Shape Memory Performance and Microstructural Evolution in PLA/PEG Blends: Role of Plasticizer Content and Molecular Weight.

Abstract

Poly(lactic acid) (PLA) exhibits excellent shape memory properties but suffers from brittleness and a high glass transition temperature (T_g), limiting its utility in flexible and durable applications. This study explored the modification of PLA properties through the incorporation of poly(ethylene glycol) (PEG), varying in both content (5-20 wt%) and molecular weight (4000-12,000 g/mol), to enhance its suitability for specific applications, such as medical splints. The PLA/PEG blend, containing 15 wt% PEG and with a molecular weight of 12,000 g/mol, exhibited superior shape fixity (99.27%) and recovery (95.77%) in shape memory tests conducted at a programming temperature (T_p) of 45 °C and a recovery temperature (T_r) of 60 °C. Differential scanning calorimetry (DSC) analysis provided insights into the thermal mechanisms driving shape memory behavior of the PLA/PEG blend. The addition of PEG to the PLA blend resulted in a reduction in T_g and an increase in crystallinity, thereby facilitating enhanced chain mobility and structural reorganization. These thermal changes enhanced the shape fixity and recovery of the PLA/PEG blend. Synchrotron wide-angle X-ray scattering (WAXS) was further employed to elucidate the microstructural evolution of PLA/PEG blends during the shape memory process. Upon stretching, the PLA/PEG chains aligned predominantly along the tensile direction, reflecting strain-induced orientation. During recovery, the PLA/PEG chains underwent isotropic relaxation, reorganizing into their original configurations. This structural reorganization highlighted the critical role of chain mobility and alignment in driving the shape memory behavior of PLA/PEG blends, enabling them to effectively return to their initial shape. Mechanical testing confirmed that increasing PEG content and molecular weight enhanced elongation at break and impact strength, balancing flexibility and strength. These findings demonstrated that PLA/PEG blends, especially with 15 wt% PEG at 12,000 g/mol, offer an optimal combination of shape memory performance and mechanical properties, positioning them as promising candidates for customizable and biodegradable medical applications.