Low-pressure Plasma Treatment Research Articles

Effect of low-pressure plasma treatment on the color and oxidative stability of raw pork during refrigerated storage.

The effect of low-pressure plasma on quality attributes of meat is an important aspect, which must be considered before application in food. The aim of this study was to determine the color, fatty acid composition, lipid oxidation expressed as thiobarbituric acid reactive substances and total antioxidant capacity of raw pork samples exposed to helium low-pressure plasma treatment (20 kPa) for 0, 2, 5, and 10 min during the storage period. The thiobarbituric acid reactive substance concentrations of all plasma-treated samples during storage were in the range from 0.26 to 0.61 mg malondialdehyde/kg. Exposure time caused significant changes only in total color difference, hue angle, and chroma after 10 min of treatment. Ferric reducing ability of plasma values of meat samples decreased from 1.93 to 1.40 mmol Trolox Eq/kg after 14 days of storage. The storage period significantly affected proportion of polyunsaturated fatty acids, with an increase about 3% after 14 days of refrigeration storage while the content of saturated fatty acids was at the same level. Helium low-pressure plasma does not induce oxidative processes. Application of this decontamination technique while maintaining product quality is possible in food industry.

Influence of chemically and plasma-functionalized carbon nanotubes on high-performance polymeric nanocomposites

This investigation highlights different surface functionalization processes of multi-walled carbon nanotubes (MWCNTs) and their effects on mechanical properties of polyetherimide nanocomposite. Surfaces of MWCNTs were modified by chemical process and by low-pressure plasma process. There is a significant change in physicochemical characteristics of MWCNTs after chemical and low plasma treatment evident from scanning electron microscopy, transmission electron microscopy, and X-ray photoelectron spectroscopy studies. Due to surface modification of CNTs, there is a significant change in surface morphology and increase in oxygen functionalities such as C=O, C–O, and COOH especially evident in low-pressure plasma treatment; however, differential scanning calorimeter and thermogravimetric analysis studies reveal that thermal properties of the composite do not alter as such. There is a significant increase in mechanical properties of high-performance polymeric nanocomposites when surface-functionalized MWCNTs are dispersed in polymeric matrix; however, surface characteristics of the composite remain almost unchanged evident from contact angle and surface energy studies.

Enhanced optical performance of APCVD zinc oxide via post growth plasma treatment at atmospheric pressure

AbstractThe use of atmospheric pressure (AP) CVD to produce highly developed Transparent Conducting oxides (TCO) for thin film photovoltaic systems has significant potential to reduce manufacturing costs and increase the product scope via in‐line processing compared to off‐line, low pressure techniques. A further advantage of APCVD is the ability control surface morphology via growth parameters, a key factor in controlling the distribution of scattered light at the TCO/absorber interface. The nano‐scale features may be further optimised via post growth etching, for example, to round sharp vertices or induce or exaggerate texture in a film material that is intrinsically smooth. This is normally achieved via low pressure plasma treatments or wet chemical processes, hence the presented novel AP plasma approach here offers reduced capital costs combined with ease of scalability and process integration. In this work we describe the multi‐scale manipulation of an APCVD grown ZnO via surface morphological modification, achieved by the application of an atmospheric pressure plasma etch system. The modified surfaces are evaluated for optical and morphological properties. Initial research has shown that under the correct plasma etch conditions, optical haze can be increased by as much as 20%, with the crucial additional ability to also tailor the film surface features. The use of audio frequency and sub‐microsecond pulsed plasmas for etching are compared in terms of activity and control. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Treatment with Ar–O2 low-pressure plasma of vulcanized rubber sole containing noticeable amount of processing oils for improving adhesion to upper in shoe industry

Vulcanized rubber (L3 rubber) containing intentionally noticeable excess of processing oils in its formulation was treated with Argon–Oxygen (Ar–O2) (2:1, vol/vol) low-pressure (LP) plasma for achieving a satisfactory level of adhesion to waterborne polyurethane adhesive. The effectiveness of the Ar–O2 LP plasma treatment of L3 rubber depended on both the configuration of the plasma chamber shelves and the treatment time. Surface modifications were assessed by attenuated total reflectance-IR and X-ray photoelectron spectroscopy, contact angle measurements, and scanning electron microscopy. Ar–O2 LP plasma treatment in direct configuration provided the most effective surface modification of the L3 rubber, and the increase in the treatment time improved the extent of the surface modifications. However, even important surface modifications were produced by Ar–O2 LP plasma treatment, adhesion of treated L3 rubber was not improved due to the creation of weak boundary layer at the polyurethane–rubber interface after joint formation. Heating at 80 °C for 12 h of the as-received L3 rubber prior to Ar–O2 LP plasma treatment enhanced the extent of the surface modifications, and improved adhesion was obtained for Ar–O2 LP plasma treatment times higher than 600 s.

Use of statistical design of experiments in the optimization of Ar–O2 low-pressure plasma treatment conditions of polydimethylsiloxane (PDMS) for increasing polarity and adhesion, and inhibiting hydrophobic recovery

Polydimethylsiloxane (PDMS) film was treated with RF low-pressure plasmas (LPPs) made of mixtures of oxygen and argon for increasing surface polarity, minimizing hydrophobic recovery (i.e. retard ageing) and increasing adhesion to acrylic adhesive tape for medical use. Statistical design of experiments has been used for determining the most influencing experimental parameters of the LPP treatment of PDMS. Water contact angle values (measured 24h after treatment) and the O/C ratio obtained from XPS experiments were used as response variables. Working pressure was the most influencing parameter in LPP treatment of PDMS, and the duration of the treatment, the power and the oxygen–argon mixture composition determined noticeably its effectiveness. The optimal surface properties in PDMS and inhibited hydrophobic recovery were achieved by treatment with 93vol% oxygen+7vol% argon LLP at low working pressure (300mTorr), low power (25W) and long duration of treatment (120s).

Effect of Laser and Plasma Surface Cleaning on Mechanical Properties of Adhesive Bonded Joints

The use of adhesives in place of traditional joining techniques as welding and riveting is becoming increasingly common in structural design. Compared to other conventional joining processes, adhesive bonding offers several advantages: including acoustic insulation, vibration attenuation, structure lightening, corrosion reduction and uniform stress distribution. These benefits can be offset if the surfaces to be bonded are not carefully cleaned, degreased and prepared. Many approaches to surface treatments based on physical or chemical modifications have been developed in the years in order to improve the surface activity. Although widely used and very efficient, these techniques present several disadvantages. Physical methods based on mechanical abrasion are supposed to extend bonding area as they increase the roughness, but cause an extensive degradation to the specimens and they are often not easy to reproduce. On the other hand, chemical treatments are typically used with the aim of modifying both morphology and chemical structure of the substrates layers, but they present serious environmental problems of waste disposal, which has moved investigations to an industrial alternative to these processes. According, the use of energetic methods of surface cleaning, such as laser and plasma cleaning processes have been recently consolidated since they are useful to modify the topmost layers of the substrates, increasing their reactivity, without affecting the bulk material properties. These treatments offer an effective and environment-friendly processing of different materials, providing strong and durable bonds with adhesives through modification of the surface morphology and functionalities. In this study, the effects of laser and low pressure plasma treatments on mechanical properties of adhesive bonded joints has been investigated and compared performing lap-shear tests.

Response surface methodology optimized dyeing of wool with cumin seeds extract improved with plasma treatment

In this study, the aqueous extract of Cuminum Ciminum L. seed was applied on wool as a novel natural colorant. Gas chromatography coupled with mass spectrometry was conducted to identify the composition of the extract. Response surface methodology and D-optimal design were employed to investigate and optimize the effects of three independent factors including mordant concentration, dyeing pH and temperature on the color strength of dyed samples. A statistical model was obtained to correlate between the amounts of three independent factors and color strength of dyed samples as the response. Low pressure plasma treatment using oxygen, argon, and their mixture was employed to improve the dyeability of wool fibers. The effect of different plasma treatments on the surface chemistry and morphology of wool fibers were studied using attenuated total reflectance-Fourier transform infrared spectroscopy and field emission scanning electron microscopy, respectively. The fastness properties of dyed samples were also investigated.

Antimicrobial activity of low-pressure plasma treatment against selected foodborne bacteria and meat microbiota.

The effects of helium and argon plasma treatments on inactivation of both pure bacterial cultures inoculated onto the surface of agarized media and the surface microbiota of meat were investigated. Cold plasmas were generated by high voltage discharge at low pressure (20 kPa) for 2, 5, and 10 min. The number of viable microorganisms was determined using a plate count method. Morphological changes were observed using scanning electron microscopy (SEM). Microbial log reduction depended on time of exposure and type of gas used. After a 10-min treatment with helium plasma, the total number of microorganisms, yeasts and molds, and psychrotrophic microorganisms was reduced in the range of 1.14–1.48 log cycles for pork and 0.98–2.09 log cycles for beef. A significant reduction of 2.00 log for Bacillus subtilis and Yersinia enterocolitica was achieved within 2 min of helium plasma treatment. Similar results were obtained for Staphylococcus aureus, Escherichia coli and Pseudomonas fluorescens after 5 min and 10 min of exposure. SEM revealed disruption and lysis of E. coli cells treated with helium plasma for 10 min, suggesting a bactericidal effect.

Cold Plasma Pretreatment of Carbon Fibre Composite Substrates to Improve Adhesive Bonding Performance

The purpose of the paper is to investigate the effects of low pressure plasma treatment on wettability of carbon fibre reinforced polymer samples and on shear properties of adhesive bonded joints based on these substrates. In particular, two plasma process parameters, exposure time and power input, were optimized, performing contact angle evaluation on lap-shear tests. The plasma treatment was also compared with a conventional mechanical abrasion and untreated and only degreased specimens. The experimental results show that choosing the optimal parameters is possible to improve the wettability of composite substrates and reduce the contact angle.

Effects of low pressure plasma treatments on DSSCs based on rutile TiO2 array photoanodes

In this paper, three types of low pressure plasma including hydrogen (HP), oxygen (OP) and nitrogen (NP) treatments have been utilized for the first time to improve DSSCs based on rutile TiO2 array photoanodes. Their effects on the photoanodes and the cell performance have been systematically compared by characterizing the dye loading amount, flat-band potential, donor concentration, electron lifetime and the photovoltaic parameters. Experimental results show that all the three plasma treatments increase the dye loading owing to improved hydrophilicity or enhanced surface roughness. It is found that NP and OP treatments significantly increase the TiO2 donor concentration and decrease trapping sites. By this way, the electron transport is enhanced and the electron recombination is effectively restrained. These comprehensive effects make NP and OP treatments beneficial for the overall performance, by which 13% and 5% increases in efficiency are achieved. However, HP treatment causes obvious reduction in the donor concentration and more severe electron recombination, which decreases the efficiency by about 15%.

Polyolefinic Surface Activation by Low and Atmospheric Pressure Plasma Treatments

Polyolefins are increasingly used in the construction of lightweight structures. Due to their low surface energy, it is difficult to have a proper bond with adhesives and paints. By using cold plasma treatments, these surfaces can be activated through the formation of highly reactive functional groups that can promote high strength adhesive bonds. This paper compares the results of cold plasma treatments using two techniques (low pressure and atmospheric plasma torch) applied on polypropylene and high density polyethylene. The obtained data allow the demonstration of a higher effectiveness of atmospheric plasma, with a significant increase in surface energy in both materials.

Production scale plasma modification of polypropylene baselayer for improved water management properties

ABSTRACTThrough its hydrophobic properties, polypropylene (PP) offers unique potential as a functional fiber for a wide range of applications, for example, in nonwovens for hygiene applications or as a baselayer in sports textiles. Current work is focused on the modification of PP presently used in baselayers for sports textiles to increase the hydrophilicity by use of a production scale plant for low pressure plasma treatment. Attention was directed toward an increase in hydrophilicity and time stability of the achieved modification during storage. Changes in the fabric were characterized by sorption of the cationic dye (methylene blue), water retention value, water transport properties, Fourier transform infrared spectroscopy and color measurement. The obtained results indicate an improved wettability and wicking. The extent of modification decreased with storage time and parallel yellowing of treated samples was observed. This indicates chemical rearrangement of the products initially formed on the fiber surface. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 41294.

Invited: Atmospheric Pressure Plasma Modified Polyaniline Crystals for Detection of Volatile Organic Compounds

Among the family of conducting polymers, polyaniline (PANI) is the most studied due to an easy and low-cost synthesis, good environmental stability, and simple doping/dedoping process based on acid/base reactions.1,2 PANI polymer can be used for different applications including in solar cells, artificial muscles, gas sensors, capacitors, acid-base indicators, etc.3 The nature of PANI conductivity is explained by its ability to form polarons and cation radicals.3,4 Moreover PANI shows significant variations in conductivity when exposed to various volatile organic compounds (VOC).4 This property arises from to the doping-dedoping of conducting PANI layer, which makes it suitable for detection of wide variety of gas molecules.Changes in the chemical states can alter the sensitivity and selectivity of PANI layer. Chemical modifications by doping of PANI with various acid dopants, co-polymerisation with various thermoplastics, co-polymerisation with aniline derivatives or enzymatic polymerisation of aniline has been used to improve the processability and solubility of PANI as reviewed by Jaymand et.al.5. Another techique is low pressure plasma treatment which has been reported to be an efficient technique for the carbon functionalization as well as changing the chemical states of the PANI surface.6,7 The variations of the chemical changes induced by low pressure oxygen plasma treatment efficiently enhanced the selectivity and sensitivity towards various gases.8 PANI exposed to various plasmas has demonstrated also increased resistivity.Urea is widely used in the manufacture of explosives and nitrogen fertilisers in industries. Eventhough expoure of urea vapor is harmless at lower concentrations, prolonged exposure of urea can cause irritations to eyes, skin or respiratory systems. We demonstrated a reusable sensor based on emeraldine polyaniline crystals coated on polyethylene terephthalate substrate at room temperatue. To enhance the signal response, we used an atmospheric pressure He plasma treatment which showed pronounced and steady increase in the signal response for six consecutive cycles. The surface changes as well as mechanism of detection after plasma treatement were studied by various analysis techniques including FT-IR, scanning electron microscopy (SEM), and X-ray photoelectron microscopy (XPS).Macdiarmid A.G., Chiang J.C., Richter A.F., Epstein A.J., Synthetic Metals., 18 (1987), 285;Hao B., Li L., Wang Y., Qian H., Tong G., Chen H., Chen K., Journal of Applied Polymer Science 127 (2013), 4273;Sambhu B., Dipak K., Nikhil K.S., Joong H.L., Progress in Polymer Science 34 (2009), 783;Ayad M.M., El-Hefnawey G., Torad N.L., Journal of Hazardous Materials 168 (2009), 85;Jaymand M., Progress in Polymer Science 38 (2013), 1287;Kang E.T., Ma Z.H., Tan K.L., Zhu B.R., Uyama Y., Ikada Y., Polymers for Advanced Technologies 10 (1999), 421;Kang E.T., Kato K., Uyama Y., Ikada Y., Journal of Materials Research 11 (1996), 1570;Kunzo P, Lobotka P, Micusik M and Kovacova E Sensors and Actuators B: Chemical 171–172 (2012), 838;

Antibacterial Activity and Physical Properties of Edible Chitosan Films Exposed to Low-pressure Plasma

The challenge for food industry is developing gentle processes concept, which will prevent food spoilage and leave a food natural, minimally processed, fresh-like and safe. A new technique of food preservation could be usage of combined methods of green process, such as cold gas plasma with bioactive substances, and protective coatings. The aim of this study was to determine the antibacterial activity of chitosan films incorporated with lysozyme exposed to helium plasma treatment as well as evaluate their physical properties. The edible films have been prepared basing on low molecular weight chitosan by casting from lactic acid solution with water solution of lysozyme in three various concentrations (0, 0.5 and 1 %). Dried films were then modified by exposition on cold helium plasma treatment for 0, 5 and 10 min. Obtained films were tested against growth of Listeria monocytogenes, Yersinia enterocolitica and Pseudomonas fluorescens. In order to characterize chitosan-based films, their mechanical properties, theromogravimetric analysis (TGA), dynamic mechanical thermal analysis (DMTA), contact angle measurement, water vapour permeability (WVP) and scanning electron microscopy (SEM) were evaluated. The films with 1 % lysozyme incorporation enhanced the inhibition efficiency of chitosan-based films against gram-positive (L. monocytogenes) and gram-negative (P. fluorescens) bacteria, where reduction zones were 42.5 and 69.8 mm, respectively. Besides that, hydrolytic changes of chitosan chain caused by lysozyme activity were confirmed by TGA and DMTA. Contact angles and WVP of tested films were not significantly affected by helium plasma exposition, nor lysozyme dosage. Hydrophilic natures of chitosan-based films were confirmed by both tests. Microscopy image of cross-section structure was smooth and continuous due to lysozyme addition in film composition. Application of chitosan films incorporated with lysozyme and low-pressure plasma treatment could be used as innovative preservation method in a wide range of food products.

Improving adhesion performance of polyethylene surfaces by cold plasma treatment

In this paper, the effects of low pressure plasma treatment on surface energy of polyethylene samples and on shear properties of adhesive bonded joints based on these substrates have been investigated. In particular, the optimization of two plasma process parameters, exposure time and power input, was studied performing contact angle evaluation and lap-shear tests. The plasma treatment was also compared with a conventional primer treatment, for which it is a clean and effective alternative. As a measure of the durability of both treatments, the bond shear strength immediately after bonding was compared with that after a storage period in the laboratory environment. The experimental results show that the optimized plasma process may remarkably increase wettability properties of polyethylene surfaces and shear strength of bonded joints, even higher than those treated with primer and that these good properties remain quite unchanged even after some days of storage in a laboratory.

Low-Pressure Plasma Treatment of Polylactide Fibers for Enhanced Mechanical Performance of Fiber-Reinforced Calcium Phosphate Cements

Calcium phosphate cements (CPCs) are extensively used as synthetic bone grafts, but their poor mechanical properties limit their applicability to non-stress-bearing applications. The aim of the present work is to evaluate the potential of plasma surface modification of polylactide (PLA) fibers for reinforcement of CPCs. Oxygen low-pressure plasma was employed at different treatment times and the surface properties of the untreated and plasma-treated PLA were evaluated. Plasma treatment on the PLA fibers reduced the setting times of the PLA–CPC composites and improved their flexural properties.

Effect of Cold Plasma Treatment on Surface Roughness and Bonding Strength of Polymeric Substrates

For an effective application of polymers, it is essential to have good adhesion behaviour to ensure good mechanical properties and durable components. Unfortunately, in general terms, polymers are characterized by high chemical inertness, which leads to very low surface energy values and, consequently, poor adhesive properties; this is particularly true for polyolefins. In this study, the effects of low pressure plasma treatment on surface roughness of polyethylene and polypropylene samples and on shear properties of adhesive bonded joints based on these substrates have been investigated. In particular, the optimization of three plasma process parameters, exposure time, voltage and working gas, were studied performing roughness measurement, contact angle evaluation and lap-shear tests. The experimental results show that the optimized plasma process may remarkably change the surface morphology, increasing wettability properties of the surfaces and shear strength of the bonded joints. These good properties remain almost unchanged even after some days of storage in the laboratory.

Low pressure plasma modified polycarbonate: A transparent, low reflective and scratch resistant material for automotive applications

Abstract During the last years, the employment of light polymeric materials, to replace those commonly used in the automotive industry, has been investigated by many equipment manufacturers. Polymeric glazing, e.g. polycarbonate, are desirable because of their ability to reduce weight and fuel consumption, while providing good optical properties and impact resistance. In this paper, we report a two steps low pressure plasma treatment composed by an etching, optimized for the nano-texturing of polycarbonate to improve its anti-reflective property by simulating the so-called “Moth eye” effect, and by a plasma enhanced-chemical vapour deposition process to enhance the scratch resistance. Reflectance/transmittance measurements showed that this approach is able to increase the anti-reflective property of the polycarbonate without drastically damaging its transmittance, while scratching test by “car wash” simulator demonstrated the increase of scrape resistance. The haze test confirmed the transparency of the plasma treated polymer also after washing.

Seed disinfection effect of atmospheric pressure plasma and low pressure plasma on Rhizoctonia solani.

Gas plasma generated and applied under two different systems, atmospheric pressure plasma and low pressure plasma, was used to investigate the inactivation efficacy on the seedborne pathogenic fungus, Rhizoctonia solani, which had been artificially introduced to brassicaceous seeds. Treatment with atmospheric plasma for 10 min markedly reduced the R. solani survival rate from 100% to 3% but delayed seed germination. The low pressure plasma treatment reduced the fungal survival rate from 83% to 1.7% after 10 min and the inactivation effect was dependent on the treatment time. The seed germination rate after treatment with the low pressure plasma was not significantly different from that of untreated seeds. The air temperature around the seeds in the low pressure system was lower than that of the atmospheric system. These results suggested that gas plasma treatment under low pressure could be effective in disinfecting the seeds without damaging them.

Investigation of Properties of Long-grain Brown Rice Treated by Low-pressure Plasma

The impact of low-pressure plasma treatment on the properties of long-grain brown rice was investigated, and the process of quick cooking brown rice was developed. The microstructure of the brown rice surface and the cooking, textural, and pasting properties of plasma-treated brown rice were determined. Indica brown rice was treated for 30 min at voltage settings of 1, 2, and 3 kV. The plasma treatment resulted in the etching of the brown rice surface, which allowed water to be easily absorbed by the rice kernel during soaking. After plasma treatment, the cooking time, elongation ratio, width expansion ratio, water absorption, and cooking loss of brown rice were all reduced. Plasma treatment caused a significant decrease in peak viscosity and breakdown. In addition, the decreases in enthalpy and crystallinity, measured by differential scanning calorimeter and X-ray diffractometer, showed that the starch structure of brown rice was influenced by low-pressure plasma. Thus, low-pressure plasma is a novel processing technology to modify and reduce the cooking time of brown rice.