Phase Diagram of Semicrystalline Blends of Poly(l-lactic acid) and Poly(ethylene glycol)

Porosity plays a critical role in determining the performance and functionality of various materials, particularly in biomedical applications where multiscale porosity is needed. This article focuses on the semimiscible nature of poly(l-lactic acid) (PLLA) and poly(ethylene glycol) (PEG) and how it can be used to induce microporosity into the PLLA after PEG dissolution. The elaboration of phase diagrams of PLLA/PEG blends was achieved by using flash differential scanning calorimetry depending on the composition of the blends and the molar mass of PEG. This analysis reveals four distinct behaviors corresponding to different temperature ranges. Above the crystallization temperature of PLLA, a homogeneous blend is observed when the PEG content is low (type I), while a higher PEG content and higher molar mass lead to liquid–liquid phase separation (type IV). Conversely, at lower temperatures, two different liquid–solid phase separations occurred due to PLLA crystallization. In blends with lower PEG content, PEG segregates within interlamellar areas (type II), whereas at higher PEG content, it accumulates within interspherulitic and interfibrillar regions (type III). The microstructural characterization of the blend by scanning electron microscopy, after PEG removal, reveals that homogeneous microporosity is achieved into PLLA spherulites whereas larger pores are obtained in the interspherulitic regions. These results are closely correlated with those obtained in the phase separation study and show that the porosity of PLLA, created after the removal of the sacrificial PEG, can effectively be modulated by tuning the miscibility of the different components in the blend material. Moreover, this method allows us to induce porosity after shaping the material. Therefore, it can be combined with other polymer processing techniques, such as 3D-printing, to introduce multiscale porosity within complex objects, offering particularly interesting prospects in biomedical engineering.