Acetaldehyde generation in poly(ethylene terephthalate) resins for water bottles

Abstract

Acetaldehyde (AA) is a degradation byproduct formed when PET is melted. For the storage of beverages in PET bottles, minimization of the AA in the bottle wall is necessary as it can leach into the drink and alter its taste. Today's PET resins can easily meet the requirement for packaging strongly-flavored drinks such as colas (<8 ppm of AA in the preforms). However, the most stringent application is the packaging of potable water for which preforms with less than 3ppm of AA are required. Major differences in the performance of commercial water-grade PET resins were observed. It is commonly believed that the key to reduced AA in preforms is a low I.V. resin (<0.75 dL/g), as it allows injection molding of preforms at low temperatures. However, this work shows that low I.V. is not a sufficient or even dominant factor for the AA obtained in preforms. It is possible to have a low I.V. resin that yields high AA in the preforms and conversely a high I.V. polymer that gives low AA. The intrinsic AA generation potential of the resin controls the AA in the preforms. This is not controlled by the resin I.V. but by the polymerization conditions.