Up-cycling coffee silverskin into biobased functional coatings

In this work, a novel route for the up-cycling of coffee silverskin (CS) based on a sustainable mechano-chemical process has been developed. CS was treated in a planetary ball milling in presence of water and the resulting suspension was used to realize thin bio-coatings deposited onto flexible packaging polylactic acid (PLA) films. CS based coatings exhibit homogeneous morphology, excellent adhesion on PLA substrates and good flexibility. The coatings display UV blocking properties, reducing the UV transmittance of PLA in the range 200–400 nm to values as low as 0.34%–2.67%, depending on the coating thickness and the process conditions. Moreover, a significant improvement of the oxygen barrier has been also recorded; CS coated films show an O2 transmission rate reduction up to 91% at 25 °C and 50% relative humidity with respect to PLA.