Crystallization under strain and resultant orientation of poly(ε-caprolactone) in miscible blends

The crystallization of poly(epsilon-caprolactone) (PCL) in stretched miscible and amorphous blends containing 25-50 wt % of poly(vinyl chloride) (PVC) was monitored by infrared spectroscopy. It was found that, under most conditions, the crystallization under strain leads to a segmental crystalline orientation perpendicular to the strain direction, whereas a parallel crystalline chain orientation is observed under conditions where the crystallization is more rapid and the draw ratio higher. This orientation behavior was confirmed by X-ray diffraction measurements. The parallel orientation can be explained by an epitaxial growth of folded-chain lamellae from row nuclei. We suggest that the perpendicular orientation is mainly the result of the folding of oriented chains leading to lamellae aligned along the strain direction. Whatever the crystalline orientation direction, the crystallization of PCL under strain gives rise to nonspherulitic morphologies, different from those found when PCL is crystallized in unstretched blends. However, the magnitude of the resultant segmental orientation, both parallel and perpendicular, is similar to the orientation achieved by stretching crystalline PCL in the solid state at room temperature that is known to transform the spherulites into microfibrils.