Effect of oxygen and hexamethyldisiloxane plasma on morphology, wettability and adhesion properties of polypropylene and lignocellulosics

In this work, the effect of oxygen plasma on the surface characteristics of polypropylene (PP) and birch was investigated. In addition, studies on the effects of hexamethyldisiloxane (HMDSO) plasma on the surface characteristics of lignocellulosics and on the adhesion properties of PP to the HMDSO-treated wood surface were carried out. Atomic force microscopy (AFM) and contact angle measurements were used to study the changes in the topography and surface free energy of the materials due to plasma treatments. AFM revealed distinct changes in the topography of PP due to oxygen plasma. Nodular structure is formed on the PP surface during the treatment and the size of the nodules increases with the treatment time. The extent of the topographical changes was nearly equal in the case of the two power levels studied. A clear increase in the surface free energy of PP and wood due to oxygen plasma was recorded. AFM studies on filter paper, kraft pulp and birch surfaces treated with HMDSO plasma showed that the plasma polymer follows the features of the substrate without forming, an actual film on the surface at the treatment levels used. The substrate surfaces became highly hydrophobic when exposed for 5 min or longer to the plasma. No improvement in the adhesion of PP film to wood was achieved by pre-treating the substrate with HMDSO plasma polymer. (C) 1998 Elsevier Science Ltd. All rights reserved.