THE IMPROVEMENT IN ADHESION OF POLYURETHANE-POLYPROPYLENE COMPOSITES BY SHORT-TIME EXPOSURE OF POLYPROPYLENE TO LOW AND ATMOSPHERIC-PRESSURE PLASMAS

The surfaces of polymers, namely polypropylene, copolymers and blends, were exposed to low pressure oxygen and atmospheric pressure air plas mas to improve their adhesion to polyurethane adhesives. A correlation is attempted between lap shear strengths of polypropylene-polyurethan e composites and the relevant XPS, AFM and NEXAFS data. It was found t hat plasma functionalization improved the adhesion to maximum values e ven when the time of exposure was low: 1 to 10 seconds for low pressur e plasmas, and 0.1 to 1 seconds in case of atmospheric plasma jet trea tments. Thus, high lap shear strengths were obtained at relatively sma ll oxygen contents. The improvement in shear strength at short time pl asma exposures seems to be correlated to the complete smoothening of t he supermolecular structure oi stretched polypropylene foils as shown by AFM. Valence band XPS and derivatization techniques revealed more d etails of the oxygen functionalization on polypropylene. NEXAFS experi ments confirmed a re-orientation of bonds and segments of the macromol ecules by plasma exposure which are assumed to be responsible for adhe sion improvement.