Poly(glycolic acid) (PGA): a versatile building block expanding high performance and sustainable bioplastic applications
The concerns about the accumulating plastic waste pollution have stimulated the rapid development of bioplastics, in particular biodegradable bioplastics derived from renewable resources. Driven by a low carbon circular economy, bioplastics production is estimated to reach a 40% share of the plastics market by 2030 (Bioplastics Market Data, 2018). It is expected to substitute petrochemical-based plastics in many applications, from food packaging, pharmaceuticals, electronics, agriculture to textiles. The current biodegradable bioplastics have met challenges in competing with engineering polymers such as PET and Nylon in terms of processing capacity at the industry scale, mechanical robustness, thermal resistance, and stability. Poly(glycolic acid) (PGA) has a similar chemical structure to PLA but without the methyl side group, which allows the polymer chains to pack together tightly and results in a high degree of crystallinity (45–55%), high thermal stability (Tm = 220–230 °C), exceptionally high gas barrier (3 times higher than EVOH), as well as high mechanical strength (115 MPa) and stiffness (7 GPa). Meanwhile, PGA is rapidly biodegradable and 100% compostable, showing a similar biodegradation profile to cellulose. To date, PGA has been mainly used in the form of copolymers, such as poly(lactic-co-glycolic acid) (PLGA). Its unique properties have often been overlooked and are yet to be explored. This is caused by its intrinsic characteristics such as high hydrophilicity, rapid degradation, insolubility in most organic solvents and brittleness that have hindered its practical applications. Here we introduced the synthetic chemistry, processing methods, modification, and applications of PGA, aiming to provide a critical discussion about the technical challenges, development opportunities, and solutions for PGA-based materials. The future direction and perspectives for high-performance PGA are proposed. Given its synthesis diversity and unique properties, PGA shows great potential to substitute engineering petrochemical-based polymers for high temperature and high gas barrier packaging applications.