Aliphatic amines for use as long-term heat stabilizers for polypropylene

It is well known that Hindered Amine Stabilizers (HAS) act as stabilizers preventing the thermo-oxidative degradation of polypropylene (PP). However, different commercial oligomeric HAS that contain a piperidinyl as well as a triazine moiety were found to differ in activity. The main difference between these types of HAS concerned the presence of different types of aliphatic amines in their backbones. We measured the influence of several aliphatic amines on the thermo-oxidative degradation of PP to find out whether this difference can explain the difference in activity of these commercial HAS. In the presence of a HAS or a phenolic antioxidant, aliphatic amines increase the thermo-oxidative stability of PP. This is probably due to their ability to react with aldehydes and in this way prevent the formation of peracids, which are known to increase the degradation rate of PP. The presence of primary or secondary amines in the chemical structure of a HAS in addition to the piperidinyl group has an influence on the activity of the HAS when it is used as a long-term heat stabilizer and may explain the difference in activity observed between some commercial HAS stabilizers. (C) 2003 Elsevier Ltd. All rights reserved.