Sebastian Dahle

In recent years, research has focused on eco-friendly techniques to find alternatives to traditional methods to reduce environmental impact. This paper examines three wood degreasing methods and their impact on two different wood coatings. Conventionally used turpentine and petroleum-based solvents were compared with an environmentally friendly diffuse coplanar surface barrier discharge (DCSBD) plasma treatment for degreasing soft and hardwoods. The effect of plasma degreasing technique was tested on an antifouling paint (both with and without epoxy primer) and on a polyurethane varnish made from a modified alkyd resin. To evaluate degreasing methods on varnishes over time, accelerated artificial ageing was conducted for 240 h. Gloss, colour, ATR FT-IR and pull-off adhesion strength test measurements were taken for evaluation. All samples showed darkening and a loss of gloss after undergoing artificial weathering, with the most significant colour changes observed within the first 120 h. ATR FT-IR analysis indicated no significant differences in the coatings based on the degreasing method used. The degreasing technique did not impact the adhesive strength of the tested coatings. This confirms that plasma degreasing is just as effective as traditional methods and does not notably affect the appearance of the coating. These results show that plasma degreasing not only performs on par with solvent-based methods but also provides a solvent-free and sustainable alternative. This emphasises the innovation and environmental advantages of using DCSBD plasma for preparing wood surfaces. The method demonstrates significant potential for industrial implementation.

Cold atmospheric plasma (CAP) is a promising advanced oxidation process for water disinfection, but most systems remain constrained to millilitre-scale volumes due to limited plasma-liquid mass transfer and poor scalability. This study designed and evaluated a bubble-enhanced dielectric barrier discharge reactor, the Spiral Plasma Aeration Reactor Column (SPARC), to improve reactive oxygen and nitrogen species transfer and enable CAP disinfection up to 1 L. Direct CAP exposure achieved rapid, near-complete inactivation of Escherichia coli and Bacillus subtilis in 200 µL, but performance decreased sharply at 100 mL, confirming strong volume dependence under surface-limited plasma-liquid contact. Coupling CAP with gas bubbling (2 L•min⁻¹) in SPARC markedly enhanced inactivation at 250-500mL, yielding ≥99.9% reductions of E. coli and ≥99-99.7% reductions of B. subtilis within 60 min, while non-aerated CAP under identical conditions remained below ~60% reduction. At 1 L, bubble-assisted CAP retained substantial efficacy but exhibited clear volume-dependent declines, particularly for B. subtilis, highlighting persistent mass-transfer constraints at litre scale. High-load trials (≈10⁹ CFU•100 mL⁻¹) demonstrated ~4-log inactivation of E. coli and ~3-3.5-log reduction of B. subtilis, including continued post-treatment inactivation consistent with plasma-activated water effects. In a protein-rich organic matrix, early-stage inactivation was attenuated, but SPARC still achieved ~2-3-log reductions, confirming robust yet matrix-sensitive performance under wastewater-like conditions.

This study aimed to assess the potential of Dielectric Barrier Discharge (DBD) cold atmospheric air plasma for E. coli and S. aureus biofilm management. The bacterial biofilms were grown on stainless-steel coupons and treated with plasma for 1 and 5 min. The results indicate the reduction of E. coli and S. aureus up to 4.3 log CFU ml⁻¹ and 3.3 log CFU ml⁻¹, respectively. The optical emission spectroscopy (OES) shows a possible presence of OH and O species as well as the abundance of N₂ and N₂ ⁺ features in the plasma. Furthermore, Fourier Transform Infrared Spectroscopy (FTIR) revealed changes in wavelengths that are specific for carbohydrates, lipids and proteins when biofilms are treated with plasma for 5 min. This effect was also confirmed by x-ray photoelectron spectroscopy (XPS) as carbon species were decreased after plasma treatment whereas phosphorus and potassium were increased due to release from destructed cell wall. Furthermore, confocal laser scanning microscopy (CLSM) shows the effect of removing biofilm from the surface, where this effect was the most predominant for 5 min plasma treatment. All in all, our study demonstrates that DBD atmospheric air plasma can effectively reduce biofilm viability due to the presence of reactive nitrogen and possible oxygen species within a phase. Moreover, the applied treatment resulted in the successful eradication of biofilms on the surface of stainless-steel coupons.

V raziskavi je bil proučen vpliv plazemske obdelave površine na lepljenje bukovine s konstrukcijskim enokomponentnim poliuretanskim lepilom. Uporabljen je bil les navadne bukve (Fagus sylvatica L.) brez obarvanja in les bukve z rdečim srcem, učinkovitost lepilnih spojev pa je bila ovrednotena s testiranjem strižne trdnosti in delaminacije v skladu s standardom SIST EN 14080:2013. Rezultati so pokazali, da je plazemska obdelava izboljšala omočljivost površine, vendar ni prispevala k izboljšanju kakovosti lepilnih spojev. Pri bukovini z rdečim srcem je bila ugotovljena višja stopnja loma po lesu, pri čemer pa so bile strižne trdnosti lepilnega spoja nižje. Z uporabo poliuretanskega lepila pri lepljenju bukovine smo v večini primerov dosegli zahteve standarda glede strižne trdnosti lepilnega spoja, vendar pa lepilni spoji niso dosegli zahtev standarda za delaminacijo lepilnih spojev. Raziskava ni pokazala večjih razlik med lepljenjem bukovine brez obarvanj in bukovine z rdečim srcem.

Wood and aluminum composites are becoming increasingly attractive due to their ability to combine the advantages of both materials: the lightweight nature of wood and the strength of aluminum. However, using conventional wood adhesives like polyvinyl acetate (PVAc) to bond these dissimilar materials is challenging and requires special surface treatments. Prior studies have demonstrated that applying a dielectric barrier discharge plasma treatment significantly enhances shear and bending strengths in beech wood/aluminum bonds. This study focuses on the molecular interactions between PVAc and aluminum or beech wood influenced by plasma surface modification. Surface-sensitive methods, including X-ray photoelectron spectroscopy, infrared reflection adsorption spectroscopy and atomic force microscopy, were employed to characterize the PVAc films on the corresponding surfaces and to identify possible interactions. The ultrathin PVAc films required for this purpose were deposited by spin coating on untreated and plasma-treated aluminum. The aluminum surface was cleaned and oxidized by plasma. Additionally, hydroxyl species could be detected on the surface. This can lead to the formation of hydrogen bonds between the aluminum and the carbonyl oxygen of PVAc after plasma treatment, presumably resulting in increased bond strength. Furthermore, the beech wood surface is activated with polar oxygen species.

Plasma in hydrogen-containing atmospheres is an efficient method for the reduction of iron oxides. Although a vast number of approaches were performed for the reduction of bulk Fe oxides with thermal hydrogen plasmas, there is almost no information about the non-thermal plasma reduction efficiency in the atmospheric pressure range. In the current article we present the reduction of natively oxidized iron surfaces applying a dielectric barrier discharge plasma in an Ar/H₂ atmosphere at 1000 hPa. By varying the surface temperature from 25 to 300 °C, we studied the plasma reduction efficiency, which was then compared with a thermal method. Whereas plasma treatments at 25 °C and 100 °C did not result in the significant reduction of iron oxidized species, experiments at 200 °C and 300 °C yielded a reduction of approximately 88% and 91% of initial oxidized components already after 10 s, respectively. Moreover, we observed an increase in the efficiency with a plasma-thermal reduction in comparison to a thermal method, which was attributed to the presence of atomic hydrogen in the plasma phase. Analysis of morphology revealed the formation of Fe–C structures on surfaces after thermal and plasma-thermal treatments at 200 °C and 300 °C that may be connected with the diffusion of bulk contaminations to the deoxidized surface and reactions between the reduced Fe with plasma-activated adventitious carbon. Conclusively, the plasma was characterized by analyzing the reactive species and the electron temperatures.

This study aimed to analyse the efficacy of a new cold plasma device adapted for treatment with a low power consumption . We tested the reduction of bacterial cells in biofilms of E. coli, S. aureus and P. aeruginosa. . The results show significant differences between bacterial cells, suggesting that Gramme-positive S. aureus is less susceptible to plasma treatment than Gramme-negative E. coli and P. aeruginosa. Increasing the exposure time and decreasing the distance decreases the number of cells in the biofilm. However, the combination of close distance and long exposure time resulted in synergistic effects. We demonstrated a reduction of up to 6.6 log CFU cm² for E. coli at 1 mm and an exposure time of 60 seconds. All these indicate that the new cold plasma jet device can be an important key to ensuring hygiene and numerous applications in medicine and engineering are possible.

In spite of being both a one-step solution to several problems associated with woodworking and also energy efficient, the application of microwave (MW) modification in wood research has remained very limited and this promising method has practically no use in wood industries across the globe. Research done so far in this field primarily sheds light on its potential in enhancing wood permeability, treatability and uniform wood drying. While MW treatments are mostly used on wet or green wood, another modification technique, plasma, has potential benefits to synergistically enhance the effects of MW treatment, but so far has not been applied on wet or green wood specimens. This study takes a first step to investigate the effects of plasma treatments (PT) on green wood specimens, as well as combinations of MW and plasma treatments. As a preliminary study, the methodology focuses on water contact angle measurements, since these are most commonly used as indicators for surface modifications in industrial applications. An exponential time dependence was found for the contact angle on the investigated samples of Norway spruce (Picea abies Karst.). Initial contact angles after droplet deposition increased due to drying and migration of organic molecules during treatments. In comparison with the literature, the effect of plasma was significantly less pronounced on wet wood specimens. The initial contact angles showed the lowest statistical variations after MW treatment, whereas plasma increased inhomogeneities. The final contact angles on treated specimens was lowest for PT-only specimens as well as specimens treated with plasma after MW. In contrast to the initial contact angles, the final contact angles showed the lowest variations after PT. Wetting rates were insignificantly improved by plasma, with reduced statistical variations after all treatments.