Physico-chemical aspects of polyethylene processing in an open mixer 4. Comparison of PE-LLD and PE-HD with PE-LD

Abstract

Melt-oxidation of various polyethylene samples has been compared at 150 and 180°C. Comparison of different low-density polyethylene (PE-LD) samples at 180°C shows mainly the impact of the polymer melt flow (MF) on the initial rate of hydroperoxide formation. The comparison of a series of linear low-density polyethylene (PE-LLD) samples at 150°C shows also the effect of melt viscosity. However, the conclusions are not as straightforward. Melt-oxidation of different polyethylene types indicates that the broadness of the molecular mass distribution might also be an important factor. All these results point to the possible role of shear for initiation of polyethylene oxidation in open mixers. The kinetics of formation of the different functional groups for the various polyethylene types examined are roughly the same as those deduced previously for PE-LD. This is especially so if induction times depending on temperature and particular polyethylene are taken into account. The present investigation also shows the importance of the presence of small amounts of transition metals such as various catalyst residues. In this respect, Cr-catalyst residues in Phillips-type high-density polyethylene (PE-HD) are especially effective for hydroperoxide decomposition. Nonetheless, even Ti-catalyst residues seem to have significant influence on formation of functional groups such as alcohols and carbonyl compounds.