Mechanism and kinetics of curing of diglycidyl ether of bisphenol a (DGEBA) resin by chitosan

Crosslinking behavior of Diglycidyl Ether of Bisphenol A (DGEBA) resins cured by chitosan was isothermally studied by Fourier Transform Infrared (FTIR) Spectroscopy for various molar ratios of chitosan at different temperatures. Results indicated that oxirane undergoes nucleophilic attack by the primary amine groups in chitosan to form crosslinked structure. Epoxy fractional conversion (α ) was calculated by following the change in area of oxirane peak at 914 cm^?1. Value of α and reaction rate (dα /dt ) increased with increase in curing temperature and chitosan concentration. The maximum epoxy fractional conversion of 70% was obtained for 1:4 molar ratio (Epoxy:Chitosan) at 200°C. A four parameter kinetic model with two rate constants was employed to simulate the experimental data. Overall reaction order and activation energy for all compositions were in the range of 2.5–3 and 25–50 kJ mol^?1, respectively. Results indicated that cure reaction is autocatalytic and does not follow simple n th order cure kinetics. Thermogravimetric analysis (TGA) performed on chitosan cured DGEBA films and compared against neat epoxy and neat chitosan films. Results showed that the degradation of chitosan crosslinked epoxy network occurred in the temperature range of 450–550°C. POLYM. ENG. SCI., 57:865–874, 2017. © 2016 Society of Plastics Engineers     

Synthesis and Characterization of Cadmium Selenide (CdSe) Nanoparticles Using Trigonal Selenium (t-Se) Nanorods as Selenium Source

Cadmium selenide (CdSe) nanoparticles were synthesized through colloidal method in aqueous medium using the reaction intermediates selenium nanorods as selenium source. Trigonal selenium nanorods (t-Se) were synthesized in water by the reduction method in the presence of sodium borohydride at 60?°C using sodium selenite (Na₂SeO₃) as selenium source. These selenium nanorods were further utilized to synthesis cadmium selenide nanoparticles at 100?°C in water. The synthesized nanorods and nanoparticles were characterized using XRD, SEM, TEM and XPS analysis. X-ray diffraction (XRD) analysis shown that the nanorods possess trigonal phase while the nanoparticles possess a cubic zinc blende structure. Scanning electron microscope (SEM) analysis of the prepared hexagonal shaped nanorods reveals the diameter of the nanorods are about 150 nm. Transmission electron microscopy (TEM) analysis shows the size of the synthesized CdSe nanoparticles are about 4–8 nm. X-ray photoelectron spectroscopy (XPS) analysis illustrates the presence of respective elements Cd, Se with its corresponding oxidation states. The activity of nano selenium rods in aqueous solution during the conversion of cadmium selenide nanoparticles was discussed.     

Facile Preparation of LaFeO<Subscript>3</Subscript>/rGO Nanocomposites with Enhanced Visible Light Photocatalytic Activity

The present work demonstrates a facile route for preparing LaFeO₃/rGO nanocomposites comprising of metal oxide nanoparticles and graphene. Structural, morphology, optical and photocatalytic studies of the samples were characterized using powder X-ray diffraction (XRD), FT-IR, Raman, high resolution scanning electron microscopy (HRSEM), high resolution transmission electron microscope (HRTEM), atomic force microscopy (AFM), thermogravimetry (TGA), X-ray photoelectron spectroscopy, UV–visible and photocatalytic. LaFeO₃/rGO nanocomposites believed as an effective photocatalyst for the degradation of methyl orange (MO) dye under visible light irradiation. The inclusion of carbon enhances the light absorption of LaFeO₃, resulting in the enhanced photocatalytic activity of the nanocomposite. The degradation of MO dye under visible light source was completely achieved using LaFeO₃/rGO as a catalyst.     

Solution-processed white graphene-reinforced ferroelectric polymer nanocomposites with improved thermal conductivity and dielectric properties for electronic encapsulation

The recent surge in graphene research has stimulated interest in the investigation of various two-dimensional (2D) nanomaterials, including 2D boron nitride (BN) nanostructures. Among these, hexagonal boron nitride nanosheets (h-BNNs; also known as white graphene, as their structure is similar to that of graphene) have emerged as potential nanofillers for preparing thermally conductive composites. In this work, hexagonal boron nitride nanoparticles (h-BNNPs) approximately 70 nm in size were incorporated into a polyvinylidene fluoride (PVDF) matrix with different loadings (0–25 wt.%). The PVDF/h-BNNP nanocomposites were prepared by a solution blending technique and characterized using Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), thermogravimetric analysis (TGA), polarized optical microscopy (POM) and scanning electron microscopy (SEM). In addition, the thermal conductivity and dielectric properties of the nanocomposites were investigated. The incorporation of h-BNNPs in the PVDF matrix resulted in enhanced thermal conductivity. The highest value, obtained at 25 wt.% h-BNNP loading, was 2.33 W/mK, which was five times that of the neat PVDF (0.41 W/mK). The thermal enhancement factor (TEF) at 5 wt.% h-BNNP loading was 78%, increasing to 468% at 25 wt.% h-BNNP loading. The maximum dielectric constant of approximately 36.37 (50Hz, 150 °C) was obtained at 25 wt.% h-BNNP loading, which was three times that of neat PVDF (11.94) at the same frequency and temperature. The aforementioned results suggest that these multifunctional and high-performance nanocomposites hold great promise for application in electronic encapsulation.     

Anti-melanogenic effect of <Emphasis Type="Italic">Prunus davidiana</Emphasis> extract in melan-a melanocyte through regulation of OCA-2, TRP-1 and tyrosinase

Prunus spp. and locally available plants (used as folkloric medicine) were screened to find a novel and natural anti-melanogenic agent. Based on p-protein promoter reporter assay (PPRA) the candidate plants were screened in the quest for p-protein inhibitor. Expression profiling of key proteins revealed the molecular mechanism of the melanin inhibition as well as TEM analysis revealed melanosome structure. The screened plant extract through PPRA showed significant down regulation of p-protein, which led to melanin inhibition. Another key melanosomal protein like tyrosinase and TRP-1 was also found to be down-regulated. However, TRP-2 was not affected. TEM analysis of treated cells also revealed that the stage IV melanosomes were lowered in number compared to control. The present study shows the plants used in this study possess good anti-melanogenic properties. However, the P. davidiana has the highest anti-melanogenic property among screened plant extracts.     

Sources and impacts of pharmaceutical components in wastewater and its treatment process: A review

Pharmaceutical compounds and their derivatives are major pollutants in the environment, as their metabolites affect the terrestrial as well as aquatic organisms in one or another way. In recent times, many papers have discussed the treatment procedures for single pharmaceutical and mixture of pharmaceutical components, but only few papers have discussed the fate and the exposure of pharmaceutical contaminants in our environment. In this paper, we discuss the sources and the forms of pharmaceutical products and their resultant in the environment and their addition to the microbial and to human communities. A detailed discussion of various treatment techniques from conventional to current techniques, their advantages and disadvantages is given here. Researchers are finding the techniques in order to completely degrade the contaminants and their transformed products from the environment. Among the technique, s nanotechnology was found to be an efficient technique, and the combination of nanotechnology with other conventional technologies gives higher removal efficiency.     

Microencapsulation of reactive amine by interfacially engineered epoxy microcapsules for smart applications

The most common approach for incorporation of extrinsic self-healing functionality relies on introducing healant-loaded micro-containers in the polymeric formulation. In this context, a healing system based on encapsulated epoxy resin and amine hardener appears to be one of the most economically viable solutions, in view of the chemical as well as mechanical compatibility with the matrix. Encapsulation of epoxy resins has been extensively studied while the high reactivity of the amine hardener renders its encapsulation rather difficult and has been attempted with only modest success. The purpose of the present work is to adopt an interfacial polymerization approach for the preparation of epoxy microcapsules encapsulating a reactive amine hardener (triethylene tetramine). The effects of experimental parameters, including reaction temperature, stirring speed and epoxy/amine concentration ratio on the microcapsule formation were investigated. A polymeric surfactant was used to stabilize the suspension to modulate the particle size distribution of the resultant microcapsules. The highest encapsulation efficiencies were obtained when the reaction medium was maintained at 70 °C under stirring (600 rpm) at epoxy/amine ratio of 10/3.2. The microcapsule dimensions and core content could be tailored, following this encapsulation approach of interfacial polymerisation. Under optimal conditions, spherical microcapsules with 100% yield and 12% core content were obtained.     

Water absorption,residual mechanical and thermal properties of hydrothermally conditioned nano-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> enhanced glass fiber reinforced polymer composites

The durability of the nano-Al₂O₃ enhanced glass fiber reinforced polymer (GFRP) composites in hydrothermal environment is necessary for hydro/hygro thermal applications. The present investigation emphasizes the effect of nano-Al₂O₃ filler concentration on moisture absorption kinetics, residual mechanical and thermal properties of hydrothermally treated GFRP nano-composites. Nano-Al₂O₃ particles were mixed with epoxy matrix through temperature assisted magnetic stirrer and followed by ultrasonic treatment. It has been observed that, the addition of 0.1 wt% of nano-Al₂O₃ into the GFRP nano-composites reduces the moisture diffusion coefficient by 10%, as well as improves the flexural residual strength by 16% and interlaminar residual shear strength by 17% as compared to the neat epoxy GFRP composites. However, the glass transition temperature has not been improved by the addition of nano-Al₂O₃ filler. Weibull design parameters have been determined for dry and hydrothermally conditioned nano-composites. A good agreement between the experimental and the simulated stress–strain results has been observed. The interface failure mechanism has been evaluated by field emission scanning electron microscope to support the new findings.