Electrical Conductivity Behavior of Biopolymer Composites

2 Electrical Conductivity Behavior of Biopolymer Composites H.S. Abdo*,**, A.A. Elzatahry†, H.F. Alharbi‡, K.A. Khalil**,‡ *CENTER O F EXCEL L ENCE F O R R E S E A R C H I N E N G I N E E R I N G MAT E R I A L S ( C E R E M) , ADVANCED M ANUFACTURI NG I N S T I T U T E , K I N G S A U D U N I V E R S I T Y, R I YA D H , S A U D I ARABI A; **FACULTY O F ENERGY EN G I N E E R I N G , A S WA N U N I V E R S I T Y, A S WA N , E G Y P T; † CE NTE R F O R ADVANCED M ATERI AL S , Q ATA R U N I V E R S I T Y, D O H A , Q ATA R ; ‡ ME C H A N I C A L ENGI NEERI NG DEPARTM ENT, K I N G S A U D U N I V E R S I T Y, R I YA D H , S A U D I A R A B I A

1 Introduction Biopolymer matrix mixed with different nano or microparticles of conductive metal is of interest for different scientific fields [1–9]. Electronic properties of these composites are approximately near the characteristics of metals, while the processing methods and mechanical characteristics are exactly same as nonconductive polymers [2,9]. Experimentally, it was reported that the size of particles and their shape are the most parameters affect the electrical conductivity of such polymers [9–11]. Silver (Ag) considers the most thermal and electrical conductivities a ​ mong all metals [12] and silver nanoparticles have used in many purposes in antimicrobials, conductive inks, and electronics [13]. The conductivity of metal nanoparticles is similar to that of the metal powder, but the dispersion of such nanoparticles in an insulating polymer matrix prevents the conductive network formation in the nanostructured, which is substantial for increasing the electrical properties in a bulk material [14]. Today there are over 25 conductive polymer systems [15]. For a list of conductive polymers, see Table 2.1.

2 Poly(ε-Caprolactone) Polymer 2.1  Pure PCL Polymer Polycaprolactone is a bioresorbable semicrystalline poly(α-hydroxyester). It degrades slowly by hydrolysis due to its high crystallinity and hydrophobic nature [16,17]. It was used in many fields, such as implantable biomaterials, biodegradable materials, and microparticles for drug delivery [18,19]. The new descent of biomaterials is going to be involved and active, therefore competent at smooth linkage with encirclement tissues. Particularly, it is needed for materials, which can integrate stimulating cues. As an illustration, stimulation Biopolymer Composites in Electronics. http://dx.doi.org/10.1016/B978-0-12-809261-3.00002-4 Copyright © 2017 Elsevier Inc. All rights reserved.

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Table 2.1  A List of Conductive Polymers and Their Abbreviations [15] No

Polymer

Abbreviation

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18

Polycaprolactone Polypyrrole Polyaniline Poly(3,4-ethylenedioxythiophene) Polythiophene Polyacetylene Poly(2,5-thienylenevinylene) Poly(3-alkylthiophene) Poly(p-phenylenevinylene) Poly(p-phenylene-terephthalamide) Polythiophene-vinylene Poly(isothianaphthene) Poly(a-naphthylamine) Polyazulene Polyfuran Polyisoprene Polybutadiene Poly(3-octylthiophnene-3-methylthiophene)

PCL PPy PANI PEDT, PEDOT PTh PAc PTV PAT PPV PPTA PTh-V PITN PNA PAZ PFu PIP PBD POTMT

Source: Creative Commons Attribution License (cc by).

of healing bones, skin, and connective tissue using electrical fields have been shown [20–23].

2.2  PCL Polymer With CNT/Ag Additives Fortunati et al. [24] have studied the effect of carbon nanotubes (CNTs) and silver nanoparticles (Ag_NP) on the multifunctional conductive biopolymer composites. They found thatAg_NP simplify the creation of conductive passageway in the presence of single-walled carbon nanotubes, statute as conductive links among nanotube bundles, and simplify the transfer of electrons (Fig. 2.1). They performed the biological test experiments on polycaprolactone + 15% silver, polycaprolactone + 1% SWCNTs, and polycaprolactone + 15% silver + 1% SWCNTs. The appropriateness of those conductive composite coatings as probable for basic human bone marrow mesenchyme system cells was exhibited displaying identical viability and cell material interaction in the tradition interval. They recommended that this strategy could serve as a design guide for other biomaterial applications of excessive effectiveness conductive biocomposites.

3  Pure Polypyrrole 3.1  Pure PPy Polymer The preparation process and polymer additives affect strongly the electronic conductivity of PPy, which is prepared chemically in aquatic solution. In addition, some of recent

Chapter 2 • Electrical Conductivity Behavior of Biopolymer Composites  15

FIGURE 2.1  Electrical conductivity of different high performance conductive composites [24]. Copyright 2016. Reproduced with permission from Elsevier Ltd.

researches illustrate that the use of polymers could control the electrical conductivity by sterical stabilization of PPy chains [25]. To achieve this target, water soluble p ­ olymers which have molecular mass more than 22,000 g/mol such as PVAc, methyl cellulose, PEO, poly(2vinylpyridine), PVP, poly(vinylmethylether), and others were studied by Rodriguez et al. [26]. They found that, by using those additives, electrical conductivity of a wide range 10−9 : 10−12 S/cm can be achieved [26]. Specially, for polyethylene-oxide (PEO) with a molar mass of 131,000 g/mol an electrical conductivity of 2.1 × 10−3 S/cm was achieved [27–31].

3.2  PPy Polymer With PEG Additives Using the oxidative polymerization process, Kang and Geckeler [31] have studied the effect of adding poly(ethyleneglycol) (PEG) additive on the multifunctional conductive PPy. They found that the electrical conductivity becomes greater than the PPy one that was produced without any additives (pure PPy). Exciter, there seemed to be an efficient relation between the electrical conductivity of PPy and the percentage of additives (Fig. 2.2).

3.3  PPy/FeCl3/Ammonium Persulfate Ilicheva et al. [32] have proposed a technique for obtaining three-component composite materials on the basis of polyethylene (PE) substrate modified with grafted polyacrylic acid (PAA) and PPy. Iron chloride (III) or ammonium persulfate were used as oxidizers (Figs. 2.3 and 2.4). They showed that the composite materials exhibit good mechanical properties due to the presence of PE film tightly bonded with PPy through PAA. The materials thus

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FIGURE 2.2  Conductivity of polypyrrole (PPy) as a function of PEG additive [31]. Copyright 2016. Reproduced with permission from Elsevier Ltd.

FIGURE 2.3  Dependence of PPy content (1) and conductivity of PPy (2) on the concentration of FeCl3 [32]. Creative commons attribution license (cc by).

obtained combine electronic and ionic conductivities with high mechanical strength. The ways of increasing electronic conductivity are determined [32]. The objective of their studies was focused on increasing the electrical conductivity of the PPy polymer due to increasing monomer concentration in the reaction mixture and repolymerization of pyrrole in the obtained composite material. It was established that increase of pyrrole concentration in the reaction mixture from 0.3 to 0.9 mol/dm3 did

Chapter 2 • Electrical Conductivity Behavior of Biopolymer Composites  17

FIGURE 2.4  Dependence of PPy content (1) and conductivity of PPy (2) on the concentration of ammonium persulfate [32]. Creative commons attribution license (cc by).

not significantly improve the electric conductivity (1.62 and 1.66 S/cm). However, under ­repolymerization of pyrrole, the electric conductivity increased more than three times: 1.66 and 5.43 S/cm for single and double polymerization, respectively [32].

4  Polyaniline Polymer 4.1  About PANI Polymer PANI was primarily found by Runge in 1834, but it was generally known as black aniline [33]. In 1862, Letheby conducted some researches to characterize and analyze this new material [33]. PANI was recognized as a polymer in mixed-oxidation phase. It consisted of oxidized quinoid sets and reduced benzoid sets [34]. In 1912, Woodhead and Green [35] discovered these interesting properties of PANI. Moreover, under certain experimental conditions, it was detected that PANI had the properties of converting between a conductor and semiconductor and an insulator [36]. Since that time, PANI (PANI) has grown to be an area as well as attractive topic of impressive attraction for researching [37,38]. PANI can be created by different amalgamation of the two sets known as X and Y elements of PANI [34]. Due to this, PANI has different unique characteristics and electrical conductivity techniques that differentiate it from the other conducting polymers. As an example, the PANI conductivity differs with the degree of oxidation and the extent of p ­ rotonation.

4.2  Polyaniline–Silver Nanocomposites Varga et al. [39] have presented a brief overview of the electrical properties of conductive composites containing silver and conducting polymer–PANI. Composites were produced by oxidation of PANI with silver nitrate (AgNO3) in the existence of different acids playing

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FIGURE 2.5  The dependence of the electrical conductivity at room temperature of polyniline-silver composites (salts of MSA, deprotonated bases of MSA, salts of AC) on the silver content [39].

the factor of doping agents. A semiconducting behavior was observed under the threshold about 21–27 vol.% of silver in composite and a metallic one above. From the temperature dependence of conductivity several charge transport mechanisms were proposed to explain experimental data with the most likely option of a superposition of the variable range hopping or the charging energy limited tunneling model with the Arrhenius-like activated transport. Changing the proportion of silver nitrate in the reaction mixture a variability in silver content in the target product was achieved, within the range of 0–27 vol.% for salts and 0–30 vol.% for bases, respectively. A powerful reliance of the electrical conductivity on metallic silver amount was observed (Fig. 2.5) with a critical value of its volume fraction (“threshold”) separating two qualitatively different regions. One being under the threshold with the conductivity about 100 S/cm typical for PANI salts, showing no significant dependence on used dopant, respectively, 10−6 S/cm for bases, a value 1000 times higher than is typical for silverless deprotonated PANI. This could be ascribed to the conductivity of a granular metal system embedded in an insulating matrix. The other region with typical conductivity about 103 S/cm is above the threshold. The high value of conductivity is believed to be a consequence of the presence of conducting paths through the material due to high amount of silver. Since the insufficient number of experimental data did not allow us to determine the exponent and the threshold, following from the percolation theory so far, we at least estimated the threshold being in the range of 21–24 vol.% for salts and 5–27 vol.% for bases [39]. The tendency of PANI morphology controlled by customizing the production circumstance has led to the generation of PANI of different structural forms including nanoparticles, nanorods, and nanotubes. These different structural forms which alienable with PANI are created achievable by the use of dopants like has large MW sulfonic-acids.

Chapter 2 • Electrical Conductivity Behavior of Biopolymer Composites  19

So that, the differences in the molecular aggregation of the polymer imply that an array of electronic characteristics is realizable with doped PANI. Thence enables the polymer to possess an extensive in biosensors and electrochemistry application [39].

5  Poly(3,4-Ethylenedioxythiophene): Poly(Styrene Sulfonate), PEDOT:PSS 5.1  Pure (PEDOT:PSS) Polymer As guaranteeing materials for electrodes in optoelectronic applications, PEDOT:PSS has surfaced. It has a lot of merits greater than further conducting polymers, like excellent thermal stability. It can be processed in watery solution [40,41]. Subsequently, it is often commonly used as a material for inkjet printing and as an electrodes buffer layer in organic chemistry [42,43]. Latterly, it was discovered that the electrical conductivity of poly(3,4 -ethylenedioxythiophene):poly(styrene sulfonate) coatings is generally developed by the inclusion of polyalcohols in high dielectric-solvents, like DMSO and DMF, to a PEDOT:PSS mixture [44–46].

5.2  Improvement of (PEDOT:PSS) Conductivity Kim et al. [47] have measured the direct current conductivity (σDC) of PEDOT doped with PSS with different organic solvents. They reported the improvement of σDC in the PEDOT/ PSS mixture by means of the modification of solvent conductivity from ∼0.8 to ∼80 S/cm−1. The temperature reveals that the PEDOT/PSS system achieves the essential system once some of the natural solvents like THF, DMSO, and DMF are used (Fig. 2.6).

FIGURE 2.6  Temperature dependence of σ DC (T) of PEDOT/PSS layers using different natural solvents [47].

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6  Polythiophene Polymer 6.1  Pure PTh Polymer PTh has been commonly used in thermally stable conjugated and environmentally biopolymer materials since 1980 [48]. It is used as optical and chemical sensors, DNA detectors, molecular devices, and many other applications [49–53]. Different polymerization approaches of thiophene are already documented in the publications. The first approach is electro-polymerization, second is chemical oxidative polymerization, and the third is metalcatalyzed coupling reactions. In 1983, Waltman et al. [54] successfully produced high conductive PTh thin layers by the first technique, but it is rarely used in electroluminescent materials preparation. Lin and Dudek [55] have documented the polycondensation of PTh catalyzed by Ni (bipy) Cl2, and identical outputs were also reported by Yamamoto et al. [48]. Latterly, Kim and his researchers [56–61] produced PTh in watery dispersion solution and characterized its characteristics.

6.2 Polythiophene/TiO2 Nanocomposites Uygun et al. [62] have possessed a core–shell structure from a mixture of PTh polymer and nanoparticles of titanium-dioxide (TiO2), It was produced using oxidative-polymerization of thiophene using iron chloride in the existence of three various surfactants: cationic, nonionic, and anionic. In the presence of surfactant materials, the electrical properties of the nanocomposites were scrutinized, and the best semiconductor features were reported for PTh/TiO2 anionic regime. Fig. 2.7A–D shows the electrical conductivity of the nanocomposites using a log σ T versus 1/T plot. It is clearly proportional to temperature up to 21–26° C. Over these ­temperature ranges and up to 36°C, the electrical conductivity unexpectedly dropped down [62].

7 Polyacetylene 7.1  About PAc Polymer Conducting biopolymers are the topic of current fundamental and industrial research [63,64]. The characteristic benefit of those kinds of materials is the conjugated dual link. Polyacetylene, (CH)x, is the least restrictive as well as the most significant representative of these different types of substance. The thermodynamically stable temperature conductivity of polyacetylene can be varied over more than 16 rules of importance making CH recommended for several purposes, like solar cells [65], rechargeable batteries [66], and also as a part of the future computers [67]. To try to answer these questions, Ehinger et al. [63] have performed DC and microwave conductivity measurements in the temperature scale of 10–330 K at doping degrees where the magnetic vulnerability is not high [68]; they find, however, that they can describe their results by conventional transporter between disturbance-induced centralized states. The theory that they apply there was originally

Chapter 2 • Electrical Conductivity Behavior of Biopolymer Composites  21

FIGURE 2.7  Temperature dependence of total electrical cond. (rT) polythiophene/TiO2 composite system. (A) NaDBSdoped polythiophene/TiO2, (B) dedoped polythiophene/TiO2, (C) TTAB-doped polythiophene/TiO2, and (D) Tween 20– doped polythiophene/TiO2 [62]. Copyright 2016. Reproduced with permission from Elsevier Ltd.

developed for amorphous inorganic semiconductors [69] and probably will not take advantage of the solitonic benefits of the defects [63].

7.2  Polyacetylene/SWCNT Composite Ku et al. [70] have synthesized water soluble SWCNT-poly-acetylene [single-walled c­ arbon nanotube-PA, single-walled carbon nanotube-P(2EPy-MeTf )] nanocomposites via surface initiated “grafting-from” method. The loading of single-walled carbon nanotube in the SWNT grafted ionic poly-acetylenes was estimated to be 21%. The SWNT-poly-­ acetylene mixture showed high water solubility (8 mg/mL). According to their results, the electrical conductivity at room temperature of the doped single-walled carbon nanotube-­ poly-acetylene composites was reported to be within the range of 1023–1024 S/cm. They observed that the single-walled carbon nanotube poly-acetylene composites are highly water soluble and the electrical conductivity of the doped single-walled carbon nanotube poly-acetylene composites is 2 degrees of magnitude higher than the previously recorded values for poly-acetylene composites. [70]

8 Conclusions A review on the electrical conductivity of different types of biopolymer matrix composites and fillers has been reported and studied in this work. It is concluded that, biopolymer itself normally is not conductive. Inorganic nanofillers are being added to the biopolymer

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matrix to enhance its electrical conductivity which greatly differ from the conventional biopolymer and exhibit unexpected properties. Different types of nanofillers have been produced for this purpose. Characteristics such as being electrically conductive, biosafe, renewable, biodegradable, and carbon neutral have made application of biopolymer important in the production of environment friendly product.

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