Physical Aging as the Driving Force for Brittle–Ductile Transition of Polylactic Acid

Abstract Polylactic acid (PLA) is an inherently brittle polymer, exhibiting a high Young's modulus and minimal elongation‐at‐break. To transition its failure mode to one that is much more ductile without loss in strength is challenging. A new strategy combining physical aging with ultraviolet (UV) radiation is carried out to reach the desired mechanical properties of PLA. Characterization of the modified resin is done by mechanical, rheological, and acoustic analysis. With the new processing strategy, the elongation‐at‐break of PLA increases from below 5% up to 18% by conditioning at −40 °C for 48 h followed by UV irradiation for 30 h. Correspondingly, results demonstrate that the yield strength and Young's modulus remain statistically unchanged. The interlocked entanglements inhibit the formation and evolution of subordered structures, which are attributed to the gained ductility. The high entanglement density and few subordered structures in the modified polymer system contribute to the unusual elongation‐at‐break without alteration of the modulus.