Through-thickness analysis of the skin layer thickness of multi-layered biaxially-oriented polypropylene films by micro-thermal analysis

A novel method is presented for the determination of the thickness of a polymer layer on a solid substrate by through-thickness local thermal analysis (LTA) measurements using a micro-thermal analyser (μTA). The feasibility of the method is illustrated for a poly(methyl methacrylate) film spin-cast on a silicon wafer. Subsequently the method is applied to determine the skin layer thickness of multi-layered biaxially-oriented polypropylene (BOPP) films. Although the melting temperatures of skin and core layer are only 15 °C different, it proved to be possible to determine the skin layer thickness. The film thickness obtained by μTA correlates well with the thickness observed by transmission electron microscopy (TEM) in a 0.1-1.6 μm range. The method is shown to be accurate, robust, and fast.