Polylactide (PLA) is a kind of biodegradable thermoplastic polyester with high-modulus and high-strength. Thanks to its favorable biocompatibility and environmental friendliness, PLA is currently one of the most promising environmental protection materials. However, pure PLA suffers from large rigidity of molecular chain, brittleness and slow crystallization rate, which largely block the wide application of PLA in diverse fields. In recent years, more and more efforts have been put into the research on toughening PLA, and plasticizing modification is one of the effective approach to toughen PLA. Plasticization can improve the mobility of PLA molecular chains and reduce the interaction between molecular chains, thereby optimizing the processing fluidity and brittleness of PLA. The poor compatibility of plasticizers with PLA and the easy migtation of small molecule plasticizers will lead to the separation of macromolecular plasticizers from PLA. For the sake of averting the harmful effects of PLA products, the research of toughening and modifying effect of environmentally friendly plasticizers on PLA have been carried out extensively. At present, citrate plasticizers, polyethylene glycol (PEG), lactic acid oligomers (OLA), vegetable oil based plasticizers constitute the most popular environmentally friendly plasticizers. The citric acid ester plasticizer exert good plasticizing effect on PLA, and its elongation at break increases to 400%. Unfortunately, the plasticized PLA materials become soft, and the mechanical properties of PLA cannot satisfy the application requirements. Moreover, the citrate plasticizer can be easily removed from the PLA, resulting in the worse final properties of the material. PEG is also an effective alternative to toughen PLA, but PEG is easy to separate from PLA as well. Researchers have grafted PEG onto the PLA chain for plasticization, and satisfactory toughening effect has been achieved. OLA and PLA show similar chemical structure with good compatibility. Significantly improved ductility of PLA can be acquired by plasticizing of linear OLA, accompanied by sharply droped strength of the material. Furthermore, the branched OLA can be employed to plasticize the PLA to balance the crystalline regions with the amorphous regions in the PLA for enhancing the toughness of the PLA. Vegetable oil-based plasticizers feature biodegradable, environmentally friendly, readily available, derived from renewable resources, but they show poor compatibility with PLA and are easily separated from PLA. This paper mainly summarizes the researches on plasticizing polylactic acid at home and abroad in recent years, and reviews the effect of citrate plasticizers, polyethylene glycol (PEG), lactic acid oligomers (OLA), and vegetable oil base on the structure and property of PLA. The problems existing in various plasticizer for plasticizing PLAs are analyzed, which is expected to provide reference for the preparation of highly transparent and high performance biodegradable PLA materials. © 2019, Materials Review Magazine. All right reserved.
