Characterization of nano scale adhesion at solid surface of oxidized PP wax/PP blends

The incorporation of oxidized PP wax OPPW additive into polypropylene resulted to the improved surface adhesion. Atomic force microscopy (AFM) was employed to show either the surface topography or the changes in adhesion force measurements between the probe tip and sample surface. The results of surface characterization tests revealed lower surface roughness and higher adhesion force for higher OPPW content in the blends. The lower surface roughness may be attributed to higher melt flow ability of OPPW and hence better mold filling during sample fabrication. The improvement of surface adhesion was in favor for wetting behavior of solid surface using three test liquids of distilled water, diiodomethane and formamide. The thermodynamic work of adhesion Wa was calculated from surface free energy components using geometric mean model of Owens–Wendt–Rabel and Kaelble (OWRK approach) and also from the theory of van Oss–Good–Chaudhary (VOGC approach). The adhesion force measurements in AFM were also employed to derive the Wa using Johnson–Kendal–Roberts (JKR approximation). The results indicate that the increase in Wa was mainly due to polar part in OWRK approach and the acid–base part in VOGC approach. However, the results of work of adhesion in JKR approximation does not in general scale linearly with the respective OPPW content for the sample series, may be due to varying in near-surface modulus. The adhesion promoting effect of OPPW in the blends seems to work mainly via increasing surface acid–base interactions, better surface wettability and to some extent by plastic deformation mechanisms during debonding.