Accelerated Crystallization and Morphology Change by Surface‐Induced Nucleation in Polypropylene/Poly(butylene terephthalate) Blends

We investigated the effect of poly(butylene terephthalate) (PBT) as a nucleating agent on the crystallization behavior and crystalline morphology of isotactic polypropylene (PP) in immiscible PP/PBT blends. Time‐resolved light scattering studies during isothermal melt crystallization revealed that (1) adding a small amount of PBT remarkably accelerated PP crystallization, (2) the blends exhibited a two‐stage crystallization process characterized by an increase in density difference followed by the development of optical anisotropy, and (3) the blends showed significantly reduced optical anisotropy in the PP spherulites. Small‐angle X‐ray scattering measurements and transmission electron microscopy observations clarified that this reduction in optical anisotropy originated from a disordered lamellar stack arrangement within the spherulites, caused by surface‐induced nucleation. Due to surface‐induced nucleation, the PBT domains were located at the centers of the PP spherulites. The enhanced interfacial adhesion resulting from this surface‐induced nucleation prevented a reduction in tensile strength, that is, the yield stress of the blends was superior to that of neat PP. These findings provide valuable insights for designing high‐performance recycled polymer materials from mixed plastic waste.