The combination of clays with polymers having different characteristics opens a way to new composite materials showing novel properties. Electrorheological (ER) fluids show phase transition from a liquid to a solid-like state between the electrodes of a rheometer due to the interactions of polarized particles. Composite systems comprising biodegradable chitosan (CS) and natural bentonite (BNT) are important in ER applications. In this study, BNT/CS composites were synthesized by the in situ method. The structure and morphology of the synthesized composites were characterized using X-ray diffraction (XRD), thermo-gravimetric analysis (TGA), and scanning electron microscopy (SEM) techniques. Thermal stability was observed to increase with the presence of BNT clay. Conductivity of the composites was found the suitable range for ER measurements. According to ER results, BNT/CS composites were found to be sensitive to external electric field strength, exhibiting a typical shear thinning non-Newtonian viscoelastic behavior

Cabuk, Mehmet

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Selection of our books indexed in the Book Citation Index in Web of Science™ Core Collection (BKCI)Interested in publishing with us? Contact book.department@intechopen.comNumbers displayed above are based on latest data collected. For more information visit www.intechopen.comOpen access books availableCountries delivered to Contributors from top 500 universitiesInternational  authors and editorsOur authors are among themost cited scientistsDownloadsWe are IntechOpen,the world’s leading publisher ofOpen Access booksBuilt by scientists, for scientists12.2%122,000 135MTOP 1%1544,800Chapter 6Clay/Biopolymer Composite andElectrorheological PropertiesMehmet CabukAdditional information is available at the end of the chapterhttp://dx.doi.org/10.5772/62270AbstractThe combination of clays with polymers having different characteristics opens a way tonew composite materials showing novel properties. Electrorheological (ER) fluids showphase transition from a liquid to a solid-like state between the electrodes of a rheometerdue to the interactions of polarized particles. Composite systems comprising biodegrada‐ble chitosan (CS) and natural bentonite (BNT) are important in ER applications. In thisstudy, BNT/CS composites were synthesized by the in situ method. The structure andmorphology of the synthesized composites were characterized using X-ray diffraction(XRD), thermo-gravimetric analysis (TGA), and scanning electron microscopy (SEM)techniques. Thermal stability was observed to increase with the presence of BNT clay.Conductivity of the composites was found the suitable range for ER measurements. Ac‐cording to ER results, BNT/CS composites were found to be sensitive to external electricfield strength, exhibiting a typical shear thinning non-Newtonian viscoelastic behavior.Keywords: Bentonite, clay/biopolymer composite, electrorheology, viscoelastic material1. IntroductionThe combination of clays with polymers having different characteristics opens a way to newcomposite materials showing novel properties [1]. The clay component of the compositesprovides a potential for high carrier mobility; band gap tunability; a range of electric, magnetic,and dielectric properties; and thermal/mechanical stabilities. On the other hand, polymercomponent of the composites offers structural flexibility, convenient processing, and tunableelectrical and electronic properties. A major attraction of such research activities is to combinethese desired advanced properties in the organic/inorganic hybrid materials, which can evenbe improved in comparison with the intrinsic properties of each component. Various polymer/clay composites can be synthesized via different preparation methods, including polymer© 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative CommonsAttribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution,and reproduction in any medium, provided the original work is properly cited.intercalation into the layers of clays, in which clay minerals are offered various advantagessuch as high thermal stability, enhanced reinforcement, small particle size, layer expandingcapabilities, and insolubility [2].Bentonite (BNT) clays are largely composed of the mineral montmorillonite. It is constructedfrom octahedral alumina sheets sandwiched between two tetrahedral silicate sheets, whichexhibit a net negative charge on the surface and can adsorb positive charges. BNT dispersionsare widely used in industrial processes because of their exceptional rheological behavior.Compatibility with various polymers is accomplished by modifying the layers of BNT withsurfactants via an ion-exchange reaction. When the BNT clay is exchanged with Na+ ion, itpossesses an excellent swelling behavior in water, and interlayer spacing becomes largeenough for the penetration of polymer chains [3].2. Electrorheological fluidsElectrorheological (ER) fluids are heterogeneous colloidal suspensions whose propertiesstrongly depend on an externally applied electric field [4]. Commonly, these kinds of fluidsare suspensions containing polarizable solid particles (dispersed phase) and non-conductingoils (continuous phase). When an electric field is imposed, suspended particles in the suspen‐sion are polarized due to the mismatches of electrical conductivity and dielectric permittivitybetween the dispersed particles and the continuous phase. The ER fluid shows phase transitionfrom a liquid to a solid-like state between the electrodes of a rheometer due to the interactionsof polarized particles (Scheme 1). This solid-like fibrillation of particles is due to the electricfield–induced increase in the apparent viscosity of suspensions [5].Sheme 1. ER response of clay/biopolymer composite particles dispersed in silicone oil.According to chemical contents of ER suspensions, dispersed phase can be composed oforganic (i.e. polymer) or inorganic (i.e. clay) particles [6]. Composite systems comprisingnatural materials such as chitosan (CS) and BNT are important in ER applications. In addition,the synthesis and ER properties of composites containing different clay groups (montmoril‐lonite, silica, etc.) were reported in the literature [7, 8].Clays, Clay Minerals and Ceramic Materials Based on Clay Minerals1522.1. Synthesis of bentonite/chitosan compositesThis study was aimed at synthesizing BNT/CS composites by the intercalation method [9]. Adefinite amount of BNT [SiO2 (54.82%), Al2O3 (20.27%), Fe2O3 (9.08%), MgO (3.02%), CaO(2.10%), Na2O (1.31%), TiO2 (0.78%), and K2O (0.06%)] was dispersed in 1 wt.% acetic acid andstirred for 2 h with the presence of 0.1 g cetyltrimethylammonium bromide (CTAB) cationicsurfactant. Then, a definite amount of CS [medium molecular weight (i.e. Mw¯ = 190,000–300,000g mol−1) with 75–85% deacetylation degree) that was dissolved in 1 wt.% acetic acid was addedinto the aqueous dispersions. The mixture was stirred for 12 h for the intercalation of CS chainsbetween BNT layers. Then, the dispersion was transferred into a flask containing 0.5 MNaOH(aq) and stirred for 2 h for neutralization. It is known that CS is soluble in weak acids andinsoluble in alkaline medium. The crude BNT/CS composite particles were recovered fromNaOH(aq) solution and washed with distilled water until the particles were neutral. Finally, theBNT/CS composites obtained were dried in a vacuum oven at 60°C for 2 days. By this method,three different biodegradable BNT/CS composites were synthesized and coded as BNT/CS(1%), BNT/CS(5%), and BNT/CS(25%).2.2. Electrorheological measurementsSilicone oil (SO) was used in a continuous phase (ρ = 0.965 g/cm3, η = 1 Pa s, ε = 2.61 at 25°C).The sample suspensions were prepared in SO at a series of concentrations (c = 5–25 wt.%),dispersing definite amount of dispersed phase in calculated amount of continuous phase (SO)according to formula (1):dispersed phasedispersed phase continuous phase100mc m mæ öç ÷= ´ç ÷+è ø(1)ER properties of the suspensions were determined with a Termo-Haake RS600 parallel platetorque electrorheometer (Germany). The gap between the parallel plates was 1.0 mm, and thediameters of the upper and lower plates were 35 mm. The voltage used in these experimentswas supplied by a 0–12.5 kV (with 0.5 kV increments) direct current electric field generator(Fug Electronics, HCL 14, Germany), which enabled the creation of resistivity during theexperiments.3. Results and discussion3.1. Characterization resultsAverage particle sizes, densities, and conductivities of the samples were given in Table 1. Thediffraction pattern of BNT indicated the crystalline nature, whereas CS showed the amorphousnature. The XRD pattern of pure BNT has sharp peaks around 2θ = 8°, 18°, 21°, 26°, and 28°that are typical of BNT [10]. The XRD pattern of BNT/CS composites has peaks with relativelyClay/Biopolymer Composite and Electrorheological Propertieshttp://dx.doi.org/10.5772/62270153lower intensities than that of BNT. This indicates that the amorphous structure of CS coversthe crystalline structure of BNT, which confirms the more amorphous nature of the composites.According to the TGA curves of the samples in contrast to pure CS, the residual amounts ofthe composites increased with increasing BNT content as follows: (89%)BNT > (86%)BNT/CS(1%) >(81%)BNT/CS(5%) > (57%)BNT/CS(25%) > (30%)CS. This tendency can be attributed to high thermalstability of the BNT component. These thermal stability results of BNT/CS composites are verysuitable for potential and industrial applications as new ER materials [11]. According to theSEM results, CS chains not only intercalated inside the interlayer spaces of BNT but also settledon the surface of BNT layers (flocculated) [12]. The flocculated formation of the compositescould be due to the hydroxylated edge–edge interaction of the silicate layers between thesilicate hydroxylated edge groups and the CS chains.Samples Conductivity(S cm−1) × 105Density(g cm−3) Average particle size ((m)CS 5.88 1.035 65BNT 1.51 1.245 11BNT/CS(1%) 1.01 1.158 14BNT/CS(5%) 1.71 1.122 23BNT/CS(25%) 3.45 1.116 51Table 1. Some physical properties of the samples.3.2. Electrorheological propertiesThe electric field viscosities of BNT/CS/SO suspensions increased with increasing electric fieldstrength and reached to 470, 980, 550, and 515 Pa s under E = 1 kV/mm, respectively (Fig. 1).BNT/SO ER fluid exhibited to enhance ER effect with applied electric field to improve theparticles’ polarization ability and a typical shear thinning non-Newtonian viscoelasticbehavior [13]. When E was applied to the ER suspension, the magnitude of the polarizationforces between particles increased and the particles rapidly formed fibrillar structure perpen‐dicular to the electrodes, which resulted in enhanced electric field–induced viscosity.For the composites, the highest electric field viscosity (980 Pa s) was obtained for BNT/CS(1%)/SO suspension under E = 1 kV/mm, whereas the lowest electric field viscosity (515 Pa s) wasobtained for BNT/CS(25%)/SO suspension under the same field strength. This result may beattributed to a decrease in the mutual action between the particles due to increasing particlesize or BNT content, which reduces the possibility of the formation of strong chains betweenthe upper and lower electrodes. Shear stress is one of the critical design parameters in ERphenomenon. The change of electric field–induced shear stress (τE) of the suspensionsincreased with the increasing electric field strength as follows: (190 Pa)BNT/CS(1%) > (118 Pa)BNT/CS(5%) > (95 Pa)BNT/CS(25%) > (88 Pa)BNT under E = 1 kV/mm.Clays, Clay Minerals and Ceramic Materials Based on Clay Minerals154Figure 2. Change in G′ and G″ with frequency, K1: BNT/CS(1%), K5 : BNT/CS(5%), and K25 : BNT/CS(25%), (c = 25 wt.%, T = 25°C, τ = 10 Pa, and E = 1 kV/mm).Figure 1. Effect of electric field strength on viscosity, K1: BNT/CS(1%), K5 : BNT/CS(5%), and K25 : BNT/CS(25%), (T =25°C, c = 25 wt.%, and γ˙ = 0.2 s−1).Clay/Biopolymer Composite and Electrorheological Propertieshttp://dx.doi.org/10.5772/62270155The external frequency is an essential factor for characterizing the dynamic viscoelasticproperties of ER fluids. Storage modulus (G′) and loss modulus (G″) values of CS/SO,BNT/SO and BNT/CS/SO suspensions slightly increased with increasing frequency (Fig. 2).These variations in G′ and G″ correspond to energy change occurring during dynamic shearprocess and are strongly dependent on the interactions between CS chains and BNT layerinterphases in the suspension [14].The G′ values of the prepared suspensions are higher than G″ values. According to this result,strong interactions were developed between CS and BNT interphases, which enhance theelastic properties of these composites.In conclusion, characterization results confirmed the introduction of the CS side chains intothe BNT layers. ER activities of the suspensions increased with increasing electric fieldstrength, dispersing particle concentration, and decreasing shear rate. Viscoelastic propertiesof the suspensions enhanced due to the interactions between BNT and CS. BNT-based ER fluidswith improved ER and viscoelastic behaviors could be a good candidate as a smart materialfor ER applications.Author detailsMehmet Cabuk*Address all correspondence to: mehmetcabuk@sdu.edu.tr; mhmtcbk@gmail.comDepartment of Chemistry, Faculty of Arts and Sciences, Süleyman Demirel University,Isparta, TurkeyReferences[1] Zhang A., Sun L., Xiang J., Hu S., Fu P., Su S. & Zhou Y. (2009) Removal of elementalmercury from coal combustion flue gas by bentonite–chitosan and their modifier,Journal of Fuel Chemistry and Technology, 37, 489–495.[2] Yılmaz K., Akgoz A., Cabuk M., Karaagac H., Karabulut O. & Yavuz M. (2011) Elec‐trical transport, optical and thermal properties of polyaniline–pumice composites,Materials Chemistry and Physics, 130 (3), 956–961.[3] Brindley G.W. & Brown G. (1980) Crystal Structures of Clay Minerals and Their X-rayIdentification. Mineralogical Society, London.[4] Jang W.H., Cho Y.H., Kim J.W., Choi H.J., Sohn J.I. & Jhon M.S. (2001) Electrorheo‐logical fluids based on chitosan particles, Journal of Materials Science Letters, 20, 1029–1031.Clays, Clay Minerals and Ceramic Materials Based on Clay Minerals156[5] Wu S. & Shen J. (1996) Electrorheological properties of chitin suspensions, Journal ofApplied Polymer Science, 60, 2159–2164.[6] Li H., Yunling J., Shuzhen M. & Fuhui L. (2007) Synthesis and electrorheologicalproperty of chitosan phosphate and its rare earth complex, Journal of Rare Earths, 25,15–19.[7] Kim J.W., Noh H.M., Choi H.J., Lee D.C. & Jhon M.S. (2000) Synthesis and electro‐rheological characteristics of SAN–clay composite suspensions, Polymer, 41, 1229–1231.[8] Park D.P., Sung J.H., Kim C.A., Choi H.J. & Jhon M.S. (2004) Synthesis and electro‐rheology of potato starch phosphate, Journal of Applied Polymer Science, 91, 1770–1773.[9] Badawy M.E.I. & Rabea E.I. (2009) Potential of the biopolymer chitosan with differ‐ent molecular weights to control postharvest gray mold of tomato fruit, PostharvestBiology and Technology, 51, 110–117.[10] Tilki T., Karabulut O., Yavuz M., Kaplan A., Cabuk M. & Takanoglu D. (2012) Irradi‐ation effects on transport properties of polyaniline and polyaniline/bentonite compo‐site, Materials Chemistry and Physics, 135 (2–3), 563–568.[11] Ksiezopolska A. & Pazur M. (2011) Surface properties of bentonite and illite com‐plexes with humus acids, Clay Minerals, 46, 149–156.[12] Lee D., Char K., Lee S.W. & Park Y.W. (2003) Structural changes of polyaniline/mont‐morillonite nanocomposites and their effects on physical properties, Journal of Materi‐als Chemistry, 13, 2942–2947.[13] Xiang L. & Zhao X. (2006) Preparation of montmorillonite/titania nanocomposite andenhanced electrorheological activity, Journal of Colloid and Interface Science, 296, 131–140.[14] Yavuz M. & Cabuk M. (2006) Electrorheological properties of pumice/silicone oil sus‐pension, Journal of Material Science, 42, 2132–2137.Clay/Biopolymer Composite and Electrorheological Propertieshttp://dx.doi.org/10.5772/62270157

Clay/Biopolymer Composite and Electrorheological Properties

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