China’s Biodegradable Plastics to Usher in Golden Decade of Development
Click:4    DateTime:Sep.22,2020

By Ji Junhui, National Engineering Research Centre of Engineering Plastics, TIPC-CAS

Synthetic polymer materials have largely replaced traditional natural materials such as glass, metal, ceramics, etc., because of their excellent properties, including lightweight and corrosion resistance. However, due to the chemical stability and wide use of plastics in the natural environment, their wastes have caused a heavy burden to the environment. Therefore, the development of biodegradable polymer materials is of great significance.   

Rich research and development category, various materials industrialized

Biodegradable polymer materials can be divided into three categories in terms of sources: natural polymer, microbial synthetic polymer and chemical synthetic polymer. Among the dozens of biodegradable plastics developed worldwide, those capable of  being put into commercial production mainly include PBAT, PLA, PBS, PHA and natural polymer starch and its blends, such as starch/PVA, starch/PBS, starch/PLA, etc. 
1. PBS
PBS is obtained by polycondensation reaction of butanediol (BDO) and succinic acid. It has a relatively high melting point and excellent degradation performance. Currently, the synthesis methods of PBS include chemical polymerization and enzymatic polymerization. The latter generates high production costs and low molecular weight. Direct esterification is mostly widely used in industrialization production.
PBS displays convenience to process, good heat resistance, and excellent comprehensive mechanical properties. It can be used in degradable packaging (food bags, bottles, lunch boxes, tableware), agricultural fields (agricultural films, fertilizer slow-release materials), and can also be used in medical fields (such as artificial cartilage, sutures, stents) etc.
2. PBAT
PBAT is an aliphatic-aromatic copolyester, with low crystallization rate, flexible aliphatic chain and rigid aromatic ring in the molecular chain, and has excellent mechanical properties.
Boasting excellent film-forming properties, PBAT finds wide applications in mulch film, film bag packaging and other fields. It is one of the fastest growing and most widely used degradable plastics. Table 1 shows PBS/PBAT capacities under construction or plan to build in China.

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3. PLA
PLA has a glass transition temperature of 55°C and a melting point of 175°C. High-molecular-weight PLA is a colorless, smooth, hard plastic with high strength and high modulus. Its mechanical properties are similar to polystyrene (PS), and its tensile and flexural modulus are higher than high-density polyethylene (HDPE), but with poor toughness. It is suitable for various processing techniques, such as injection molding, blow molding, thermoforming, extrusion, casting, melt spinning and electrostatic spinning.
PLA can be completely degraded under composting conditions. It has good biocompatibility and bio-absorption, therefore being widely used in biomedical materials. Table 2 shows PLA units under construction or plan to build in China.

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4. PHA
PHA has good biocompatibility, biodegradability and thermal processing properties of plastics. It can be a homopolymer of the same fatty acid or a copolymer of different fatty acids. Its material properties vary with the composition of monomers and molecular weight.
PHA is suitable for applying in biomedical materials (implanted in human body or sustained-release drugs), packaging materials, non-woven fabrics, high-performance adhesives, etc. due to poor heat resistance and film-forming properties and high prices. The introduction of other HA structures into the PHA backbone for copolymerization can effectively improve the mechanical properties and processing properties of PHA materials. PHA also boasts biocompatibility, gas barrier properties and optical activity, making it have more special applications.
The most typical and widely used PHA is PHB. Synthesized by microorganisms, PHB has high crystallinity, similar in performance to PE, with a melting point of 173~180℃ and a glass transition temperature of about 5℃. However, PHB is relatively fragile. The use of genetic engineering and recombinant PHA synthesis pathways to realize the copolymerization of PHB with HA monomers of different structures can obtain materials with better performance. For example, PHBV, a copolymer of 3-hydroxybutyrate (HB) and 3-hydroxyvaleric acid (HA), is a biodegradable "green material" with great potential value. 
In China, Ningbo Tianan Biopolymer has realized large-scale production, with capacities reaching 2 kt/a. Tianjin Green Bio built up a 10 kt/a PHA production line in Tianjin. It plans to set up a new 100 kt/a plant in Jilin under the cooperation of Beijing Fuchong Investment. Table 3 shows existing PHA units, PHA units under construction and plan to build in China. 

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5. PPC
PPC is an aliphatic polycarbonate polymer synthesized from carbon dioxide mineral sources or industrially produced carbon dioxide waste gas and catalytically synthesized with propylene oxide or ethylene oxide. Currently, it is mainly used in foam materials, film packaging and medical materials.
Inner Mongolia Mengxi Group adopts the technology of Changchun Institute of Applied Chemistry (CIAC) and has established a 3 kt/a carbon dioxide/epoxy compound copolymer unit. China National Offshore Oil Corporation (CNOOC) cooperated with CIAC in the 3 kt/a carbon dioxide copolymer degradable plastic project in Hainan Dongfang Chemical Industrial City. Since June 2016, Zhejiang Taizhou Bangfeng Plastics Company began to use the patented technology of CIAC and set up a 30 kt/a carbon dioxide-based plastics production line in Zhejiang Wenling Shangma Industrial Zone. Henan Tianguan Group has built a thousand-ton PPC industrial production line with independent intellectual property rights. Jiangsu Zhongke Jinlong Chemical established a 220 kt/a carbon dioxide-based polypropylene carbonate polyol production line and a 1.6 million m2 high flame retardant insulation material production line.
6. Other degradable polymer materials
Poly ε-caprolactone (PCL) has a melting point of only 60°C and is rubbery at room temperature. It can be blended and processed with other biodegradable polyesters (such as starch and cellulose materials). It finds wide applications in elastomers, coatings, and adhesives. PCL is similar in structure to extracellular matrix and has biocompatibility, so it can be used as a biomedical material and is a promising tissue engineering material .
Polyvinyl alcohol (PVA) contains a large number of hydroxyl groups in the molecule. Therefore, PVA materials have excellent water solubility, film-forming properties, cohesiveness, reactivity, as well as good biocompatibility and certain degradability.
Among the natural material-based biodegradable plastics, thermoplastic starch and plant fiber molding have been industrialized, while others are still in the basic research stage. Wuhan Huali Biomaterial has established a complete industrial chain. Its modified starch (PSM) bioplastics capacity reached 30 kt/a, with products containing pellets, films, sheets and injection molded products, etc. Its newly-built 60 kt/a PSM bioplastics and products research and development production base uses tapioca starch and straw fiber as the main raw materials. Shenzhen Hongcai New Material Technology adopts the patented technology of non-grain cassava starch and chitin two composite thermoplastic bio-based modified plastics to build a 15 kt/a bio-modified resin plant and plans to set up the second-phase 50 kt/a composite thermoplastic bio-based plastic project. Suzhou Hanfeng New Material has 40 kt/a cassava modified starch capacity and plans to build a large-scale 30 kt/a pellets and products project.
 
Alloying and cheaper are the main directions of modification

At present, the price of degradable plastic resin is relatively high, and most of the degradable plastic products are ordinary daily necessities. This will seriously hinder the large-scale promotion and application of degradable plastic products. The application of inexpensive agents, such as starch, calcium carbonate, and talc in the degradable plastic modification system that do not affect the degradation performance of products and can be absorbed by the environment has become one of the important technologies for the degradable plastic products development. Common modification techniques in the application of degradable plastics include filling modification, alloying modification and copolymerization modification.
1. Filling modification
Filling modification is adding non-melting powder additives to degradable plastic resins, mainly including starch and inorganic powder. A commonly used filling auxiliary is starch. The most important concern in the filling technology is the need to plasticize the starch to make it better bond with the plastic matrix.
Another filling additive is inorganic powders such as calcium carbonate and talc. They can effectively reduce the cost of and increase the strength of modified materials to a certain extent. Therefore, it is very common to use calcium carbonate in products that do not require high mechanical properties.
2. Alloying modification
Alloying modification is one of the most important technologies in the application of degradable plastic modification. Alloyed materials refer to degradable plastics of two or more different varieties, which are combined into special materials through melt blending, to meet the needs of more products.
3. Copolymerization modification
Copolymerization modification refers to the introduction of other structural units into the molecular chain of the polymer to modify the material. For example, the copolymerization of PLA and hydrophilic polymers (such as polyethylene glycol, polyglycolic acid, polyethylene oxide) improves the hydrophilicity and degradation rate of PLA materials.
PHBV can be modified by grafting, introducing the polar functional group polyvinylpyrrolidone (PVP) into the PHBV main chain to synthesize PHBV and PVP graft copolymer PHBV-g-PVP. The crystallization rate and crystallinity of the copolymer are reduced, the hydrophilicity of the film is increased, and the drug release rate is increased.

More mature technology, rapid development in applications

In recent years, the application of biodegradable plastics has been on the fast growth track.  The degradable plastic products currently produced and applied mainly include packaging films, garbage bags, tablewares, and medical and agricultural mulching films.
Shopping bags have the largest domestic output and most mature technology among all degradable plastics products. Shopping bags bore the brunt of China’s ban on free plastic bags. At present, there are many manufacturers of fully biodegradable packaging bags in China, and the products can not only meet domestic demand, but can also be exported on a large scale.
The booming food delivery industry has aroused concerns over the pollution caused by disposable tableware. At present, a large number of degradable tableware on the market are still paper products. With the development of production and the improvement of degradation and modification technologies, the fully biodegradable plastic tableware are expected to soon meet market demand.
Mulch film has been widely used in agricultural production, but the residual film after the use of a large area of ultra-thin mulch film cannot be completely cleaned and recycled. Using PBAT resin as the main raw material, the fully biodegradable mulch technology through modified blow molding has gradually become mature and is expected to replace PE mulch.

Degradable plastics usher in a golden development phase on favourable policies

Since 2006, China’s National Development and Reform Commission (NDRC) has successively established special funds such as bio-based and resource comprehensive utilization to support the development of bio-based materials. In 2010, the Ministry of Science and Technology proposed a major project in 863 program for advanced biological manufacturing of major chemical products in the fields of biology and medical technology. In 2012, the NDRC implemented a pilot program for exemption of value-added tax or income tax for environmentally friendly products. In 2014, the NDRC implemented the degradable plastic industry cluster subsidy policy. In April 2018, China for the first time clearly released a ban on plastics and the promotion of degradable plastics. On September 9, 2019, the Central Committee for Comprehensively Deepening Reforms made arrangements to deal with the problem of plastic pollution and called for “actively promoting recycling and easy-to-recyclable degradable alternative products”. On January 19, 2020, the NDRC and the Ministry of Ecology and Environment announced the "Opinions on Further Strengthening the Control of Plastic Pollution", requiring that by the end of 2020, China will take the lead in banning and restricting the production, sales of certain plastic products in certain regions and areas, and use; by the end of 2022, promote the use of degradable shopping bags in shopping malls, supermarkets, pharmacies, and bookstores; promote the use of bio-based products such as straw-coated lunch boxes and alternative products such as degradable plastic bags in the catering take-out field, and focus on the coated areas to promote degradable mulch film.
Degradable plastics are on track for its best development period, driven by China’s ban on free plastic bags. In recent two years, a large number of companies have entered the field of degradable plastics, and the capacities of degradable plastics are expanding rapidly. It is estimated that the next 10 years will be the golden development phase for China’s degradable plastics industry.