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Microbial inactivation efficacy of plasma generated by a custom-made floating electrode dielectric barrier discharge (FE-DBD) or cold plasma at three different frequencies (1 kHz, 2 kHz, and 3.5 kHz) was experimentally evaluated for its inactivation of the pathogen surrogate Enterobacter aerogenes on a glass surface to obtain inactivation kinetics. COMSOL Multiphysics® was used to numerically simulate the amount and the distribution of reactive species within an FE-DBD system. Microbial inactivation kinetics was predicted using species concentrations and microbial inactivation rates from the literature and compared with experimental data. The results showed that the FE-DBD plasma treatment achieved a microbial reduction of 4.3 ± 0.5 log CFU/surface at 3.5 kHz, 5.1 ± 0.09 log CFU/surface at 2 kHz, and 5.1 ± 0.05 log CFU/surface at 1 kHz in 2 min, 3 min, and 6 min, respectively. The predicted values were 4.02 log CFU/surface, 4.10 log CFU/surface, and 4.56 log CFU/surface at 1 kHz, 2 kHz, and 3.5 kHz, respectively. A maximum 1 log difference was observed between numerical predictions and the experimental results. The difference might be due to synergistic interactions between plasma species, UV component of FE-DBD plasma, and/or the electrical field effects, which could not be included in the numerical simulation. [ABSTRACT FROM AUTHOR]

BACKGROUND: Pesticides have been widely used to control pests on agricultural products in China, and large amounts of pesticide residues have caused a serious threat to human health. Thus, developing a high‐efficiency pesticide degradation method for fresh vegetables represents a great challenge. The present study investigated the effects of dielectric barrier discharge (DBD) plasma on the degradation of malathion and chlorpyrifos in aqueous solutions and on lettuces. RESULTS: DBD treatment significantly degraded malathion and chlorpyrifos in water and on lettuce. After cold plasma treatment at 80 kV for 180 s, the degradation efficiency of malathion (0.5 μg mL−1) and chlorpyrifos (1.0 μg mL−1) in aqueous solutions reached 64.6% and 62.7%, respectively. The degradation intermediates were explored by HPLC‐mass spectrometry and the DBD plasma degradation pathways of malathion and chlorpyrifos were proposed. There was no significant damage to the quality of lettuces, including color and chlorophyll content, after plasma treatment. Ascorbic acid decreased significantly during long‐term treatment with DBD plasma. To ensure the quality of lettuces during processing, the treatment time was shortened to 120 s. Under this condition, the degradation efficiency of malathion (0.5 mg kg−1) and chlorpyrifos (1.0 mg kg−1) on lettuces was found to be 53.1% and 51.4%. More importantly, we noted that cold plasma treatment significantly inactivated the microorganisms on lettuces. CONCLUSION: The results of the present study show that cold plasma is an effective and safe method for the degradation of organic pesticide residues on fresh vegetables at the same time as retaining the original quality. © 2020 Society of Chemical Industry [ABSTRACT FROM AUTHOR]

A technique for measuring the internal stresses in polymer films deposited on a glass substrate in gas discharge plasma is developed. Using this technique, the dependence of internal stress in thin films of polymethylmethacrylate and polystyrene on the deposition time and the current density of the barrier discharge at atmospheric pressure is studied. It is found that, when forming thin polymer coatings from monomers with high polymerization efficiency, the average value of internal stresses is higher than that for coatings obtained from monomers having low polymerization efficiency in barrier discharge plasma at atmospheric pressure. This can be explained by an increase in the specific number of cross-links in the first type of films under the action of ultraviolet radiation from the plasma. The quasi-optimal deposition time of the polymer film coating from styrene is found in which the value of the internal stress is minimal at a film thickness acceptable for a number of practical applications. [ABSTRACT FROM AUTHOR]

A barrier plasma, created at atmospheric pressure, was used to improve the surface and adhesive properties of polyester (PES) film with respect to wood using polyurethane adhesives. The modification of PES film surfaces using barrier discharge plasma is attractive for various applications. Plasma pre-treatment initiates and participates in grafting, polymerization, or cross-linking reactions on the PES surface. This method of surface modification is clean, dry, ecological, and very efficient. The enhancement of the wettability of the polyester film was necessary for promoting higher adhesion to wood with water-based adhesives. The treatment of polyester films by barrier plasma led to a considerable increase in the surface free energy of the film and subsequently an increase in the peel strength of the adhesive joint of PES film-oak wood with polyurethane adhesive.

The technique of deposition of polymer films from the barrier gas discharge plasma on top of dielectric substrates is developed. The film precursor is a monomer material highly dispersed in a transport plasma gas. The plasma formation of the continuous polymer film can be divided into two stages. The first stage is deposition of liquid monomer droplets with subsequent polymerization on the dielectric barrier surface resulting in growth of a discontinuous film. It is found that the ratio of the height of droplets to their lateral size is almost constant and for polystyrene it is equal to ~0.01. The second stage is expansion of the droplets into islands and their coalescence into a continuous polymer film on the dielectric barrier surface. The polymer coating thickness and the amount of cross bonds essentially depend on the current density and concentration of the monomer in the transport discharge gas. A continuous polymer film, which is not contaminated with the monomer destruction products, can be obtained in the current density range of 7-25 mA/cm2. Experiments with several monomers, like methylmethacrylate, styrene and acrylonitrile, have shown that the growth rate is maximal for monomers with oxygen-free molecules. At the same time, a higher growth rate provides low cross-bond coatings, whereas to get high density of the cross-linked bonds one has to utilize low deposition rates. The minimal thickness at which continuity of the film is achieved increases when the monomer concentration in the plasma rises. In general, the coating thickness depends linearly on the discharge current density; the particular figures depend on the type and concentration of the monomer. The technological parameters are established and given for the three aforementioned monomers. [ABSTRACT FROM AUTHOR]

The waste from industrial fruits processing is utilized for the extraction of limonene, a renewable terpene biomass compound obtained from orange peels. This was followed by limonene oxidation, which produces highly useful oxygenated derivatives (carveol, and perillyl alcohol, 1,2-epoxylimonene and its diol). New catalysts were obtained by treating relatively inexpensive commercially available EuroPh and FPV activated carbons with plasma. These catalysts were characterized by the following instrumental methods XRD, sorption of N 2 and CO 2 , SEM, EDS, TEM, XPS, and Raman spectroscopy. The activities of the plasma-treated catalysts were measured in the oxidation of limonene by means of either hydrogen peroxide or t-butyl hydroperoxide as the oxidizing agents. During the oxidation with hydrogen peroxide the new plasma-treated catalysts were more active than their untreated counterparts. This effect was noticeable in the considerable increase in the conversion of limonene. The mechanism explaining this property is proposed, and it takes into account the role of the appropriate functional groups on the surface of the catalysts. This work has shown for the first time that the commercial EuroPh and FPV activated carbons, after having been treated by plasma, are active catalysts for the selective limonene oxidation for the production of value-added industrial products. [ABSTRACT FROM AUTHOR]

A barrier plasma, created at atmospheric pressure, was used to improve the surface and adhesive properties of polyester (PES) film with respect to wood using polyurethane adhesives. The modification of PES film surfaces using barrier discharge plasma is attractive for various applications. Plasma pre-treatment initiates and participates in grafting, polymerization, or cross-linking reactions on the PES surface. This method of surface modification is clean, dry, ecological, and very efficient. The enhancement of the wettability of the polyester film was necessary for promoting higher adhesion to wood with water-based adhesives. The treatment of polyester films by barrier plasma led to a considerable increase in the surface free energy of the film and subsequently an increase in the peel strength of the adhesive joint of PES film-oak wood with polyurethane adhesive. [ABSTRACT FROM AUTHOR]

The pyroelectric properties of polymer-pyroceramic composites with components premodified under the action of a barrier discharge plasma and the pyroelectric properties of composites crystallized under the simultaneous action of a barrier discharge plasma and temperature are studied. It is shown that the plasma-assisted crystallization technology is more efficient for improving the pyroelectric properties of the composites. Plasma-assisted crystallization provides a high and stable pyroelectric state if the activation energy of the local levels formed in the quasi-bandgap of the polymer phase is higher than the deorientation energy of the domains of the pyrophase of the composite. [ABSTRACT FROM AUTHOR]