Mechanisms of oxygen permeation through plastic films and barrier coatings

Abstract

Oxygen and water vapour permeation through plastic films in food packaging or other applications with high demands on permeation are prevented by inorganic barrier films. Most of the permeation occurs through small defects (<3 µm) in the barrier coating. The defects were visualized by etching with reactive oxygen in a capacitively coupled plasma and subsequent SEM imaging. In this work, defects in SiO x -coatings deposited by plasmaenhanced chemical vapour deposition on polyethylene terephthalate (PET) are investigated and the mass transport through the polymer is simulated in a 3D approach. Calculations of single defects showed that there is no linear correlation between the defect area and the resulting permeability. The influence of adjacent defects in different distances was observed and led to flow reduction functions depending on the defect spacing and defect area. A critical defect spacing where no interaction between defects occurs was found and compared to other findings. According to the superposition principle, the permeability of single defects was added up and compared to experimentally determined oxygen permeation. The results showed the same trend of decreasing permeability with decreasing defect densities.

Role of SiC substrate surface on local tarnishing of deposited silver mirror stacks

“…However, the marked increase on the SiC sample is consistent with the presence of penetration pathways (i.e channels), associated with the presence of the substrate surface defects (i.e. pores) and enabling the permeation of the contaminants from the atmosphere [36][37][38].…”

“…Ag2S growth was promoted at high aspect ratio defects (surface pores) of the SiC substrate as a result from a failing protection by the covering SiO2 layer. It was proposed that, in the failure sites, permeation channels connect the silver layer to its environment through the deposited protection layer, like observed with silicon dioxide barrier layers on polymer substrates [36][37][38], and would enable local H2S entry and Ag2S growth until eruption at the stack surface.…”

Advances in surface modification and functionalization for tailoring the characteristics of thin films and membranes via chemical vapor deposition techniques

“…However, depending on the process conditions and procedure, defects could occur in the coating with possible impacts on the mass transport and diffusion. 209 Table 12 provides an overview of different CVD techniques for altering the barrier properties of selected membranes and thin films with respect to certain gases to reveal part of the ongoing trends in the field. It can be realized that the popularity of PET, PLA and PEN is high for being used as the substrate.…”

“…Their best membrane showed 96% and 92% decrease in oxygen and water vapor transmission rates, respectively, compared to the neat PET. However, depending on the process conditions and procedure, defects could occur in the coating with possible impacts on the mass transport and diffusion 209 . Table 12 provides an overview of different CVD techniques for altering the barrier properties of selected membranes and thin films with respect to certain gases to reveal part of the ongoing trends in the field.…”

Influence of pore spacing in barrier coatings on the mass transport through plastics—a simulative and experimental approach

“…In comparison with other materials, however, they have a high permeability to gases and flavors [3,4]. Thin coatings bulk coating material or on Free Diffusion and Knudsen Diffusion through pores and defects [8][9][10][11]. For the optimization and design of high gas barrier coatings or for the development of semi-permeable membrane coatings, however, the understanding of the permeation pathways through the coatings is essential.…”