In general it can be seen that the desired properties for packaging applications are attained from the intrinsic properties of PET polymer. Therefore additives such as antioxidants, plasticizers, heat or UV stabilizers are not required.
Colorants in low concentrations (usually less than 500 ppm) are used for some PET commercial grades and, like catalysts, become encapsulated or incorporated as part of the polymer chain. They are added at either the resin or pack manufacturing stage and possess extremely low extractability.
The three major packaging applications of PET are as containers (bottles, jars and tubs), semi-rigid sheet for thermoforming (trays and blisters) and thin oriented films (bags and snack food wrappers).
PET bottles and jars are manufactured by the process of injection stretch blow moulding, a process developed specifically to maximize the beneficial properties of PET. Selection of the optimum ‘blowing temperature’ is vital to achieve the best balance of properties. Impact resistance, transparency, stiffness, gas barrier properties and creep are all optimized during this part of the operation.