Surface modifications of polycarbonate (PC) and polyethylene terephtalate (PET) by cold remote nitrogen plasma (CRNP)

Industrial PC and PET specimens have been treated by CRNP with pure N-2 or with N-2-O-2 mixtures in order to modify their adhesion and surface properties, Scanning electron microscopy (SEM), IR ellipsometry, XPS analyses and wettability measurements reveal interesting modifications at the surface of these materials which extent mainly depends on the conditions used during the plasma treatment, a key parameter being the amount of O-2 introduced in the mixture. IR ellipsometry gives evidence of the presence of new functional groups after CRNP exposure at 1270 cm(-1) (PC and PET) and in the 1650-1800 cm(-1) (PC) or 1700-1750 cm(-1) (PET) regions. Assignments to vibrational stretching modes of C-O, C-N and C=O bonds are discussed. XPS also allows identification of new surface groups associated with O and N species but when O-2 is present in the plasma, no N species is present on PC. Moreover, during the XPS analyses, the surface of treated PC is progressively modified by desorption of small oxygenated fragments which presence was induced by the plasma treatment. Wettability of treated PC increases initially very sharply with the duration of the CRNP treatment and then reaches a constant value. Presence of 10% O-2 in the N-2-O-2 mixture is detrimental for high wettability and also induces surface roughness as detected by SEM.