Contribution of the surface layer to the straight-chain-segment length distribution in oriented polyethylene fibers
Abstract
Abstract The evolution of LAM contours in the Raman spectrum of polyethylene fibers as draw ratio increases is studied. Profiles of the length distribution of straight-chain segments (SCS) have been determined from the spectra. In fibers up to 20 μm thick, bimodal SCS length distribution occurs. A double maximum has also been observed in the spectra of samples prepared from the blend of polyethylenes with molecular weights of 8 × 104 and 2 × 106. In one-component polymer the peak of the SCS length distribution function relating to shorter regular sequences is attributed to the contribution of the surface layers enriched by the low-molecular fraction of the molecular mass. This conclusion is confirmed by the results of chain orientation studies carried out by infrared ATR spectroscopy: At a distance of 2–4 μm from the fiber surface, there has been detected a layer with an orientation which is considerably lower than that in the bulk of a sample.