Y.K. Bhardwaj

Synthesis and swelling characteristics of poly (N-isopropylacrylamide) temperature sensitive hydrogels crosslinked by electron beam irradiation

Abstract Temperature sensitive fast response poly (N-isopropylacrylamide) (PNIPAAm) hydrogels have been synthesized by simultaneously polymerizing and crosslinking NIPAAm monomer in aqueous solutions by electron beam (EB) and gamma irradiation and their equilibrium and dynamic swelling behavior have been investigated. The weight change kinetic studies show that radiation crosslinked hydrogels swell/deswell to attain equilibrium at much faster rate with diffusion coefficient values D ≈4.0×10 −7 cm 2 s −1 and 15×10 −5 cm 2 s −1 for swelling and deswelling respectively. The effect of radiation characteristics such as irradiation dose, dose rate on the lower critical solution temperature (LCST), gelation dose ( D g ) and swelling behavior of the resultant PNIPAAm gels has also been investigated.

Development of adsorbent from Teflon waste by radiation induced grafting: Equilibrium and kinetic adsorption of dyes

Mutual radiation grafting technique was employed to graft polyacrylic acid (PAA) onto Polytetrafluoroethylene (Teflon) scrap using high energy gamma radiation. Polyacrylic acid-g-Teflon (PAA-g-Teflon) adsorbent was characterized by grafting extent measurement, FTIR spectroscopy, SEM and wet ability & surface energy analysis. The PAA-g-Teflon adsorbent was studied for dye adsorption from aqueous solution of basic dyes, namely, Basic red 29 (BR29) and Basic yellow 11 (BY11). The equilibrium adsorption data were analyzed by Langmuir and Freundlich adsorption isotherm models, whereas, adsorption kinetics was analyzed using pseudo-first order, pseudo-second order and intra-particle diffusion kinetic models. Equilibrium adsorption of BR29 was better explained by Langmuir adsorption model, while that of BY11 by Freundlich adsorption model. The adsorption capacity for BY11 was more than for BR29. Separation factor (R(L)) was found to be in the range 0 < R(L) < 1, indicating favorable adsorption of dyes. Higher coefficient of determination (r(2) > 0.99) and better agreement between the q(e,cal) and q(e,exp) values suggested that pseudo-second order kinetic model better represents the kinetic adsorption data. The non-linearity obtained for intra-particle diffusion plot indicated, more than one process is involved in the adsorption of basic dyes. The desorption studies showed that ~95% of the adsorbed dye could be eluted in suitable eluent.

Electron Beam Grafted Polymer Adsorbent for Removal of Heavy Metal Ion from Aqueous Solution

Abstract An electron beam grafted adsorbent was synthesized by post irradiation grafting of acrylonitrile (AN) on to a non‐woven thermally bonded polypropylene (PP) sheet using 2 MeV electron beam accelerator. The grafted poly(acrylonitrile) chains were chemically modified to convert a nitrile group to an amidoxime (AMO) group, a chelating group responsible for metal ion uptake from an aqueous solution. The effect of various experimental variables viz. dose, dose rate, temperature, and solvent composition on the grafting extent was investigated. PP grafted with the amidoxime group (AMO‐g‐PP) was tested for its suitability as an adsorbent for removal of heavy metal ions such as Co2+, Ni2+, Mn2+, and Cd2+ from aqueous solution. Langmuir and Freundlich adsorption models were used to investigate the type of adsorption of these ions. The adsorption capacities of the adsorbent for the metal ions were found to follow the order Cd2+>Co2+>Ni2+>Mn2+. The kinetics of adsorption of these ions indicated that the rate of adsorption of Cd2+ was faster than that of other ions studied.

Structure–reactivity studies on the crosslinking of poly(vinyl methyl ether) in aqueous solutions: a pulse radiolysis study

Pulse radiolysis techniques have been utilized to generate, characterize and study the kinetics of crosslinking reactions of the radicals of a temperature-sensitive polymer poly(vinyl methyl ether)(PVME) in aqueous solutions. The transient species formed on reaction with ˙OH has an absorption maximum at 310 nm with molar absorptivity (Iµ)= 1060 ± 330 dm3 mol–1 cm–1. The rate constant for the reaction of ˙OH with PVME has been determined as 3.2 × 108 dm3 mol–1 s–1 by competition kinetics at 296 K. The decay profile of the transient species has been found to vary with the polymer concentration and/or dose rate indicating different modes of recombination under various conditions of irradiation. These results have been interpreted in terms of intra- and inter-molecular crosslinking reactions of polymer radicals and it has been shown that when the intramolecular crosslinking reaction predominates, the decay kinetics deviates from the classical second order and shows a time-dependent behaviour. Since the polymer undergoes a coil–globule transition above 307 K, the bimolecular rate constant for the reaction of ˙OH with the polymer and the decay kinetics of radicals formed have also been investigated at 318 K.

Polychloroprene rubber/ethylene-propylene diene monomer/multiple walled carbon nanotube nanocomposites: synergistic effects of radiation crosslinking and MWNT addition

Synergistic effect of MWNT induced reinforcement and high energy radiation induced crosslinking on the physico-mechanical and thermal characteristics of polychloroprene rubber (PCR)/ethylene-propylene diene rubber (EPDM)/MWNT elastomeric nanocomposites was investigated. The extent of reinforcement, as assessed using the Kraus equation suggested high reinforcement of the blend on MWNT addition; though, the thermal stability and glass transition of the PCR and EPDM components were not significantly affected by MWNTs. The elastic modulus increased with the radiation dose as well as with the increase in MWNT content. The reinforcing mechanism of the nano-composites was studied by various micromechanics models all of which predicted higher moduli than the experimentally observed results, indicating agglomeration in the nano-composites. Nevertheless, in all the composites synergistic effect of radiation crosslinking and MWNT induced reinforcement were seen, suggesting radiation induced crosslinking between polymer and MWNT interface.

An insight into the effective advanced oxidation process for treatment of simulated textile dye waste water

The efficiencies of the advanced oxidation processes (AOP) viz. photocatalysis, ozonolysis and gamma radiolysis in the absence and presence of potassium persulfate (K2S2O8) were systematically investigated for the treatment of simulated textile dye waste water (STDWW) containing Reactive Red 120. The oxygen-equivalent chemical-oxidation capacities of photocatalysis, ozonolysis and gamma radiolysis in the absence and presence of K2S2O8 for 16% mineralization of STDWW were calculated as 4.02, 16.19, 0.13, 0.05 kg equiv. O2 m−3, respectively. The gamma radiolysis in the presence of K2S2O8 showed the maximum extent of mineralization among these three AOPs. The pulse radiolysis studies revealed that the favourable reaction of SO4˙− with SDBS (the most robust organic component of STDWW) producing benzyl and hydroxycyclohexadienyl type of radicals caused the enhancement in the extent of mineralization of STDWW during gamma radiolysis in the presence of K2S2O8. The COD of the STDWW was brought down to 1558 ppm from 3128 ppm by gamma radiolysis at 50 kGy dose in the presence of K2S2O8; though that index could not meet the allowed discharge limit (COD ≤ 250 ppm) of industrial effluent in the main water stream. Conversely, on replacing organic acid (CH3COOH) by inorganic acid (H2SO4) in the pH adjustment step, COD of STDWW was brought down to 245 ppm by gamma radiolysis at 60 kGy in the presence of K2S2O8. This paper recommends using H2SO4 in place of CH3COOH in the pH adjustment step followed by the gamma radiolysis of STDWW in the presence of K2S2O8 for an effective effluent treatment.

Evaluation of efficiencies of radiolysis, photocatalysis and ozonolysis of modified simulated textile dye waste-water

The efficiencies of the advanced oxidation processes (AOPs), viz. electron beam radiolysis in the presence of K2S2O8, gamma radiolysis in the presence of K2S2O8, photocatalysis, photocatalysis in the presence of K2S2O8, photolysis in presence of K2S2O8, ozonolysis and ozonolysis in the presence of K2S2O8, were systematically investigated for the treatment of modified (pH adjusted with H2SO4) simulated textile dye waste-water (MSTDWW) containing Reactive Red-120. The efficiencies of these AOPs were investigated in terms of their oxygen-equivalent chemical oxidation capacity, and the cost of energy and other ancillary inputs. The least amount of oxidant was required by electron beam radiolysis compared to the other AOPs studied here, to achieve the same extent of mineralization of MSTDWW. To the best of our knowledge, this study is the first to report an approach to calculate the equivalent cost of gamma radiolysis in comparison to other AOPs consuming electrical energy. Among these AOPs, the electron beam treatment of MSTDWW in the presence of K2S2O8 had the lowest effective cost.

Correlation between surface energy and uptake behavior of radiation-grafted methacrylic acid-g-LDPE

An efficient and low-cost effluent adsorbent has been developed by grafting an ionizable monomer onto polyolefin surface and its efficacy was tested for dyes and metal ion uptake from aqueous medium. The grafted matrix was synthesized by optimizing various experimental parameters such as irradiation dose, dose rate, monomer concentration, inhibitor concentration, surfactant concentration, and backbone thickness. Grafting yield decreased with dose rate and thickness and increased with the concentration of methacrylic acid and inhibitor. Grafting kinetics studies indicated that grafting rate is comparatively much affected by dose rate that monomer concentration. Surface energy of the grafted surface was accessed from dynamic contact angle measurements. Uptake study of Basic Red 29, Methylene Blue showed high correlation with grafting yield and polar component of the surface energy; however, metal ion uptake was exceptionally high at ~25 grafting (%), highlighting anomalous behavior of MAA-g-LDPE with respect to surface energy and total ion uptake capacity.

Radiation Processed Styrene-Butadiene Rubber/Ethylene-Propylene Diene Rubber/Multiple-Walled Carbon Nanotubes Nanocomposites: Effect of MWNT Addition on Solvent Permeability Behavior

Different compositions of SBR/EPDM 50:50 blends containing multiple-walled carbon nanotubes (MWNT) as nanoparticulate fillers (0.5%–10%) were evaluated for radiation sensitivity and solvent permeability. The efficiency of radiation ***cross-linking was analyzed by gel-content and Charlesby–Pinner parameter measurements. ***Gamma-radiation-induced cross-linking extent was found to increase with radiation dose and MWNT concentration, which was reflected in different extents of swelling. Rigorous analysis of swelling and diffusion data, on the basis of the transport exponent (n) values and diffusion/relaxation rate indicated anomalous diffusion behavior for most of the nanocomposites. The swelling extent in different solvents was found to be a function of polymer-solvent interaction as well as stearic hindrance due to the structure/size of the solvent molecules. Polymer-filler interaction investigated by a Kraus plot indicated high reinforcement of the SBR/EPDM matrix on MWNT addition. There was no significant change in surface energy or hydrophilicity of the SBR/EPDM matrix on introduction of MWNT into it.

Swelling response of radiation synthesized 2-hydroxyethylmethacrylate-co-[2-(methacryloyloxy)ethyl] trimethylammonium chloride hydrogels under various in vitro conditions.

High-energy 60Co gamma radiation has been used to synthesize 2-hydroxyethylmethacrylate-co-[2-(methacryloyloxy)ethyl]trimethylammonium chloride (HEMA-co-MAETC) polyelectrolyte hydrogels. HEMA-co-MAETC co-polymer gels were characterized and investigated for swelling behaviour in different swelling conditions. Fourier transformed infrared spectroscopy (FT-IR) and scanning electron microscopy (SEM) techniques were used to characterize the co-polymer gels. Swelling extent of the gels was found to be a linear function of MAETC content in the gels. The effect of ionic strength, temperature, pH, some solutes of biological importance like glucose, urea, and surfactants such as Triton-X and deoxycholic acid on swelling behavior have been reported. The swelling of gels at higher temperature enhanced the swelling rates but not the swelling extent. HEMA-co-MAETC hydrogel exhibited an excellent responsive characteristic to the ionic strength of the swelling medium. It was found that the swelling of the co-polymer gel at 60°C reduced the swelling–deswelling cycle time by approx. 30% without altering the swelling extent. The gels were also investigated for their swelling in aqueous solutions of anionic dyes, acid blue 25 (AB25), acid blue (AB74) and acid yellow 99 (AY99), and were found to be suitable for dye uptake applications.