Description
Plasma surface treatment is widely used to modify wood surfaces by increasing surface energy, removing weak boundary layers, and introducing polar functional groups, thereby enhancing adhesive interactions. This study investigated the effect of low temperature plasma treatment on the bonding performance of European beech (Fagus sylvatica L.) and Norway spruce (Picea abies Karst.) using a melamine urea formaldehyde (MUF) adhesive. Two experiments were conducted. In the first, two beech lamellae were bonded together, cut into shear test specimens, treated differently prior to testing (i.e. treatment classes A1 to A5) and tested according to EN 302-1:2023 [1]. In the second, twelve three layer beams—beech, spruce, and hybrid configurations—were prepared and tested for delamination [2]. For both experiments, half of the lamellae were treated with low-temperature plasma (Plasmatreat Openair®) and half were left untreated as controls.
Low-temperature plasma treatment reduced the contact angle of distilled water, indicating improved surface wettability. Although plasma treatment did not significantly influence shear strength overall, differences were observed across treatment classes, with the greatest improvements found in classes A3–A5. Specimens subjected to cold water and boiling water conditioning showed enhanced adhesion after plasma treatment as the average shear strengths were higher. In delamination tests (EN 14080:2013, methods B and C), a difference in the degree of delamination was observed between the control and plasma-treated beech specimens. Low-temperature plasma treated beech specimens exhibited reduced delamination, confirming improved bond durability.
Overall, low temperature plasma treatment enhanced adhesion in beech laminates bonded with MUF adhesive, particularly under moisture inducing conditions, while spruce and hybrid laminates showed consistently high bonding quality regardless of surface treatment.