Effects of Type of Polymerization Catalyst System on the Degradation of Polyethylenes in the Melt State Part 1: Unstabilszed Polyethylenes (Including Metallocene Types)

摘要

Several polyethylene resins namely, high-density polyethylene (HDPE) (Phillips metal oxide catalyst) and linear low-density polyethylenes (LLDPE) (formed by using Ziegler-Natta and metallocene catalyst technologies), were used in order to acquire insight into the effect of different polymerization catalyst systems on the production of degradation products during melt processing. Infrared spectroscopy, color measurement, hydroperoxide determination, and melt flow rate measurement were used to monitor the degradation as a function of the number of passes through a twin-screw extruder. The metallocene PEs were shown to exhibit superior melt stability relative to Phillips HDPE. The latter showed high levels of hydroperoxide formation. The superior thermo-oxidative stability of the metallocene PEs was attributed to low levels of metallic catalyst residues, together with low vinyl unsaturation content. In all of the PEs examined, the rate of crosslinking was greater than that of chain scission. IR spectroscopy indicated that crosslinking (most prevalent in the Phillips HDPE) proceeded via the addition of macroradicals to vinyl unsaturation. The Ziegler-Natta LLDPE showed an intermediate tendency for crosslinking but notable formation of trans-vinylidene and the most noticeable color development. J. VINYL ADDIT. TECHNOL., 17:28-39, 2011.