The effect of surface energetics and molecular interdiffusion on adhesion in multicomponent polymer systems

The interfacial region of coated plastics is an example of a multicomponent polymer system. Practical adhesion, as determined by the peel test, has been found to be strongly dependent on the composition of the system and the degree of interaction between its components. Several interactions are possible during the coating process of polypropylene (PP)/ethylenepropylene-diene-monomer (EPDM) blends with chlorinated polyolefin (primer) and polyurethane (PUR) paint. Wettability, a necessary but not sufficient condition alone for molecular interdiffusion, was found to be good in all cases. The lack of interfacial adhesion between PP and PUR and between EPDM and PUR was explained by high interfacial tensions calculated from surface energetics, which, in turn, were determined by contact angle and inverse gas chromatography (IGC) measurements. The improvement of interfacial adhesion between PUR and PP by chlorinated polyolefin was explained by acid-base interactions detected by IGC. The creation of surface topography by extraction of low molecular weight fractions during the coating process does not influence the adhesion. Molecular interdiffusion was shown to be facilitated by solvents.