Enhancement of strength of adhesive bond between wood and metal using atmospheric plasma treatment

Abstract

Combinations of wood and metal are interesting hybrid composite materials, joining together the low density of wood with the stiffness and strength of metals. Different types of adhesives are used to connect wood and metal elements, but the compatibility between adhesives used and load-bearing materials must be sufficient, which often is challenging. In adhesive bonding technology, surface treatments are a crucial step in the process. In this study, an atmospheric plasma discharge was employed to enhance the adhesion strength of joints between common beech (Fagus sylvatica L.) wood, metals (steel and aluminum alloy), and four different types of adhesives. The optical properties of plasma discharges and its influence on treated substrates' surface morphology depended on the inherent properties of the treated materials. X-ray photoelectron spectroscopy revealed the surface oxidation of all the materials after plasma treatment. Consequently, the surface free energy of all materials increased as well. The positive effect of the plasma treatment on the tensile shear strength of single-lap joints shows a high potential of atmospheric plasma treatment technology for enhancement of adhesives strength of joints combining wooden elements, wood and steel, or wood and aluminum alloys. In addition to that, expensive epoxy and polyurethane adhesives could be replaced by more affordable polyvinyl acetate and melamine-ureaformaldehyde adhesives, and still perform at equal levels if the plasma was applied prior to bonding.

Effect of Sanding and Plasma Treatment of 3D-Printed Parts on Bonding to Wood with PVAc Adhesive

“…In addition to the highest increase in bond shear strength, there was also the highest change in contact angles on ABS samples after plasma treatment. Comparable positive effects of plasma treatment on adhesion and bond shear strength on different printed surfaces and with different adhesives were reported before [11,14,17]. Overall, the measured adhesive bond strengths are very well in line with the contact angles.…”

“…The increase in bond strength was highest for the ABS samples, which also exhibited the highest change in WCA. The positive effect of plasma treatment on adhesion and bond shear strength for different printed surfaces and with different adhesives was reported before [ 11 , 14 , 17 ], particularly highlighting the effect of polar chemical groups on the surfaces produced by the plasma treatments [ 33 , 40 ].…”

“…Plasma treatments are promising techniques that enable rapid and chemical-free surface modifications [ 13 ]. Treatments of polymeric substrates with non-thermal plasma discharges in air increase the surface free energy and improve surface wettability, which is crucial for bonding with liquid water-based adhesives, thus improving the tensile strength of the adhesive bonds [ 11 , 14 , 15 , 16 , 17 ].…”

“…In an earlier study [ 17 ], it was shown that plasma treatments can enhance bond strengths of mixed material joints and thereby enable new applications for adhesive systems. Specifically, it was shown that low-cost PVAc wood adhesives can be used instead of expensive epoxy adhesives for bonding wood and metal specimens (steel, aluminium) with the same performance.…”

An open-source surface barrier discharge plasma pretreatment for reduced cracking of outdoor wood coatings

“…In general, plasma technology is used with woodbased biomaterials to enhance gluing, composites, and coatings (Ž igon et al 2018). Plasma pretreatments were shown to improve adhesion strengths (Král et al 2015;Ž igon et al 2020a), while reducing susceptibility to humidity (Avramidis et al 2010;Wascher et al 2017) and weathering (Ž igon et al 2018). Further, plasma treatments can deposit functional coatings, such as super-hydrophobic, super-hydrophilic, or photocatalytic functional layers (Podgorski et al 2001;Mai and Militz 2004;Wallenhorst et al 2018).…”