Accelerated crystallization and crystal-crystal transition of PB induced by PP with optimized content

Isotactic polybutene-1 (PB)/isotactic polypropylene (PP) blends, typical crystalline/crystalline polymer blends with low-melting-temperature (Tm) PB and high-Tm PP, exhibit complicated interactions between their components in both molten and solid states. However, the intrinsic influences of PP component on crystallization of PB form II, form II-I transformation, and the dependence of these phase transitions on PP content are unclear. In this work, the influences of PP content ranged from 5 wt% to 40 wt% on PB crystallization were investigated. It was found that the content of PP played significant roles on the phase morphologies of the blends in molten state and then the subsequent crystallization of PB whatever in form II or form I. The PP components with ≤20 wt% addition acting as heterogeneous nucleation sites promoted crystallization nucleation, increased the crystallinity and lamellar thickness of PB, accelerated PB form II-I transformation and increased transformation degree with the increase in PP content. Whereas, the PP components with ≥30 wt% incorporation reduced the crystallinity and lamellar thickness of PB, retarded PB form II-I transformation and transformation degree with the increase in PP content. Interestingly, the PB/PP (80/20) blend presented the fastest II-I transformation rate as well as the highest transformation degree of PB. The dependence of crystallization and crystal structures of PB form II, form I, and form II-I transformation kinetics on PP concentration was discussed. PB form I′ was not observed in the present study. This work provides a theoretical and practical guide for the preparation of novel PB materials with desired structures and excellent performance, especially with anxiously accelerated crystal-crystal transition and transition degree of PB.