IMPROVEMENT OF POLYPROPYLENE FILM ADHESION IN MULTILAYERS BY VARIOUS CHEMICAL SURFACE MODIFICATIONS

Several techniques have been applied to the surface of polypropylene ( PP) film to improve its adhesion properties: grafting of poly(acrylic acid) by peroxidation after either irradiation by gamma-rays or activa tion by argon plasma, acrylic acid plasma polymerization and nitrogen plasma. A first evaluation of their efficiency was made by measuring t he adhesion energy of a two-layer complex containing the modified PP f ilm and an acrylic adhesive tape. Grafting of poly(acrylic acid) eithe r by pre-irradiation or by argon plasma treatment did not give a satis factory improvement of the adhesion. On the contrary, nitrogen as well as acrylic acid plasmas induced a peeling energy that was up to 10 ti mes higher than the value obtained for an untreated PP film towards th e acrylic adhesive tape. The adhesion of PP films was also tested on b ilayer laminates with (a) an extrusion-oxidized polyethylene film and (b) a terpolymer film of ethylene, acrylic acid and acrylate. Good adh esion was achieved between nitrogen-plasma-treated PP film and the oxi dized polyethylene film (600 J m(-2)) as well as the terpolymer film ( 427 J m(-2)). However, the poly(acrylic acid) plasma-deposited layer i nduced an improvement of the adhesion only with the preoxidized polyet hylene film (390 J m(-2)).