Polylactic Acid

Polylactic acid (PLA, figure 1) is a kind of lactic acid (LA) derivative produced from renewable resources. Whereas lactic acid is a naturally occurring organic acid traditionally produced by fermentation from renewable resources such as wheat, straw, corn, and sorghum. Polylactic acid has emerged as an important polymeric material for various applications on account of its properties such as biocompatibility, biodegradability, mechanical strength and process ability.

Fig. 1 Structure of polylactic acid

Synthesis of Polylactic Acid

Polylactic acid is a biodegradable, aliphatic polyester derived from lactic acid which is a monomer with two optical isomers, L‐lactic acid and D‐lactic acid, as shown in Figure 2.

Fig. 2 Enantiomers of lactic acid

There are three main methods for the synthesis of polylactic acid (Mw>10,000): (a) condensation polymerization of lactic acid; (b) lactide ring‐opening polymerization; and (c) azeotropic dehydration condensation, as shown in Figure 3 ^[1].

Fig. 3 Synthesis of polylactic acid from L‐ and D‐lactic acids

• Condensation polymerization of lactic acid

Condensation polymerization of lactic acid usually yields low molecular weight, brittle, glassy polylactic acid. External coupling agents, such as esterification-promoting adjuvants and chain-extending agents, are used to obtain higher molecular weight polylactic acids.

• Ring‐opening polymerization of lactide

The ring‐opening polymerization (ROP) of lactide is one of the methods for industrial production of high‐molecular‐weight polylactic acid. Depending on the catalyst, the ring‐opening polymerization of lactide can adopt one of three mechanisms: cation, anion, and coordination/insertion. It is difficult to obtain high molecular weight polylactic acid by cationic ring‐opening polymerization of lactide. Moreover, anionic mechanism ring‐opening polymerization of lactide usually leads to problems in controlling the molecular weight and molecular weight distribution of the polylactic acid, which is mainly caused by side reactions and inter-/intra-molecular transesterification reactions. Therefore, the study of metal complexes that catalyze lactide polymerization via a coordination/insertion mechanism has become an important topic.

• Azeotropic condensation polymerization of lactic acid

Azeotropic polycondensation method has been using for the processing of polylactic acid. This method can yield high molecular weight polymer without the use of additional chain extenders or adjuvants. After removing the solvent, high molecular weight polylactic acids can be isolated for use as is or for further purification.

Life Cycle of Polylactic Acid in Nature

Polylactic acid is derived from renewable and degradable resources such as corn and rice, which can help alleviate the energy crisis as well as reduce the dependence on fossil fuels of our society; polylactic acid and its degradation products, namely H₂O and CO₂, are neither toxic nor carcinogenic to the human body, making it an environmentally friendly polymer. Figure 4 shows the life cycle of polylactic acid in nature.

Fig. 4 Life cycle of polylactic acid (PLA) in nature

Applications

Since the availability of high molecular weight polylactic acid, its products can be fabricated via all the manufacturing methods, especially extrusion and injection molding. Owing to the comparable properties of polylactic acid with polystyrene and polyethylene terephthalate, polylactic acid covers a wide range of applications, as shown in Figure 5 ^[2].

Our Bio-based Polylactic Acid

Alfa Chemistry provides a range of polylactic acids which are based on renewable raw materials.

Alfa Chemistry is a professional supplier of polylactic acid. For high quality products, professional technical service, use suggestion and latest industry news, please feel free to contact us.

References

1. Pang, X., Zhuang, X., Tang, Z., & Chen, X. Polylactic acid (PLA): Research, development and industrialization. Biotechnology Journal, 2010, 5(11), 1125–1136.
2. Rezvani Ghomi, Erfan, Khosravi, Fatemeh, Saedi Ardahaei, Ali, et al. The Life Cycle Assessment for Polylactic Acid (PLA) to Make It a Low-Carbon Material. Polymers. 2021, 13. 1854.

Our products and services are for research use only.