Polyethylene Oxide Enhanced Ductility and Toughness of Polylactic Acid: the Role of Mesophase
Less understanding on the structure-property relationship of polylactic acid (PLA)-based polymer composite system makes it a challenge to manufacture products with optimized mechanical performance by precisely regulating the microscopic structure and morphology. Herein, we choose the PLA/polyethylene oxide (PEO) blends as a model to investigate the structural reason for the enhanced ductility and toughness of this kind of material. We have demonstrated a considerable amount of PLA mesophase existing in the melt quenched films that display high ductility and toughness, in contrast to the PLA crystal in their counterparts of slowly cooled films dominated by brittle fracture. The mesophase formed by melt quenching is attributed to a moderate acceleration of PLA chains mobility due to the plasticizing effect of flexible PEO. In situ experiments have revealed the further formation of oriented mesophase induced by tensile deformation, which presents a high consistence between its content increase and the tensile stress intensification. We illustrate that the mesophase directly develops into a microfibrillar morphology to transmit the external stress and prevent the crack propagation under deformation. This work emphasizes the essential role of PLA mesophase in acquiring the enhanced ductility and toughness of PLA/PEO composite films, which may be generalized to other similar PLA-based polymer composite materials.