[nanoPost] Nanoscale silicon oxide barrier layers for packaging applications

Research Centre Germany

Presently, high-barrier polymer materials used for food packaging applications mainly consist of a multi-layer structure of
different polymers. This kind of multi-layer polymer packaging material provides excellent barrier properties towards the
permeation of oxygen or water vapour, for example, but the comparatively high production costs pose an increasing
disadvantage to packaging industry. Homopolymeric materials would offer a cost and material saving option, but
generally no homo-polymeric material can provide all requirements in regard to barrier properties.
Adding the missing barrier functionalities by low-pressure microwave plasma deposition of nano-scale SiOx barrier layers
on the surface of homo-polymeric materials not only provides an excellent and low-cost alternative to commercially
available multi-layer polymer packaging, but also does not affect the recyclability of the polymer material. Moreover, even
heat-sensitive polymer materials like polypropylene can be easily functionalised by low-pressure microwave plasmas.
Two different low-pressure microwave plasma sources, a Duo-Plasmaline® type plasma source forming an axially
homogeneous plasma and an Electron-Cyclotron-Resonance plasma source, have been applied for the deposition of
nanoscale SiOx barrier layers on polypropylene foil material, using oxygen as working gas and hexamethyldisiloxane
(HMDSO) and hexamethyldisilane (HMDSN) as precursors. Subject to the process parameters gas mixture, working
pressure and plasma treatment time, different nano-scale SiOx barrier layers were deposited on the polypropylene foil
material. The quality of the SiOx barrier layers with regard to the remaining permeability of oxygen was determined with
the carrier-gas method by means of a ceramic (zirconium dioxide) detector, while the morphology and the chemical
composition of the barrier surface were characterised by optical light microscopy, scanning electron microscopy, energy
dispersive X-ray analysis and Fourier transform infrared spectroscopy measurements, respectively.
The experiments on polypropylene foil material are targeted on the development of SiOx based nanoscale barrier layers
deposited by low-pressure microwave plasmas on 3-dimensional polypropylene packaging for food applications which is
much more critical with regard to the homogeneity of the layer thickness.