Physico-chemical aspects of polyethylene processing in an open mixer: 7. Polyethylene hydroperoxide distribution in the melt

Abstract

Polyethylene processing in air yields hydroperoxide groups in a non-homogeneous way. In the initial stages of processing, the hydroperoxide groups were formed in separated clusters. In these clusters the ratio of associated hydroperoxides to total hydroperoxides was constant. In advanced stages of processing, the additional clusters formed were overlapping increasingly with the clusters produced previously. The resulting distribution of hydroperoxide groups was examined from a theoretical and an experimental point of view. The hydroperoxide groups were found to be associated hydroperoxides. The free hydroperoxides detected by IR spectroscopy had to be seen essentially as “statistically free” hydroperoxide groups. There was no significant amount of “isolated” hydroperoxides. The additional associations resulting from cluster overlapping were well accounted for by a Poisson-type equation. The physico-chemical nature of the hydroperoxides is of prime importance for the thermolysis reactions. It was found that the dependency of the amount of hydroperoxides associated with other hydroperoxides on the total amount of hydroperoxides involves both a linear and a quadratic term. It might explain, at least in part, the complexity of the hydroperoxide decomposition reactions.