The end of the year shopping spree is in full swing, "campaign" major online platform "buy buy buy" at the same time, a variety of express parcels, plastic packaging and other waste increases the problem also came. According to data released by the global environmental organization Greenpeace, if effective measures are not implemented to control, according to the current development trend of express delivery, China's consumption of various types of express packaging materials will reach 41,270,500 tons in 2025, bringing a huge resource burden and environmental pressure. Can these packaging materials be replaced with more environmentally friendly materials? Many people will look to biodegradable plastic. Will this new type of plastic be the way forward for the environment? In this edition of Curiosity Lab, we invite Associate Professor Shen Yucai from the School of Materials Science and Engineering of Nanjing University of Technology to explain.

"Biodegradable plastic, also known as biodegradable plastic, is a plastic that is degraded in nature (e.g. soil, sand, freshwater, seawater) or under specific conditions (e.g. composting or anaerobic digestion) by the action of microorganisms that exist in nature, and eventually degrades completely into carbon dioxide or/and methane (depending on the ambient oxygen content), water, mineralized inorganic salts of the elements it contains, and a new plastic. of mineralized inorganic salts and new biomass of the plastic." Shen Yucai told Technology Weekly that biodegradable plastics can be classified into two categories: bio-based biodegradable plastics and petrochemical-based biodegradable plastics, according to the source of raw material components. Among them, bio-based biodegradable plastics include plastics obtained by direct processing of natural materials, such as thermoplastic starch; polymers obtained by joint participation of microbial fermentation and chemical synthesis, such as polylactic acid (PLA); and polymers directly synthesized by microorganisms, such as polyhydroxyalkanoate (PHA). Petrochemical-based biodegradable plastics are those obtained by polymerization of petrochemical monomers by chemical synthesis, such as polybutylene terephthalate (PBAT), polybutylene succinate (PBS), carbon dioxide copolymer (PPC), and polycaprolactone (PCL).

Due to the different structures of different plastic matrix polymers, their degradation processes are very different. Some polymers are easily hydrolyzed by themselves, while others are difficult to degrade under various environments, so the biodegradation of plastics needs to go through a series of complex processes. As an example of PLA degradation, Yucai Shen explained that the initial degradation of PLA occurs after exposure to water through abiotic hydrolysis processes (inactive chemical and physical factors), resulting in random chain breaks and molecular weight reduction, which makes the polymer brittle. Subsequently, PLA oligomers can diffuse out of the native polymer and eventually be degraded by microorganisms.

"Earlier this year, known as the most stringent 'plastic restriction' introduced, we found that lunch boxes, straws and other new materials, the use of more matrix material is PLA; and our usual shopping bags, garbage bags, courier bags, cling film and other kinds of film bag products, most of them contain PBAT Shen Yucai explained that the mainstream biodegradable plastic raw materials in the market are mainly thermoplastic starch, PBAT and PLA, taking into account the cost performance and comprehensive performance requirements, the biodegradable products in the market usually choose one or two raw materials compounded with processing aids and fillers, etc. for blending and modification.

Data show that in the past five years, the average annual growth rate of China's biodegradable plastic consumption is about 20%, and in 2019, China's biodegradable plastic consumption is about 260,000 tons. With the intensive introduction and gradual implementation of plastic ban policies, the booming development of take-out and other industries further promotes the increase of biodegradable plastic consumption, which is expected to exceed one million tons in 2024. "With the support of policies and the rising awareness of environmental protection among the public, the future development trend of biodegradable plastics is undoubtedly positive. Bio-based biodegradable materials meet the goals of low carbon emission and resource recyclability, and are not missing as one of the effective ways to reduce environmental pollution."