Poly(ethylene terephthalate) (PET) is a packaging material commonly used by the food and beverage industry; therefore, its thermal stability has been studied by many investigators. Some of these studies have placed emphasis on the generation of acetaldehyde (AA). The presence of AA within PET articles is of concern because it has a boiling point at or below room temperature (21_C). This low temperature volatility will allow it to diffuse from the PET into either the atmosphere or any product within the container. Diffusion of AA into most products should be minimized, since the inherent taste/odor of AA is known to affect flavors of some packaged beverages and foods. There are several reported approaches for reducing amounts of AA generated during the melting and processing of PET. One approach is to optimize the processing conditions under which PET containers are manufactured. These variables, which include melting temperature, residence time, and shear rate, have been shown to strongly affect the generation of AA. A second approach is the use of PET resins which have been specially tailored to minimize the generation of AA during container manufacturing. These resins are more commonly known as ‘‘water grade PET resins’’. A third approach is the use of additives known as acetaldehyde scavenging agents.
AA scavengers are designed to interact with any AA that is generated during the processing of PET. These scavengers do not reduce PET degradation or acetaldehyde formation. They can; however, limit the amount of AA that is able to diffuse out of a container and thus reduce any effects upon the packaged contents. Interactions of scavenging agents with AA are postulated to occur according to three different mechanisms, depending upon the molecular structure of the specific scavenger. The first type of scavenging mechanism is a chemical reaction. In this case the AA and the scavenging agent react to form a chemical bond, creating at least one new product. In the second type of scavenging mechanism an inclusion complex is formed. This occurs when AA enters the internal cavity of the scavenging agent and is held in place by hydrogen bonding, resulting in a complex of two distinct molecules connected by means of secondary chemical bonds. The third type of scavenging mechanism includes the conversion of AA into another chemical species through its interaction with a catalyst. Conversion of AA into a different chemical, such as acetic acid, can increase the migrant’s boiling point and thus reduce its ability to alter the flavor of the packaged food or beverage
Post time: May-10-2023