seven strong characteristic peaks representing α 27



crystalline phase (110, 040, 130, 111, 041, 160 and 020) at 14.58°, 17.30°, 19.02°, 21.50°, 22.23°, 25.82° and 29.03°, respectively.

PP/EVA-g-MA blend also exhibited similar α-

crystalline peaks of PP matrix with the same angles, but an additional peak was observed at 16.5° with the plane of (300). This indicates that the EVA-g-MA did not alter the crystal lattice of the PP chain and additionally promoted β crystalline phase in the blend, supported by the higher toughness value. Achaby et al observed that the addition of graphene aided to disturb the β-crystal phase conformation of the PP blend matrix.12 However, in the current study, the addition of TRG haven’t disturbed the crystalline planes including the β-crystal phase of the PP/EVA-g-MA blend matrix up to 3 wt. %. This results suggested that the TRG didn‘t disturb the β-crystal phase conformation of the PP due to it mainly located in EVA-g-MA phase at lower content, which is also supported the impact strength of the nanocomposites.

(002)

TRG

Intensity(a.u)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 28 of 43

PP/EVA-g-MA/5 wt.% TRG β (300)

PP/EVA-g-MA/3 wt.% TRG

β (300)

PP/EVA-g-MA/1 wt.% TRG

β (300)

α(110)

α(040)

PP/EVA-g-MA α(130)

Pure PP

α(111) α(131+041) α(060)

10

20 2θ θ (deg)

α(220)

30

Figure 9: XRD analysis of PP, EVA-g-MA, PP/EVA-g-MA blend and PP/EVA-g-MA/TRG nanocomposites 28


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The higher content of TRG into the PP/EVA-g-MA blend matrix induces changes in its crystals conformation, resulting in the complete disappearance of the β-crystal phase and exists only the α-crystalline peaks in the TRG filled nanocomposites, which is similar to the plane of pure PP. Also, the characteristic peaks of diffraction pattern (002) for graphene sheets at 26.5o (d=3.35 A °) was absent in the nanocomposites, indicating that the TRG sheets were well-exfoliated and dispersed in the polymer matrix. Besides, three strong diffraction peaks (110, 040 and 130) in PP/EVA-g-MA/TRG nanocomposites were shifted to lower angles of 14.36°, 17.19° and 18.91°. This could be explained by increased inter-planar distances of diffraction peaks at 110, 040 and 130 lattice planes from 6.07, 5.12 and 4.66 Å to 6.16, 5.15 and 4.69 Å, respectively. This suggests that the polymer chains were penetrated in between the TRG sheets, producing a tactoid morphology, especially in nanocomposites with high TRG content.

4. Conclusions In the present work, we successfully developed electrically and thermally conductive PP/EVA-gMA/TRG nanocomposites with high thermal stability and enhanced mechanical properties. EVA-g-MA was homogenously distributed into the PP matrix and significantly improved impact strength of PP. The incorporation of TRG not only held the impact strength of PP/EVA-g-MA blend up to the content of 3 wt. %, but also increased the tensile modulus of about 40% as compared to pure PP. It was confirmed that TRG sheets were completely exfoliated and localized in EVA-g-MA phase at low contents (< 3 wt. %). On the other hand, they were randomly dispersed through the whole matrix at the content of 5 wt. % because of induced cocontinuous morphology with fine domain sizes. The incorporation of EVA-g-MA increased the 29



crystallinity of PP and the increased crystallinity maintained in PP/EVA-g-MA/TRG nanocomposites. The nanocomposites possessed higher thermal stability due to the efficient heat transfer from PP to TRG. Rheological analysis revealed that complex viscosity and storage modulus of nanocomposites were elevated with the addition of TRG. At the content of 5 wt. %, TRG sheets were distributed both the EVA and PP phase in the nanocomposite, leading to higher thermal and electrical conductivities. In conclusion, these nanocomposites can be used as an advanced engineering thermoplastic composite material in the wide range of applications especially in microelectronic and automobile engineering fields in which high mechanical, electrical, and thermal properties are required.

Supporting Information (SI) This Supporting Information material is available free of charge via the Internet at http://pubs.acs.org/. BET isotherm of TRG (Figure S1); XPS analysis of TRG (Figure S2); SEM image of TRG (Figure S3); Raman spectra of PP, PP/EVA-g-MA, PP/EVA-g-MA/3 wt.%TRG, and TRG sheet (Figure S4a); PP in the range of 750-1500 cm-1 (Figure S4b); PP/EVA-g-MA in the range of 750-1500 cm-1 (Figure S4c); TEM images of (a-b) PP/EVA-g-MA/0.5 wt.%TRG, (c-d) PP/EVA-g-MA/1%TRG, (e-f) PP/EVA-g-MA/3%TRG, and (g-h) PP/EVA-g-MA/5%TRG (Figure S5); TGA graph of PP, EVA-g-MA, PP/EVA-g-MA blend, and PP/EVA-g-MA/TRG nanocomposites in air medium (Figure S6); Band assignment for Raman spectrum of PP (δ: bending, r: rocking, ν: stretching, t: twisting, w: wagging) (Adapted from ref 7-9 in SI) (Table S1; TGA data of PP, EVA-g-MA, PP/EVA-g-MA blend, and PP/EVA-g-MA/TRG nanocomposites in air medium (Table S2) 30


Page 30 of 43

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Authors’ contributions Mr. Anish, Dr. Vengatesan Muthukumaraswamy Ranagraj and Dr. Sung Cik Mun are equally contributed in this work. ORCID Vengatesan Muthukumaraswamy Rangaraj: 0000-0002-2520-729X Notes The authors declare no competing financial interest Acknowledgements Dr. Vengatesan Muthukumaraswamy Rangaraj and Dr. Vikas Mittal sincerely thank the ADNOC Research and Innovation Centre (Project grant LTR14003) and The Petroleum Institute (as a part of KUST) for the financial support. This work was also supported by the Petroleum Institute through its Joint Polymer Processing Research Program with the University of Minnesota. Parts of this work were carried out at the University of Minnesota Characterization Facility, which receives partial support from the NSF through the MRSEC (DMR-1420013), ERC, MRI, and NNIN programs and the CSE through the OVPR program.

31



Page 32 of 43

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List of figures and tables Fig.1: TEM images of a) PP/EVA-g-MA blend, b) PP/EVA-g-MA/0.5 wt.%TRG, c-d) PP/EVAg-MA/1wt.%TRG, e-f) PP/EVA-g-MA/3wt.%TRG and g-h) PP/EVA-g-MA/5wt.%TRG nanocomposites Fig.2: Wetting coefficient as a function of vinyl acetate content. Fig.3: Rheological analysis of PP/EVA-g-MA/TRG nanocomposites; a) Log-log plot of complex viscosity with function of angular frequency, b) Log-log plot of storage modulus with function of angular frequency, c) Log-log plot of loss modulus with function of angular frequency and d) G’and G” vs TRG content at 0.1 Hz Fig.4: DC electrical conductivity of PP/EVA-g-MA/TRG nanocomposites Fig.5: a) Variation of thermal conductivity of PP, PP/EVA-g-MA blend, and PP/EVA-gMA/TRG nanocomposites with temperature and b) Variation of thermal conductivity of PP/EVA-g-MA/TRG nanocomposites with TRG content at room temperature Fig.6: SEM fractographs of

a) PP/EVA-g-MA blend, b) PP/EVA-g-MA/1 wt.%TRG and c)

PP/EVA-g-MA/5 wt.%TRG nanocomposites Fig.7: DSC isotherm of PP, EVA-g-MA, PP/EVA-g-MA blend, and PP/EVA-g-MA/TRG nanocomposites Fig.8: TGA graph of PP, EVA-g-MA, PP/EVA-g-MA blend, and PP/EVA-g-MA/TRG nanocomposites Fig.9: XRD analysis of PP, EVA-g-MA, PP/EVA-g-MA blend and PP/EVA-g-MA/TRG nanocomposites. 41



Table 1: Surface energy (γ), its dispersive (γd) and polar component (γp) of graphene, polyethylene (PE), polyvinyl acetate (PVAc), ethylene vinyl acetate copolymer (EVA), and polypropylene (PP) at 180 oC (γ, γd, and γp in mN/m). Table 2: Interfacial energy (γij) between materials at 180 oC (in mN/m) Table 3: Mechanical properties of PP, PP/EVA-g-MA blend, and PP/EVA-g-MA/TRG nanocomposites Table 4: DSC analysis data of PP, PP/EVA-g-MA blend, and PP/EVA-g-MA/TRG nanocomposites Table 5: TGA data of PP, EVA-g-MA, PP/EVA-g-MA blend, and PP/EVA-g-MA/TRG nanocomposites.

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Table of Content

L o g (D C c o n d u c tiv ity ) (S /c m )

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


-8 PP/EVA-g-MA/TRG nanocomposites

-9 -10 -11 -12 -13 -14

0


5

43


Maleic Anhydride Grafted

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