Supertoughened and heat-resistant poly(L-lactide) (PLLA)/ elastomer blends were prepared by controlling the distribution of stereocomplex (sc) crystallites and the morphological change from sea−island structure to cocontinuous-like structure. To control the distribution of sc and the phase morphology, poly(D-lactide) (PDLA) was first blended with ethylene−vinyl acetate−glycidyl methacrylate elastomer (EVMG) to prepare EVMG/PDLA masterbatch comprising both free PDLA and EVMG-g-PDLA copolymers. The free and grafted PDLA would collaborate with PLLA to form sc in the matrix and at the interface, respectively, during subsequent melt-blending of the masterbatch with PLLA. Consequently, the in situ formed sc crystallites not only enhanced the interfacial adhesion but also increased the melt viscosity and crystallization rate of the PLLA matrix. The sc crystallites amount can be tuned via PDLA content to achieve designable properties and cocontinuous-like morphology, leading to highly improved toughness of PLLA; e.g., the notched impact strength of PLLA was increased by 84 times. Moreover, the PLLA/(EVMG/PDLA) blends exhibit both excellent impact toughness (>70 kJ/m 2 ) and heat resistance (E′ 140°C > 130 MPa) after a simple annealing. This work provides an effective approach toward high performance PLA materials which may expand the application of PLA to more advanced domains.

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Polyglycolic acid (PGA) with outstanding biodegradability and gas barrier is promising in the packaging field. Unfortunately, the poor toughness limits its application. Biodegradable and flexible polycaprolactone (PCL) was used to improve the toughness, and multifunctional epoxy polymers (MEPs) were selected as reactive compatibilizers. The spreading coefficient model indicated that MEP would be encapsulated by the dispersed phase of PCL in PGA/PCL/ MEP blends. Terminal carboxyl/hydroxyl groups of both PCL and PGA can in situ react with MEP, and the compatibility between PGA and PCL was improved greatly. The dimension of PCL domains decreased to 0.9 μm with 0.75 wt % of MEP. The fracture toughness of PGA/PCL increased by 370%, while the tensile strength increased to 49.6 MPa. When the total content of MEP was more than 0.75 wt %, excess MEP would migrate to the PGA matrix, resulting in an increase in the viscosity of the PGA matrix and a morphology evolution of PGA/ PCL blends from "sea-island" to the "co-continuous-like" structure. Therefore, this work will provide a facile method to prepare toughened sustainable green PGA-based materials with balanced strength.

The application of biocompostable poly(glycolic acid) (PGA) is hindered by the conflict between its strength and ductility. In this work, we address an effective strategy to obtain designable strength and ductility of PGA/poly(butylene adipate-co-terephthalate) (PBAT) films by tuning the drawing temperature. At low temperatures (35–40 °C), the poor chain mobility leads to a predominance of stress-induced amorphous chain orientation rather than relaxation and crystallization, and the drawn films exhibit high tensile strength (145 MPa) with remarkable strain hardening. Then, the chain relaxation becomes pronounced due to the increased chain mobility at a temperature range of 45–50 °C, resulting in a low orientation, low crystallinity, and consequently high ductility (elongation at break of 320%). At the high temperature region (55–60 °C), further enhanced chain mobility facilitates the formation of oriented PGA crystallites, which restrict chain relaxation and provide more strengthened elements. As a result, PGA-based films with excellent strength, stiffness, and ductility (e.g., 103 MPa, 2800 MPa, and 220%, respectively) are achieved. Therefore, this work provides an effective route to tune the mechanical properties of PGA materials, and in principle it should be applicable to other semicrystalline polymeric systems as well.