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

该项目旨在通过DLC涂层对四种不同的生物聚合物(聚乳酸、聚乙二醇酯、聚乙二醇酯、聚对苯二甲酸丁二醇酯)进行表面修饰，以改变它们的气体阻隔性能和润湿性。这种方法的特点不是像往常那样使用额外的(非均质)中间层，而是针对良好的附着力和完美的DLC这两个关键因素，优化和调整DLC涂层本身的等离子体沉积参数。通过RF-PECVD工艺在上述生物聚合物薄膜上应用一种特别适用于软衬底的商用DLC涂层，即FMC(柔性医用碳)。涂层的性能将通过调整等离子体参数(如射频功率、沉积时间等)而改变。并通过XPS、NEXAFS和FTIR光谱对薄膜厚度、(微观)粗糙度(AFM和SEM测量)、化学成分和环境进行了分析，通过接触角测量对水蒸气渗透性和表面润湿性进行了分析。由于多种原因，我们将主要使用较薄的涂层，范围在20-50 nm。首先，在这个范围内，接触角将显著不同，即与原始生物聚合物表面相比将是最小的，也将不同于较厚的涂层。在此范围内，接触角应为最小值。其次，我们认为，即使是如此薄的涂层，也已经提供了一层完美且几乎封闭的DLC层，具有所有的好处。这意味着，与未涂覆的材料相比，气体阻隔性能显著增强。此外，薄而柔软的涂层(在DLC层内沿低内应力方向)可以避免微裂纹的形成，从而降低阻挡性能。在等离子体过程中，样品向等离子体源的位置起着至关重要的作用。它的影响将被研究为选择的生物聚合物材料上的FMC涂层。从两个已知的极端开始，r-DLC类型(直接朝向等离子体源的样品)和f-DLC类型(与等离子体源相反的样品)，在沉积期间，样品取向将在这两种可能性之间变化。柔性DLC涂层类型的FMC通过在等离子体源前面旋转样品来施加，这意味着在两个极端之间重复样品位置。所得到的涂层性能，特别是水蒸气阻隔性能和润湿性，将根据沉积参数的变化进行研究和评估。

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.