Biodegradable Plastics Embrace for a Bright Future
Year:2020 ISSUE:1
COLUMN:POLYMERS
Click:121    DateTime:Jan.06,2020


By Ji Junhui, Technical Institute of Physics and Chemistry of the Chinese Academy of Sciences (TIPC-CAS)


Synthetic polymer materials, boasting excellent properties, such as of lightweight and corrosion resistance have largely replaced traditional ones (such as glass, metal, ceramics, etc.). However, plastic wastes are big burden to the environment, due to their chemical stability in the natural environment. Therefore, the development of polymer materials with biodegradable properties is of great significance for solving plastic waste pollution.

   Biodegradable plastics are biodegradable under the conditions of nature (such as soil and / or sandy soil, etc.), and / or under specific conditions (such as composting or anaerobic digestion or in aqueous culture medium), with the existence of microorganisms. Biodegradable materials are becoming a new leading industry for scientific and technological innovation and economic development, because of their green, environmentally friendly, resource-saving features and wide applications.

   According to the industrial restructuring catalogue issued by China’s National Development and Reform Commission (NDRC) in 2015, the degradable agricultural films, degradable polymers, degradable materials, biodegradable plastics and their products, and biodegradable fibers are listed as the industries, of which, development is encouraged by the government. 

   There are currently dozens of degradable plastics under research and development globally, but only some can be put into industrial production, including chemically synthesized polylactic acid (PLA), PBS, and its copolymer polybutyleneadipate-co-terephthalate (PBAT), microbially synthesized polyhydroxyalkanoates (PHA), natural polymer starch and blends of these varieties, such as starch / PVA, starch / PBS, starch / PLA, etc.

1. PBS/PBAT

   The synthesis methods of PBS / PBAT include direct esterification, transesterification and chain extension. Direct esterification is the most widely used industrial production method, of which, key research contents cover the development of efficient catalysts, increasing molecular weight, and reducing side reactions.  

   Major domestic PBS/PBAT plants include Zhejiang Hangzhou Xinfu Pharmaceutical’s 23 kt/a plant, Shandong Huiying New Materials’ 25 kt/a plant, Xinjiang Lanshan Tunhe’s 5 kt/a unit, Guangdong Jinfa Technology’s 30 kt/a PBSA plant, Shanxi Jinhui Zhaolong High and New Tech’s 20 kt/a PBS/PBAT unit etc. The global ban on plastic wastes and rising awareness to protect environment have led to rapid development of PBS/PBAT products. At present, there are many PBS / PBAT plants under construction or expansion in China, and some of them have capacities up to 100 kt/a.

2. PLA

   PLA is also called polylactide. Its raw material is lactic acid or its derivative lactate. The polymerization of lactic acid can be divided into two types: indirect synthesis and direct synthesis. At present, PLA technology that realizes large-scale production is based on indirect method. The indirect synthesis process is commonly used, as its products are of high molecular weight and a narrow molecular weight distribution, and the production process is easy to control.  

   Global PLA capacities are over 240 kt/a. In China, Changchun Institute of Applied Chemistry (CIAC), Chinese Academy of Sciences and Zhejiang Haizheng Biomaterials have achieved 15 kt/a production capacities and are building up a 50 kt/a production line. Anhui Fengyuan has put its 3 kt/a pilot plant into production. COFCO Corporation’s 5 kt/a and Jiangsu Yunyoucheng’s 10 kt/a plants have realized mass production. Shanghai Tong-Jie-Liang Biomaterial and Jiangsu Jiuding Group are testing their PLA plants. Jiujiang Keyuan Biomaterial Co., Ltd. started up its phase I thousand-ton project in 2017 and is constructing its phase II 10 000-ton high-performance PLA and modified biodegradable material production line. In August 2018, COFCO Jilin made a successful trial run at its 10 000-ton PLA plant and has started planning for its 100 kt/a PLA project. In 2018, Jindan New Biomaterials adopted organic guanidine catalyzed directional polymerization to produce lactide and PLA process, first developed by Nanjing University and built up in Henan a 10 kt/a L-lactide/1 kt/a PLLA plant. The plant is expected to expand to 100-150 kt/a in 2020. In the first half of 2018, Hengtian Changjiang set up a 10 kt/a PLA continuous polymerization molten direct-spun fiber and product line. In June 2018, Fengyuan Group settled its 100 kt/a PLA project in Guzhen county of Anhui province and is constructing the corn-lactic acid-lactide-PLA production line. In March 2019, Tongliao Economic Development Zone and Fengyuan Group signed an agreement on the million-ton new biomaterials PLA project, with a total investment of RMB12 billion. The phase I project, with an investment of RMB5 billion, is designed to produce 300 kt PLA annually and expected to be completed in 2021.  

3. PHA

   Most monomers of PHA are 3-hydroxy fatty acids with a chain length of three to 14 carbon atoms. PHA can be a homopolymer of the same fatty acid or a copolymer of different fatty acids. There are currently four generations of industrialized varieties. Homopolymer poly 3-hydroxybutyrate (PHB) is a representative of the first-generation product, the second-generation product, 3-hydroxybutyrate/3-hydroxyvalerate copolymer (PHBV), the third-generation product, 3-hydroxybutyrate/3-hydroxyhexanoate copolymer (PHBHHx), and the fourth-generation product poly 3-hydroxybutyrate/4-hydroxybutyrate copolymer (P34HB).

   Ningbo Tian’an Biomaterials has realized large scale PHA production, with PHB capacity of 2 kt/a. Tianjin Guoyun Biosciences has built up a 10 kt/a PHA production line in Tianjin. Shenzhen Ecomann Biotechnology has established a 10 kt/a production line. The major problem facing PHA production is the high production costs, which hamper the promotion and application of the product.  

4. PPC

   Inner Mongolia Mengxi Hi-Tech has built up a 3 kt/a PPC plant. China National Offshore Oil Corporation (CNOOC) is collaborating with Changchun Institute of Applied Chemistry (CIAC), Chinese Academy of Sciences in setting up a 3 kt/a carbon dioxide copolymer degradable plastic device in Dongfang city, Hainan province. Zhejiang Taizhou Bangfeng Plastics Co., Ltd. established a 30 kt/a carbon dioxide-based plastics production line in Wenling city, Zhejiang province. Henan Tianguan Group set up a thousand-ton PPC industrial production line by adopting proprietary intellectual property technology. Jiangsu Zhongke Jinlong Chemical built up a 22 kt/a carbon dioxide-based polypropyl carbonate polyols production line. 


Common degradation plastic products

   1. Disposable plastic products (packaging film, garbage bags, tableware)

   Biodegradable plastics are used to make shopping bags and household garbage collection bags; biaxially stretched biodegradable plastic films are suitable for packaging of fresh vegetables and fruits; Biodegradable resin is used to make combs, toothbrushes, shampoo bottles and other disposable utensils used in hotels; disposable tableware uses degradable plastic, which can be composted or landfilled after being discarded, so it does not cause pollution.

   2.  Mulch film

   Mulch film can regulate ground temperature, maintain moisture, control weeds and prevent diseases and insect pests. However, the use of PE mulch film may cause severe white pollution as a large number of ultra-thin mulch fragments cannot be recovered and are left in the farmland. The use of biodegradable plastic mulch can control the biodegradability and can be decomposed without special treatment, which is the future development direction.

   3.  Nursery bowl, tree planting bowl, civil engineering material

   A hefty volume of nursey bowls and tree planting bowls, which are soft plastic containers, are used in agriculture. The use of biodegradable seedling bowls and tree planting bowls, with no need for separation of seedlings and bowls, can reduce pollution and control the rate of biodegradation according to the type of plants.

   In recent years, cheap but strong fiber (PE/PP) bags are used as mud and sand bags for slope protection and bank protection. However, their residues do not decompose in the environment and are hard to treat as a result. The problem can be solved by using biodegradable mud bags. At present, Japan has been using biodegradable bags in lakeshore construction and beach restoration projects.