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Garg P.,Defence Research and Development Establishment | Garg P.,Indian Institute of Technology Delhi | Singh R.P.,Center for Fire | Choudhary V.,Indian Institute of Technology Delhi
Separation and Purification Technology | Year: 2011

The paper describes the preparation of poly(dimethyl siloxane) (PDMS)/clay nanocomposite membranes by in situ crosslinking of vinyl terminated PDMS (V-PDMS) resin in the presence of clay content varying from 1% w/w to 10% w/w in order to evaluate the influence of layered silicate on pervaporation characteristics of PDMS. Two commercial clays, Cloisite 30B and Nanomer 1.30P functionalized with polar and nonpolar surfactants were chosen for this purpose and PDMS membranes were prepared in the absence/or presence of varying amounts of different clays. Structural, mechanical and thermal characterization was done using Fourier transform infrared spectroscopy (FTIR), tensile testing system and thermogravimetric analyzer. Morphological characterization using X-ray diffraction and transmission electron microscopy showed intercalation or partial exfoliation of silicate layers. Surface characterization using scanning electron microscope showed an uniform dispersion of nanoclays in PDMS matrix. Two nanocomposite membranes having PDMS/nanoclay (10% w/w) were selected based on their mechanical properties and evaluated for their performance in separating azeotropic toluene/methanol mixture. Composite membranes showed higher selectivity as compared to neat PDMS and toluene was a preferred permeant. The total flux for composite membranes was lower as compared to PDMS membrane. This study demonstrates that polymer nanocomposite membranes could be an alternative way for tuning between permeation flux and selectivity in addition to enhanced thermal and mechanical properties. © 2011 Elsevier B.V. All rights reserved. Source

Verma A.K.,University of Delhi | Jha R.R.,University of Delhi | Kasi Sankar V.,University of Delhi | Singh R.P.,Center for Fire
Tetrahedron Letters | Year: 2013

An efficient tandem approach for the selective synthesis of 4,5-dihydroimidazo[1,5-a]quinoxalines 6a-g and imidazo[1,5-a]quinoxalines 7a-h by the reaction of 2-imidazolyl anilines 4a-c with aryl aldehydes 5a-k under mild reaction conditions is described. Introduction of electron releasing alkyl groups in substrates 4a-b was found to be instrumental for the success of the reaction. © 2013 Elsevier Ltd. All rights reserved. Source

Garg P.,Defence Research and Development Establishment | Garg P.,Indian Institute of Technology Delhi | Singh R.P.,Center for Fire | Choudhary V.,Indian Institute of Technology Delhi
Separation and Purification Technology | Year: 2011

The paper describes the preparation and investigation of membranes based on new interpenetrating polymer network (IPN) of vinyl terminated poly(dimethyl siloxane) (PDMS) and aromatic polyimide (PI) with respect to their thermal and pervaporation properties. The modified membranes were prepared using simultaneous IPN (SIPN) technique by variation of polyimide loading of 5, 10 and 15 wt% respectively. These membranes were characterized by different thermal, mechanical, morphological, spectroscopic and pervaporative techniques and compared with those of neat PDMS membranes. The IPN membranes exhibited synergistic improvement in the thermal stability in the range of 445-490 °C in air and 410-520 °C in inert atmosphere for 10% loss. Activation energies for the decomposition of polymers and their IPN's were calculated using Coats and Redfern equation. Permeation properties of PDMS and IPN blends were evaluated by water diffusion, measured by Fourier transform-attenuated total reflectance (FT-ATR) method and moisture vapour transmission rate (MVTR) as per ASTM E 96. 15 wt% polyimide content in PDMS membrane slows down the water diffusion and MVTR significantly. All the IPN's form mechanically strong membrane with tensile strength up to 15.5 MPa and elongation at break up to 20%. IPN membranes prepared in this work were employed in pervaporation separation of azeotrope forming toluene/methanol mixtures. The pervaporation properties could be tuned by adjusting the blend composition. All the blend membranes tested showed a decrease in flux with increasing polyimide content for methanol/toluene liquid mixtures. Toluene permeated preferentially through all tested blend membranes, and the selectivity increased with increasing polyimide content. The pervaporation characteristics of the blend membranes were also strongly influenced by the feed mixture composition. The flux increased exponentially with increasing toluene concentration in the feed mixtures, whereas the selectivities decreased for liquid mixtures. This study demonstrates that polymer IPN blends is a simple way to modulate membrane's transport properties and can achieve higher performance than the pristine polymer materials. © 2010 Elsevier B.V. Source

Roy P.K.,Center for Fire | Hakkarainen M.,KTH Royal Institute of Technology | Albertsson A.-C.,KTH Royal Institute of Technology
Polymer Degradation and Stability | Year: 2012

The addition of montmorillonite (MMT) nanoclays shifted the degradation product patterns of polylactide towards shorter lactic acid oligomers as compared to the product patterns of plain polylactide and halloysite modified polylactide hydrolysed under same conditions. The addition of the two MMT sheet type nanoclays led to substantial improvement in the barrier properties of polylactide, which was attributed to the inherent restriction offered by the inorganic filler towards the movement of gases through the film. This could be connected to the observed change in the degradation product patterns as the formed degradation products, especially the longer oligomers, could be partially trapped inside the films leading to catalytic effect, higher mass loss at later stages of hydrolysis as well as release of shorter lactic acid oligomers into the ageing water. The nanocomposites generally exhibited higher contact angles indicating increased hydrophobicity. However, hyperbranched polyesters additives were found to be preferentially present at the surface of the films which led to increased surface hydrophilicity for these materials. The hydrolytic degradation was performed at 60 °C for up to 12 weeks and the process was monitored by mass loss measurements, molar mass changes and calorimetric studies. The water-soluble degradation products were examined by electrospray ionization-mass spectrometry (ESI-MS). © 2012 Elsevier Ltd. All rights reserved. Source

Jain M.,Guru Jambheshwar University of Science and Technology | Garg V.K.,Guru Jambheshwar University of Science and Technology | Kadirvelu K.,Center for Fire
Journal of Environmental Management | Year: 2010

This paper reports the adsorption of Cr(VI) ions from aqueous solution by sulphuric acid treated sunflower waste. Two adsorbents, namely SHC and SSC, were prepared from sunflower plant head and stem waste. The adsorbents were characterized by FT-IR, SEM and EDX. The surface areas of SHC and SSC were 1.17 and 1.28 m2 g-1, respectively. The effect of various process parameters namely pH, temperature, initial metal ion concentration, adsorbent dosage and contact time has been studied. The optimum conditions for removal of Cr (VI) were found to be pH = 2, contact time = 2 h, adsorbent dosage = 4.0 g/L, concentration = 250 mg/L, temperature = 25 ± 1 °C, rpm = 180. The percent removal at these optimum conditions was found to be 75.7% and 85.4% for SHC and SSC respectively. The Freundlich, Langmuir and D-R models were applied for mathematical description of adsorption equilibrium. Adsorption data were well described by the Langmuir isotherm with maximum adsorption capacities of 53.76 mg/g and 56.49 mg/g for SHC and SSC, respectively. Overall, the experimental results suggest that SHC and SSC could be used as low cost alternative adsorbents for the treatment of Cr(VI) containing wastewater. A comparison of different kinetic models showed that our data fitted well to the pseudo-second order model. © 2009 Elsevier Ltd. All rights reserved. Source

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