# Recent Approaches to the Plasticization of Poly(lactic Acid) (PLA) (A Review)
###### Abstract  
Poly(lactic acid) (PLA) is a polyester attracting growing interest every year in different application fields, such as packaging, cosmetics, food, medicine, etc. Despite its significant advantages, it has low elasticity that may hinder further development and a corresponding rise in volume of consumption. This review opens a discussion of basic approaches to PLA plasticization. These considerations include copolymerization and blending with flexible polymers, introducing oligomers and low-molecular additives, as well as structural modification. It was demonstrated that each approach has its advantages, such as simplicity and low cost, but with disadvantages, including complex processing and the need for additional reagents. According to the analysis of different approaches, it was concluded that the optimal option is the application of copolymers as the additives obtained via reactive mixing to PLA and its blends with other polymers. poly(lactic acid) (PLA); plasticization; additives; elongation at break; glass transition point; polymer blends; copolymerization; reactive mixing +
Footnote †: journal: Polymers  
0000-0001-5880-3880][PERSON] 0000-0002-0002-3330][PERSON] 0000-0002-0002-0003  
world [4], although it is still not a commodity polymer. PLA is widely used in the following areas: medicine, the production of industrial and food packaging, the automotive industry and electronics [4]. Moreover, among all 3D printing materials, PLA is one of the most popular component for materials used for additive manufacturing for filament fabrication. The basic technology of additive manufacturing from PLA is fused deposition modeling (FDM). Figure 1 illustrates a comparison of the performance of PLA with that of other common biodegradable polyesters [5]. PLA is characterized by an increased elastic modulus; however, it has low impact strength [6], which makes it unsuitable for the manufacture of flexible polymeric products. The elongation at the break of PLA is 2.5-6% [7], which initiated the prospect of plasticizing it to increase flexibility. It is also important to note that PLA is characterized by a narrow temperature-viscosity processing range and low melting strength, which causes additional difficulties when processing this polymer [8]. In addition, PLA is prone to hydrolytic degradation during processing at elevated temperatures in the presence of moisture absorbed from the environment. Polymer chains undergo thermal, thermomechanical and hydrolytic degradation due to high temperature and shear, which results in a significant loss in molecular weight. It should be noted that PLA is biodegradable just at temperatures higher than its glass transition point (approximately 60 \({}^{\circ}\)C). The decomposition of PLA below its glass transition point occurs at extremely low rates (up to 5 years) [9]. Therefore, to utilize PLA, it is advisable to use the industrial composite method under conditions in which the temperature can spontaneously increase to 65-70 \({}^{\circ}\)C. Unfortunately, the industrial composite infrastructure is currently not well developed. Therefore, the development of approaches to regulating its decomposition period is an urgent task. Another problem is that PLA decomposes under composting conditions, releasing carbon dioxide and water, which increases its carbon footprint and reduces its environmental friendliness. Therefore, the related task of modifying PLA is to accelerate the process of biodegradation by using components capable of more accelerated degradation [10]. Figure 1: Comparison chart for biodegradable polyester properties (Reprinted from Compatibilization strategies and analysis of morphological features of poly(butylene adipate-co-terephthalate) (PBAT)/poly(lactic acid) PLA blends: A state-of-art review. [PERSON]; [PERSON]; [PERSON]; [PERSON] [PERSON] Eur. Polym. J. 2022, 173, 111304.