Diamond-like carbon coating of a pure bioplastic foil

Bioplastic materials are a promising replacement for petroleum-based plastics. Coating is an often used method to improve characteristics of traditional plastic materials. We present results of the coating of a 50 μm thick pure bioplastic foil, a mixture of 92% polyhydroxybutyrate and 8% polyhydroxyvalerate, with diamond-like carbon (DLC) via a radio frequency plasma enhanced chemical vapor deposition process. Two different types of DLC are deposited on the foil, an sp3-rich (r-DLC) and an sp2-rich (f-DLC). The first type results in a more robust the second in a more flexible kind of coating. The surface morphologies of layers with various thicknesses are examined, r-DLC up to 1000 nm, f-DLC up to 200 nm. DLC layers up to around 450 nm are intact, further deposition results in cracking and exfoliation of the DLC coating. The exfoliated DLC flakes roll up during the ongoing plasma process. This process is observed again on the thereby newly exposed substrate between the flakes. Rolling of the DLC flakes shows the presence of internal stress in the deposited DLC coating.