Surface Layer Engineering of 3D-Printed PET-G: Effect of Printing Parameters on Surface Roughness and Wettability—Considerations for Tribological Applications

The aim of this study was to investigate the effect of 3D printing parameters on the surface topography and surface wettability properties of PET-G samples intended for potential tribological applications. Surfaces produced with varying fill rates and two layer heights were examined using focus variation microscopy and water contact angle measurements. The statistical analysis showed that the infill percentage has a significant influence on wettability, but did not reveal a significant influence of layer height on the observed contact angles. The results showed that surface characteristics are strongly dependent on process conditions, and the relationships between roughness parameters and wettability are mostly nonlinear. The parameters Są and Sq tended to decrease the contact angle as roughness increased, whereas Sp, Sv, and Sz showed no clear relationship with contact angle values. In contrast, Ssk and Sku showed a positive, linear correlation with the contact angle, indicating an important role of the statistical shape of the surface height distribution. The results confirm that the functional properties of additively manufactured surfaces depend not only on the amplitude of surface irregularities but also on their spatial organization and asymmetry.