Changing the wettability and barrier properties for bioplastics by plasma generated amorphous carbon coatings

• Applicant: Professor Dr. Stefan Wehner, since 11/2017
• Subject Area: Coating and Surface Technology
• Term: from 2017 to 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 387344394

The project aims to modify the surface of four different biopolymers (PLA, PHBV, PCL, PBAT) via DLC coating to change their gas barrier properties and their wettability. The special feature of this approach is not to use as usual an additional (heterogeneous) interlayer, but to optimize and adjust the plasma deposition parameters of the DLC coating itself for the two crucial factors of good adhesion and flawless DLC.A commercially available DLC coating, namely FMC (flexible medical carbon), which is particularly applicable on soft substrates, is applied on the above mentioned biopolymer foils by Rf-PECVD process. The properties of the coating will be varied by adjustment of the plasma parameters (i.e. Rf power, deposition time, etc.) and analyzed with regard to film thickness, (micro)roughness (AFM and SEM measurements), chemical composition and environment by means of XPS, NEXAFS and FTIR spectroscopy, water vapor permeability and surface wettability by contact angle measurements.We will mainly use relatively thin coatings in the narrow range of 20 - 50 nm due to several reasons. Firstly, in this range the contact angle will differ significantly, i.e. it will be smallest in comparison to the original biopolymer surface, and will differ from thicker coatings, as well. In this range a minimum for the contact angle is expected. Second, we assume that even such thin coatings already provide a flawless and almost closed DLC layer, with all its benefits. This means, gas barrier properties are significantly enhanced in comparison to uncoated material. Besides, the thin and flexible coating (which goes along a low intrinsic stress within the DLC layer) may avoid the formation of micro cracks, which would diminish the barrier properties.During the plasma process the sample position towards the plasma source plays a crucial role. Its impact is to be studied for the FMC coating on the chosen biopolymeric materials. Starting from the two known extremes, the r-DLC type (sample directed towards the plasma source) and the f-DLC type (sample opposite to the plasma source), the sample orientation will be varied between these two possibilities during the depostion. The flexible DLC coating type FMC is applied by rotating the sample in front of the plasma source meaning so to say a repetitive sample position between the two extremes. The resulting coating properties especially water vapor barrier properties and wettability are to be studied and evaluated with respect to changing deposition parameters.

• DFG Programme: Research Grants
• Ehemaliger Antragsteller: Professor Dr. Christian Fischer, until 11/2017