Barrier Properties Improvement of Biopolymers by Means of Bipolar Pulsed DC PACVD Coatings

Biopolymers are very promising materials that find use in several industrial applications, ranging from packaging and food industry to the pharmaceutical and biomedical fields. Their main advantages include biocompatibility, biodegradability, non-toxicity and renewability. Despite all their great benefits,biopolymer foils also exhibit a few drawbacks that limit their application, such as poor barrier properties. To overcome these restraints, thin-layer coatings can be applied. In this work, the possibility of coating biopolymer foils using a commercially available bipolar pulsed DC plasma assisted chemical vapor deposition (PACVD) system was studied. This technique turns out to be cheap and relatively easy to scale up. Starch-, polylactic acid- and cellulose-based foils were used as substrates.Silicon- and carbon-based coatings were deposited, using hexamethyldisiloxane and acetylene as precursors. The effect of coating thickness (5- and 15-minutes deposition time) on the barrier properties was examined. ATR-FTIR spectroscopy of the generated films showed the typical siloxane absorption bands for the silicon-based films. Coating thicknesses were between 50 and 150 nm. Surface free energy was in the range 41-48 mN/m for C- and 19-28 mN/m for Si-coatings. Water vapor transmission rates were substantially reduced for cellulose based films (up to 65%), but not for PLA or starch. A reduction of over 95% in oxygen transmission rate was measured for regenerated cellulose. This study highlights the opportunity to use bipolar pulsed DC PACVD as an alternative for coating polymeric materials, with the appropriate adjustments.