There are a number of ways to reduce the AA level. First of all, choose the right PET resin. Resins are available with properties that are specifically tailored to the needs of water containers. For example, Voridian Aqua PET resins 18696 and 20837 are considered leaders in low AA levels. Each has a low intrinsic viscosity (IV) of 0.72 and 0.76 respectively. The low I.V. minimizes AA generation during melt-processing. However as the I.V increases, the chains become longer, the mechanical strength increase and the resistance to stress cracking is improved. For example, carbonated soft drinks require materials with an I.V. of 0.78 or higher because the internal gas pressure makes it susceptible to stress cracking. That is to say it is important to choose a PET solution with the proper balance between low AA levels and high performance.
Optimization of molding condition by minimizing melt temperature and residence time can also reduce the AA generation. However it cannot be entirely eliminated. Since AA boils at below room temperature, it eventually migrates out of the PET into the atmosphere or into the packaged contents, affecting taste. The amount of AA that migrates is directly related to storage time and temperature.
|
--