Preparation and properties of acrylonitrile–butadiene rubber–graphene nanocomposites

The graphene oxide (GO) was prepared by sonication‐induced exfoliation from graphite oxide, which was produced by oxidation from graphite flakes with a modified Hummer's method. The GO was then treated by hydrazine to obtain reduced graphene oxide (rGO). On the basis of the characterization results, the GO was successfully reduced to rGO. Acrylonitrile–butadiene rubber (NBR)–GO and NBR–rGO composites were prepared via a solution‐mixing method, and their various physical properties were investigated. The NBR–rGO nanocomposite demonstrated a higher curing efficiency and a change in torque compared to the gum and NBR–GO compounds. This agreed well with the crosslinking density measured by swelling. The results manifested in the high hardness (Shore A) and high tensile modulus of the NBR–rGO compounds. For instance, the tensile modulus at a 0.1‐phr rGO loading greatly increased above 83, 114, and 116% at strain levels of 50, 100, and 200%, respectively, compared to the 0.1‐phr GO loaded sample. The observed enhancement was highly attributed to a homogeneous dispersion of rGO within the NBR matrix; this was confirmed by scanning electron microscopy and transmission electron microscopy analysis. However, in view of the high ultimate tensile strength, the NBR–GO compounds exhibited an advantage; this was presumably due to strong hydrogen bonding or polar–polar interactions between the NBR and GO sheets. This interfacial interaction between GO and NBR was supported by the marginal increase in the glass‐transition temperatures of the NBR compounds containing fillers. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42457.     

A new proposed model for dielectric behavior of PVC/rice husk composites

Ecofriendly materials are becoming a need of the day. We have severe setback when there is lot of use of agro wastes in plastics. To reduce pure plastic use in agriculture, this study has been made to find some remedial measure. In the process, we sought the effect of addition of rice husk (RH) in polyvinylchloride (PVC) on the dielectric properties at different frequency and temperature has been studied. Measurements have been performed in the frequency range from 1 to 10 kHz and temperature range of 32–80°C. The experimental results show that dielectric constant (ε′) increases with the addition of RH in PVC. Dielectric constant (ε′) decreases with increasing frequency, which indicates that the major contribution to the polarization comes from orientation polarization. Dielectric constant (ε′) increases with increasing temperature due to greater freedom of movement of dipoles within PVC at higher temperatures. A theoretical model for dielectric constant with temperature and frequency dependent is proposed. Experimental results are in good agreement with the proposed theoretical model. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Adsorption equilibrium,thermodynamics, kinetics,mechanism and process design of zinc(II) ions onto cashew nut shell

Cashew nut shell (CNS) is an agricultural waste was investigated as a new adsorbent for the removal of zinc(II) from aqueous environment. Effects of solution pH, CNS dose, contact time, initial zinc(II) concentration and temperature on removal efficiency were tested and optimum conditions were evaluated. The equilibrium data were fitted well with Langmuir isotherm model and pseudo‐second‐order kinetic model. Langmuir monolayer adsorption capacity of CNS was examined as 24.98 mg/g. Changes in standard Gibbs free energy (?G°), standard enthalpy (?H°) and standard entropy (?S°) showed that the sorption of zinc(II) ions onto CNS are spontaneous and exothermic at 303–333 K. Sorption process was found to be controlled by both surface and pore diffusion. A batch adsorber was designed for different CNS dose to effluent volume ratios using Langmuir equation. Effective diffusivity values were found to be 1.927 × 10^?11 (10 mg/L), 2.135 × 10^?11 (20 mg/L), 2.267 × 10^?11 (30 mg/L), 2.305 × 10^?11 (40 mg/L) and 2.362 × 10^?11 (50 mg/L) m²/s. © 2011 Canadian Society for Chemical Engineering     

Chloride-free biodegradable organic acid hydrolyzed zinc silicate coating

Partially hydrolyzed ethyl silicate has widely been used as a binder to formulate inorganic zinc silicate paint for anticorrosive coating applications. Hydrochloric acid is used most popularly to catalyze the hydrolysis of ethyl silicate. Although different acids have been tried as catalysts for ethyl silicate hydrolysis, no attempt has been made to make stable paints out of those hydrolyzed silicate binders. In this study, environment benign biodegradable organic acids such as oxalic acid, citric acid, lactic acid and acetic acid were used for the hydrolysis of ethyl silicate and compared with the hydrolysis using conventional hydrochloric acid. The hydrolyzed silicate sols were pigmented further with silica powder and evaluated for their stability. Of the various organic acids catalyst used, only oxalic acid catalyzed sol acted as a stable binder system. The pigmented binder was then mixed with metallic zinc to formulate anticorrosive inorganic zinc silicate paint. The resultant coatings were characterized for various physical, surface, mechanical and chemical resistance properties such as drying, hardness, adhesion (cross hatch) and solvent resistance. Corrosion resistance properties were analyzed by means of salt spray, open circuit potential (OCP) and electrochemical impedance spectroscopy (EIS). The results revealed that the physical, mechanical, chemical and anticorrosive properties of the coating hydrolyzed with hydrochloric acid and oxalic acid are comparable. Thus, a chloride free biodegradable organic acid hydrolyzed inorganic zinc silicate primer is reported and due to its long term stability same also can be scaled up commercially.     

An Assessment of the Applicability of Particle Light Scattering Theories to Birefringent Polycrystalline Ceramics

The applicability of particle light scattering theories to light attenuation in birefringent polycrystalline ceramics was investigated by measuring light transmittance in a model two‐phase system. The system consisted of microspheres of silica dispersed in a solution of glycerol in water. The composition of the liquid medium was chosen to produce a mismatch between the refractive index of the particles (n_p) and of the medium (n_m) equal to the root mean square of the refractive index variation in polycrystalline magnesium fluoride. The variations of the scattering coefficients (γ) with volume fraction of silica microspheres for three different particle diameters (0.5, 1.0 and 1.5 μm) were compared with theoretical predictions based on scattering efficiency of single particles (K) and linear extrapolation to multiparticle dispersed systems. The measured scattering coefficients were significantly greater than the theoretical values for particle volume fractions greater than 0.2. These results suggest that application of particle scattering theories to a birefringent polycrystalline ceramic, an intrinsically high volume fraction system, is tenuous at best.     

A Functionally Graded Carbide in the Ta–C System

Hard materials used in such abrasive wear applications as cutting tools and wear inserts in drilling tools require high hardness to resist wear, high fracture toughness to withstand mechanical and thermal shock, and high chemical and thermal stability. Such a combination of properties is difficult to achieve in single‐phase materials. Functional grading is an approach that overcomes this limitation by designing and processing a graded microstructure that provides high hardness and chemical resistance at the surface with a tough interior or bulk. While functional grading is a widely used practice in the cemented carbides industry, it has not been demonstrated with “pure” carbides. This article reports the feasibility of designing and processing a graded carbide in the Ta–C binary system. It is shown that a simple carburization treatment of the high‐toughness carbide, ζ‐Ta₄C_3?x, can lead to the formation of the hard carbide phase, γ‐TaC_y, on the surface. The thickness, microstructure (grain size), and composition (C/Ta atomic ratio, y) of the γ‐TaC_y layer can be optimized to obtain both high hardness and high strength for the graded material.     

The outlook of zeolite-Y hampered metal–ligand framework as heterogeneous catalysts: synthesis,spectral account and catalytic features

Zeolite-Y enslaved complexes were prepared by the Flexible ligand method. Synthesized materials were characterized by various spectral tools like powder X-ray diffraction, spectral studies (UV–Vis and FT-IR), chemical analysis (ICP-OES and elemental), scanning electron microscopy, AAS and ¹H-NMR techniques. Further, BET and thermogravimetric (TG) analysis were also done for characterization of surface area, pore volume, thermal behavior, and related parameters. Baeyer–Villiger oxidation of cyclohexanone was carried out over Zeolite-Y enslaved complexes using hydrogen peroxide (H₂O₂) as an oxidant. The performance of the heterogeneous system with the homogeneous system was compared to determine the protection effect of the zeolitic matrix over the active center on the catalytic properties. In addition, the effect of experimental variables (various solvents, amount of catalyst, the mole ratio of substrate and oxidant, temperature, and reaction time) was examined in order to get absolute reaction conditions. Under the optimized reaction conditions, [Fe(nbab)₂]-Y was found to be a potential candidate, achieving 70 % ?-caprolactone selectivity.     

Chemical hydrodynamics of a downward microbubble flow for intensification of gas‐fed bioreactors

Bioreactors are of interest for value‐upgrading of stranded or waste industrial gases. Reactor intensification requires development of low cost bioreactors with fast gas–liquid mass transfer rate. Here we assess published reactor technology in comparison with a novel downward bubble flow created by a micro‐jet array. Compared to known technology, the advanced design achieves higher volumetric gas transfer efficiency (k_La per power density) and can operate at higher k_La. We measure the effect of four reactor heights (height‐to‐diameter ratios of 12, 9, 6, and 3) on the gas transfer coefficient k_L, total interfacial area a, liquid residence time distribution, energy consumption, and turbulent hydrodynamics. Leading models for predicting k_L and a are appraised with experimental data. The results show k_L is governed by “entrance effects” due to Higbie penetration dominate at short distances below the micro‐jet array, while turbulence dominates at intermediate distances, and finally terminal rise velocity dominates at large distances. © 2017 American Institute of Chemical Engineers AIChE J, 64: 1399–1411, 2018     

Sustainable bionanocomposite from d,l‐lactide/δ‐valerolactone triblock and bionanowhiskers: Preparation,characterization, and properties

Bionanocomposites were prepared using d ,l ‐lactide–δ‐valerolactone–d ,l ‐lactide triblock and unmodified and modified cellulose nanowhiskers (CNs) at different loadings (0, 2, 4, 8 wt %). Poly(δ‐valerolactone) chains were grafted on CNs for modification. These were characterized by various techniques. The broadening of OH (hydroxyl) stretching region and the presence of low‐intensity peaks at 1064 cm^?1 for C? O/C? C stretching vibration and 1426 cm^?1 for bending vibration of CH₂ group_, were evident in Fourier transform infrared spectra of the nanocomposites. The increase in crystallinity was noticed as the amount of nanowhiskers was increased. The nanowhiskers having the width in the range of 80–300 nm were uniformly dispersed in the triblock matrix. The tensile strength and modulus increased by 130% and 50% respectively at 8 wt % of filler loading. The storage modulus, loss modulus, complex viscosity, and tan δ values increased with increased filler loading. Further improvement in mechanical properties was observed with the modified CNs. The modulus mapping from atomic force microscopy confirmed the effective reinforcement behavior of the nanowhiskers. Scaffold fabrication using the bionanocomposite exhibited porous nature, having a homogeneous dispersion of CNs on the surface of the scaffold. The 3‐(4,5‐Dimethylthiazol‐2‐yl)‐2,5‐diphenyltetrazolium bromide assay confirmed the suitability of the composite material for scaffold application. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 135, 46035.     

On the Effect of Birefringence on Light Transmission in Polycrystalline Magnesium Fluoride

Light transmission in polycrystalline magnesium fluoride was studied as a function of the mean grain size at different wavelengths. The mean grain size was varied by annealing hot‐pressed billets in argon atmosphere at temperatures ranging from 600°C to 800°C for 1 h. The grain‐size and grain‐orientation distributions were characterized by electron back scatter diffraction. The scattering coefficients were calculated from the in‐line transmittance measured at various wavelengths. The scattering coefficient of polycrystalline magnesium fluoride increased linearly with the mean grain size and inversely with the square of the wavelength of light. It is shown that these trends are consistent with theoretical models based on both a limiting form of the Raleigh–Gans–Debye (RGD) theory of particle scattering and light retardation theories that take refractive index variations along the light path. Quantitative predictions of the theories are, however, subject to uncertainly due to the restrictive assumptions made in the theories and difficulties in representing the microstructure in the theoretical models. In particular, grain‐size distribution has a significant influence on the scattering coefficient calculated using particle scattering models.