The Development and Commercialization of Biobased,Biodegradable Plastics in China

Poly(lactic acid)

PLA, a well known biobased material is derived through the chemical conversion of lactic acid produced from various starches, sugars, and other biomass materials through biological fermentation. PLA has high transparency and elasticity and is amenable to thermoplastic processing like conventional plastics. It is widely used in the application of disposable products such as cutlery, cups, and films. ^{8 –10} PLA is typically produced in a chemical synthesis process from L-lactic acid obtained by starch fermentation. The main suppliers of PLA in the market are NatureWorks (Minnetonka, MN) and Zhejiang Hisun Biomaterials (Taizhou). The four main PLA manufacturers in China are listed in Table 1. The largest producer, Zhejiang Hisun Biomaterials, has a capacity of 5 kt/y at present and manufactures products with a melt flow rate of 2–15 g/10 min and a tensile strength of ≥50 MPa.

To improve the thermal property, toughness, and processing ability, Sichuan University modifies PLA by copolymerization with other materials. The elongation at break of modified PLA reaches 300%, and the processing characteristics are improved, especially the blow molding process properties. Other companies such as Zhejiang Hangzhou Seemore New Material Technology (Zhejiang), Zhejiang Nanyi Biological Science and Technology (Yongkang), and Hefei Hengxin Environmental Science & Technology (Hefei) have also developed types of modified PLA resin. Sichuan Corn-T Biology Technology (Chengdu) developed modified PLA with a melt flow rate of 2–3 g/10 min, melting temperature range of 140–145°C, tensile strength ≥20MPa, elongation at break ≥130%, and angle tear strength ≥110N/min. The products in which these modified forms of PLA have been used include shrinkable film, plastic bags, and garbage bags. ¹¹

Polyhydroxyalkanoates

PHA, which is produced by bacterial fermentation from agricultural raw materials, has good biodegradability, biocompatibility, and thermoplasticity. ^{12 –14} At present it is mainly used in biomedical materials and biodegradable packaging and has become a hot area worldwide in the biobased materials sector. In China, PHA research began relatively early and is fairly advanced on the world stage. The chemical structures of various forms of PHA are shown in Figure 1. ^{12 –16}

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Fig 1.

The chemical structures of polyhydroxyalkanoates (PHA): (a) P(3HB); (b) P(3HB, 4HH); (c) P(3HB,4HV); (d) P(3HB,4HB).

Ningbo Tianan Biologic Material (Ningbo), a manufacturer of poly (hydroxybutyrate-co-hydroxyvalerate) (PHBV), has achieved 3 kt/y production capacity and is now preparing a 10,000-ton scale production line. PHBV is a good example of this type of material, which is produced by bacterial fermentation from agricultural raw materials. It has attracted attention from both academia and industry because of its biodegradability, biocompatibility, and thermoplasticity. PHBV can be processed into a variety of useful products, for which biodegradability and natural sourcing are quite beneficial. Tianjin GreenBio Materials (“GreenBio,” Tianjin) has commercialized poly(3-hydroxybutyrate-co-4-hydroxybutyrate) [P(3HB,4HB)] at a scale of 10 t/y. Shenzhen Ecomann Biotechnology (Shenzhen) has also announced that it has the capability to produce 5 kt/y of P(3HB,4-PHB). ¹⁷

PBS and PBSA

PBS is the polycondensation product of butanediol and succinic acid, and PBSA is the copolymer of butane diacid, butanediol, and adipate. Currently, some manufacturers have accomplished large scale production, as listed in Table 2. The products made from PBS or PBSA include foams, films, and injection products.

The main research institutes working on PBS in China are the Technical Institute of Physics and Chemistry of the Chinese Academy of Sciences (CAS, Beijing), Tsinghua University, and Sichuan University. The five main PBS manufacturers in China are Zhejiang Hangzhou Xinfu Pharmaceutical (Zhejiang), Anqing Hexing Chemical (Anhui), Shandong Fuwin New Material (Shandong), Xinjiang Blue Ridge Tunhe Polyester (Xinjiang), and Jinhui Zhaolong High Technology (Shanxi). PBS resins for injection molding and extrusion have been introduced into the market. Zhejiang Hangzhou Xinfu Pharmaceutical, in cooperation with the Chinese Academy of Sciences, has built up a production line of 10 kt/y and developed several series of PBS with a melting point of 110–120°C, Vicat softening point of 101°C, tensile strength ≥35MPa, and elongation at break ≥600%. Anqing Hexing Chemical, using the technology of Tsinghua University, has completed a pilot plant at a scale of 10 kt/y that can produce PBS with the following properties: number average molar weight ( \documentclass{aastex}\usepackage{amsbsy}\usepackage{amsfonts}\usepackage{amssymb}\usepackage{bm}\usepackage{mathrsfs}\usepackage{pifont}\usepackage{stmaryrd}\usepackage{textcomp}\usepackage{portland, xspace}\usepackage{amsmath, amsxtra}\pagestyle{empty}\DeclareMathSizes{10}{9}{7}{6}\begin{document}$$\overline{M}_n$$ \end{document} )=100,400; weight average molecular weight ( \documentclass{aastex}\usepackage{amsbsy}\usepackage{amsfonts}\usepackage{amssymb}\usepackage{bm}\usepackage{mathrsfs}\usepackage{pifont}\usepackage{stmaryrd}\usepackage{textcomp}\usepackage{portland, xspace}\usepackage{amsmath, amsxtra}\pagestyle{empty}\DeclareMathSizes{10}{9}{7}{6}\begin{document}$$\overline{M}_w$$ \end{document} )=184;500; tensile strength≥20MPa, and elongation at break≥280%. ¹⁹ Some departments at institutions such as Tianjin Research Institute of Industrial Microbiology and Nanjing University of Technology have improved the technology and are using microbial fermentation processes to obtain butane diacid, which is the raw material to synthesize PBS or PBSA. ²⁰

Poly(butylene adipate-co-terephthalate) (PBAT)

PBAT is a copolymer polymerized from adipate, terephthalic acid, and 1,4-butanediol and is a well-known biodegradable plastic. It is a flexible material with a high elongation at break and has good hydrophilic and processing properties. PBAT has been widely used in the processing of blown films and other associated membrane products. ^{21 –23}

BASF's (Ludwigshafen am Rhein, Germany) product, Ecoflex^®, has a very similar processing property as polyethylene-low density (PE-LD), and thus it could be extruded into films. The Ecoflex^® FBX 7100 trademark has the following properties: product density 1.25g/cm³; melt flow index (MFI) 2.7–4.9g/10 min; melting point 110–120°C; heat deflection temperature 82°C; tensile strength ≥45 MPa; elongation at break ≥560%. Sichuan University investigated aliphatic-aromatic copolyesters of polyethylene terephthalate (PET), polyethersulfone (PES), and PBS, and has been awarded a patent. Beijing Chemistry Technology Institute pursues research on the modification of aliphatic-aromatic copolyester. It obtained the copolymer (PBST) of terephthalic acid, butane diacid, and butanediol and is preparing to initiate pilot-scale production. The weight-average molecular weight of the resulting PBST is greater than 60,000, and the melting point is about 135°C, tensile strength ≥20MPa, and elongation at break ≥700%. ^24–25

Carbon dioxide copolymer

This is a family of polymers produced using carbon dioxide waste gas as the raw material, copolymerized with propylene oxide or epoxy ethane. Poly(propylene carbonate) (PPC) is an alternating copolymer of carbon dioxide and propylene oxide that has the molecular structure shown in Figure 2. Inoue Shiyouhei in Japan showed that carbon dioxide could be copolymerized with epoxy compounds to form aliphatic polycarbonate, with numerous application and development prospects. ²⁶ At present, the main application of PPC focuses on packaging and medical materials.

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Fig 2.

Molecular structural formula of poly(propylene carbonate) (PPC).

Early research in China on PPC was carried out by the National Natural Science Foundation of China. Now, several institutes are focused on this area, such as Changchun Institute of Applied Chemistry of Chinese Academy Of Sciences, Sun Yat-sen University Guangzhou Institute of Chemistry of Chinese Academy Of Sciences, and Zhejiang University (Hangzhau). Companies that have achieved large-scale production are listed in Table 3.

Inner Mongolia Mengxi High-Tech Group (Wuhai), in cooperation with Changchun Institute of Applied Chemistry, has established a plant with annual production capacity of 3 kt/y using carbon dioxide released from cement manufacturing. The product is mainly used in the field to produce packaging and for medical applications. Mass-produced PPC has a density of 1.25–1.30 g/cm³; and tensile strength of 30 MPa. In partnership with Changchun Institute of Applied Chemistry, Zhejiang Bangfeng Science and Technology (Taizhou) set up a plant with a capacity of 10 kt/y in Zhejiang Province. Henan Tianguan Group (Nanyang), using technology of Sun Yet-sen University, uses CO₂ raw material produced by alcoholic fermentation. Under the catalytic effects of efficient nano-catalysts, the CO₂ is copolymerized with propylene oxide to form PPC. The company set up a 5 kt/y production line. ²⁷ Technology developed at Guangzhou Institute of Chemistry is being used by Jiangsu Zhongke Jinlong-cas Chemical (Taixing) to produce low molecular weight polycarbonate at 50 kt/y scale, which is then polymerized with other compounds such as isocyanate. The product is used in a variety of materials and in packaging of household electrical products.

Polycaprolactone (PCL)

PCL is synthesized by ring opening and polymerization of heptatomic ring ɛ-caprolactone in the presence of a catalyst. The main research institutes focusing on PLA in China are the National University of Defense Technology and Sichuan University. Sichuan University has developed a one-step method using hexylene glycol to synthesize monomers of caprolactone polymer. Shenzhen Esun Industrial is manufacturing the product at pilot scale.

Poly(p-dioxanone) (PPDO)

PPDO is synthesized by ring opening and polymerization of p-dioxanone, as showed in Figure 3. The glass transition temperature of PPDO is in the range of -17-10°C; the melting point is 110°C; and heat deflection temperature is at 90°C. This type of material exhibits high strength and toughness and has good prospects for application and extension. The material was first identified by the American company Ethicon in the 1970s and was used in surgical sutures with the trademark PDS. However, because of its high cost, it did not enter the general materials market. In recent years, Sichuan University achieved a breakthrough in the synthesis method, making it possible to produce PPDO at low cost and high performance, making it a competitive product among synthetic biodegradable plastics. One outstanding feature of this material is its relative high molecular mass and ability to be processed through blow molding. Another feature is the ability of PDO monomer to be recycled through a thermochemical method, with a coefficient of recovery reaching 93–96%. The recycled monomers can be used for direct synthesis of PPDO. Sichuan University`s PPDO has a tensile strength ≥29MPa and elongation at break ≥200%. Furthermore, PPDO nano-composite material has even better properties: tensile strength ≥50MPa; elongation at break ≥500%. Manufacturers are now industrializing the production process. ²⁸

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Fig 3.

Polymerization scheme of poly(p-dioxanone) (PPDO).