
Selection criteria 439
not retain its fizz. Polyethylene terephthalate appears to be the best choice.
This material is in fact widely used for carbonated drink containers. PVC is
used in France for non-carbonated drinks such as wine.
The data for the materials can be considered in terms of a limits on
properties analysis. Thus there could be an upper limit on permeability of
carbon dioxide of 120 x 10~
18
mol mN"
1
s
_1
and a similar upper
limit on permeability to water. With regard to toughness, using the 1,2,3 scale
of classification of materials, there could be a lower limit of category 2. This
would then rule out brittle materials. With regar ...