During the melting and processing of poly(ethylene terephthalate) (PET), degradation of the material may occur. One of the more common degradation products is acetaldehyde (AA). Due to its low boiling point, 21°C, AA is able to diffuse out of PET and into either the atmosphere or the packaged contents of the PET container. The diffusion of AA into packaged contents is of concern, because many food products have a limited threshold for the sweet, fruity taste and odor of AA. One of the ways to limit the AA affects is through the addition of AA scavenging agents. While these additives do not limit the generation of AA; they are designed to interact with and reduce the amount of AA that can be release from PET articles.
The purpose of this study was not only to study these AA and AA scavenger interactions and quantify their abilities in reducing AA concentrations in PET; it was also to develop an initial model to predict effectiveness of adding AA scavengers to multi-cavity PET injection molding systems. Through this work, it was determined that anthranilamide and meta-xylenediamine (MXDA) reduce AA concentrations in PET by means of a reaction mechanism. Alpha-cyclodextrin, however, scavenges AA through a hydrogen bonding/size-enclosing scheme. Regardless of the mechanism, it was proven that these three scavengers are capable of reducing detectable AA concentrations in PET. It was generally found that the greater the AA scavenger concentration, the great the effect.
Additionally, the changes in the physical properties of PET due to AA scavenger addition were studied. It was shown that melt-blending these additives into PET could adversely affect the intrinsic viscosity (I.V.) and color of the PET blend resin and/or container. The thermal properties and oxygen permeation of PET were not affected by AA scavenger addition.
The modification of an existing multi-cavity injection molding program was applied to account for the addition of AA scavengers, to PET resin, when predicting the accumulation of AA within PET preforms. The approach to modify this original program and methodologies to quantify the appropriate kinetic terms has been described in detail. Finally, the modified simulation program was then used to predict the effectiveness of various AA scavenger/PET blends in reducing detectable AA concentrations in PET preforms. While complete agreement between the modeling results and observed trends from single-cavity injection molding was not achieved, the groundwork was laid to make further improvements and advance predictability for future modeling programs.