Storage stability of the oxygen plasma-modified PLA film

Polylactide (PLA) is the second most popular biodegradable plastic in the world currently and is a growing alternative to traditional plastics. Similar to most of the polymers, PLA requires surface activation before further processing, among others plasma activation. Hydrophobic recovery is a major problem of plasma-treated polymer; therefore, authors performed extensive research on the storage stability of the oxygen plasma-treated PLA film. For that purpose the low-temperature plasma with oxygen was applied on PLA film and its influence on surface-free energy (SFE) and contact angle (CA) with water, diiodomethane and ethylene glycol was analysed together with their subsequent hydrophobic recovery during storage. In addition, chemical changes were measured with X-ray photoelectron spectroscopy (XPS), mass loss was determined by weight measurement and the surface topography was measured by means of confocal microscopy. The best wettability of the substrate was observed after 2 and 10 min activation time, which was confirmed by the lowest CA, as well as the highest values of SFE. The degree of hydrophobic recovery depends on treatment time and is most stable for 6 min treatment. The PLA hydrophobic recovery reached its peak after a storage period of 14 days, after which the hydrophilic properties improved again, regardless of the activation time.