Permeance (§) to (O2) and (CO2 ) was evaluated under two relative humidity conditions: 0% and 90%.
Table 1 shows the values for all the samples.
As can be seen, the incorporation of the coating results in an increase in barrier which is very considerable in dry conditions.
The permeance to both O2 and CO2 is reduced by more than 100-fold.
This effect is to be expected, owing to the well-known high barrier properties of EVOH. Nevertheless, the effect is severely reduced by humidity because of water plasticization of EVOH.
The permeance decrease caused by the coating process on the PP film was 1.5-fold for O2 and 4-fold forCO2 in the coated area.
Permeance values for the materials with the agents could not be measured because of the sensitivity of the Oxtran sensor to volatile organic compounds and their interference with
the chromatographic detector used in the assays with CO2.
Effect of the agents in the barrier properties of the coatings should be negligible since, plasticization should not be expected from the addition of apolar substances to a polar matrix and agents with double functionality which could promote chain cross-linking are not present.