Orientierung und Streckmechanismen in amorphen und teilkristallinen Polycarbonatfäden

Heat-stretched fibres of bisphenol-A-polycarbonate may be produced in the fully amorphous as well as in the semi-crystalline state, depending on the choice of the molecular weight of the polymer and the spinning and stretching conditions. Investigations are made as to the influence of the stretching conditions on the orientation of the amorphous regions of the semi-crystalline material and on the orientation of the fully amorphous fibres. The orientation of the fully amorphous fibres is determined by measuring the birefringence, whereas that of the amorphous regions in semi-crystalline material results from the difference in birefringence of the entire structure of the fibres and the birefringence of the crystalline regions. The latter is calculated from the factor of orientation documentclass{article}pagestyle{empty}begin{document}$ [ text{f}_text{k} text{ = }frac{1} {2}(3overline {cos ^2 } text{ }varphi −1) ] $end{document}, which in turn is measured by wide-angle X-ray scattering. From the polarizabilities of the individual atomic bonds it was possible, on the basis of known interatomic distances and valence angles, to calculate the components of the polarizability tensor for polycarbonate. These values were used to determine the maximum birefringence of amorphous and crystalline polycarbonate. It was shown that the calculated values for birefringence, which were obtained using orientation functions determined by X-ray scattering, agreed very well indeed with those measured from the optical birefringence. Equally good agreement for the oriented filament yarns was obtained between the values for the mean angle existing between chain direction and fibre axis as determined by X-ray examination, and the results calculated from IR-dichroism. In the case of the highly stretched polycarbonate filament yarns, it was observed that, despite the rigid molecule structure, the orientation of the crystalline regions was as high as with, for example, polyethylene-terephthalate fibres. (Mean angle between chain direction and fibre axis approx. 16°). The formation of stretch-induced crystallites with fibres of higher molecular weight polycarbonate can be explained by assuming a heterogeneous stretching mechanism with necking. In the case of low molecular weight polycarbonate fibres consolidated domains of high density cannot be destroyed by heat stretching; instead, they merely slide past each other, with the result that the stretching process takes place homogeneously without initiating any crystallization.