Dušan Kováčik

How various plasma sources may affect seed germination and growth

Germination and early growth of buckwheat (Fagopyrum aesculentum) after low-temperature plasma discharge treatment in air gas generated in various devices were tested. Three pre-treatment times were used: 180 s, 300 s and 600 s. Seed cultivation was carried out in laboratory conditions. Number of germinating seeds was counted, length and weight of seedling sprouts were measured. The data were analysed with two-way ANOVA: a significant influence of the type of plasma apparatus, time of exposure and combination of both factors were found. A positive effect on germination and early growth was observed after the application of GlidArc device (low-temperature plasma generated in air gas under atmospheric pressure between two electrodes). The opposite effect of surface dielectric barrier discharge (SDBD) apparatus, which is characterized by plasma with high power density, was observed. Shorter pre-treatment times for SDBD device must be therefore used. Effects of seed germination and early growth of seeds strongly depended on the type of the used plasma apparatus.

Polylactic acid surface activation by atmospheric pressure dielectric barrier discharge plasma

Abstract Polylactic acid (PLA) is suitable for applications in packaging and biomedicine due to its biodegradability. To improve PLA surface adhesion a plasma-chemical treatment using nonthermal plasma generated in ambient air via diffuse coplanar surface barrier discharge (DCSBD) was used. The optimal treatment time and power were investigated. Interaction between active plasma species and the polymer surface, and the resulting surface changes were studied by contact angle measurement, surface energy determination, FTIR, and XPS. The most hydrophilic surface was obtained after only 3–4 s treatment. Treatment up to 10 s did not damage the polymer but longer treatments (30 and 60 s) caused partial degradation. The plasma broke C-C/C-H bonds and formed more C-O, O-C=O and C-O-C bonds. During storage surface oxygen decreased and a negligible amount of nitrogen was adsorbed. The oxygen-containing functional groups probably sank into the PLA volume after treatment. Graphical Abstract

Chitosan immobilization to the polypropylene nonwoven after activation in atmospheric – pressure nitrogen plasma

Abstract Atmospheric-pressure air and nitrogen plasmas generated by surface dielectric barrier discharges have been used to incorporate new functionalities at the surface of polypropylene nonwoven fabric. The main goals were to activate the polymer surfaces for subsequent immobilization of chitosan from water solution without using any crosslinking and wetting agents. The samples were analyzed by diffuse reflectance infrared Fourier transform spectroscopy, scanning electron microscopy, and X-ray photoelectron spectroscopy. The nitrogen plasma treatment resulted in relatively high oxygen incorporation, about 9 atomic % mainly in aliphatic C=O type bonds and about 4 at.% of nitrogen incorporation in amine and other nitrogen functionalities. Chitosan was immobilized on the fabric fibers surfaces very homogeneously in amount of 2 - 5 g m-2. The chitosan coated samples exhibited a good laundering durability and strong antimicrobial activity against Bacillus subtilis and Escherichia coli. Graphical Abstract

Cold plasma treatment triggers antioxidative defense system and induces changes in hyphal surface and subcellular structures of Aspergillus flavus

The cold atmospheric-pressure plasma (CAPP) has become one of the recent effective decontamination technologies, but CAPP interactions with biological material remain the subject of many studies. The CAPP generates numerous types of particles and radiations that synergistically affect cells and tissues differently depending on their structure. In this study, we investigated the effect of CAPP generated by diffuse coplanar surface barrier discharge on hyphae of Aspergillus flavus. Hyphae underwent massive structural changes after plasma treatment. Scanning electron microscopy showed drying hyphae that were forming creases on the hyphal surface. ATR-FTIR analysis demonstrated an increase of signal intensity for C=O and C-O stretching vibrations indicating chemical changes in molecular structures located on hyphal surface. The increase in membrane permeability was detected by the fluorescent dye, propidium iodide. Biomass dry weight determination and increase in permeability indicated leakage of cell content and subsequent death. Disintegration of nuclei and DNA degradation confirmed cell death after plasma treatment. Damage of plasma membrane was related to lipoperoxidation that was determined by higher levels of thiobarbituric acid reactive species after plasma treatment. The CAPP treatment led to rise of intracellular ROS levels detected by fluorescent microscopy using 2′,7′-dichlorodihydrofluorescein diacetate. At the same time, antioxidant enzyme activities increased, and level of reduced glutathione decreased. The results in this study indicated that the CAPP treatment in A. flavus targeted both cell surface structures, cell wall, and plasma membrane, inflicting injury on hyphal cells which led to subsequent oxidative stress and finally cell death at higher CAPP doses.

High-speed low-cost surface treatments using a novel atmospheric-pressure plasma source

The surface properties of materials used commercially are often more important to their function and marketability than their bulk properties and are determined by an extremely thin region that can be as small as a few atomic diameters. Plasma surface treatment is usually fast, affects about 10 nanometers of the very surface layer, and have many potential benefits including minimal waste and control of surface functionality. New plasma applications are continuously emerging in the vastly growing area of nanotechnology. In a contrast to common plasma applications for surface modifications of high-added value materials for microelectronics, medicine, etc. a novel type of atmospheric plasma source developed at CEPLANT research centre (www.ceplant.cz) makes possible low-cost inline treatment of a wide scale of standard flat and web materials. Advantageously in comparison to competitive plasma techniques this plasma source is capable of generating visually uniform “cold” high power-density diffuse plasmas in any working gas, including ambient air, pure atmospheric-pressure oxygen and hydrogen, without the use of expensive He or Ar. Very high plasma power densities achieved (~100 W/cm3) allows for short plasma exposure times on the order of 0.1 s and, consequently, high treatment speeds [1, 2]. The plasma source is technically simple, safe at the contact with human body and can be operated in humid and dusty environment.atomic diameters.

Atmospheric pressure plasma treatment of polyamide-12 foils

Abstract The surface of a polyamide-12 (PA-12) foil was modified in order to improve the adhesive properties by two types of atmospheric pressure plasma sources. The samples were characterized using contact angle measurement, adhesive properties measurement and X-ray photoelectron spectroscopy (XPS). The ageing of the plasma modification was also studied. A significant increase in wettability was observed at different treatment times. The same effect was also seen in the adhesive properties - the adhesion was increased almost 12 times for 10 s DCSBD treatment in comparison to untreated PA-12. XPS analysis confirmed chemical changes due to the plasma modification of the PA-12. It was concluded that both plasma sources improve the adhesive properties of PA-12, with DCSBD obtaining better results. Graphical Abstract

Layer-by-layer assembly of thin organic films on PTFE activated by cold atmospheric plasma

Abstract An air diffuse coplanar surface barrier discharge is used to activate the surface of polytetrafluoroethylene (PTFE) samples, which are subsequently coated with polyvinylpyrrolidone (PVP) and tannic acid (TAN) single, bi- and multilayers, respectively, using the dip-coating method. The surfaces are characterized by X-ray Photoelectron Spectroscopy (XPS), Attenuated Total Reflection – Fourier Transform Infrared Spectroscopy (ATR-FTIR) and Atomic Force Microscopy (AFM). The XPS measurements show that with plasma treatment the F/C atomic ratio in the PTFE surface decreases, due to the diminution of the concentration of CF2 moieties, and also oxygen incorporation through formation of new C–O, C=O and O=C–O bonds can be observed. In the case of coated samples, the new bonds indicated by XPS show the bonding between the organic layer and the surface, and thus the stability of layers, while the gradual decrease of the concentration of F atoms with the number of deposited layers proves the creation of PVP/TAN bi- and multi-layers. According to the ATR-FTIR spectra, in the case of PVP/TAN multilayer hydrogen bonding develops between the PVP and TAN, which assures the stability of the multilayer. The AFM lateral friction measurements show that the macromolecular layers homogeneously coat the plasma treated PTFE surface.

Acrylic Acid Plasma Treatment of Polypropylene Nonwoven Fabric

Nowadays hydrogel materials are being used in medical practice for wound dressing purposes. Hydrogel/textile composites can be formed to increase the mechanical strength and handling capability of hydrogel materials. Nonwoven textiles are optional for such applications, however, it is often necessary to improve their surface properties. Here plasma activation/ grafting of polypropylene (PP) nonwoven fabric with an acrylate layer to improve its adhesive properties is reported. A diaphragm discharge was used for the plasma treatment of the PP fabric. The discharge was burnt in a solution of acrylic acid (AAc), which resulted in a single step process of plasma activation and plasma grafting of the fabric. Results of wettability testing and ATR-FTIR measurements showed the existence of a thin poly(acrylic acid) (PAAc) layer grafted on the fabric surface. Peel strength measurements showed a 4.7 fold increase in the peel strength when compared with untreated PP fabric.

The effect of low-temperature plasma treatment on the plant seeds

The effect of low-temperature plasma (LTP) on the germination rate of three plants species: wheat, maize and pea was investigated. The impacts of LTP on inactivation of naturally occurring epiphytic, phytopathogenic and toxigenic fungi on the surface of wheat and maize seeds and also on the surface of artificially infected both seeds by chosen fungi was determined. The plasma source used in our study, so called Diffuse Coplanar Surface Barrier Discharge (DCSBD) [1] generates at atmospheric pressure in ambient air low-temperature plasma with high volume power density, therefore to achieve the required effect the short treatment time is needed. The aim of our study was to establish a correlation between the effect of the plasma on the surface sterilization and germination of seeds and the physical and chemical changes achieved via plasma, in particular, changes in surface wettability and in surface chemical composition.

Continuous plasma-chemical processing of fabrics at atmospheric pressure

Many textile finishing operations use wet processing techniques with a detrimental impact on the environment. In addition, the wet processes use approximately 60% of the energy consumed in the textile industry. The use of non-equilibrium atmospheric-pressure plasmas is emerging as an environmentally attractive alternative for the safe and economical surface treatment of fabrics. Since the growth rates of nonwovens production are extremely high, when compared with the conventional textiles industry, the novel plasma techniques for nonwovens surface hydrophilization are of particular interest, and there is an urgent need for the development of efficient, robust and cost-effective plasma treaters capable of in-line operation at 100-1000 m/min nonwovens processing speeds.