Theoretical prediction of pressure loss in pressurized plastic containers

Relations describing the time dependence of pressure loss in pressurized plastic containers are presented and discussed. These relations are expected to be useful in predicting the shelf life performance of pressurized plastic containers in applications such as aerosol and carbonated beverage containers. The time dependence of pressure loss in pressurized plastic containers is shown to be dependent on at least three independently contributing factors, namely gas absorption, gas permeation, and material viscoelastic characteristics. The influence of these three qualities is shown to be time dependent and expressions are presented which allow the relative importance of each to be assessed in terms of quantities that are conveniently measured in the laboratory. The pitfalls associated with defining quantitatively the effectiveness of a plastic barrier material as predicted by a steady state analysis is discussed. It is shown that such steady state analysis may be extremely misleading and may not necessarily be a measure of a material's time dependent qualities.