Plastic pollution is a major environmental challenge, primarily due to the non-biodegradable nature of products, notably single-use items like bags and bottles. These plastics persist in the environment, breaking down into micro and nanoplastic particles, posing risks to ecosystems and human health. Additionally, some plastics contain toxic substances like phthalates and bisphenol A, leaching into the environment and endangering ecosystems and human well-being.

Though plastic pollution poses significant challenges, completely eliminating plastic use is not feasible. Plastic serves as a lightweight and durable material, essential for industries such as food packaging and beverages, where it helps reduce energy consumption and carbon emissions during transportation. Additionally, plastics offer vast opportunities, particularly in advanced types like composite plastics, which provide valuable insights for lightweight aerospace design

Bioplastics: Pioneering Green Innovations in the Plastic Industry

The plastic industry has proposed solutions to address plastic pollution, such as eliminating non-recyclable plastics in favor of recyclable ones to promote a circular economy. This involves emphasizing recycling and exploring more effective recycling methods to ensure plastics can be reused multiple times throughout their lifecycle, reducing the demand for new raw materials.

Additionally, the industry is developing bioplastics from renewable resources like plant starch and biodegradable polymers, which have better degradability and reduce environmental impact.

Bioplastics promotion is seen as key to green development in the plastic industry. Reports indicate that bioplastics production capacity was about 2.18 million tons in 2023 and is projected to reach 7.43 million tons by 2028, reflecting optimism about their future.

Bioplastics are a category of materials whose raw materials can be fully or partially replaced by renewable biomass or possess biodegradable properties. "Bio-based" refers to materials fully or partially derived from renewable biomass, while "biodegradable" indicates that the material can be decomposed by microorganisms in soil or water, eventually converting into carbon dioxide and water.

Based on being bio-based or biodegradable, bioplastics can be classified into three major categories. The first category includes bio-based and biodegradable bioplastics like starch-based bioplastics (TPS), polylactic acid (PLA), and polyhydroxyalkanoates (PHA). The second category is bio-based but non-biodegradable bioplastics, such as bio-polyethylene (Bio-PE) and bio-based polyethylene terephthalate (Bio-PET). The third category comprises fossil-based but biodegradable bioplastics, such as polycaprolactone (PCL), polybutylene succinate (PBS), and polybutylene adipate/terephthalate (PBAT).

Commercialization of Bioplastics: PLA and TPS

Polylactic acid (PLA) and starch-based plastics are the most commonly used commercial bioplastics, both being bio-based and biodegradable.

PLA is an aliphatic polyester made from the condensation polymerization of lactic acid, primarily produced through bacterial fermentation of sugars. The U.S. Food and Drug Administration (FDA) classifies PLA as GRAS (Generally Recognized as Safe). PLA bioplastics are increasingly used in products like disposable coffee cups, with Starbucks adopting PLA for their single-use cups.

PLA is recyclable and can replace PET in soft drink packaging. However, PLA requires industrial composting environments (above 60°C) for biodegradation and is not biodegradable in marine environments. This necessitates improved public sorting awareness and government regulation to build industrial composting facilities for effective biodegradation and green recycling of PLA.

TPS is a starch-based bioplastic. Pure starch bioplastics are too brittle for extrusion processing, so plasticizers like glycerol, ethylene glycol, and sorbitol are added to form thermoplastic starch (TPS). TPS, being a marketable form of starch-based bioplastics, constitutes half of the global bioplastics market. Nestlé Waters uses TPS bottles for some products to reduce reliance on traditional PET plastics.

Nonetheless, TPS is sensitive to moisture and has poor mechanical and thermal properties. High costs and limited availability of biomass resources, along with the complexity of agricultural biomass synthesis, pose significant challenges for large-scale deployment of TPS in food packaging.

Development of Bio-PET: Challenges and Potential

Bio-PET belongs to the category of bioplastics made from renewable resources but not biodegradable.

PET(Polyethylene terephthalate), as a recyclable thermoplastic polyester, finds extensive applications in the packaging industry. PET bottles account for 42% of the bottled water packaging sector and 29% in the beverage packaging sector. While PET can be recycled, furthering the industry towards green circularity would be possible if its raw materials could originate from bioresources or achieve biodegradability.

Currently, the development of bio-PET has become a focal point in the plastic industry. The monomers for bio-based PET can be derived from biomass sources, but bio-based PET does not possess biodegradability; it inherits PET's recyclability.

PET production involves two monomers: terephthalic acid (PTA) and monoethylene glycol (MEG). Typically, PET production consists of a ratio of 70% PTA and 30% MEG. To achieve 100% bio-PET, both monomers must originate from renewable resources. However, currently, only a portion of MEG (30% of the total biomass content) can be obtained from biomass, while the remaining 70% still comes from fossil resources.

While deriving PTA from biomass poses challenges, the extraction of the rigid diacid monomer FDCA from agricultural biomass demonstrates significant promise as a viable alternative to petroleum-derived terephthalic acid (TPA or PTA). This advancement paves the way for the development of a 100% bio-based polymer known as polyethylene furanoate (PEF), which stands as a promising renewable substitute for PET.

Advancing PEF: Exploring the Potential and Applications of Bio-PET Alternatives

PET consists of terephthalic acid (PTA) as a monomer, whereas PEF employs 2,5-furandicarboxylic acid (FDCA) as a monomer. FDCA, a bio-based monomer, can be derived from biomass sources such as corn, non-food crops, straw, and wood chips. The structural similarity between FDCA and PTA positions PEF as a viable substitute for PET.

The preparation and application of bio-based PEF are emerging as critical research areas. This material has the potential to reduce energy consumption and greenhouse gas emissions. PEF boasts a higher modulus than PET, allowing for the production of containers with equivalent mechanical strength using less material. Compared to PET 250 mL bottles, PEF bottles can significantly reduce lifecycle greenhouse gas emissions by 50-74%. Additionally, PEF exhibits excellent barrier properties, with oxygen and carbon dioxide barriers several times higher than PET. Moreover, PEF offers superior mechanical strength and thermal performance, rendering it suitable for various applications such as high-barrier packaging materials, high-performance fibers, and engineering plastics.

While PEF is considered non-biodegradable, its renewable nature, recyclability, and decarbonization potential make it a contributor to advancing the new plastic economy.

Chinese Academy of Sciences, in collaboration with Wankai New Materials Co., Ltd., has successfully completed the world's first ton-scale production of PEF polyester, marking the successful industrialization of PEF polymer materials.

Conclusion

The escalating threat of plastic pollution underscores the critical need for a paradigm shift towards eco-friendly solutions within the plastic industry. Bioplastics, exemplified by Bio-PET and the emerging alternative PEF, stand at the forefront of this transition, offering promising and sustainable pathways to combat this pressing environmental challenge. By embracing these innovative materials, we can forge a more resilient and environmentally conscious future for generations to come.