Physico-chemical aspects of polyethylene processing in an open mixer 2. Functional group formation on PE–LD processing

Abstract

Processing of polyethylene in an open mixer is being re-examined. To complete the data already available in the literature, additional work has been performed with respect to the identification of the functional groups formed on oxidative degradation of polyethylene. To this avail, model hydroxyl and carbonyl compounds have been incorporated into low-density polyethylene (PE–LD) by melt blending. This procedure allowed confirmation of the formation of in-the-chain ketones and carboxylic acids, as expected. It also permitted exclusion of the presence of significant amounts of peracids and diacyl peroxides. The presence of peresters in the melt-processed samples is also rather unlikely. However, ester and γ-lactone groups are clearly identified, even if the corresponding concentrations are relatively small. There is no doubt about the presence of free and associated hydroperoxide groups already clearly identified in previous work. One of the most important tasks was clear identification of the groups absorbing at 3633 cm−1 as free secondary alcohols. This is especially important because if the hydroperoxide groups are the dominant hydroxyl group for polyethylene processed at low temperature, the alcohols become very rapidly the dominant hydroxyl species at temperatures above 180°C.