Quantitative x‐ray studies of order in amorphous and crystalline polymers. Quantitative x‐ray determination of crystallinity in polyethylene

Abstract

Various quantitative scattering relationships for polymers have been examined experimentally in order to test their validity as assumptions in the x‐ray determination of crystallinity. These are (a) the proportionality between the scattered intensity and the pt value of the specimen (p is the density and t the thickness of the material), (b) the relationship between equal pt values for two different specimens of the same material and the corresponding scattering masses in the beam, (c) the scattering from equal masses of a polymer in the amorphous or crystalline states, and (d) the values of the total scattered intensity from equal masses of different polymers. It has been demonstrated, at least in the case of polyethylene, that the percentage of crystalline material in a polycrystalline polymer can be determined quantitatively by means of x‐ray diffraction methods. The method used in this study, viz., a comparison of the amorphous scattering from the sample with that from a completely amorphous sample, has been applied to an investigation of the temperature variation of crystallinity in unstretched and stretched polyethylene. The comparison between the x‐ray and density results for the case of the unstretched material has been pointed out. The technique has also permitted a determination of the orientation of the crystallites. By means of these methods, it has been shown that the x‐ray diffraction results are in essential agreement with previous stress‐birefringence data on stretched polyethylene; and that the nature of the stretchng process is different at high and at low elongations.