The development of advanced packaging materials for the food industry relies on precise and efficient materials characterization capabilities.
For the food industry a precise knowledge of CO2 sorption properties by the packaging is particularly important for product quality for the development of plastics and coatings for bottles, and for fundamental understanding of absorption and diffusion properties.
In this application the interest was the precise determination of CO2 gas sorption properties of the well known packaging material, polyethylene terephthalate (PET). The PCTPro-E§E was used to measure a series of sorption isotherm on amorphous and crystalline PET.
About 2 grams of PET (cut in wide strips) was inserted into the standard sample holder. After dead volume calibration, CO2 was introduced in pressure steps (from 0.001 to 68 bar) and the absorption was measured isothermally at 29.5°C. CO2 is desorbed subsequently in pressure steps to obtain the desorption curve.
The curves provide the CO2 concentration in PET according to the pressure. For crystalline PET (fig 1) the PCT isotherms demonstrated only a slight modification with the cycles. On the contrary the properties of amorphous PET (fig 2) are strongly modified during the first absorption. The kinetics of CO2 sorption can also be determined from the time resolved data of the same measurements (not shown on the graphs).
The measurements demonstrate that CO2 uptake in PET can easily be measured using the automated measurement capabilities of the PCTPro-E§E. This type of investigation can apply to any food packaging materials.