Abstract
Polymer–polymer systems with special phase morphology were prepared, leading to an exceptional combination of strength, modulus, and ductility. Two immiscible polymers: poly(ε-caprolactone) (PCL) and polyhydroxyalkanoate (PHA) were used as components for manufacturing a nanoblend and a nanocomposite characterized by nanodroplet-matrix and nanofibril-matrix morphologies, respectively. Nanofibrils were formed by high shear of nanodroplets at sufficiently low temperature to stabilize their fibrillar shape by shear-induced crystallization. The effects of nanodroplet vs. nanofiber morphology on the tensile mechanical behavior of the nanocomposites were elucidated with the help of in situ 2D small-angle X-ray scattering, microcalorimetry and 2D wide-angle X-ray diffraction. For neat PCL and a PCL/PHA blend, the evolution of the structure under uniaxial tension was accompanied by extensive fragmentation of crystalline lamellae with the onset at strain e = 0.1. Limited lamellae fragmentation in the PCL/PHA composite occurred continuously over a wide range of deformations (e = 0.1–1.1) and facilitated plastic flow of the composite and was associated with the presence of a PHA nanofiber network that transferred local stress to the PCL lamellae, enforcing their local deformation. The PHA nanofibers acted as crystallization nuclei for PCL during their strain-induced melting–recrystallization.
Highlights
Poly(ε-caprolactone) (PCL) is one of the most versatile thermoplastic polymers with good mechanical properties, biocompatibility, non-toxicity vs. biological tissues, and biodegradability in several biotic environments
The character of the melting temperature change correlates with the observed behavior of the maximum intensity and the long period (Figures 5 and 6)
In the case of a composite, a gradual decrease in the melting temperature is observed in the strain region 0.1–1.1, which is consistent with the observed characteristic behavior of the maximum intensity and the long period
Summary
Poly(ε-caprolactone) (PCL) is one of the most versatile thermoplastic polymers with good mechanical properties, biocompatibility, non-toxicity vs. biological tissues, and biodegradability in several biotic environments. The structural formation of PCL under different conditions has attracted much attention [1,2,3]. In recent years, experimental evidence supports the idea that the morphology of the minor phase can pay a critical role in the improvement of the mechanical properties of PCL, leading to an exceptional combination of strength, modulus, and ductility. This was achieved by transformation of polymer blend into polymer–polymer composites [15,16,17].
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