Effect of reprocessing on polymers: Part II—Polypropylene

The melt rheology and long-term stability of unstabilised polypropylene are found to be grossly affected during reprocessing. Hydroperoxides are formed which lead to subsequent thermal-oxidative and photo-oxidative instability. Antioxidants and stabilisers show widely different abilities to protect the polymer under all the conditions that may be encountered during polymer recycling and it is concluded that the most cost-effective materials are the light stable transition metal sulphur complexes typified in the present work by the transition metal dithiocarbamates (II).