Organization of Oriented Lamellar Structures in a Miscible Crystalline/Crystalline Polymer Blend under Uniaxial Compression Flow near the Melting Temperature

Oriented lamellar structures were developed in a blend of poly(1,4-butylene succinate) (PBSU) and poly(vinylidene fluoride) (PVDF), a miscible crystalline/crystalline polymer blend, by uniaxial compression flow using a pair of channel plates. The temperatures of the compression flow were varied in the range 140−163 °C, at which PBSU was completely melted and PVDF was partially melted. Small-angle X-ray scattering (SAXS) and transmission electron microscopy (TEM) were used to analyze the lamellar morphologies, whereas the crystal orientation of PVDF and PBSU was determined by wide-angle X-ray diffraction (WAXD). The lamellar structure was highly oriented irrespective of processing conditions, but its morphology markedly depended upon the processing temperature. The lamellar stacks of the two polymers were mutually excluded from the interlamellar region (interlamellar exclusion), when the blended film was compression-processed below 150 °C. On the other hand, the lamellae of the two polymers were mutually included in the interlamellar regions, forming an alternately stacked lamellar sequence (interlamellar inclusion), when the processing temperature was higher than 150 °C. The interlamellar inclusion and interlamellar exclusion phenomena were explained by the formation and relaxation of the tie molecules between the lamellae. The crystal orientation of PBSU crystals was closely correlated with the lamellar morphologies. The WAXD results indicated that the crystal b -axis of PBSU was oriented parallel to the flow direction for the interlamellar exclusion structure and that the crystal c -axis of PBSU was preferentially oriented in the flow direction for the interlamellar inclusion structure. The oriented crystallization of PBSU was explained by the confined crystal growth of PBSU, which forces the fastest growth axis of PBSU crystals to align parallel to the ribbonlike domains of the interlamellar exclusion structure and in the lamellar plane of the interlamellar inclusion structure.