Morphological Evolution and Structural Orientation of Poly(ε-caprolactone)/Poly(lactic acid) Biodegradable Blend Films under Complex Coupling Flow

Abstract

Herein, complex coupling flow from layer-multiplying elements (LMEs) and the postdrawing process were applied to in situ-generated flattened poly(lactic acid) (PLA) phase domains surrounded by poly(ε-caprolactone) (PCL) interface crystals in each confined PCL layer. Different postdrawing ratios (PDRs) were used to explore the structural development of PCL/PLA blend films with gradually decreasing layer space. Scanning electron microscopy (SEM), two-dimensional wide-angle X-ray diffraction (2D-WAXD), 2D small-angle X-ray scattering (2D-SAXS), polarized Fourier transform infrared reflection (FTIR), and differential scanning calorimetry (DSC) characterizations demonstrated the evolution behavior of phase, crystallites, and amorphous chains of PCL and PLA, including the transformation from spherical to flattened PLA domains with a larger length (diameter) and width-to-thickness ratio (∼2.24), the fragmentation and packing behavior of crystallites at PDR < 6, and the alignment behavior of amorphous chains at PDR > 6. As a result, the dynamic rheological storage modulus of the produced PCL/PLA blend films exhibited an impressive 4 orders of magnitude improvement at low frequency, and the tensile strength and elastic modulus at room temperature increased 186.4 and 277.5%, respectively, as PDR increased from 1 to 21. The study findings provide insight for applying the LME-postdrawing technique to the performance regulation of biodegradable materials to widen their applications, based on controllable phase morphology and confined interface construction.