Influence Of Microwave Radiation Research Articles

Rapid Synthesis of Graft Copolymer of MMA Onto Saccharum spontaneum L. Under Microwave Irradiation for Enhanced Thermal Modifications

In this article, synthesis of graft copolymers of methyl methacrylate (MMA) onto Saccharum spontaneum L. fiber under the influence of microwave radiation (MWR) was carried out. Different reaction parameters such as time, initiator molar ratio, monomer concentrations, microwave power, pH, and solvent were optimized for maximum graft yield (62.3%). The graft copolymers thus formed were characterized by FT-IR, SEM, XRD, and TGA, DTA, and DTG techniques. Moreover, graft copolymers have been found to be more moisture resistant and also showed higher chemical and thermal resistance.

The influence of microwave radiation on the behaviour of Rattus norvegicus

The use of mobile phones has been the target of a great controversy due to possible biological and behavioural effects. This research presents a preliminary evaluation, regarding the learning and stress levels in subjects of the species Rattus norvegicus, submitted to microwave radiation. The psychological analysis was based on laboratory tests using the aquatic maze (tank of Morris), to determine the capacity of learning and memorisation and the elevated cross maze, designed to evaluate the levels of anxiety and stress. The consumption of water and food was monitored as well as the weight of the animals. The experiments were accomplished using irradiated rats (Experimental Group), and non-irradiated rats (Control Group). No significant differences were observed in the learning or performance of the groups in the aquatic maze experiment. For the elevated cross maze tests, the subjects of the Experimental Group manifested lower stress levels.

Influence of microwave radiation on soil bacteria

Cultures of different soil bacteria were used in the experiment. Both the suppression and the stimulation of the growth were observed for different bacterial species under the impact of microwaves. Spore suspensions responded to microwave radiation upon a shorter time of exposure than suspensions of vegetative bacterial cells. The influence of microwave radiation on the biomass accumulation and the intensity of other physiological processes in different species of streptomycetes led to changes in the number and activity of these microorganisms in the soil microbial complex. Changes in the capacity of streptomycetes for assimilation of substrates under the impact of microwaves were identified by the method of multisubstrate testing.

Preparation of microwave radiation induced graft copolymers and their applications as reinforcing material in phenolic composites

AbstractFlax fiber was modified through grafting of binary vinyl monomers mixtures such as methyl methacrylate (MMA)/vinyl acetate (VA), MMA/acrylamide (AAm), and MMA/styrene (Sty) under the influence of microwave radiations. 24.64% grafting was found at 210 W microwave power under optimum reaction conditions. Graft copolymers obtained were characterized with FTIR spectroscopy, scanning electron microscopy, and TGA/DTA techniques. Graft copolymers were found to be moisture retardant with better tensile strength. Phenolic composites using graft copolymers vis‐à‐vis flax as reinforcing material were subjected for the evaluation of different mechanical properties such as wear resistance, tensile strength, compressive strength, modulus of rupture (MOR), modulus of elasticity (MOE), and stress at the limit of proportionality (SP). Composites reinforced with graft copolymers showed better mechanical properties in comparison to composites reinforced with flax. Phenolic composites reinforced with Flax‐g‐poly(MMA/Sty) showed maximum wear resistance followed by reinforcement with flax, Flax‐g‐poly (MMA/AAm), and Flax‐g‐poly(MMA/VA). Composites reinforced with Flax‐g‐poly(MMA/Sty) and flax fibers have been found to show 150 N tensile strength with extension of 3.94 and 2.17 mm, respectively. It has also been found that composites reinforced with Flax‐g‐poly(MMA/Sty) showed maximum compressive strength (1,000 N) with compression of 3.71 mm in comparison to other graft copolymers and flax fibers reinforcement. Reinforcement of phenolic resin with Flax‐g‐poly(MMA/Sty) and flax fibers could improve the MOR and MOE. POLYM. COMPOS., 2008. © 2008 Society of Plastics Engineers

Graft copolymerization of MMA onto flax under different reaction conditions: a comparative study

In the present paper, grafting of methyl methacrylate (MMA) onto flax fiber was carried-out under different reac- tion condition such as in air (IA), under pressure (UP) and under the influence of micro-wave radiations (MWR). Maximum percentage grafting (41.7%) has been observed in case of graft copolymerization carried-out in air at 55°C followed by grafting under pressure (36.4%) at 0.8 MPa and under the influence of microwave radiations (24.6%) at 210 W microwave power. Graft copolymers were characterized with FTIR spectroscopy, scanning electron microscopy (SEM), thermal analy- sis (TGA/DTA) and X-ray diffraction (XRD). Thermal stability of flax decreases on grafting under different reaction con- ditions. In case of XRD studies, cellulose crystals are better oriented in flax fiber followed by Flax-g-poly(MMA)-MWR, Flax-g-poly(MMA)-UP and Flax-g-poly(MMA)-IA.

Mechanical Properties of Phenolic Composites Reinforced with Flax‐g‐copolymers Prepared under Different Reaction Conditions ‐ A Comparative Study

Graft copolymers of methyl methacrylate (MMA) and its binary mixtures such as MMA + ethyl acrylate (EA), MMA + acrylonitrile (AN), MMA + acrylic acid (AA), MMA + vinyl acetate (VA), MMA + acrylamide (AAm) and MMA + styrene (Sty) with flax fiber have been prepared in air (IA) and under the influence of microwave radiations (MWR). Synthesized flax‐g‐copolymers under two different reaction conditions were used as reinforcing material in the preparation of phenol‐formaldehyde composites. Mechanical properties such as wear resistance, modulus of rupture (MOR), modulus of elasticity (MOE) and stress at the limit of proportionality (SP) were measured and a comparative studied has been made. It has been found that composites reinforced with flax‐g‐copolymers‐MWR showed better mechanical properties in comparison to composites reinforced with flax‐g‐copolymers‐IA

Microwave Enhanced Synthesis of Flax‐g‐poly(MMA) for Use in Phenolic Composites as Reinforcement

Graft copolymerization of methyl methacrylate (MMA) onto flax fiber under the influence of microwave radiations (MWR) was carried out. 24.64% grafting was found at 210W microwave power under optimum reaction conditions. The graft copolymers were characterized with FTIR spectroscopy, scanning electron microscopy (SEM) and X‐ray diffraction (XRD) techniques. Graft copolymers thus prepared were used in the preparation of phenol‐formaldehyde (PF) composites. Modulus of rupture (MOR), modulus of elasticity (MOE) and stress at the limit of proportionality (SP) of composites were measured and it has been found that composites reinforced with Flax‐g‐poly(MMA) showed better mechanical properties in comparison to composites reinforced with raw flax.

Grafting of Flax Fiber (Linum usitatissimum) with Vinyl Monomers for Enhancement of Properties of Flax-Phenolic Composites

Binary vinyl monomers such as methylmethacrylate (MMA)/Ethylacrylate (EA), MMA/Acrylonitrile (AN) and MMA/Acrylic acid (AA) have been graft co-polymerized onto flax fibers under the influence of microwave radiations (MWR). Various reaction parameters have been optimized and maximum grafting (25%) was observed in reaction time of 30 min at 210 W microwave power. Flax-g-copolymers thus prepared were used as reinforcing material in the preparation of flax-phenolic composites. Wear resistance was maximum with reinforcement of Flax-g-poly(MMA/AA). Composites reinforced with Flax-g-poly(MMA/EA) showed better tensile strength and can bear load upto 225 N with extension of 3.28 mm and composites reinforced with Flax-g-poly(MMA/AA) showed better compressive strength and can bear load upto 1000 N with compression of 1.74 mm. Maximum values of MOR, MOE and SP were found to be 108.0 N/mm2, 5295.62 N/mm2 and 99.29 N/mm2 for the composites reinforced with Flax-g-poly(MMA/AA). On grafting of flax fibers with vinyl monomers, fibers become more and more moisture retardant. It has been found that strength of Flax-g-copolymers was found more than that of raw flax fibers. Flax-g-poly(MMA/AA) has been found to show good thermal stability in comparison to other graft co-polymers and raw flax fibers. Phenol-formaldehyde (PF) composites reinforced with graft co-polymers of flax fibers showed better mechanical properties in comparison to composites reinforced with raw flax fibers. Composites reinforced with Flax-g-poly(MMA/AA) showed the increased values of MOR, MOE and SP.

GRAFTING MMA ONTO FLAX UNDER THE INFLUENCE OF MICROWAVE RADIATION AND THE USE OF FLAX-g-POLY(MMA) IN PREPARING PF COMPOSITES

Abstract This paper deals with the graft co-polymerisation of methylmethacrylate (MMA) onto flax fibre under the influence of microwave radiation (MWR). The graft co-polymers are characterised by FTIR spectroscopy, scanning electron microscopy (SEM), thermal analysis (TGA/DTA) and X-ray diffraction (XRD). Graft co-polymers are subjected to the evaluation of some physical, chemical and mechanical properties. Graft co-polymers thus prepared are used in the preparation of phenol-formaldehyde composites. Wear resistance, tensile strength and compressive strength of composites are measured, and it is found that composites reinforced with flax-g-poly(MMA) showed better mechanical properties in comparison to composites reinforced with raw flax.

Influence of microwave radiation on bacterial community structure in biofilm

Organic matter exposed to microwave radiation triggers standard thermal effects as well as a range of so called non-thermal effects. The present work examined the non-thermal effects of microwave radiation on the biofilm in bioreactors with immobilised biomass. Microwave-exposed and conventionally heated reactors were used and both groups of reactors operated on analogous technological parameters. The analysis of the treated sewage demonstrated a significant increase in nitrification and denitrification efficiency in the bioreactors treated with microwave radiation. An analysis of bacteria diversity based on DGGE method showed significantly different bacterial communities developed in the reactors exposed to the microwave radiation in comparison to the control reactors. Moreover, bacterial richness measured by Shannon index was significantly higher in the microwave treated samples (Mann–Whitney's test, p < 0.05). These findings indicate that microwave radiation can affect the structure and function of bacterial communities independent of thermal effects.

Influence of microwave radiation on synaptic structure and function of hippocampus in Wistar rats

To investigate the effect of microwave radiation on synaptic structure, characteristic of synaptosome, the contents and release of neurotransmitters in hippocampus in Wistar rats. Wistar rats were exposed to microwave radiation with average power density of 30 mW/cm(2). Electron telescope was used to study the change of the synaptic structure at 6 h after radiation and to identify synaptosome. Flow cytometry and electron spin resonance were used to study the change of the concentration of Ca(2+) in synapse and the fluidity of membrane proteins of synaptosome. High performance liquid chromatography (HPLC) and spectrophotometer were used to study the changes of contents and release of amino acids and acetylcholine in hippocampus. Microwave radiation of 30 mW/cm(2) caused deposits of synapse vesicle, elongation of active zone, the increase of thickness of postsynaptic density (PSD) and curvature, and perforation of synapse. The concentration of Ca(2+) in synapse (P<0.01) and tc of membrane proteins (P<0.01) of synaptosome increased contents of glutamic acid and glycine (P<0.01) and release of GABA increased the increase of contents and release of acetylcholine, and activity of acetyl cholinesterase (P<0.01) increased. Microwave radiation can induce the injure of synaptic structure and function of hippocampus, and then induce the disorder of the ability of learning and memory in rats.

Synthesis and Transformations of Heterocyclic Compounds under the Influence of Microwave Radiation

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.

Influence of microwave radiation on the textural properties of layered double hydroxides

Two series of layered double hydroxides (LDHs) with compositions Mg,Al–CO 3 and Mg,Cr–CO 3 were prepared by microwave and conventional hydrothermal treatment to study the role of microwave radiation on their physicochemical properties. Aging temperature was 125 °C in all cases. The samples were fully characterised by element chemical analysis, powder X-ray diffraction, differential thermal analysis and thermogravimetric analysis, 27Al MAS NMR, FT-IR and UV–Vis diffuse reflectance spectroscopies, and specific surface area and porosity assessment by N 2 adsorption at −196 °C. In all cases, the only crystalline phase obtained was hydrotalcite which crystallinity is further enhanced by microwave hydrothermal treatment than by conventional hydrothermal treatment. The microwave-aged samples also have larger amounts of interlayer water and smaller particle size than those prepared by conventional hydrothermal ageing. The textural properties of the solids are strongly modified during the ageing treatment, and large specific surface areas values are observed at shorter times for those samples subjected to microwave radiation.

Influence of Microwave Radiation on the Growth of Gold Nanoparticles and Microporous Zincophosphates in a Reverse Micellar System

The water core of reverse micelles has been extensively used as the site for synthesis of a variety of materials. However, water-in-oil reverse micelles have a limited range of temperatures over which they are stable as a single phase. Directing heat to the water cores, the usual site of synthesis without heating the bulk provides added opportunities for synthesis. Microwave radiation is a method for superheating the water cores. In this study, we use an H2O-sodium bis(2-ethylhexyl) sulfosuccinate (AOT)-heptane reverse micelle system for the synthesis of Au particles by hydrazine reduction of HAuCl4 in the presence and absence of microwave radiation. The duration of the microwave radiation was limited to a 2-min duration at a power of 300 W, thereby ensuring that the reverse micelle phase is maintained during the synthesis. At all hydrazine concentrations studied (0.5-2 M), the presence of microwave radiation led to an increase in the particle size of Au. The second system examined was the growth of microporous zincophosphate-X (ZnPO-X, an analogue of the faujasite structure) synthesized from H2O-dioctyldimethylammonium chloride (DODMAC)-heptane reverse micelle system. Microwave radiation was applied for 1 min at 150 W at various stages of the nucleation and growth process, and did not disrupt the reverse micelle system. Product analysis after 48 h of reaction showed that the 1-min microwave pulse, if applied during the nucleation stage (the first 4 h), promoted the formation of NaZnPO4.H2O over ZnPO-X. The effect of the microwave pulse at the growth stage was to promote the formation of ZnPO-X. Absorption of the microwave radiation by the water core and surrounding polar surfactant molecules leads to a rapid rise in local temperature (predicted to be approximately 150 degrees C/min for the AOT system), increasing the rates of intramicellar reactions.

Influence of microwave radiation on free Candida antarctica lipase B activity and stability

The influence of microwave heating on free Candida antarctica lipase B activity and stability was studied over the temperature range from 40 to 110 degrees C. Concerning the lipase activity, identical initial rate and conversion yield were obtained under microwave radiation and classical thermal heating for the alcoholysis between ethyl butyrate and butanol in a solvent-free system. On the other hand, the kinetics of the free lipase inactivation in butanol appears to be influenced by the heating mode. The Arrhenius plot obtained under classical heating was linear over all the temperature range studied whereas a biphasic Arrhenius plot was obtained under microwaves. The non-classical effect of the microwave heating on the initial rate of the enzymatic inactivation was thus dependent on the temperature of incubation.

Synthesis and Transformations of Heterocyclic Compounds under the Influence of Microwave Radiation. (Review)

Published data on the synthesis and transformations of heterocyclic compounds with microwave treatment are analyzed and classified according to the types of products formed. The results of analogous reactions conducted with normal heating are given for comparison.

Microwave photoresponse in the two-dimensional electron system caused by intra-Landau-level transitions

The influence of microwave radiation on the DC-magnetoresistance of 2D-electrons is studied in the regime beyond the recently discovered zero resistance states when the cyclotron frequency exceeds the radiation frequency. Radiation below 30 GHz causes a strong suppression of the resistance over a wide magnetic field range, whereas higher frequencies produce a non-monotonic behavior in the damping of the Shubnikov-de Haas oscillations. These observations are explained by the creation of a non-equilibrium electron distribution function by microwave induced intra-Landau level transitions.

Kubo formula for Floquet states and photoconductivity oscillations in a two-dimensional electron gas

The recent discovery of the microwave induced vanishing resistance states in a two dimensional electron system (2DES) is an unexpected and surprising phenomena. In these experiments the magnetoresistance of a high mobility 2DES under the influence of microwave radiation of frequency $\omega$ at moderate values of the magnetic field, exhibits strong oscillations with zero-resistance states (ZRS) governed by the ratio $\omega /\omega_c$, where $\omega_c$ is the cyclotron frequency. In this work we present a model for the photoconductivity of a two dimensional electron system (2DES) subjected to a magnetic field. The model includes the microwave and Landau contributions in a non-perturbative exact way, impurity scattering effects are treated perturbatively. In our model, the Landau-Floquet states act coherently with respect to the oscillating field of the impurities, that in turn induces transitions between these levels. Based on this formalism, we provide a Kubo-like formula that takes into account the oscillatory Floquet structure of the problem. We study the effects of both short-range and long-range disorder on the photoconductivity. Our calculation yields a magnetoresistance oscillatory behavior with the correct period and phase. It is found that, in agreement with experiment, negative dissipation can only be induced in very high mobility samples. We analyze the dependence of the results on the microwave power and polarization. For high-intensity radiation multi-photon processes take place predicting new negative-resistance states centered at $ \omega / \omega_c=1/2$, and $ \omega / \omega_c= 3/2$.

Influence of microwave radiation on the association processes of rhodamine 6G molecules in aqueous solutions

The influence of the microwave radiation of two frequency ranges (2.0 mm and 6.9 dm) on the absorption spectra of the cationic dye rhodamine 6G has been investigated. A reversible decrease in the quantity of the dimers of the dye molecules after exposure of its aqueous solution to microwave radiation and also the phenomenon of destruction of the associates of the dye molecules under the influence of the microwave field have been revealed. They are discussed from the standpoint of the structural characteristic features of water.

Three-component solvent-free diastereoselective formation of oxo-thiazolidinylthiazoles under microwave irradiation

The one-pot diastereoselective cyclisation of 4,4′-bis(2″-aminothiazol-4″-yl)bibenzyl to 4,4′-bis[2″-(2″′-aryl-5″′-methyl/carboxymethyl-4″′-thiazolidinon-3″′-yl)thiazol-4″-yl]bibenzyls, in high yields (85-96%) under the influence of microwave radiation, is described.