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RESEARCH PRODUCT

Determination of degree of crystallinity of drawn polymers by means of density measurements

subject

description

The well known procedure of determining the degree of crystallinity by means of measuring the density presupposes the knowledge of both the densities ρc and ρa of the crystalline and of the noncrystalline regions. By combination of small-angle and wide-angle x-ray scattering and of density measurements it can be shown that this method is not justified in the case of drawn polyethylene if the values of ρc and ρa known from isotropic material are used. Both ρc and ρa depend considerably on annealing and drawing conditions. In addition the effective density ρc* of the more densely packed phase in a two-phase structure is much lower than the value ρc calculated from the positions of the x-ray reflections due to a large number of lattice defects. This conclusion is based on the results of three independent sets of experiments: determination of the mean-square fluctuation of density 〈η2〉 by means of x-ray small-angle scattering; x-ray wide-angle measurements of the positions of the crystal reflections and of the halo arising from the noncrystalline regions; and comparison of densities and long periods of samples treated at various annealing temperatures.