Impact of improved phosphite hydrolytic stability on the processing stabilization of polypropylene

It is well known that some high-performance phosphite antioxidants are particularly sensitive to hydrolysis. This process has two principal consequences: 1) the creation of potential handling issues, as the product can become sticky, and 2) a possible loss in the performance of this type of antioxidant. In this article both of these are addressed. First, changes in the hydrolytic stability of a high-performance phosphite are examined by formulating with co-additives of different chemical natures. Second, changes in the hydrolytic stability of the phosphite when using different additive physical forms are investigated. Third, the influence of hydrolysis on the processing stabilization performance of the high-performance phosphite is evaluated. It is seen that the rate of hydrolysis of the high-performance phosphite is drastically reduced both by altering the physical form of the additive package and by the correct selection of the co-additive package. This selection not only extends the storage life of the high-performance phosphite but also minimizes the risk of any handling issues. Furthermore, it is concluded that hydrolysis does not necessarily mean a loss in performance but, contrary to general perception, can actually lead to an enhancement of the processing stability. The final conclusion of this study is that the hydrolysis mechanism of the phosphite is strongly influenced by the physical form of the additive package and by the chemical nature of the co-additives. This difference in mechanism is responsible for a different level of processing performance but is not discussed in detail in this publication.