SURFACE MODIFICATION OF A POLYPROPYLENE FILM BY MICROWAVE PLASMA AND THE ADHESION OF A VACUUM-DEPOSITED ALUMINUM LAYER

In order to improve the adhesion properties of polypropylene on a thin aluminium layer deposited under vacuum, a superficial modification of the polymer has been carried out by exposing the polymer surface to a microwave plasma from gas of different nature and composition. The concentration of the present species in the sample proximity (downstream) has been measured by emission spectroscopy. Superficial polymer modifications have been analysed by ESCA and by measuring contact angles with polar and apolar liquids. The adhesion measurements have been performed by pull-off tests. The wettability increase has been attributed to the creation of a very thin superficial layer which is partially soluble in methanol and includes carboxylic and ethylenic functions being observed by ESCA. Wettability and adhesion depend on the composition of the gas mixture used. They increase with the atomic oxygen quantities which are created in the discharge and carried away in post-discharge by the gas flow. A relationship has been established between the tensile stress values obtained by the pull-off test and the polar interaction values measured during dewetting.