Fascinating morphology and crystallization behavior of melt miscible binary blends of crystalline homopolymers depicting nearly simultaneous melting transitions

Abstract We report on the interesting crystallization behavior of crystalline/crystalline polymer blends, composed of poly(butylene adipate) (PBA) and poly(ethylene oxide) (PEO), with nearly simultaneous melting and crystallization transitions. The miscibility of the two components ensured that the crystallization, on cooling, occurred from the homogenous phase in the melt. The crystalline morphology and structure was investigated using a combination of DSC, PLOM, WAXD and SAXS measurements. The crystalline structure and morphology of the PEO/PBA blends were found to be governed by a strong competition between the faster crystallization kinetics of PEO and relatively much higher nucleation density of PBA. In the PEO-rich blend, the faster crystallization kinetics of the PEO dominated the crystallization morphology development such that the minority component i.e. PBA was found to get entrapped in the interlamellar and interfibrillar regions of PEO spherulites. Interestingly, the resulting crystallization of PBA, within the confined intraspherultic regions of PEO, favored the formation of β phase crystals even at very high isothermal crystallization temperatures. In the symmetric and PBA-rich blends, the higher nucleation density of PBA had a dominant influence on the crystalline morphology development, especially at high degree of supercooling. This resulted in the formation of a variety of interesting morphologies which included interpenetrating spherulites, PEO templated PBA and PBA templated PEO spherulites. Furthermore, the α crystal phase of PBA was found to be more stable in a large supercooling window plausibly due to the dilution effect of PEO. The present study provide novel insight into the competitive role of crystallization rate and nucleation density on the crystallization behavior of crystalline/crystalline blends, with similar melting points, which has been scarcely studied in the past.