Acetaldehyde (AA) is produced by degradation of PET in a molten state. The higher the melt temperature, the greater the degradation and the more aa released. The screw speed, back pressure, and injection rate all directly affect the temperature of the fusion, so they also have a certain influence on the production of aa.
In order to store the beverage in the PET bottle, minimization of AA in the bottle wall is necessary because it can be immersed in the beverage and change its taste.
For now, PET resins can easily meet the requirements of packaging strong flavored beverages such as cola (<8 ppm AA in bottle preforms). However, the most stringent application is the packaging of drinking water, where PET preforms with less than 3 ppm AA in the bottle preforms. The main differences in the performance of commercial aqueous PET resins were observed. It is generally believed that the key to get lower AA in the preform is to use lower I.V. resin (<0.75 dL / g). Because it allows the preform to be injection molded at low temperatures. However, this work indicates a low I.V. resin. This is not a sufficient or even dominant factor for the AA obtained in the preforms. It is possible to have a low I.V. resin that produces high AA in the preform, whereas a high I.V. produces a low AA polymer. The inherent AA generation potential of the resin controls the AA in the preform. This is not controlled by the resin I.V. However, it is determined by the polymerization conditions.
