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The results of silicon oxide permeation barrier coating and plasma sterilization are shown using a low-pressure microwave plasma reactor system based on a Plasmaline antenna developed for the treatment of polyethylene terephthalate bottles and foils. The influence of the coating composition on the barrier properties is analyzed and a good correlation is found. The optimized barrier coatings are analyzed regarding coating defects, which are visualized by means of capacitively coupled oxygen plasma etching of the coated substrates. The capabilities of plasma sterilization are exemplarily demonstrated for spores of Bacillus atrophaeus allowing for a spore reduction according to today's regulations for aseptic food packaging.

A microwave driven low pressure plasma reactor is developed based on a modified Plasmaline antenna for plasma processing of polyethylene terephthalate (PET) foils and bottles. It allows for the treatment of thermolabile packaging materials, e.g. plasma sterilization and permeation barrier coating. Silicon oxide films are deposited on PET foils as a permeation barrier coating. A pulsed hexamethyldisiloxane:oxygen plasma is ignited under various conditions and the oxygen permeation is investigated. A criterion for the homogeneous deposition of SiO x coatings is described depending on the residence time of process gases. Additionally, the composition of the coatings is analyzed by means of Fourier transform infrared spectroscopy regarding carbon and hydrogen content. A strong relation between barrier properties and film composition is found: good oxygen barriers are observed as carbon content is reduced and films become inorganic, quartz-like. A residual permeation as low as J = 1.0 ± 0.3 cm 3 m − 2 day − 1 bar − 1 for SiO x coated PET foils is achieved. The dependencies of important plasma parameters, such as gas mixture, process pressure, power and pulse conditions on oxygen permeation through packaging foil are shown to optimize the coating process.

Silicon oxide barrier layers are deposited on polyethylene terephthalate as permeation barriers for food packaging applications by means of a low pressure microwave plasma. Hexamethyldisiloxane (HMDSO) and oxygen are used as process gases to deposit SiOx coatings via pulsed low pressure plasmas. The layer composition of the coating is investigated by Fourier transform infrared spectroscopy and energy dispersive x-ray spectroscopy to show correlations with barrier properties of the films. The oxygen permeation barrier is determined by the carrier gas method using an electrochemical detector. The transition from low to high barrier films is mapped by the transition from organic SiOxCyHz layers to quartz-like SiO1.7 films containing silanol bound hydrogen. A residual permeation as low as J = 1 ± 0.3 cm3 m−2 day−1 bar−1 is achieved, which is a good value for food packaging applications. Additionally, the activation energy Ep of oxygen permeation is analysed and a strong increase from Ep = 31.5 kJ mol−1 for SiOx CyHz-like coatings to Ep = 53.7 kJ mol−1 for SiO1.7 films is observed by increasing the oxygen dilution of HMDSO:O2 plasma. The reason for the residual permeation of high barrier films is discussed and coating defects are visualized by capacitively coupled atomic oxygen plasma etching of coated substrates. A defect density of 3000 mm−2 is revealed.