Cold atmospheric pressure plasma facilitated nano-structuring of thermally modified wood

Recently, a nanoscale structuring effect on the wood surface after plasma treatment by diffuse coplanar surface barrier discharge was observed. This type of discharge was applied to the treatment of aspen (Populus tremuloides) and thermally modified aspen wood, and the effect of treatment time and distance between the planar electrode and the sample on the formation of nano-structures was investigated. These structures may influence surface properties of wood, which can result in different adhesion strengths, soaking time of liquids and their penetration depth. In this study, the previously proposed mechanism of plasma etching for the formation of these nano-structures was studied. It was also proposed that these structures are composed of lignin. The formed structures were examined by confocal and scanning electron microscopy and attenuated total reflectance Fourier-transform infrared spectroscopy. The size of the structures was in the range of 20-100 nm, but no effect on the mean height of the surface was detected, i.e., the microscale surface roughness was unchanged. Increased treatment time influences surface structuring as a result of plasma etching. The optimal gap was found to be around 0.2-0.3 mm for this configuration. Infrared spectra indicated that plasma-treated surfaces exhibited a higher content of aromatic structures present in lignin.