Development and Application of Degradable Plastics at Home and Abroad (I)

Status and trends at home and abroad

Resources and the environment are major issues facing mankind in achieving sustainable development in the 21st century. Biotechnology will become a key technology to solve this problem. Among the many factors that cause environmental pollution, the pollution caused by plastic waste has caused widespread concern in society. According to relevant information, at the beginning of the 21st century, the amount of plastic packaging materials used in China is very large, and the annual consumption will reach 50 million tons. If 30% of these are disposable foam plastics, there will be more than 15 million tons of waste annually in the country. plastic. In addition, 500 million mu of land can be used in the country. At present, only 30% of the land utilizes plastic film. In addition, the nursery stocks and cling film for agricultural and sideline products are used. These plastic wastes also have 10 million tons per year. Other waste plastics also have 10 million tons. In this way, the total amount of waste plastics in the country will reach 35 million tons every year, and the environmental pressure caused by the pollution is self-evident. If 30% of these waste plastics are degradable plastics, our environment will be greatly improved.

At present, the development of China's degradable plastics is still only an initial stage, compared with foreign technology there is a certain gap. According to incomplete statistics, there are only more than 100 manufacturers producing degradable plastics in the country, with a production capacity of less than 100,000 tons, which is far behind the market demand. In order to accelerate the production of degradable plastics, a batch of plants with an annual output of 20,000 tons of degradable plastics are being built throughout the country.

Degradable plastics can be divided into photodegradable plastics, biodegradable plastics, chemical degradable plastics, and composite degradable plastics according to the environmental conditions that cause degradation. Photodegradable plastics are plastics that decompose by absorbing sunlight and causing photochemical reactions. Biodegradable plastics are plastics that can be decomposed by microorganisms in the soil. They decompose materials into carbon dioxide, water, cellular porous materials, and salts by means of bacteria or their hydrolytic enzymes. Chemical degradable plastics are plastics that decompose through the oxygen in the air or the moisture in the soil, including oxidatively degradable plastics and hydrolytically degradable plastics. At present, the world's major producers of degradable plastics are the United States, Japan, Germany, Italy, Canada, Israel, and other countries. The varieties include photodegradation, photo/biodegradation, disintegrative biodegradation, and completely biodegradable plastics.

The future development trend of degradable plastics: First, according to different uses and environmental conditions, to further deepen research, and through molecular design research, improve formulas, develop punctually controllable environmental degradation of plastics, has become a key research topic in many countries. The second is to actively research and develop high-efficiency, low-cost photosensitizers, oxidants, biological inducers, degradation accelerators, stabilizers, etc., to further improve on-time controllability, rapid degradation after use and complete degradability. The third is to facilitate the disposal of disposable plastic waste while guaranteeing an inexhaustible and abundant source of raw materials. It is fully biodegradable using natural polymers, microbial synthetic polymers and biodegradable synthetic polymers as raw materials. Plastics are getting more and more attention, but in order to overcome the shortcomings of their price and limited use, accelerating the development of biodegradable plastics or ordinary plastics and starch, cellulose or inorganic materials fill blending or alloying technology and fully biodegradable plastics and natural Material coating lamination technology has become a hot spot. Fourth, hydrolyzable plastics and edible materials have attracted attention from the world due to their special functions and applications, which has become another hot spot for environmentally friendly materials. Fifth, in order to accelerate the development of degradable plastics, countries are working to accelerate research and establish a unified definition of degradable plastics, degradation mechanisms, evaluation methods and standards. Sixthly, it is to explore and cultivate strains that can degrade ordinary plastics so that common plastics that are widely used at present have easy degradability after use to meet environmental protection requirements. At the same time, it attaches great importance to the cultivation of biological plants that can produce polyester, so as to reduce the cost of biodegradable plastics, and is conducive to popularization and application.

It can be seen that biodegradable plastics are the most promising in biodegradable plastics. At present, the world's biodegradable plastics are mainly made of aliphatic polyester or aliphatic polyester mixed starch. Aliphatic polyesters mainly include polycaprolactone (PCL), polybutene (P BS) and its copolymers synthesized from petroleum as raw materials, and polylactic acid produced from renewable resources as raw materials, produced by microorganisms. Polyhydroxybutyric acid (PHB) and so on. After biodegradable plastics are decomposed into water and carbon dioxide, they will not be harmful to the environment. At the same time, it can also be used to make compost and return to nature as a fertilizer or soil conditioner. Of particular interest lately is the use of polylactic acid to make biodegradable plastics. Carrick Dow Polymers announced that it has begun construction of a polylactic acid plant. By the end of 2001, the annual output of 140,000 tons of equipment has been put into production. Japan's Mitsubishi Plastics, Zhongfang Synthetic Fibers, Uniqarka, and Kurarei have signed contracts with the US company to expand the application of polylactic acid in Japan. Mitsubishi Plastics Co., Ltd. is building an annual production capacity of 3,500 tons of biodegradable thin film manufacturing equipment, and will expand to 10,000 tons per year by 2002, and strive to become Japan's largest manufacturer of degradable plastics.

In order to improve the physical properties of aliphatic polyesters, various countries are producing biodegradable plastics by copolymerizing aliphatic polyesters with aromatic terephthalic acid or nylon polymers. Soon, high-performance, degradable plastics will continue to be developed. As one of the environmental protection technologies, the process of using synthetic enzyme catalysts instead of heavy metal chemical catalysts to synthesize polymer materials will also be available. In addition to aliphatic polyesters, polyphenols, polyanilines, polycarbonates, polyaspartic acid, etc. have been successfully developed.

At present, biodegradable plastics can only be used to make some sporting goods (fishing thread, golf clubs, etc.), agricultural and forestry aquaculture materials (films, moisturizing materials, seedbed materials, etc.), garbage bags, and hygiene products (disposable diapers, etc.) ). Its new uses are very broad, such as for the production of cosmetics containers, toothbrushes, cushioning materials, packaging materials, shopping bags, disposable gloves. If the safety problem is solved, it can also be used to make food containers. As a new polymer functional material, biodegradable plastics can also be applied to fertilizers, pesticides, free radical packaging materials and medical supplies packaging. In the future, non-plastic fields such as adhesives and printing inks can also be used.



(to be continued)