Prediction of a-C:H layer failure on industrial relevant biopolymer polylactide acide (PLA) foils based on the sp2/sp3 ratio

• Published in: Surface & coatings technology 2019-06, Vol.368, p.79-87
• Main Authors: Schlebrowski, T., Beucher, L., Bazzi, H., Hahn, B., Wehner, S., Fischer, C.B.
• Format: Article
• Language: English
• Subjects: Acetylene; Biodegradability; Biopolymers; Carbon; Chemical composition; Contact angle; Cord buckling; Crude oil; Environmental impact; Fine structure; Foils; Fourier transforms; Gradual deposition of thin films; Mechanical properties; Organic chemistry; Photoelectrons; Plasma coating; Plasma enhanced chemical vapor deposition; Reflectance; Residual stress; Scanning electron microscopy; Surface properties; Synchrotron radiation; Thickness; Topography; Wettability; X ray absorption; X ray photoelectron spectroscopy
• ISSN: 0257-8972; 1879-3347
• DOI: 10.1016/j.surfcoat.2019.03.069

A common problem with most polymers is their crude oil-based production and hence their negative environmental impact. Therefore, changing to bio-based and biodegradable polymers like polylactide acide (PLA) as promising candidate could be a reasonable alternative. PLA is characterized by very good mechanical properties, but rather poor surface properties for functional applications. A material-friendly and frequently used technique for surface modification is the deposition of hydrogenated amorphous carbon (a-C:H) by plasma-enhanced chemical vapor deposition (PECVD) using acetylene. Here, a 50 μm thick PLA foil was coated with a-C:H layers of various thickness (50 nm up to 500 nm). Surface topography is analyzed with scanning electron microscopy (SEM), chemical composition by diffuse reflectance infrared Fourier transform (DRIFT), and wettability by contact angle. Additionally, layers were investigated by X-ray photoelectron spectroscopy (XPS) and near edge X-ray absorption fine structure (NEXAFS) at the synchrotron facility BESSYII resulting in thickness dependent changes of the sp2-/sp3-binding ratio. As the layer thickness increases, the topography also changes, showing internal stress-induced cord buckling and delamination phenomena for the carbon layers. Present results provide an improved understanding for the coating of the organic biopolymer PLA with the predominantly inorganic a-C:H via in situ growth. [Display omitted] •Plasma generated, thickness dependent a-C:H coatings on biopolymer PLA•Layer failures (cord buckling, delamination) occurred with increasing deposits.•sp3/sp2 content and chemical environment revealed thickness depended layer failures.•sp3 binding dominance shifts to sp2 with increasing thickness and causes failures.•Stable a-C:H layers resp. thicknesses on PLA were found in both regimes.