STRUCTURAL STUDIES OF ULTRAHIGH-MODULUS POLYETHYLENE USING NITRIC-ACID ETCHING AND GEL-PERMEATION CHROMATOGRAPHY .2. INFLUENCE OF POLYMER MOLECULAR-WEIGHT, DRAW TEMPERATURE, AND ANNEALING

In the reported study, the technique of nitric acid etching followed by gel permeation chromatography has been used to determine the crystal length distribution in ultrahigh-modulus polyethylenes. The crystal length distribution has been studied as a function of draw ratio, polymer molecular weight, processing conditions, and annealing. The results confirm that although there is a considerable broadening of the crystal length distribution on drawing, the majority of crystals have lenghts less that 500 A. There are detailed changes in the length distribution due to changes in draw temperature, molecular weight, and annealing which are not always reflected in corresponding changes in the long period determined from small-angle x-ray scattering. Possible reasons for these discrepancies are discussed.