Effect of Wood Surface Modification by Atmospheric-Pressure Plasma on Waterborne Coating Adhesion (original) (raw)
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Holzforschung, 2020
Plasma treatment is becoming a mature technique for modification of surfaces of various materials, including wood. A better insight in the treatment process and the impact of the plasma on properties of wood bulk are still needed. The study was performed on Norway spruce and common beech wood, as well as their thermally modified variations. The formations of the airborne discharge, as well as mass changes of the treated wood, were monitored. The impact of such treatment on wood-coating interaction was investigated by evaluating the dynamic wettability and penetration into wood. At the wood surface, plasma streamers were observed more intense on denser latewood regions. Wood mass loss was higher with increasing number of passes through the plasma discharge and was lower for thermally modified wood than for unmodified wood. Plasma treatment increased the surface free energy of all wood species and lowered the contact angles of a waterborne coating, these together indicating enhanced wettability after treatment. Finally, the distribution and penetration depth of the coating were studied with X-ray microtomography. It was found that the coating penetrated deeper into beech than into spruce wood. However, the treatment with plasma increased the penetration of the coating only into spruce wood.
Modification of Wood by Atmospheric Discharge Plasma
2011
The atmospheric discharge plasma has been used to improve the wetting and adhesion properties of wood. The low-temperature plasma processes are attractive for wood industry applications because of their lower cost, and ability to operate in-line without vacuum systems. However, using the sessile droplet technique, we have identified a significant increase of polar component of surface free energy. Polar part of surface free energy is associated with the presence of acid/base forces (electron donor–acceptor bonds). The treatment of wood exhibited a substantial aging effect; nevertheless the treated surface never recovers to its initial hydrophobic state. The enhancement of wood wettability is a necessary condition to promote a better adhesion with a water-based adhesives and coatings, which is currently being studied.
Modification of wood by low-temperature atmospheric discharge plasma
Modification of wood by low-temperature atmospheric discharge plasma. Discharge plasma at atmospheric pressure was used to improve the wetting and adhesion properties of wood. Although also lowpressure plasma processes and namely atmospheric pressure processes are more attractive for wood industry applications because of their lower cost, higher throughput, and ability to operate in-line without vacuum systems. Atmospheric pressure plasma system is typically based on volume diffuse barrier discharge arrangement, where the treated material is placed between the discharge electrodes. However, using the sessile droplet technique, we have identified a significant increase of polar component of surface free energy. Polar part of surface free energy is associated with the presence of acid/base forces (electron donor-acceptor bonds). The treatment of wood exhibited a substantial aging effect; nevertheless the treated surface never recovers to its initial hydrophobic state. The enhancement of wood wettability is a necessary condition to promote a better adhesion with a water-based adhesives and coatings, which is currently being studied. The involvement of planar plasma source in our case makes the quality of the plasma treatment completely independent on the thickness and electrical conductivity of the wood material treated.
Plasma Chemistry and Plasma Processing, 2010
Surface inactivation is a phenomenon that causes poor adhesion. A wood surface exposed to contaminants such as dust or atmospheric grime can experience surface inactivation. Inactivation mechanisms can reduce the attractive forces on the wood surface and lead to a decrease in wettability. Plasma treatment has been applied to recover inactivated wood surfaces for better adhesion and bonding. Plasma treatment technology is very simple and the cost is rather low. In addition, this treatment produces no environmental pollution. In this study, low pressure plasma treatment was applied to reactivate the surfaces of spruce wood for glue bonding and to increase wettability after a 9-year period of natural surface inactivation. Changes in contact angles, surface energy, surface colour and bonding strength of inactivated and oxygen plasma treated wood surfaces were studied. Wettability, bonding and other mechanical strength properties of plywood panels increased with the oxygen plasma treatment.
European Journal of Wood and Wood Products
The wettability of a freshly cut wood surface will change over time, which is denoted as natural ageing. Water contact angle measurements indicated that the thermal modification of European beech reduces its wettability, but does not affect the rate at which the contact angle increases within a 4-week period. A plasma treatment of fresh wood surfaces enhanced the wettability and equaled the wettability properties of unmodified and thermally modified wood surfaces. The contact angle on plasma-treated wood surfaces increased faster than on unmodified wood surfaces, but a reduction in contact angle by the plasma treatment was still evident after ageing for 4 weeks.
The wood products industry is going through hard times in both Canada and the US. It is faced with competition from emerging economies and substitution products. The North American economy is slowing down with decreasing demand for wood products. Under these conditions, the industry should be innovative and develop the next generation of wood products. Plasma technology could be used to improve wood surface properties and compensate for the variations to be expected from an organic living material, which is sensitive to its environment (moisture, water, temperature, ultraviolet light). In recent years, the plastic and textile industries have begun experimenting with plasma technology to activate surfaces, mainly to improve coating/substrate adhesion. The literature on potential applications of plasma treatment to wood surfaces is very limited. This report describes the results of an exploratory study on the effect of plasma treatments on sugar maple wood using different gases and mixtures (N 2 , H 2 , O 2 , and Ar) at different pressures (13.3 -665 Pa). Water wettability and adhesion between surface and waterborne polyurethane acrylate coatings were also studied. The results show that it was possible, under certain conditions, to significantly increase wood/coating adhesion by 30 -100%. This improvement is correlated with improvements in wood surface energy and coating penetration depth. In addition, chemical analyses showed that, with some plasma types, the treatment led to new atoms being grafted.
Materials, 2022
This research investigates the effect of plasma treatment with air, nitrogen (N2), and carbon dioxide (CO2) gases on the performance of waterborne (acrylic) and solvent-borne (polyester) coated fir (Abies alba M.) wood samples. The properties of the plasma-coated samples were analyzed before and after exposure to accelerated weathering and compared with those of untreated and solely treated ones. According to pull-off testing, the coating adhesion of the wood samples was considerably improved by plasma treatment, and obvious differences were observed between different plasma gases. The effect was more pronounced after the weathering test. Similar results were obtained for the abrasion resistance of the samples. The water contact angle measurement illustrated more hydrophilic character in the solely plasma-treated wood in comparison with the untreated wood. The application of coatings, however, strongly improved its hydrophobic character. The performances of waterborne and solvent-bo...
Modifying Wood Surfaces with Atmospheric Diffuse Coplanar Surface Barrier Discharge Plasma
Wood and Fiber Science, 2014
This study presents possibilities of influencing the surface properties of Sessile Oak (Quercus petraea), European Ash (Fraxinus Excelsior), Norway spruce (Picea Abies), and European Larch (Larix decidua) by a low-temperature atmospheric plasma treatment (diffuse coplanar surface barrier discharge [DCSBD]) in various conditions of the plasma treatment. Effect of mutual distance from the surface of the electrode to a plasma-treated wood surface (from 0-1.2 mm), effect of plasma treatment duration (3, 5, and 10 s) usable on industry lines as well as the effect of the atmosphere used during the plasma treatment (air, N 2 , and CO 2) were studied. Effects of plasma treatment on the wood surface were evaluated by measurement of water droplet contact angle, which expressed changes in the surface polarity. Mutual distance from the surface of the DCSBD planar electrode to the surface of a treated wood sample plays a crucial role in the final change of the surface polarity. If the mutual distance is set in the range from 0 to 0.4 mm, the hydrophilization effect is reflected on the surface of treated wood. Increased polarity can be expressed by measuring the contact angle of water droplets. In this case, this is reflected by lower values of contact angles than those of the reference plasma-untreated wood samples. Conversely, by setting mutual distance within a range of 0.5-1.2 mm, the hydrophobization effect was observed, as demonstrated by the increase in the contact angle values of plasma-treated wood samples compared with the reference sample, which in this case was wood hydrophobization. Hygrophobization of the wood surface was unlike many other published experiments and was achieved without the addition of other specialty chemicals only by setting the appropriate mutual distance. Conditions for possible industrial use of the plasma modification for all tested wood samples were found.
Pre-treatment of beech wood by cold plasma
Annals of Warsaw University of Life Sciences - SGGW. Forestry and Wood Technology, 2013
Pre-treatment of beech wood by cold plasma. Adhesive joints of wood could be strengthened by plasma treatment of the surface. The low-temperature discharge plasma has been used to improve the wetting and adhesion properties of wood. The contact angle of water drop showed a steep decrease after activation by RF plasma in air and the surface energy and its polar component of beech wood were increased with time of plasma activation.
In this work, surface activation of European beech wood (Fagussylvatica) treated by diffuse coplanar surface barrier discharge plasma (DCSBD) is presented. Plasma activation was performed in air atmosphere. The power of plasma in the treatment was 400 W and exposure times were of 3, 5 and 10 s. The wettability of wood was investigated through the measurement of water droplet contact angle. DCSBD plasma generates a wide range of reactive species in ambient air. These species react with the treated sample surface and provide a convenient resource for surface activation of wood material and its components. DCSBD plasma activation demonstrated that plasma treatment is an effective method for changing the wood surface wettability depending on the surface/electrode distance (from 0 to 1.6 mm). At a distance of up to 0.4 mm, the surface becomes hydrophilic when compared with the untreated sample. On the contrary, if the distance exceeds 0.8 mm, the surface becomes hydrophobic.The hydrophobic effect evolved during storage time.