Aging Degradation of Polypropylene

The structural state of the polymer largely determines the aging resistance of the material. There are a large number of unstable tertiary carbon atoms in the polypropylene chain. In the presence of oxygen, only a small amount of energy can be used to remove hydrogen from tertiary carbon atoms into tertiary carbon radicals. Tertiary carbon free radicals are very active, which can cause various reactions of molecular chains, including chain growth and chain degradation, so that the original energy of PP is lost and the PP material is aging.

During the preparation process of polypropylene, catalyst residues will remain more or less. The presence of these metal ions, especially transition metal ions, will increase the auto-oxidation rate of the polymer, accelerate the decomposition of hydroperoxides, and turn them into free radicals. Increase the initiation rate.

The traditional method to improve the weather resistance of polypropylene is mostly to add organic additives to the formulation of polypropylene materials. These organic additives can be divided into two categories according to the different mechanism of action: one type can prevent or promote polypropylene to the greatest extent. Various harmful factors of photo-aging degradation, such as light-shielding agents, ultraviolet absorbers, heavy metal ion inhibitors, etc.; the first type is the hydroperoxide and peroxy free radicals that can lead to the oxidative degradation of polypropylene by removing or capturing.