ABSTRACT
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.
ABSTRACT
The front cover artwork is provided by Prof. Maus-Friedrichs' group at the Clausthal University of Technology. The image shows the molecular interaction formed at the interface between the adhesive cyanoacrylate and a natively oxidized copper or aluminium surface. Read the full text of the Research Article at 10.1002/cphc.202300076.
ABSTRACT
Cyanoacrylates are an extremely reactive class of adhesives. Despite their commercial use as instant adhesives, the adhesion mechanism, especially to technically relevant oxidized metal surfaces, has not yet been sufficiently investigated. In the present work, ultra-thin ethyl cyanoacrylate films are deposited on copper oxide and aluminum oxide by spin coating and cured there. Various surface sensitive spectroscopy methods are used to identify possible interactions. X-Ray photoelectron spectroscopy (XPS) indicates, among other information, hydrogen bonding of the carbonyl group to the oxidized surfaces. Metastable induced electron spectroscopy (MIES) measurements support the theory of this preferential molecular orientation. In addition, XPS shows the presence of an ionic carboxylate (COO- ) species at the interface. Infrared reflection adsorption spectroscopy (IRRAS) measurements confirm this ionic interaction and furthermore allow to investigate the influence of water on the reaction. A possible interaction mechanism of cyanoacrylates with metal oxides could be proposed. The formation of a carboxylate species probably occurs by hydrolysis of the ethyl group via the intermediate of a carboxyl (COOH) species.
