Colloid & Polymer Science Colloid & Polymer Sci 262:435-444 (1984) Small angle X-ray studies on the core crystals in oriented polypropylene/polybutene-1 blends A. Wasiak and W. Wenig Universit~it-GH-Duisburg, Laboratorium fiir Angewandte Physik, Duisburg Abstract:The equatorial small-angle x-ray scattering of blends of polypropylene and po- lybutene-1 crystallized from the oriented melt, has been analyzed by means of Guinier- and Porod analysis and absolute intensity measurements. The thickness of the core crys- tals, which appear to have an ellipsoidal shape, is of the order of 160 A and does not vary with sample composition. Measurements oF the half widths of the (110)- and (220)-wide angle x-ray diffraction lines indicate a decrease of the lateral dimension of the core crystals for both components. Calculations of the scattering power through a three-phase model for the electron densities indicate a non-proportional distribution of crystalline and amorphous phases in the blends. Key words: core-fibrils, polypropylene/polybutene-1 blends, small-angle x-ray scatter- ing. Introduction The crystallization of polymers in a high flow grad- ient of a stirred solution has been studied by Pennings and coworkers [1, 2]. Andrews [3] introduced a me- thod of crystallizing homopolymers as well as poly- mer blends in the shear field of a highly extended melt. Petermann et al. [4-10] applied this method to a num- ber of systems. As a common feature, the so prepared samples all reveal crystals in the form of needlelike en- titles. These systems have been characterized by a va- riety of physical techniques. Petermann et al. [5] measured the small angle x-ray scattering of polybutene-1 having different molecular weights. From a hump_in the equatorial scattering of low molecular PB-1 (Mw - 5.5... 8.10 s) the authors conclude a periodicity as a result of dense packing of the fibrils. In higher molecular PB-1 (Mw > 10. l0 s) no interparticle interference can be seen in the scattering curve. From Guinier plots of the SAXS, the fibril dia- meter is computed to the order of 100 A, which agrees with phase contrast TEM results. An analysis of the meridional scattering demonstrates that a density mo- dulation along the fibril axis exists. This density varia- tion, which occurs also in polypropylene fibrils, has been more closely investigated by Schultz et al. [6] us- ing dark field electron microscopy and small angle x-ray scattering. It is observed that the SAXS peak is dependent on the thermal treatment of the sample, but no second order maxima could be found. These results led the authors to the conclusion that the axial density modulation is a spinodal decomposition of the mate- rial into crystalline and amorphous regions. A more recent investigation by Petermann et al. [7] confirms this and explains the microstructural rearrangement to be a result of the motion of very mobile chain defects ("defect clustering"). Gohil and Petermann [8] report results of morpho- logical investigations on blends of polypropylene and polybutene-1. The applied methods include transmis- sion electron microscopy, electron diffraction, wide angle x-ray scattering, differential thermal analysis and mechanical testing. From the measurements it is con- eluded that the two components build up mixed crys- talline phase (solid solutions) up to 20 % of PP or PB-1 concentration. The width of the needle crystals, as de- rived from TEM micrographs, is about 300 A and ap- parently independent of sample composition. Thus the observed increase in half width of the WAXS diff- raction peaks is explained to be due to an increase in disturbance in the crystalline order; a contribution of the crystallite size effect is ruled out. Since this is an essential point that also effects the discussion of the crystallization behaviour of these blends, other measurements like small x-ray scattering would be of interest. Such results are presented in this paper. We discuss the morphology of PP/PB-1 blends, K 735