Impact of hydrophobic plasma treatments on the barrier properties of poly(lactic acid) films

Abstract

Different hydrophobic plasma treatments (CF₄, CF₄/H₂, CF₄/C₂H₂, tetramethyl silane (TMS)) were applied to the poly(lactic acid) (PLA) film in order to improve its water and oxygen barrier properties. The plasma parameters, such as power, gas flow and treatment time, were optimized according to the water contact angle measurements. X-ray photoelectron spectroscopy measurements revealed the presence of either fluorine (CF, CF₂, CF₃) or silicon (SiO_xC_y) functional groups on the film surface after the fluorinated or TMS plasma treatments, respectively. The thermal properties of the treated PLA films were studied by means of the differential scanning calorimetry (DSC) measurements and were found not to be influenced by the plasma treatment. The water permeability measurements showed an improvement of the PLA barrier properties as a result of all plasma treatments used and, particularly, after CF₄/C₂H₂ plasma. The water vapour sorption measurements confirmed well the improvement of the water barrier properties by the reduction of the water solubility. No impact of the plasma treatment on the oxygen barrier properties of the PLA film was observed, even at high relative humidity (up to 90%).