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Resources and the environment are major challenges that humanity must address in order to achieve sustainable development in the 21st century, and biotechnology will be one of the key technologies for solving these problems. Among the various factors that cause environmental pollution, the public hazards caused by plastic waste have drawn widespread attention from society. At the beginning of the 21st century, China used a large amount of plastic packaging materials, with an annual consumption reaching 50 million tons. If 30% of this amount consisted of disposable foam plastics, then the country would generate over 15 million tons of plastic waste each year ； There are 500 million mu of land across the country suitable for using plastic mulch, yet only 30% of this land makes use of it. Together with seedling trays and plastic wrap used for preserving agricultural products, these plastic wastes amount to about 10 million tons per year ； There are about 10 million tons of waste plastics in other categories ； In this way, the total amount of waste plastic nationwide will reach 35 million tons per year, and the environmental strain caused by such pollution is self-evident. If 30% of this discarded plastic consists of biodegradable plastics, then our environment will see **improvement**. According to incomplete statistics, there are only over 100 manufacturers in our country that produce biodegradable plastics, with a production capacity of less than 100,000 tons, which is far from meeting market demand. Currently, the main countries in the world that produce biodegradable plastics are the United States, Japan, Germany, Italy, Canada, and Israel, among others. The types of such plastics include photo-degradable, photo-biodegradable, disintegrating biodegradable, and fully biodegradable plastics. Biodegradable plastics have the greatest potential among all degradable plastics. Biodegradable plastics in the world are mainly made from aliphatic polyesters or a mixture of aliphatic polyesters and starch. Aliphatic polyesters primarily include polycaprolactone (PCL) and polybutylene succinate (PBS), which are synthesized from petroleum, as well as their copolymers; there are also polylactic acid produced from renewable resources, and polyhydroxybutyrate (PHB) produced by microorganisms. When biodegradable plastics are broken down, they turn into water and carbon dioxide, so they do not pose a threat to the environment. Recently, the technology for producing biodegradable plastics using polylactic acid has attracted particular attention; the American company Carriel Dow Polymers has begun building a factory for the production of polylactic acid, and by the end of 2001, a facility with an annual production capacity of 140,000 tons was already in operation ； Japanese company Mitsubishi Resins is building manufacturing equipment for biodegradable films with an annual production capacity of 3,500 tons, with the aim of expanding this capacity to 10,000 tons per year by 2002. To improve the properties of aliphatic polyesters, various countries are producing biodegradable plastics by copolymerizing aliphatic polyesters with aromatic terephthalic acid or nylon polymers, and high-performance biodegradable plastics will continue to be developed in the near future. As one of the environmental protection technologies, a process that uses enzyme catalysts instead of heavy-metal chemical catalysts for the synthesis of polymer materials is also set to emerge. In addition to aliphatic polyesters, polyphenols, polyaniline, polycarbonates, polyaspartic acid, and others have already been successfully developed. From the perspective of the application areas for biodegradable plastics, of the total 880,000 tons of biodegradable plastics sold in North America in 1989, 760,000 tons were used for packaging purposes. Of this amount, 560,000 tons were used for packaging bags (of which 475,000 tons were garbage bags and 85,000 tons were shopping and retail bags), 105,000 tons were used for beverage can lids, 95,000 tons were used for other types of packaging (including 55,000 tons of non-woven materials for sanitary purposes and 25,000 tons for agricultural use), and 40,000 tons were used in other fields. At that time, it was predicted that by the year 2000, the usage of packaging materials would reach 2.48 million tons, with non-woven fabrics accounting for 300,000 tons, agricultural uses accounting for 160,000 tons, and other applications accounting for 260,000 tons. From 1989 to 1994, the average annual growth rate for packaging was 16.2%, for non-woven materials it was 21.4%, for agricultural use it was 22.9%, and for other fields it was 20.1%. The average annual growth rate from 1994 to 2000 was 7.5% for packaging, 12.9% for non-woven materials, 14.8% for agricultural use, and 17.3% for other sectors. Classification and Development Trends of Biodegradable Plastics Biodegradable plastics are generally divided into four categories, with the main trends in research and development focusing on biodegradable plastics as well as chemically synthesized and blended plastics. Classification of biodegradable plastics Biodegradable plastics can be classified into types such as photodegradable plastics, biodegradable plastics, chemodegradable plastics, and hybrid degradable plastics, based on the environmental conditions that trigger their degradation. Photodegradable plastics refer to plastics that decompose through photochemical reactions caused by the absorption of sunlight. Photodegradable plastics refer to a type of plastic material that undergoes degradation and decomposition under sunlight or exposure to other strong light sources, thereby losing their mechanical strength and breaking down. As long as structures or groups that promote photodegradation are added to polymer materials, they can become photodegradable plastics. There are two methods for preparing photodegradable plastics: the copolymerization method and the additive method. The copolymerization method involves introducing appropriate photosensitive groups such as carbonyl groups or double bonds into the monomers used to form polymer structures, thereby creating plastics. Examples include the ethylene-carbon monoxide copolymer developed by Brubaker and others at Dupont, as well as the vinylidene-ethylene polymer developed by Gullet in Canada. The photolysis rate of these polymers can be controlled by adjusting the concentrations of carbon monoxide and other components; essentially, this is a form of copolymerization modification using ethylene. This process requires complex equipment and stringent technical conditions, making it difficult to implement domestically in the short term. The additive method involves adding photosensitizers such as diphenylmethane derivatives to polymer materials; under light exposure, these photosensitizers absorb ultraviolet rays and remove hydrogen from the polymers, generating free hydrogen that induces oxidation reactions in the polymer materials, thereby causing their degradation. Photodegradable plastics are obtained by introducing weak bonds or chromophores into their polymers, or by adding photosensitizers to ordinary plastics; as a result, photochemical reactions occur under light exposure, causing the plastic to become brittle and crack, thereby breaking down into increasingly small fragments. The photosensitizer undergoes a photochemical reaction in the polymer, generating free radicals to achieve controlled photodegradation. Alkylthiocarbamate photosensitizers developed by Professor G. Scott and others at Ston University in the UK have been industrialized, and stearate and ferrocene derivatives are also in use. There are also many in the domestic market, and research and development are relatively advanced. The disadvantage of photodegradable plastics is that they require light exposure. When buried in soil or shaded by plants, it cannot degrade or does so at too slow a rate; even the fragments resulting from degradation cannot continue to break down, and the pollution problem cannot be completely resolved. The most prominent feature of biodegradable film masterbatches is their dual degradation by light and microorganisms. Plastics that undergo only photodegradation are affected by the intensity and duration of light exposure; once they break down into fragments, they are not easily decomposed by microorganisms in the soil. Although biodegradable plastics can theoretically be completely broken down into water and carbon dioxide by microorganisms, in practice, the rate and extent of degradation are influenced by factors such as the types and quantities of microorganisms in the soil, temperature, humidity, soil pH, and fertility, making complete decomposition difficult. To overcome the shortcomings of the two types of degrading materials, light-degrading agents and chemical co-degrading agents are added to enable controlled dual degradation, allowing for both photodegradation and biological synergistic degradation. Biodegradable plastics refer to plastics that can be broken down by microorganisms in the soil. With the help of bacteria or their hydrolytic enzymes, these materials are converted into carbon dioxide, water, honeycomb-like porous structures, and salts; they can then be completely decomposed further by microorganisms and returned to the biosphere. This area is currently a focus of research and development in various countries. Therefore, biodegradable plastics generally refer to new types of plastics that possess certain mechanical strength and can be fully or partially decomposed in the natural environment by microorganisms such as bacteria, molds, and algae, without causing environmental pollution. The mechanism of biodegradation mainly involves bacteria or their hydrolases breaking down high-molecular-weight polymers into low-molecular-weight fragments, which are then further broken down by bacteria into substances such as carbon dioxide and water. There are mainly four types of biodegradable plastics: The first is the microbial fermentation (synthesis) type. Using enzymes produced by microorganisms, biodegradable polymers found in nature (such as polyesters) are depolymerized and hydrolyzed, and then further broken down and absorbed to synthesize high-molecular compounds. These compounds include microbial polyesters and microbial polysaccharides; however, the use of such polymers synthesized through microbial fermentation is limited due to their high cost. Generally speaking, polymers produced by microbial fermentation are also known as biofermentable plastics; representative products include copolymers of hydroxybutyrate and valerate (PHBV). The British company ICI has already introduced mass-produced products under the name Biopol; these materials exhibit excellent biodegradability. However, their production process is complex and the costs are high, making large-scale production difficult in China at present. Polymers synthesized by microorganisms are generally referred to as biopolymers, and they possess the characteristic of being fully biodegradable. Macromolecular substances synthesized within living organisms can all be referred to as biopolymers, such as proteins, nucleic acids, starch, etc. Biopolymers refer to polyesters synthesized by microorganisms; they represent a new class of natural polymers that are distinct from proteins, nucleic acids, and starch. Polyesters produced by microorganisms have attracted attention due to their biodegradability as well as their processability similar to that of conventional polymer materials. Polyesters synthesized by microorganisms are collectively referred to as polyhydroxyalkanoates (PHA for short). Many bacteria are capable of synthesizing and accumulating PHA within their cells; when these bacteria lack nutrients, they hydrolyze PHA to obtain nutrients. More than a hundred bacterial species have been found to possess the ability to synthesize and accumulate PHA, and the genes for PHA synthase have been cloned from over 20 such bacteria. Recently, it has been discovered that bacteria capable of synthesizing and accumulating PHA can be divided into two groups; one group, represented by Alcaligenes eutrophus, primarily synthesizes short-chain PHAs composed of C3-C5 monomer units ； Another group, represented by Pseudomonas oleovorans, can synthesize PHA units with a medium chain length of C6-C14. PHA actually includes a range of polyesters: methyl side-chain hydroxybutyrate, Poly(-hydroxybutyrate), abbreviated as PHB ； Ethyl side-chain polyhydroxyvalerate, abbreviated as PHV ； Poly(-hydroxybutyrate-co-hydroxyvalerate), abbreviated as PHBV. The biosynthesis of PHA is shown in Figure 1. The structural characteristics of short-chain monomers such as C3-C5 facilitate the degradation of PHA in the environment. It has been shown that PHA can be degraded by certain bacteria commonly found in the environment, which are capable of secreting depolymerases or hydrolases for PHA. The biosynthesis of PHA occurs under conditions of limited oxygen but sufficient carbon; many aerobic or anaerobic bacteria can synthesize and accumulate submicron-sized inclusion bodies composed of PHA, the main component of which is PHB, forming spherical structures with a diameter of about 0.5 μm. The molecular weight of the synthesized PHB depends on the type of bacteria, as well as the separation method used; for example, solvent extraction or direct isolation of natural PHB particles can yield PHB with a high molecular weight, ranging from 100,000 to several million, or even higher. Studies have also shown that a single PHB particle typically contains several thousand PHB molecules. It was found that within a cell of bacteria capable of synthesizing PHB, there are at least 18,000 PHB polymerase molecules, and this number remains constant throughout the process of PHB accumulation. As can be seen from the biosynthetic process of PHB, this process involves three enzymes: thiolyase, acetyl-CoA, and PHB synthase. These three enzymes serve as biocatalysts that enable the synthesis of PHB; in other words, genes corresponding to these three enzymes exist on the chromosomal DNA of bacteria that synthesize PHB. M. M. Satowski and colleagues in the United States, using various methods to study the relationship between the morphology of PHA and its enzymatic degradation, indicated that the degradation of PHA is related to its crystal structure, which in turn is influenced by blending and heat treatment. Therefore, it is necessary to determine the crystal structure of PHA quantitatively in order to control the degradation rate. Biological synthesis methods have been used in the production of several biodegradable polyesters, which are actually polyhydroxyalkanoates. These are intercellular substances obtained in large fermentation reactors, where various bacteria accumulate under certain non-equilibrium growth conditions, once growth reaches equilibrium. Within the cells of these polyester bacteria, in addition to the known simple polyesters, copolymers containing other hydroxyacid units were also found, such as trihydroxypentanoates, tetrahydroxybutanoates, and pentahydroxypentanoates. As biodegradable thermoplastic materials, these polyesters are highly favored by manufacturers, and blend systems of them with other polymers also exist. Secondly, the synthetic polymer type. Synthetic polymer-based biodegradable plastics are essentially chemically synthesized biodegradable plastics, which mainly include aliphatic polyesters (PCL), polyamides, polysaccharide copolymers, polylactic acid, etc. Many biodegradable synthetic polymer materials have been developed, such as polylactic acid (PLA), polyvinyl alcohol (PVA), and polycaprolactone (PCL). PLA is polymerized from lactic acid monomers, which are produced by special bacteria through the conversion of starch. PLA is expensive and is currently mainly used in the pharmaceutical industry. The structural formula of PLA is as follows: Aliphatic polyesters (such as polycaprolactone PCL) exhibit good biodegradability and good compatibility with other widely used plastic resins, but they have poor heat resistance and mechanical strength. Aromatic polyesters, such as ethylene terephthalate, have high melting points and strong mechanical strength, but poor degradation properties. Copolymers can be synthesized by blending them in the presence of anhydrous zinc carbonate under a nitrogen atmosphere; these copolymers, obtained through transesterification between polymer chains, possess good biodegradability as well as high heat resistance and mechanical strength. The structural formula of PCL is as follows: PVA has good water solubility, which is why it is widely used in industrial products such as fiber surface treatment agents. One category of synthetic polymer-based degradable materials consists of blends of natural and synthetic polymers. Blending natural polymers such as starch and cellulose with synthetic polymers can improve the biodegradability of the latter. In the blend, when the position of the polysaccharide is biodegraded, it makes the porous plastic more susceptible to further oxidative degradation. The blend of polyethylene and starch has been named Ecostar as a commercial product by St.Lawrence Starch in Canada. To improve the compatibility between the two components in this blend, the starch surface was silylated to endow it with hydrophobicity that is compatible with synthetic plastics. Extensive studies on the production and degradation of PE/starch blends have shown that only starch is biodegradable, while PE undergoes only limited oxidative degradation; therefore, from an ecological perspective, many starch-based composites are unacceptable. Third, natural polymer type. Natural polymer materials and their modified forms include starch, cellulose, chitin, prussian blue, etc. However, natural product plastics suffer from difficulties in processing (the casting method is generally used to form films), and the resulting films have drawbacks such as poor water resistance, low strength, and unstable quality; as a result, they have not yet reached a practical level of use. Nevertheless, significant progress has been made in research and application development in recent years. Another approach to reducing the environmental damage caused by polymers relies on the use of polymers that are inherently biodegradable. However, widely available low-cost polysaccharides such as starch and cellulose have not yet been successfully converted into inexpensive thermoplastic materials. Natural and synthetic polymers, including natural polymers and their derivatives as well as their blends. Chitin, also known as chitosan, is a high-molecular-weight linear polysaccharide composed of N-2-acetyl-D-glucosamine linked together by (1,4)-glycosidic bonds. It is widely found in the exoskeletons of crustaceans, on the surface of insects, and in the cell walls of fungi, and it is the second most abundant polysaccharide in nature after cellulose. When chitin is treated with concentrated alkali, all of the acetyl groups can be removed, resulting in chitosan. Chen Liqiao and others from Fuzhou University conducted experiments in which chitosan was ground into powder, and then mixed with an acetic acid aqueous solution, a polyvinyl alcohol aqueous solution (PVA), and a third component namely glycerol, in certain proportions, to form a viscous liquid. This liquid was then cast onto a flat mold, and after drying to remove the solvent and undergoing heat treatment, a biodegradable film was obtained, as shown in Figure 2. Tests have shown that this type of film decomposes in soil within 3 to 4 months, and it becomes brittle due to aging in the atmosphere over about 1 year; moreover, both the tensile strength and elongation rate of the blended film meet the standards of ordinary plastic films. Biodegradable polymers include natural and synthetic polymers, such as bacterial polyesters, aliphatic polyesters, and water-soluble polymers. In the development of biodegradable polymers, a key step is the evaluation of various factors that affect biodegradation, such as environmental factors like water, temperature, pH value, and oxygen, which play a significant role in microorganisms’ ability to degrade the polymers. Meanwhile, the chemical structure of the polymers also influences the speed and extent of biodegradation. Natural and synthetic polymers have different structures, and as a result their biodegradation properties also differ. In some cases, the molecular weight of the polymer is quite important; for example, high-molecular-weight polyethylene is quite durable, while low-molecular-weight polyethylene (N<500) is easy to degrade. Compared to aromatic polymers, aliphatic polymers are more susceptible to microbial attack. Functional groups such as –NH2–, –COOH, and –OH can increase the hydrophilicity of the polymers, making them easier to degrade under the action of microorganisms. Natural polymer-based degradation materials fall into two categories: natural polymers and derivatives of natural polymers. The first category includes natural polymers; starch films are fragile and have a high water absorption rate. By using aqueous dispersions of starch and ethylene acrylate copolymer (EAA), and employing processing methods such as casting, extrusion, and blow molding, products with a starch content of over 50% can be obtained. These products possess good optical transparency, water resistance, thermal stability, and biodegradability. However, this process is expensive due to the high cost of EAA and the need to remove large amounts of water. High-molecular-weight amylose, processed under controlled high-temperature conditions, can yield biodegradable thermoplastic materials. Due to its brittleness, plasticizers such as glycerides and sorbitol are added; the resulting materials can be used for packaging or to manufacture disposable products, and can replace the PS and PP that are currently widely used. The second category consists of derivatives of natural polymers, namely cellulose esters or ethers with a substitution degree (DS) of 1.7–3.0, which can be obtained from natural cellulose and recycled paper; these materials possess mechanical properties comparable to those of PS ； Furthermore, the addition of appropriate plasticizers allows for melt processing using the same methods employed in the production of conventional thermoplastic polymers. Cellulases, which play an important role in the cellulose degradation by microorganisms, do not hydrolyze derivatives with a DS greater than 1; however, it has been found that in composite door and window materials containing complex microbial communities, cellulose esters with a DS of less than or equal to 2.5 can be completely degraded, even at a low degradation rate for unsubstituted cellulose. Fourth, the blended type. Plastics made through blending are also known as biodegradable plastics; they are produced by mixing bioactive substances such as cellulose, starch, and other polysaccharides with synthetic polymers that are not biodegradable. In 1973, Griffin was granted a patent for filling plastics with modified starch, paving the way for research into the production of biodegradable plastics using starch as a filler. Starch-degradable plastics refer to plastics that lack biodegradability, to which a certain amount of starch is added to endow them with degradability. Starch improves the degradation performance of common thermoplastics; however, starch has poor thermoplasticity, and heating it causes it to decompose and caramelize ； Furthermore, starch is crystalline, highly polar, with hydrogen bonds existing both within and between its molecules; it is a highly hydrophilic substance. In contrast, common synthetic resins have very low polarity and are hydrophobic substances, and under normal circumstances it is difficult to blend the two together. Biodegradable plastics can break down into small fragments under the action of soil organisms, and are then decomposed by microorganisms to become part of the soil. The process of producing biodegradable plastics through blending is simple; among these methods, the synthesis of starch-polyethylene blends is the most developed. Notable examples include St.Lawpacet’s Ecostar masterbatch, ADM’s Poly-green masterbatch, and Ampacet’s Poly-Grade(11) masterbatch. In recent years in China, regions such as Beijing, Jiangxi, Shanxi, and Tianjin have been conducting research in this area. The basic approach is to blend starch with polyvinyl alcohol, or to graft vinyl monomers onto starch in order to improve its compatibility with materials such as polyethylene. The starch-polyvinyl alcohol blend studied by the Jiangxi Academy of Sciences, when cast into films, has been tested on a pilot scale. Chemically degradable plastics refer to plastics that are broken down by oxygen in the air or moisture in the soil, including oxidatively degradable plastics and hydrolytically degradable plastics. General synthetic polymers are not easily biodegradable, which is to some extent related to their hydrophobicity (i.e., water-repelling nature). Several methods have been employed, such as the introduction of hydrophilic groups to facilitate biodegradation; the addition of polar groups and the synthesis of polymers with structures similar to those of natural polymers are also considered viable approaches. Hydrophilic polymers, such as polyvinyl alcohol, are biodegradable water-soluble polymers; however, their decomposition temperature is lower than their melting point, making melt processing difficult. Polyvinyl alcohol obtained through the hydrolysis of polyvinyl acetate is soluble in hot or cold water, depending on the amount of residual acetic acid functional groups; the melt-processable and biodegradable materials thus produced have been widely used in agrochemicals and medical packaging. Synthetic polymers, which have structures similar to those of natural polymers, such as polyamides, polyesters, and polyanhydrides. Some are extremely prone to breaking down due to microbial attack; for example, polyamides, whose structure is similar to peptides in proteins, have well-documented and recognized biodegradability. Currently, aliphatic polyesters obtained by polymerizing glycolic acid, lactic acid, and caprolactone are important biodegradable materials. Lactic acid can be produced by fermenting hydrocarbons using Lactobacillus, and high-molecular-weight materials are obtained by polymerizing its cyclic dimer (lactide) ； Polylactic acid (PLA) has high strength and can be processed into products such as fibers, films, and cylinders, but it is prone to hydrolysis. To improve its mechanical properties, it is copolymerized with lactide or caprolactone; the resulting copolymers are both biodegradable and composable. Studies on blends of PLA with some degradable and non-degradable polymers have been reported. Polycaprolactone (PCL) can be obtained by polymerizing caprolactone. It is similar to linear low-density polyethylene, has a smooth feel, and is completely biodegradable. Although PCL has been commercially available for over 20 years, it is only now being widely used as a biodegradable plastic in plastic mulch, packaging materials, and drug transportation. The properties of blends of PCL with PHB (polyhydroxybutyrate), nylon 6, PET, PO, etc., are under investigation; these blends improve the mechanical properties of PCL, and at the same time enhance the biodegradability of the second component, which otherwise cannot be biodegraded. Recently, Domb reported the synthesis of biodegradable polyanhydrides; other biodegradable polymers such as PC, polyesters, and polyphosphazenes have also been reported. Composite degradable plastics refer to the comprehensive degradation resulting from multiple factors such as photolysis, microorganisms, and physicochemical processes. Development trends of biodegradable plastics Further research is being conducted based on different applications and environmental conditions, and improving formulations through molecular design to develop environmentally degradable plastics that can be degraded in a controlled manner has become a key focus for many **. By synthesizing various literature sources, it is possible to generally predict the future research and development trends in degraded plastics: active efforts will be made to develop highly efficient and cost-effective photosensitizers, in order to further improve controllability, rapid degradation, and complete degradation. It is beneficial for the treatment of single-use plastic waste, while also ensuring a plentiful supply of raw materials. There is growing interest in developing fully biodegradable plastics using natural polymers, microbially synthesized polymers, and biodegradable synthetic polymers as raw materials. Hydrolyzable plastics and edible materials have attracted worldwide attention due to their unique functions and applications, thus becoming another hot topic in environmentally friendly materials. To accelerate the development of biodegradable plastics, countries are striving to speed up research and establish unified definitions, degradation mechanisms, evaluation methods, and standards for such plastics. Explore and develop strains capable of degrading common plastics, so that these widely used plastics can be easily degraded after use in order to meet environmental protection requirements ； At the same time, great emphasis is placed on cultivating biological plants that can produce polyester, in order to reduce the cost of biodegradable plastics and facilitate their wider use. In addition, Huang Xudong and others from Sichuan United University have provided the following prospects for research on biodegradable plastics in terms of material synthesis and processing: First, microbial synthesis methods can be used to produce biodegradable polymers; new models and concepts can be developed to utilize microbial fermentation to obtain polymers with novel structures ； Recyclable agricultural raw materials to develop efficient methods for producing bacterial polymers ； Using enzyme-catalyzed polymer synthesis to create new materials ； The synthesis and modification of biological polymers are carried out under the action of enzymes using enantioselective monomers. Biodegradable polymers are prepared using organic synthesis methods, such as synthesizing polymers with structures similar to those of natural polymers, in order to establish the relationship between polymer structure, morphology, and biodegradability ； Ring-opening polymerization of lactones, epoxides, cyclic carbonates, anhydrides, etc., is carried out to obtain new biodegradable polymers ； Polysaccharides are modified to obtain new biodegradable processing materials. Secondly, new technologies for processing and blending are developed to produce derivatives of biological polymers ； New biodegradable materials such as polysaccharides and degradable polyesters are obtained using reactive processing methods ； Develop co-extrusion technology to expand the applications of hydrophobic polymers ； Determine the blend composition to optimize performance, biodegradability, and production cost ； Blending degradable plasticizers with biodegradable polymers improves the processing properties of the latter, resulting in degradable blended materials ； Blending biodegradable plasticizers, fillers, and polysaccharides with biodegradable polyesters improves processing properties and reduces costs ； The study investigates the effects of blending ratios, compatibility, morphology, etc., on the kinetics as well as the physical and chemical properties of biodegradable blends. Industrial development directions for biodegradable plastics Focusing on biodegradable plastics, industrial development efforts will be concentrated on the following areas: Development of biodegradable plastics Materials that have been developed for easy degradation include PCL, PBS, PLA, PHB, CAPE, etc. Polycaprolactone (PCL): This plastic possesses good biodegradability, with a melting point of 62°C; the microorganisms that degrade it are widely found in both aerobic and anaerobic conditions. As a biodegradable material, it is used by mixing it with starch or cellulose-based materials, or by polymerizing it with lactic acid. Due to its low melting point, it maintains stable performance under high-temperature and high-humidity conditions compared to other aliphatic polyesters. Polyhexylene succinic acid (PBS) and its polymers: The technology for producing various high-molecular-weight polyesters using PBS (with a melting point of 114°C) as the base material has reached industrial production levels. Products developed using it include foam materials, which are used as packaging materials for household appliances and electronic devices. Japanese companies such as Catalyst Corporation and Mitsubishi Gas Chemical Company have incorporated carbonates (esters) into PBS, successfully developing water-resistant and biodegradable plastics. Polylactic acid (PLA): It has a melting point of 175°C, and can be processed into films or fibers; it exhibits good resistance to hydrolysis. In Germany, lactic acid boxes produced using this material were commercialized in 1998; this substance also has the effect of promoting plant growth, so it is expected to be used to make containers for plant transplantation or cultivation. In 1994, the Japanese company Shimadzu built a facility for producing polylactic acid, and it has found applications in various fields; through rolling, it can also be turned into transparent fibers, films, containers, and lenses with excellent mechanical properties. Poly3-hydroxybutyrate (PHB) and its polymers: Many efforts are currently being made to develop thermoplastic polymer materials using microorganisms, among which poly3-hydroxybutyrate offers the highest production efficiency. However, it has high crystallinity, poor mechanical properties, is prone to thermal decomposition, and is difficult to process; mixing PHB with PCL can improve its properties. Technologies for producing PHB and polyhydroxyvaleric acid polymers using microorganisms have emerged, and the UK has been using this material to manufacture shampoo bottles and similar products since the 1970s. Plastics using starch: A technology for producing biodegradable plastics by mixing aliphatic polyesters with starch has also been developed successfully. Starch is very important as a direct or indirect raw material for producing biodegradable plastics; in addition to corn and sweet potatoes, starches from cassava, sago palms, taro, and others can also be utilized. In Europe and the United States, mixtures of gelatinized starch and aliphatic polyesters are widely used to produce products such as garbage bags. Starch gelatinizes when heated in the presence of water, gaining plasticity; however, its drawback is its lack of water resistance. By controlling the structure of the gelatinized starch and PCL, it is possible to create mixtures with excellent water resistance and mechanical properties. Copolymers of aliphatic polyesters and polyamides (CPAE) are materials developed to improve the properties of aliphatic polyesters; they exhibit enhanced characteristics such as melting point and tensile strength, and represent a new generation of biodegradable plastics. However, its lipase-cleavable property, along with the successful development of CAPEs for nylon and polyesters that allow them to be polymerized with polyethylene glycol, has also enabled the creation of plastics with biodegradability and photodegradability. Product types of biodegradable plastics Regarding easily degradable materials, a variety of products have been developed and produced to date: First, there are degradation resins and masterbatches, including fully biodegradable resins, photo-biodegradable masterbatches, and composite degradation masterbatches. Secondly, degraded plastic products include composting bags, garbage bags, shopping bags, electronic packaging bags, plastic mulch, tableware, golf tees, and foam materials, among others. Thirdly, common plastic products include shopping bags, garbage bags, and office supplies, etc. Main application areas of biodegradable plastics The application areas of biodegradable plastics vary from country to country; here is a brief overview of the main application areas both domestically and internationally. Overview of International Applications The production and use of photodegradable plastics internationally have a history of over 10 years. Biodegradable plastics, especially those with starch added, have seen rapid development in recent years. According to Freedoia, sales of biodegradable plastic products in the United States were 230,000 tons in 1987, 830,000 tons in 1989, and reached 3 million tons by the year 2000 ； Sales of degradable plastic products in Canada were 50,000 tons in 1989, rising to 200,000 tons in 2000. According to a survey conducted by StructureAnalysis&Surveys in the United States in the early 1990s, the development of biodegradable plastics was faster in Europe and Japan. It was predicted that by 1995, the U.S.’s share of the global market for biodegradable plastics would drop from 60% in 1990 to 41%, while Europe’s share would rise from 38% to 53%, and Japan’s share would increase from 2% to 6%. Based on an analysis of the types of biodegradable plastics, in North America, the amount of such plastics was 160,000 tons in 1989. It was predicted at that time that by the year 2000, the total demand for biodegradable plastics would reach 3.2 million tons, of which 1.1 million tons would be bio-degradable plastics, 1.05 million tons photo-degradable plastics, 900,000 tons photo-bio-degradable plastics, and 150,000 tons other types of biodegradable plastics ； From 1994 to 2000, the average annual growth rates were 7.1% for biodegradable plastics, 9.6% for photodegradable plastics, 11.2% for photo-biodegradable plastics, and 5.3% for other degradable plastics; based on this, it is predicted that photo-biodegradable plastics will experience the fastest growth. Application areas in China In our country, biodegradable plastics are mainly used in agriculture, food packaging, decomposable foam nets, and disposable fast-food containers. Agricultural plastic films are among the three key products in agricultural production (fertilizers, pesticides, and agricultural films). They were originally **strictly controlled products, and demand for them has always been high in the market. Since 1979, the technique of cultivation using agricultural plastic film has been widely promoted in China. In 1980, the area covered by such film was only 25,000 mu, but by 1992 it had reached 50 million mu. The application areas of agricultural plastic films have evolved from cotton and vegetables initially, to the cultivation of cash crops such as peanuts, melons and fruits, beets, sugarcane, tobacco, as well as food crops like rice, early-maturing rice, wheat, and corn. The promotion and widespread use of agricultural plastic films have yielded significant economic benefits; according to statistics, the increase in crop yields resulting from these films between 1982 and 1987 amounted to 7.1 billion yuan ； From 1978 to 1989, mulching cultivation techniques resulted in an increase in crop yields of 28 billion kilograms for both food crops and cash crops. As can be seen from the above statistics, the adoption of agricultural plastic films brought about very significant economic benefits. At present, China’s production of agricultural plastic films amounts to about 650,000 tons. Although China is now the country with the largest area covered by agricultural plastic films in the world, such films are currently used to cover only around 25% of the country’s arable land. China had planned to have an area of 150 million mu covered by agricultural plastic films by the year 2000, which would require more than 1.5 million tons of such films – indicating a very large market potential. Films for food and medical use: This includes food packaging films, disposable household films, disposable medical films, and packaging films for industrial products. In 1993, the demand was 1.4 million tons, with an annual increase of 15%; the main consumers were supermarkets and large department stores. Due to the widespread use of these membranes, especially in large and medium-sized cities, severe environmental pollution has resulted. Therefore, the promotion and application of degradable membranes will surely receive attention from ** and society; they offer a broad market potential and hold great significance. As a new product, no manufacturers in China produce degraded foam nets, giving it very promising market prospects. Our country produces tens of millions of tons of various fruits. Together with packaging materials such as glass, alcohol, and ceramics, the market volume for these products is extremely large; therefore, the market prospects for such products are very promising. It is estimated that the annual domestic demand is around 50,000 tons. Disposable foam plastic tableware: According to statistics, in 1995 China’s demand for fast-food containers reached 2.5 billion units, of which 1 billion were used by the railway system alone. 200 million units were needed for the production of instant noodles, generating an annual output value of 1.2 billion yuan ； In 1997, the demand reached 3.2 billion units, indicating very broad market prospects. In short, the most prominent advantage of biodegradable plastics is their ability to decompose without polluting the environment. It is an inevitable trend for them to replace plastics such as polyethylene, and it is also necessary to upgrade plastic film products. It is estimated that the current size of this market is 30 billion yuan, and it is growing at a rate of 30%-50% per year. Author: Lv Xuanzhong, School of Chemistry, University of Science and Technology of China