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Vijayalekshmi V.,Rubber Technology Center | Khastgir D.,Rubber Technology Center
Journal of Membrane Science | Year: 2017

Methanesulfonic acid (MSA) and sodium salts of dodecylbenzene sulfonic acid (SDBS) were introduced into chitosan matrix to improve the proton conductivity and solvent stability through cross-linking with sulfuric acid. 15 wt% MSA doped chitosan membrane shows a proton conductivity of 2.86×10−4 S/cm at 100 °C, but when doped with 10 wt% SDBS, the conductivity of 4.67×10−4 S/cm was obtained at the same temperature. The MSA and SDBS doped membranes exhibited better performance compared to pristine chitosan (CS) membrane in terms of mechanical properties and electrical resistance. In addition, the doped membranes are thermally stable up to 260 °C. Thus doping of chitosan with MSA and SDBS is found to provide an efficient route to improve thermal stability, mechanical properties and proton conductivity required for polymer electrolyte membranes for fuel cell applications. Moreover, the cost effectiveness and eco – friendliness of CS-MSA and CS-SDBS membranes make their applicability in fuel cell more attractive than the state – of – art (Nafion). © 2016 Elsevier B.V.

Nayak L.,Rubber Technology Center | Kumar Chaki T.,Rubber Technology Center | Khastgir D.,Rubber Technology Center
Polymer Engineering and Science | Year: 2016

This study is aimed to investigate the electrical conduction behavior of polyimide (PI)/multiwall carbon nanotubes (CNTs) nanocomposites in cryogenic environment (temperature from 10 to 300 K) prepared by in-situ polymerization technique. The experimental results of direct current (DC) electrical conductivity have been fitted with different theoretical models to check their applicability and to understand the conduction behavior for the present nanocomposite system. The PI/CNT nanocomposites show low electrical percolation threshold. Negative temperature coefficient effect of resistivity is observed for all the composites under investigation. The analysis shows that Mott's variable range hopping (VRH) model is more applicable compared to Arrhenius and Kivelson models for the present composites over the entire range of measurement temperature. The electronic transport behavior in each composite at temperature above 70 K can be ascribed to thermally activated tunneling of charge carriers through insulating barriers between CNTs; however, the electronic transport behavior at temperature below 70 K can be attributed to three dimensional VRH of charge carriers through the networks of CNTs in the polymer composite. The current-voltage characteristics of the composite show non-ohmic behavior for temperature below 60 K and become ohmic in nature as temperature rises to 300 K. POLYM. © 2016 Society of Plastics Engineers.

Kumar Chaki T.,Rubber Technology Center | Khastgir D.,Rubber Technology Center
Journal of Applied Polymer Science | Year: 2016

In this study, we focused on the behavior of the direct-current (dc) conductivity/resistivity in a cryogenically low temperature region (10-300 K) for ethylene vinyl acetate copolymer, acrylonitrile butadiene copolymer, and their 50/50 blend composites filled with different conductive carbons. The composites were prepared through a melt-mixing technique. Different behaviors of the dc resistivity/relative resistivity for the composites were observed; these behaviors depended on the nature of the polymers, the filler types, and the filler concentration when plotted with respect to the temperature. The results of dc conductivity were fitted with some existing theoretical models, including Arrhenius, Kivelson, and Mott's variable range hopping, to check their applicability for these composite systems. We observed that none of the models was applicable within the entire range of measurement temperatures but were confined within limited temperature ranges. The reason behind the nonapplicability of the models is discussed with consideration of their drawbacks and limitations. © 2016 Wiley Periodicals, Inc.

Annadurai P.,Naval Physical Oceanographic LaboratoryCochin682021 Kerala India | Kumar S.,Rubber Technology Center | Mukundan T.,Naval Physical Oceanographic LaboratoryCochin682021 Kerala India | Sarkar P.,Rubber Technology Center | Chattopadhyay S.,Rubber Technology Center
Polymer Composites | Year: 2015

Elastomeric composites based on nitrile rubber (NBR), carbon black (CB), and organically modified nanoclay (NC) were prepared using a laboratory two-roll mixing mill. Influences of the hybrid filler system (CB+NC) on various properties of NBR compound were analyzed. It was found that the addition of hybrid filler (CB+NC) over only carbon black enhances various properties. It was also found that the addition of nanoclay to the rubber matrix effectively improved key properties. Acoustics and electrical properties were modified with reduced water absorption because of layered clay platelets. The lower volume resistivity of NBR composites reflected better electrical conductivity attributed to the presence of nanoclay leading to effective filler connectivity. X-ray diffraction and transmission electron microscopy measurements revealed that nanoclays were mostly intercalated and were uniformly dispersed. Use of calcium stearate facilitated dispersion of nanoclay in the rubber matrix which was observed through the formation of nanostructures including “nano“ and “halo“ units. Time temperature superposition in dynamic mechanical analysis test of the composites indicated lower mechanical loss in the frequency range of interest. The advantages accruing due to overall property enhancement, including lower water absorption, and better electrical and excellent acoustic properties of NBR composites make it suitable as underwater acoustic transparent materials for transducer encapsulation application. © 2014 Society of Plastics Engineers.

Selvakumar M.,Rubber Technology Center | Pawar H.S.,Indian Institute of Technology Kharagpur | Francis N.K.,Indian Institute of Technology Kharagpur | Das B.,Indian Institute of Technology Kharagpur | And 2 more authors.
ACS Applied Materials and Interfaces | Year: 2016

Guided bone regeneration (GBR) scaffolds are unsuccessful in many clinical applications due to a high incidence of postoperative infection. The objective of this work is to fabricate GBR with an anti-infective electrospun scaffold by ornamenting segmented polyurethane (SPU) with two-dimensional Aloe vera wrapped mesoporous hydroxyapatite (Al-mHA) nanorods. The antimicrobial characteristic of the scaffold has been retrieved from the prepared Al-mHA frame with high aspect ratio (∼14.2) via biosynthesis route using Aloe vera (Aloe barbadensis miller) extract. The Al-mHA frame was introduced into an unprecedented SPU matrix (solution polymerized) based on combinatorial soft segments of poly(ε-caprolactone) (PCL), poly(ethylene carbonate) (PEC), and poly(dimethylsiloxane) (PDMS), by an in situ technique followed by electrospinning to fabricate scaffolds. For comparison, pristine mHA nanorods are also ornamented into it. An enzymatic ring-opening polymerization technique was adapted to synthesize soft segment of (PCL-PEC-b-PDMS). Structure elucidation of the synthesized polymers is established by nuclear magnetic resonance spectroscopy. Sparingly, Al-mHA ornamented scaffolds exhibit tremendous improvement (175%) in the mechanical properties with promising antimicrobial activity against various human pathogens. After confirmation of high osteoconductivity, improved biodegradation, and excellent biocompatibility against osteoblast-like MG63 cells (in vitro), the scaffolds were implanted in rabbits as an animal model by subcutaneous and intraosseous (tibial) sites. Improved in vivo biocompatibilities, biodegradation, osteoconductivity, and the ability to provide an adequate biomimetic environment for biomineralization for GBR of the scaffolds (SPU and ornamented SPUs) have been found from the various histological sections. Early cartilage formation, endochondral ossification, and rapid bone healing at 4 weeks were found in the defects filled with Al-mHA ornamented scaffold compared to pristine SPU scaffold. Organ toxicity studies further confirm the absence of appreciable tissue architecture abnormalities in the renal hepatic and cardiac tissue sections. The entire results of this study manifest the feasibility of fabricating a mechanically adequate tailored nanofibrous SPU scaffold based on combinatorial soft segments of PCL, PEC, and PDMS by a biomimetic approach and the advantages of an Aloe vera wrapped mHA frame in promoting osteoblast phenotype progression with microbial protection for potential GBR applications. © 2016 American Chemical Society.

Dey A.,High Energy Materials Research Laboratory | Maity A.,CSIR - Central Electrochemical Research Institute | Shafeeuulla Khan M.A.,High Energy Materials Research Laboratory | Sikder A.K.,High Energy Materials Research Laboratory | Chattopadhyay S.,Rubber Technology Center
RSC Advances | Year: 2016

A green method for the synthesis of a graphene-iron oxide nanocomposite (GINC) and its PVAc based polymer nanocomposites was reported in an earlier communication. The fabricated PVAc-GINC film exhibited a conductivity of 2.18 × 104 S m-1 with a Seebeck coefficient of 38.8 μV K-1. Hence, the power factor (PF) reached a value of 32.90 μW m-1 K-2 which is 27 fold higher than a thermoelectric material based on a PVAc-graphene composite as reported in the contemporary literature. In continuation of the above mentioned study, PEDOT:PSS was used to further enhance the power factor (PT) and figure of merit (ZT) of the system. During evaluation, a PEDOT:PSS/GINC composite (5:95) showed a remarkable increase in various thermoelectric properties like electrical conductivity (8.0 × 104 S m-1) with a Seebeck coefficient of 25.42 μV K-1 and thermal conductivity 0.90 W m-1 K-1. Hence PF and ZT reach up to 51.93 μW m-1 K-2 and 0.017, respectively. To improve the mechanical strength of the polymer composite, cellulose fibre was also employed. By the addition of cellulose fibre, though the mechanical strength of the composite increases the PF reaches 5.6, which is 10 times lower than the PEDOT:PSS/GINC composite. © The Royal Society of Chemistry 2016.

Idris N.F.,Rubber Technology Center | Kamarulzaman N.H.,Rubber Technology Center | Nor Z.M.,Rubber Technology Center
Chemical Engineering Transactions | Year: 2012

Malodourous emission from raw natural rubber (NR) processing activities has become a public nuisance since residential and public development areas are gradually expanding near raw NR processing factories. The malodourous vapour mainly consists of volatile fatty acids (VFA) released from the breakdown of non-rubber constituents during drying stage of the raw rubber processing. An improved sampling methodology to characterise and monitor VFA from the drying stage was implemented. This study focused on the drying stage as the major source of malodour in the raw rubber processing. The thermal desorption-gas chromatography technique enabled direct sampling of air pollutants with minimal errors. It was found that acetic acid and propionic acids were present with highest concentrations. In general, concentrations of individual VFA varied throughout the drying stage. The raw NR processing factories were able to eliminate more than 71 % of total VFA using the relevant water scrubber treatment systems. The malodour characterization technique used in this study provides new technical information useful to develop more efficient malodour control systems for the raw NR processing industry. Copyright © 2012, AIDIC Servizi S.r.l.

Fernando M.,Tun Abdul Razak Research Center | Fei W.H.,Rubber Technology Center | Hull C.,Tun Abdul Razak Research Center
Rubber Chemistry and Technology | Year: 2012

Curing rubber is a complex process that involves the insertion of cross-links to convert the rubber into a useful functional material. The estimation of the cure time needed for product manufacture of small or thin walled products is often arrived at by means of a rheometer trace. Although this has been recognized as adequate for thin walled products, the production of large rubber articles requires a more rigorous analysis of cure kinetics for an essentially non-isothermal process. Often finite element analysis is used to generate non-isothermal temperature histories in a thick component, and then an appropriate cure kinetic equation is solved to predict the state of cure. In addition to generating the capability for cure time prediction, there is a need in the industry to minimize cycle time, improving productivity and therefore costs involved in product manufacture. For large products, the viability of the use of extrusion molding, where the rubber is extruded into a heated mold at the same temperature as the mold, has been demonstrated in previous reported work in this laboratory. The present work explores, via simulation, the feasibility of using extrusion molding as a manufacturing method for large components. The cure simulation module of Autodesk Moldflow has been used to compare the state of cure of a laminated bearing manufactured by conventional compression molding and extrusion molding. Previous experimental data on the temperature histories of a large laminated bearing manufactured using compression molding are compared with simulation data. Simulation data are then presented on manufacturing the bearing using extrusion molding. The aim is to demonstrate the usefulness of extrusion molding for very large components and to illustrate the advantages of using simulation codes to assist in shortening the cycle time in product manufacture.

Manoharan P.,Rubber Technology Center | Naskar K.,Rubber Technology Center
Journal of Applied Polymer Science | Year: 2016

In this article, we provide an extensive analyses of various properties that are required for tire tread based on developed highly dispersible (HD) silica-filled epoxidized natural rubber composites. Silica in an HD form has become a staple filler in tire tread applications because of its inherent advantages. In this study, epoxidized natural rubber with 25 mol % epoxide (ENR 25) and natural rubber were mixed with two different types of HD silica for superior reinforcement. A standard tire tread formulation was used as the base compound. The magic triangle properties were conspicuously influenced by the viscoelastic characteristics of the vulcanizates. The introduction of polar rubber (ENR 25) into the HD silica greatly improved rheological, physicomechanical, bound rubber content, and dynamic mechanical properties, and this led to a better, fuel-efficient tire. We successfully achieved this, even in the absence of a silane coupling agent. ENR 25 played an imperative role in showing an extraordinary rubber-filler interactions and was primarily responsible for these observations. In this study, we explored the HD silica dispersion with transmission electron microscopy observations. Morphological studies revealed well-dispersed HD silica with the formation of a rubber-filler network. © 2016 Wiley Periodicals, Inc.

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