Francisco A. Delfin^1,2, Christian Forsich¹, Manuel Schachinger¹, Stefan Augl¹, Sonia P. Brühl², Christoph Burgstaller¹, Daniel Heim^1
1University of Applied Sciences Upper Austria, Wels, Austria
²Universidad Tecnológica Nacional, Concepción del Uruguay, Argentina
Plastic litter has become the predominant contaminant in our lands and oceans today. Prioritizing waste recycling is essential to halt this ecologically damaging problem. However, the recycling process is hindered when products like food packaging are made of several layers of different polymers co-extruded together to have acceptable barrier properties. This issue can be addressed by depositing thin coatings using plasma-assisted techniques on single-layer polymer foils, to achieve comparable resistance against water and oxygen permeation. Given the nanometric thickness of these coatings, recycling could be potentially carried out without any inconvenience. This study compares the potential of two plasma-assisted techniques for depositing thin coatings on polymer foils: Plasma-Assisted Chemical Vapor Deposition (PA-CVD), implementing a bipolar DC pulsed discharge, and Magnetron Sputtering Physical Vapor Deposition (MS-PVD). Carbon and silicon-based coatings were successfully deposited with PA-CVD using acetylene and hexamethyldisiloxane as precursors, respectively. MS-PVD was used to apply carbon, silicon, and aluminium coatings. Polypropylene (PP), Low Density Polyethylene (LDPE) and Polyethylene Terephthalate (PET) with a thickness of 20 µm were used as substrate. The effect of coating thickness and chemical composition on the barrier properties was examined. Characterization included Fourier Transform Infrared Spectroscopy (FTIR), Raman Spectroscopy, Scanning Electron Microscopy (SEM), Surface Free Energy (SFE), Water Vapor Transmission Rate (WVTR) and Oxygen Transmission Rate (OTR). The FTIR spectra of the Si-coated films showed a characteristic band at around 1075 cm^-1, corresponding to the asymmetric stretching vibrations of Si–O–Si. C-based coatings exhibited a broad band at around 1600 cm^-1 related to C=C boding vibrations. SFE was about 45 mN/m for carbon- and 20 mN/m for silicon-coatings. SEM cross-sections permitted the estimation of a coating thickness between 50 and 150 nm. Barrier properties improved 20 to 50% depending on thickness and chemical composition, where Al-PVD coating improved up to 10 times.