Permeability of Cork to Gases

Abstract

The permeability of gases through uncompressed cork was investigated. More than 100 samples were assessed from different plank qualities to provide a picture of the permeability distribution. A novel technique based on a mass spectrometer leak detector was used to directly measure the helium flow through the central area of small disks 10 mm in diameter and 2 mm thick. The permeability for nitrogen, oxygen, and other gases was measured by the pressure rise technique. Boiled and nonboiled cork samples from different sections were evaluated. An asymmetric frequency distribution ranging 3 orders of magnitude (roughly from 1 to 1000 μmol/(cm·atm·day)) for selected samples without macroscopic defects was found, having a peak below 100 μmol/(cm·atm·day). Correlation was found between density and permeability: higher density samples tend to show lower permeability. However, boiled cork showed a mean lower permeability despite having a lower density. The transport mechanism of gases through cork was also examined. Calculations suggest that gases permeate uncompressed cork mainly through small channels between cells under a molecular flow regime. The diameter of such channels was estimated to be in the range of 100 nm, in agreement with the plasmodesmata size in the cork cell walls.

Gas transport through cork: Modelling gas permeation based on the morphology of a natural polymer material

“…Helium has been previously used in a detailed study where the variability of gas permeation using more than one hundred samples from different cork plank qualities was assessed [20].…”

“…The volumetric flow-rate of the gas i through the cork disk, Q vol,i [Pa m 3 s À 1 ], was recorded by connecting the leak detector directly to the computer. The experiment was performed for a time long enough to obtain a stable value of Q vol,i , and hence ensuring steady-state conditions [20].…”

Vacuum physics applied to the transport of gases through cork

“…However, there are very small channels (plasmodesmata) between cells, across the cell wall with a diameter of about 100 nm [7]. These channels should play an important role in the transport of gases through cork, as suggested in a previous work by Faria et al [8].…”

“…Detailed discussion on it was previously published in Ref. [8]. In this paper we shall focus on a multi series/ parallel conductance approach to describe the flow through the small channels between cork cells.…”

Cork structural discontinuities studied with X-ray microtomography

“…Therefore the initial high ingress rate of oxygen into the bottle should be related to the cork structural discontinuities, i.e., more specifically to the void fraction and the air located there. Apart of the first period, gas transport through the cork cells occurs with very low diffusion rates through small channels (i.e., through the plasmodesmata) present in the cork cells walls ( Faria et al 2011 ).…”