Faculty Publications

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    Electrospinning: From Fundamentals to Applications
    (CRC Press, 2016) Senthil, T.; George, G.; Srinivasan, A.
    Electrospinning is not only a unique and fascinating process for the production of polymeric nanobers with diameters ranging from 3 nm to 20 µm, but also the simplest and inexpensive technique to fabricate ultrane continuous polymeric bers. Electrospinning is also known as electrostatic spinning and electrospraying. In the last few years, electrospinning has become popular among academic researchers and industries as it overcomes the various processing diculties in the other nanober-forming techniques. Some of the other techniques for the production of polymer nanobers are drawing, template synthesis, phase separation, and self-assembly (Table 5.1). While electrospinning can produce nanobers, its conventional counterparts, such as melt spinning, dry spinning, gel spinning, and wet spinning, can only produce microbers (Figure 5.2) (Gibson et al. 2001). Almost all the straight chain homopolymeric materials have been actively investigated for developing nanobers by electrospinning. Meanwhile, various FIGURE 5.1 Electrospun nanobers have high surface area. (Reprinted from Colloids Surf., A, 187-188, Gibson, P., Gibson, H.S., and Rivin, D., Transport Properties of Porous Membranes Based on Electrospun Nanobers, 469-481. Copyright 2001, with permission from Elsevier.) semicrystalline and amorphous polymers, natural and synthetic biopolymers, polymer blends, and block copolymers can also be converted into nanobers via the electrospinning technique. © 2017 by Taylor and Francis Group, LLC.
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    Polymer Nanocomposites for Food Packaging Applications
    (CRC Press, 2016) George, G.; Kumar, B.; Srinivasan, A.
    Polymers are widely used in packaging of food, chemicals, medicines, industrial components, agriculture, and household items as listed in Table 26.1. Polymer consumption has an average growth rate of 5% and it will touch a gure of 227 million metric tons in 2015. Criteria for selection of a particular polymer for packaging is its biodegradability, migration of hazardous compounds, barrier properties, processability, strength, and inertness. Polymers are made to order in a variety of fashions using additives, functionalization, crosslinking, and so on for a particular application. A successful packaging material should be able to maintain the quality of the packed commodities to meet the customers’ expectation as it moves from manufacturer to customer. © 2017 by Taylor and Francis Group, LLC.
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    Sol-gel electrospinning of diverse ceramic nanofibers and their potential applications
    (Elsevier, 2020) George, G.; Senthil, T.; Luo, Z.; Anandhan, S.
    Ceramics are composed of both metallic and nonmetallic elements and commonly exist as compounds of oxides, nitrides, and carbides. Two decades back, the use of ceramics was limited to a handful of applications, as in household utilities and some industrial uses. In the era of nanotechnology, the definition and application of materials are altered, especially in the case of ceramics. By the development of various fabrication techniques of nanostructured ceramics, the scope of ceramic materials is radically transformed, making them the most beneficial among the materials ever designed for several critical applications. The fabrication of ceramic nanostructures is challenging from an industrial point of view since many fabrication techniques need sophisticated instrumentation, skilled personnel, purity of chemicals, specificity of the medium, controlled atmosphere, etc. and are anticipated for lab-scale production. The electrospinning process is an exception, which can address all the former problems associated with other fabrication techniques. This chapter covers the electrospun ceramic nanofibers such as oxides, carbides, nitrides, sulfides, etc. from various precursors and their application in the field of biomedical engineering, filtration, energy, electronics, sensor, catalysis, etc. and their peculiar properties, such as photoluminescence, thermoelectric, piezoelectric, and magnetic. Nevertheless, the application of ceramic nanofibers, far more than what is discussed here, and advanced studies are essential to explore the applications of ceramic nanofibers in numerous untouched areas where conventional materials can be replaced. © 2021 Elsevier Ltd All rights reserved.
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    PFWD, CBR and DCP evaluation of lateritic subgrades of Dakshina Kannada, India
    (2008) Nageshwar Rao, Ch.; George, G.; Shivashankar, R.
    The performance of pavements depends to a large extent on the strength and stiffness of the subgrades. Among the various methods of evaluating the subgrade strength, the use of portable falling weight deflectometers (PFWD) is gaining popularity in the recent years. This is due to its simplicity in design, portability, and the added advantages of providing quick and reliable estimates of the Young's modulus of elasticity of pavement subgrades. Hence it was felt that there is a need to study the correlation between results obtained using the PFWD and those obtained using the traditional approaches such as the California bearing ratio (CBR) test, the dynamic cone penetrometer (DCP) test. The work described herein focuses on exploring the correlations between the results obtained using the PFWD, and the results obtained using the CBR method and DCP for lateritic soils at various locations of Dakshina Kannada district of the State of Karnataka, India. Regression models were developed as part of this study to enable the prediction of CBR values based on the average of observed values of the Young's modulus obtained using the PFWD (Epfwd), and prediction of Epfwd from the average penetration-rates of DCPs performed for field density, and field-moisture content.
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    Dispersion analysis of nanofillers and its relationship to the properties of the nanocomposites
    (Elsevier Ltd, 2021) George, G.; Dev, A.P.; Asok, N.N.; Anoop, M.S.; Anandhan, S.
    The dispersion and distribution characteristics of the reinforcements are the key reasons that influence the mechanical properties of the nanocomposites. In this paper, the dispersion and distribution analysis of nanofillers in a representative polymer is performed and the results are correlated to the crystalline and mechanical properties of the nanocomposite. The nanocomposite used in the present study is Elvaloy®4924 (EVACO)/halloysite nanotubes (HNTs) composite. The dispersion of halloysite nanotubes in the EVACO matrix is recorded as aluminum elemental maps obtained from energy dispersive spectroscopy (EDS). The dispersion and distribution of fillers in the composite are quantified using an image processing technique and it is correlated to the crystalline and tensile properties of the composites. The better dispersion and distribution of HNTs at 1wt.% filler loading resulted in a remarkable improvement in the crystallinity of the composite, which is measured by X-ray diffraction (XRD) and differential scanning calorimetry (DSC). The tensile strength was highest for composites loaded with 1 wt.% filler, and the strength decayed as the loading was further increased. Agglomeration of halloysite nanotubes and polymer-filler debonding was the major reason behind the reduction in tensile strength with filler loading, as observed in the scanning electron micrographs of the fractured surfaces. © 2021 Elsevier Ltd. All rights reserved.
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    Effect of nanofillers on the crystalline and mechanical properties of EVACO polymer nanocomposites
    (Elsevier Ltd, 2021) George, G.; Hareendran, H.; Kumar, T.M.A.; Joshy, S.; Sanju, A.C.; Anandhan, S.
    In this work, the effect of different fillers on the crystalline and mechanical properties of the poly(ethylene-co-vinyl acetate-co-carbon monoxide) (EVACO) terpolymer composite is studied systematically. Alumina trihydrate nanoparticles (nano-ATH), halloysite nanotubes (HNTs), and the multiwalled carbon nanotubes (MWCNTs) are the representative fillers used in the present study. The surface of MWCNTs are decorated using carbonyl, however, nano-ATH and HNTs are used without any surface treatment. The mechanical properties of the composites are evaluated using a tensile test and the improvement in the mechanical properties can be correlated to the improvement in the crystallinity in the composite. The presence of nanofillers in the EVACO matrix significantly influenced the crystallinity, which was determined by X-ray diffraction. The fractography studies reveal the presence of agglomerates at high filler loading results in the subsequent reduction in the tensile properties. Interestingly, the MWCNTs at very low filler loading significantly enhances the tensile properties of EVACO. © 2021 Elsevier Ltd. All rights reserved.
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    Parametric study of manufacturing ultrafine polybenzimidazole fibers by electrospinning
    (Springer, 2012) Anandhan, S.; Ponprapakaran, K.; Senthil, T.; George, G.
    Polybenzimidazole (PBI), a high performance polymer, was synthesized from 3,3?-diaminobenzidine (DAB) and isophthalic acid (IPA) through polycondensation. The chemical structure of PBI was confirmed by Fourier transform infrared spectroscopy. Thermal characterization of PBI was done by thermogravimetry and differential scanning calorimetry. PBI nanofibers were fabricated by electrospinning of N, N-dimethyl acetamide solutions of PBI of different solution concentrations, at different voltages. The effects of solution and process parameters (namely, solution concentration and DC voltage) on morphology and average diameter of electrospun PBI fibers were investigated. The electrospun ultrafine fibers' diameter and morphology were characterized by using scanning electron microscopy. Nanofibers were obtained only from PBI solutions of concentrations 12 and 14 % (w/v). At concentrations of 8, 10, and 16 %, fibers could not be obtained. The process parameters were optimized by using the statistical tool, factorial or two-way ANOVA (analysis of variance), DOE (design of experiments) and the results indicate that the applied voltage and the interaction of voltage and solution concentration are influential in determining the diameter and morphology of the electrospun ultrathin PBI fibers. Electrospun PBI fibers, as small as 56 nm, could be successfully produced by using the right combination of solution concentration and spinning voltage. © 2012 Central Institute of Plastics Engineering & Technology.
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    Chemical-resistant Ultrafine Poly(styrene-co-acrylonitrile) Fibers by Electrospinning: Process Optimization by Design of Experiment
    (2013) Senthil, T.; George, G.; Anandhan, S.
    The effects of solution and processing parameters on the morphology and diameter of electrospun poly(styrene-co-acrylonitrile) fibers were investigated by design of experiment. Morphology of the electrospun fiber mats were investigated by scanning electron microscopy. With increasing solution concentration, fiber morphology changed from that of a spindle-like beaded one to smooth, and the average fiber diameter increased from 96 to 876 nm. Average fiber diameter gradually increased with applied voltage; however, fiber morphology was only slightly influenced by flow rate. Regression analysis results reveal that solution concentration has the most significant impact on the average and standard deviation of fiber diameter. © 2013 Copyright Taylor and Francis Group, LLC.
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    Structural characterization of nano-crystalline Co3O4 ultra-fine fibers obtained by sol-gel electrospinning
    (2013) George, G.; Anandhan, S.
    In this paper, we report the obtention of ultrafine fibers of cobalt oxide (Co3O4) by combining electrospinning method with high-temperature calcinations from the precursor sol of poly(2-ethyl-2- oxazoline) (PEtOx)/cobalt acetate tetrahydrate [Co(CH3COO) 2·4H2O] in water. The optimum electrospinning conditions for obtaining precursor composite nanofibers from PEtOx/Co(CH 3COO)2·4H2O solution in water, to produce ceramic nanofibers, were studied. The average fiber diameter of the precursor composite fibers measured by scanning electron microscopy (SEM) was approximately 200 nm. Thermogravimetric analysis of PEtOx was performed to estimate the suitable calcination temperature of the precursor fibers. SEM images of the ceramic fibers obtained after calcination revealed the shrinkage in diameter due to complete degradation of the polymer and Co(CH 3COO)2·4H2O. Fourier transform infrared spectroscopy was used to ensure the complete pyrolysis of polymer during calcinations of the composite fibers. Crystalline properties of the ceramic fibers were studied by X-ray diffraction and high resolution transmission electron microscopy. The ceramic fibers are polycrystalline with an average grain size of ?40 nm obtained at a calcination temperature of 773 K. It was observed that the grain sizes increased as the calcination temperature was increased, due to self assembly mechanism. © 2013 Springer Science+Business Media New York.
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    Use of nano-ATH as a multi-functional additive for poly(ethylene-co-vinyl acetate-co-carbon monoxide)
    (Springer Verlag service@springer.de, 2014) George, G.; Mahendran, A.; Anandhan, S.
    Flame retardant aluminum hydroxide (ATH) nanoparticles of size ?10-20 nm were dispersed in ethylene-vinyl acetate-carbon monoxide terpolymer (EVACO) via solution casting. The effect of filler loading on the crystallizability, thermal, mechanical, flammability, optical and electrical properties of EVACO was evaluated. At 1 % filler loading nano-ATH particles exhibited very good dispersibility in the EVACO matrix and the % crystallinity of EVACO is the highest at this filler loading. The changes in crystallinity were studied by X-ray diffractometry and differential scanning calorimetry. The highest tensile strength was observed for the composite with 1 % nano-ATH loading, which has the best filler dispersion, and the decay in the tensile properties at higher filler loading is due to agglomerations of ATH nanoparticles and polymer-filler interface debonding. The UV absorption of these composites is augmented irrespective of the nano-ATH loading and ATH emerges as a good absorber of UV light. The DC electrical conductivity study of the composites proves that the addition nano-ATH is an efficient way to improve the dielectric properties of EVACO. The presence of nano-ATH improves the flame retardance of these composites. © 2014 Springer-Verlag Berlin Heidelberg.