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Impact of plasma treatment under atmospheric pressure on surface chemistry and surface morphology of extruded and injection-molded wood-polymer composites (WPC)

: Hünnekens, B.; Avramidis, G.; Ohms, G.; Krause, A.; Viöl, W.; Militz, H.


Applied surface science 441 (2018), pp.564-574
ISSN: 0169-4332
Journal Article
Fraunhofer IST ()
WPC; dielectric barrier discharge; surface chemistry; surface morphology

The influence of plasma treatment performed at atmospheric pressure and ambient air as process gas by a dielectric barrier discharge (DBD) on the morphological and chemical surface characteristics of wood-polymer composites (WPC) was investigated by applying several surface-sensitive analytical methods. The surface free energy showed a distinct increase after plasma treatment for all tested materials. The analyzing methods for surface topography —laser scanning microscopy (LSM) and atomic force microscopy (AFM) — revealed a roughening induced by the treatment which is likely due to a degradation of the polymeric surface. This was accompanied by the formation of low-molecular-weight oxidized materials (LMWOMs), appearing as small globular structures. With increasing discharge time, the nodules increase in size and the material degradation proceeds. The surface degradation seems to be more serious for injection-molded samples, whereas the formation of nodules became more apparent and were evenly distributed on extruded surfaces. These phenomena could also be confirmed by scanning electron microscopy (SEM). In addition, differences between extruded and injection-molded surfaces could be observed. Besides the morphological changes, the chemical composition of the substrateś surfaces was affected by the plasma discharge. Infrared spectroscopy (ATR-FTIR) and X-ray photoelectron spectroscopy (XPS) indicated the formation of new oxygen containing polar groups on the modified surfaces.