Thermokinetics behavior of epoxy adhesive reinforced with low viscous aliphatic reactive diluent and nano-fillers

Amit Kumar Singh,Bishnu Prasad Panda,Smita Mohanty,Sanjay Kumar Nayak,Manoj Kumar Gupta 한국화학공학회 2017 Korean Journal of Chemical Engineering Vol.34 No.11

The current study reports the effect of low viscous aliphatic reactive diluent (RD), MWCNT and VGCF on the curing kinetics of amine cured epoxy adhesive system employing non-isothermal differential scanning calorimetric (DSC) technique. Non-isothermal DSC thermograms of epoxy adhesive were studied at various heating rates: 5, 10 and 15 oC/min. The decrease in the exothermic peak height with the introduction of MWCNTs and VGCFs was taken as proof of the acceleration effect of nano-fillers on the epoxy-amine curing reaction. Also, increased Tonset, TP and ΔHcurs values were observed for epoxy/RD adhesive system at all heating rates. The value of activation energy (Ea) was determined using Kissinger and Flynn-Wall-Ozawa methods. Experimental results showed that the addition of 10 wt% RD increased the Ea from 60 to 63 kJ/mol on account of the reduced viscosity, allowing better contact of resin with the curing agent. Furthermore, MWCNTs have an accelerating effect on the cure kinetics that does not change the autocatalytic cure reaction mechanism of epoxy resin. It was also found that the addition of MWCNT and VGCF decreases the overall degree of conversion, as evident with lower ΔHcure and Ea of the cured adhesive when compared with epoxy/RD system. The dependency of Ea on degree of conversion ranging from α =0.1 to 0.9was also investigated. The two normalized functions y(α) and z(α) were also considered in order to study the complex curing mechanism. The kinetic parameters m, n and lnA were obtained by using two parameter autocatalytic Sestak-Berggren model. The curves revealed good agreement between experimentally determined and theoretically obtained MWCNT/VGCF reinforced epoxy adhesive systems.

Surface Modification Induced Photoluminescence Enhancement of GaN Nanowall Network Grown on c-Sapphire

Varun Thakur,Sanjay Kumar Nayak,Kodihalli Keeriti Nagaraja,Sonnada Math Shivaprasad 대한금속·재료학회 2015 ELECTRONIC MATERIALS LETTERS Vol.11 No.3

Surface nitridation of the c-sapphire substrate is used to improve the optical and structural quality of a GaN nanowall network film grown by plasma assisted molecular beam epitaxy. The nitridation results in the formation of a thin AlN layer on the sapphire surface. Several in-situ and ex-situ characterization are complementarily used to probe the changes in epitaxial growth, band edge emission and strain in the films. The GaN nanowall network layer formed on the pre-nitrided substrate shows a two order higher intensity of band edge luminescence than that of a GaN epilayer, demonstrating its potential for light-emission applications.

Influence of thermally induced, dehydroxylated nanoclay on polymer nanocomposites

Priyanka Pandey,Sanjay Kumar Nayak,Smita Mohanty 한국화학공학회 2014 Korean Journal of Chemical Engineering Vol.31 No.8

This work reports a novel approach towards a chemical-free treatment of nanoclay through extensive thermalexposure. Dehydroxylation at high temperature was utilized to enhance the influence of nanoclay on the propertiesof polymer. The effect of this treatment of nanoclay, on the polymer properties, with reference to Polypropylene (PP)has been investigated. The FTIR spectra revealed the successful removal of water from the intergallery spacing of thenanoclay. The maintained structural configuration of the clay was confirmed using WAXD pattern. The uniform dispersionand exfoliation of thermally treated clay layers inside the polymer matrix was confirmed through enhancedmechanical properties. Improved crystallization properties, thermal stability and flame retardant characteristic werealso noticed in the nanocomposites reinforced with thermally dehydroxylated clay. This study revealed that the dehydroxylationapproach of modification of nanoclay may provide much enhanced properties of polymer, without involvementof any chemical for modification.

Nanotoxicity of Rare Earth Metal Oxide Anchored Graphene Nanohybrid: A Facile Synthesis and In-Vitro Cellular Response Studies

Sriparna De,Smita Mohanty,Sanjay Kumar Nayak,Suresh K. Verma,Mrutyunjay Suar 성균관대학교(자연과학캠퍼스) 성균나노과학기술원 2015 NANO Vol.10 No.6

Graphene, a single sp2 bonded carbon, is now a burgeoning interest with various fascinating properties in a large number of biomedical applications. Consequently, the impact of graphenebased functional nanohybrid and its potential risk to human health have raised considerable public concerns. In this present study, we have synthesized cerium oxide (CeO2) anchored reduced graphene oxide (RGO) nanohybrid and a detailed study on its nanotoxicity profile has also been scrutinized. To confirm the efficient synthesis of nano-CeO2/RGO nanohybrid, the systematic characterization has been carried out using FTIR, Raman and UV-Vis spectroscopic analysis. The successful imprint of CeO2 nanoparticles (NPs) on RGO nanosheet was also evident from the scanning electron microscopy (SEM) and transmission electron microscopy (TEM) micrographs. A dose-dependent in vitro nanotoxicity of the nanohybrid has been assessed by using monocyte macrophage cells-Raw264.7 and colon cancer cells-HCT116 as compared with RGO and CeO2. The results conferred that as compared with single nanostructures (RGO or CeO2), nanohybrid showed excellent biocompatibility and no such prominence morphological alteration of the cell structure. Moreover, after exposure of different nanomaterials to HCT116 cells, the possible cellular interaction was investigated through reactive oxygen species (ROS) measurements using flow cytometry analysis dicholoro-dihydro-fluorescen dia-acetate (DCF) assay. These results conveyed that nanohybrid adapts an oxidative stress mechanism upon cellular interaction where it utilizes the scavenging property of CeO2, which induces the cell proliferation. Overall, the nano-CeO2/RGO nanohybrid exhibits a prolonged biocompatibility and cell viability, which is highly desired for biomedical applications.

Study of UV aging on the performance characteristics of vegetable oil and palm oil derived isocyanate based polyurethane

Sonalee Das,Priyanka Pandey,Smita Mohanty,Sanjay Kumar Nayak 한국화학공학회 2017 Korean Journal of Chemical Engineering Vol.34 No.2

The impact of UV aging on the characteristic properties of synthesized polyurethane (PUs) from castor oil and transesterified castor oil with palm oil based isocyanate and 1,4 butanediol was investigated at different exposure time of 0, 250, 500, 750 and 1,000 h, respectively. The aging properties of the PU films were analyzed through differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), Scanning electron microscopy (SEM) and Tensile tests. The PU films derived from castor oil showed noticeable changes in chemical structure after 250 h of UV exposure owing to chain scission of the urethane group. A considerable decrease in the thermal and tensile properties of the developed PU films was observed due to the plasticization phenomenon. SEM micrographs revealed morphological changes through the appearance of cracks and blisters composed of primary amines on the surface of exposed PU films. However, PUs derived from transesterified castor oil with a higher hydroxyl value exhibited improved UV resistance characteristics due to higher crosslinking and degrade only after 750 h of exposure. Thus, the synthesized green PUs based on transesterified castor oil with palm oil based isocyanate compositions can be candidate materials for developing UV resistant coating material.

Effect of nanofillers on selectivity of high performance mixed matrix membranes for separating gas mixtures

Suchhanda Srabanee Swain,Lakshmi Unnikrishnan,Smita Mohanty,Sanjay Kumar Nayak 한국화학공학회 2017 Korean Journal of Chemical Engineering Vol.34 No.8

Techniques for separation of gas mixtures obtained from various sources, such as effluents from industries, and biogas, have always fascinated researchers. The advent of mixed matrix membranes (MMMs) has opened up a new window of opportunity for developing membranes coupled with flexibility, processability, and permeability of polymers and selectivity of inorganic nanomaterials. This review is a detailed overview of the effect of various nanofillers on the separation performance of MMMs including the major factors affecting the perm-selectivity and possible solutions for overcoming the emerging challenges. The paper also presents contemporary approaches for cost-effective implementation of MMMs. Methodologies for designing MMMs with improved interfacial morphology to exploit their full potential in tailoring the selectivity efficiency are also discussed in detail. This review can act be a guideline for the future development of high-performance MMMs for industrial applications without compromising long-term separation performance, durability, and stability to processing conditions.

Nanomaterial Enhanced Polyelectrolyte Membranes for Hydrogen-Oxygen Fuel Cells

Abdul Kalam Azad,Lakshmi Unnikrishnan,Smita Mohanty,Sanjay Kumar Nayak 한국고분자학회 2021 폴리머 Vol.45 No.1

The solid electrolyte membrane for a hydrogen-oxygen fuel cell was prepared and investigated from the potential of sulfonated poly(ether ether ketone) (SPEEK) embedded together with montmorillonite (MMT). Acid hydrophilized poly(ether ether ketone) (PEEK) and MMT with varying sulfonation levels of 25-70% prepared through solvent casting were investigated for their performance. The nuclear magnetic resonance (1H NMR) spectra at 7.5 ppm affirmed the occurrence of sulfonation reaction, and its degree was studied by both 1H NMR and titration method. The reaction time was varied to achieve sulfonation levels from 25 to 70%. The effect of incorporation of pristine and sulfonated MMT into SPEEK was examined. The membranes, prepared using solvent casting technique, were involved for water uptake over the wide range of temperature, thermal stability, and proton conductivity measurements. The cross-sectional surface arrangement of the membrane and clay dispersion was deliberated using SEM. The proton exchange membrane fuel cell (PEMFC) single cell’s tests revealed that sulfonated PEEK membrane demonstrated service performance comparable to that of Nafion, as validated using MATLAB software.

Synthesis and Characterization of Vegetable Oil Based Polyurethane Derived from Low Viscous Bio Aliphatic Isocyanate: Adhesion Strength to Wood-Wood Substrate Bonding

Swarnalata Sahoo,Hemjyoti Kalita,Smita Mohanty,Sanjay Kumar Nayak 한국고분자학회 2017 Macromolecular Research Vol.25 No.8

In the current study, biobased polyurethane (PU) adhesives at three different stoichiometric ratios of hard (NCO) to soft segment (OH) (1.1:1, 1.3:1, 1.5:1) were prepared by reacting castor oil (CO) based polyol with partially biobased polyisocyanate (PBPI) in the presence of dibutyltin dilaurate (DBTDL) as catalyst. The synthesis of PU adhesive films such as CO-PU1.1:1, CO-PU1.3:1, and CO-PU1.5:1 was confirmed by Fourier transform infrared (FTIR) spectroscopy. The effect of stoichiometric ratios on the bonding strength of wood-to-wood substrate was studied using lap shear strength test. The change in lap shear strength of PU adhesive films subjected to acid and alkali solution was tested. The chemical resistance, surface properties and wetting energies of PU adhesive films were evaluated using scanning electron microscopy (SEM) analysis and contact angle measurement. Thermal stability and activation energy of the films were determined employing thermogravimetric analysis (TGA). The experimental result showed that CO-PU1.3:1 exhibited higher adhesive strength, where as CO-PU1.5:1 exhibited higher thermal stability.

Biobased Epoxy Blends from Epoxidized Castor Oil: Effect on Mechanical, Thermal, and Morphological Properties

Sudha G. S.,Hemjyoti Kalita,Smita Mohanty,Sanjay Kumar Nayak 한국고분자학회 2017 Macromolecular Research Vol.25 No.5

In the present study, in-situ epoxidation was employed to prepare epoxidized castor oil (ECO). Fourier transform infrared spectroscopy and proton nuclear magnetic resonance spectra analysis were used to analyze the chemical structures of ECO. Biobased epoxy blends were synthesized from diglycidyl ether of bisphenol A (DGEBA) and ECO at variable wt% using triethylenetetramine as curing agent. The thermal, mechanical and morphological behavior of blends has been investigated. The morphological study showed homogeneous mixing of the ECO and DGEBA blends. The blend prepared using 20wt% of ECO showed optimum impact and flexural strength as compared with commercially available epoxy resin. The fracture toughness parameters, critical stress intensity (KIC) and the critical strain of blends were also observed to increase as compared with the virgin matrix which revealed enhancement in toughness. The tensile property of the blend reduced with the increasing ECO content which confirmed the fact that the addition of the high amount of ECO reduces the crosslink density of the biobased epoxy.

Insight into mechanical, thermal, and chemical stability of polysulfone-based membranes for the separation of O2/N2

Suchhanda Srabanee Swain,Lakshmi Unnikrishnan,Smita Mohanty,Sanjay Kumar Nayak 한국화학공학회 2022 Korean Journal of Chemical Engineering Vol.39 No.3

MMMs have opened up a new window in gas separation and purification applications, but the actual viability can be reckoned on the basis of performance achieved in realistic feed conditions. This research highlights the selection of silica-decorated graphene for the first time to prepare nanocomposite membranes. XRD, Raman, and UV validated the existence of different fillers within the host Polysulfone (PSf), while TEM authenticated their distribution. The burst strength and thermal properties were also investigated for the prepared samples. This study also covered a prudent step towards resolving the dominant ingredients, which routinely appraise the stability and durability of the membranes. These indexes are long-term gas permeation stability up to 120 hours coupled with sustainability against hydrothermal and chemical resistance under various conditions similar to real-life gas separation applications. Finally, the report demonstrates that the nanohybrid integrated membrane systems display optimum performance and stability in all the aspects as compared to their parent counterparts: PSf/mSiO2 and PSf/GO.