Molecular and lamellar structure of an extrusion-grade medium-density polyethylene for gas distribution

An extrusion-grade medium-density polyethylene was fractionated by size exclusion chromatography and selective solvent extraction. The fractions were studied by infrared spectroscopy, differential scanning calorimetry, and transmission electron microscopy. Infrared spectroscopy showed that chain branching was concentrated to the low molar mass material. Transmission electron microscopy showed the presence of roof-shaped crystals in the low molar mass samples and curved S- or C-shaped lamellae in the high molar mass samples. These features could be used for identification of different molar mass species in the unfractionated sample.
INTRODUCTION The development of polyethylenes of greater fracture toughness has occurred stepwise or through different 'generations.' The first generation of high-density polyethylenes (HDPE) used in gas pipes installed before 1975 [...]