CORONA VERSUS LOW-PRESSURE PLASMA TREATMENT - EFFECT ON SURFACE-PROPERTIES AND ADHESION OF POLYMERS

Low density polyethylene (PE) and polyethylene terephthalate (PET) fil ms were treated in air plasma of a low pressure (500 mTorr) large area microwave (2.45 GHz) discharge, or in a corona discharge at atmospher ic pressure. The modified surfaces were characterized by X-ray photoel ectron spectroscopy (XPS) for their oxygen content [O] and surface che mical structure, which were related to the corresponding peel strength of PE/PE and PE/PET laminates. Although the oxygen concentration at t he surface increased monotonically with the degree of treatment, the p eel force reached a maximum and then sharply decreased. Regardless of the treatment type, the maximum peel force occurred for [O] values bet ween 10-15 at.%. The highest peel force has been found to occur when t he concentration of C-O (hydroxyl, ether, epoxy,...) groups is highest and that of O=C-O (carboxyl) groups is lowest, which corresponds to t he situation when the effect of a weak boundary layer, due to low mole cular weight materials, is minimal (low O=C-O concentration).