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Biodegradable plastic is considered as one of the most promising green packaging materials, and it is a new type of material that can quickly degrade and disappear in the natural environment after being discarded, and does not cause environmental pollution.
According to the definition defined by the American Society for Testing Materials ASTM in 1989, a degradable material is a plastic whose chemical structure changes in a specific environment that causes performance loss in a specific time. The development of biodegradable plastic packaging materials and the gradual elimination of non-degradable plastic packaging materials are the major trends in the development of science and technology in the world and are one of the hot topics in the research and development of materials. As degradable plastics are easy to process and shape, and prices are declining, the use of biodegradable plastics to make packaging has increased dramatically. According to the US Market and Technology Forecast report, the United States currently has more than 40 companies producing degradable plastics, 1987. The output was 23,000 tons, which had risen to 380,000 tons in 1992 and 17 times in five years. At present, biodegradable plastics in the United States have been widely used in food packaging, turnover containers, grocery bags, tool packaging, and external packaging boxes for some electromechanical products.
Currently, biodegradable polymers that have been identified include only biosynthetic fatty polyesters such as PHB and PHBV synthesized by fermentation, ether- and polyhydroxy-containing polymers such as starch and cellulose, and synthetic polyamides. Polyurethanes, polymers containing ether bonds, and PVA. Among these polymer materials, polyurethanes, polyamides, polyesters, and PVAs are good packaging materials and are widely used as packaging films, packaging containers, or tying materials. However, these kinds of completely degradable packaging materials have a limited variety and are far Can not meet the requirements of many packaging technologies and packaging protection performance. PHB, PHBV, and polyethers, for example, have low melting point and strength and are not very useful. However, packaging materials that can be completely degraded by microorganisms have attracted the attention of various countries because of their complete harmlessness to the environment. Development in this area is still underway.
The incomplete substance degradable plastic (starch + PE type) blended with starch, also known as bio-disintegrating plastic, is a material that has rapid research and development, many industrialization results, and is expected to continue to reduce costs. In order to improve the compatibility of starch and polymer blends, it is necessary to modify the starch, and the surface of the modified starch granules is covered with an alkyl group, etc., which weakens the effect of hydrogen bonding, thereby increasing the compatibility with polyethylene and poly. Compatibility of polymers such as vinyl alcohol.
China began to develop degradable starch plastics in the early 1980s, and the starch plastics developed by Jiangxi Academy of Sciences should be the first to succeed. In 1987, it passed the appraisal and established the first small-scale starch plastic production line in China, achieving product performance. The same type of plastic international standard. Beijing Huaxin Starch Degradable Resin Products Co., Ltd. took starch as the main raw material, replacing some of the polyethylene as raw materials, and produced biodegradable food packaging bags in 1991.
The problem with starch-degradable plastics is that only part of the starch is biodegraded in a short time during degradation, whereas plastics such as polymers such as PK, PS, and PVC cannot be biodegraded. The degradation results in deterioration of the blends. The performance is declining, but it still remains in the soil or the environment. To achieve complete degradation into the ecological environment, it must be at least 20 years. Therefore, this is an incomplete biodegradable material that can only play a role in the disposal of plastic waste. Not fundamental governance.
Photodegradable packaging materials obtained by adding photosensitizers have been reported. Such materials can be obtained by adding a suitable photosensitizer to commonly used plastics such as PE and PP. The TPR green packaging material developed by Sweden's Filltec Co., Ltd. is obtained by compounding calcium carbonate with a special process and polypropylene added with a photolysis agent. Its composition is very similar to the eggshell, almost harmless to the environment, and can be thermoformed, blow molded, Injection molding and extrusion molding, TPR smooth and smooth, different thickness of the film in the light of 4 to 18 months, that is degraded into powder, is now used in butter, ice cream and other packaging.
Photodegradable packaging materials currently have the following problems: 1) The contradiction between the photodegradation rate and the photodegradable polymer performance. If the photodegradation rate is too fast, it is beneficial to the disposal of waste plastics, beautify the environment and reduce pollution, but it is obviously unfavorable for the use performance and lifespan; 2) the impact of photodegradation products on the ecological environment, if the products after photodegradation can continue Biodegradation eventually becomes the carbon energy or harmless material that is absorbed by microorganisms. Of course, it is ideal. However, in fact, the copolymers of ethylene, propylene and vinyl ketone have very little biodegradability in the soil or underground water channels after photodegradation, and whether the photodegradation products are harmful to the ecological environment are also worth studying.
At present, biological and light double-degradable plastics entering the market are mainly prepared by blending or graft modification of general-purpose polymers such as PE and PP with degradable polymers such as starch or cellulose. Photoinitiators that induce photodegradation were obtained and research and application in this area are very active. Polyketones can be chemically modified with oxidizing agents such as hydrogen peroxide and peroxyacids, and oxidized into polymers containing both polyester and polyketone structure, and become packaging materials having both biodegradability and photodegradability. The bio/photo-degradable plastics developed by the Department of Chemistry of Lanzhou University can be directly used in the production of fast food lunch boxes and garbage bags. It uses non-starch type photosensitizers and biodegradable agents. Its strength and transparency are superior to those of starch plastics, and its photodegradation performance Excellent, it can be embrittled within 50 ~ 100 days, and its degradation products can be further degraded by microorganisms such as mold, and eventually become the carbon source of microorganisms, returning to nature. The double-degradable plastic film produced by Shenzhen Huipeng Resin Factory in Guangdong Province is mainly composed of PE and starch. The content of modified starch is up to 70%. The blown film is used for packaging. The film can be degraded under the influence of biology and light. In recent years, many countries have increased their efforts in the deep processing of agricultural and sideline products in order to increase the overall efficiency of agriculture. The use of agricultural and sideline products to produce environmentally friendly food plastic packaging materials has become a research hotspot.
At present, the application of "biodegradable resin" to replace existing plastic packaging is in full swing. Corn is a delicious and nutritious food. It is also widely used in the manufacture of sweeteners and animal feeds. With the advancement of technology, the use of corn can also produce a variety of plastic products, such as the recent successful study in Japan and Taiwan. The "corn starch resin" is a new type of green environmental protection material. The resin is made of corn and processed and plasticized. It first extracts the sugar from the corn and extracts the base of plastic and fiber through fermentation distillation. The material is then processed into a material called polylactide (PLA), which is a fine particle with a diameter of only 4.57 mm. It can be used to make a variety of disposable supplies, such as cups, plastic bags, commodity packaging and so on. According to experiments, this kind of packaging material can be disposed of through burning, biochemical decomposition and insect feeding, thus eliminating "white pollution".
Foreign companies have been optimistic about this new type of environmentally friendly materials, such as the Coca-Cola Company used 500,000 disposable cups at the Winter Olympics in Salt Lake City, all of which were made of corn plastics. Such cups disappeared in the open air in only 40 days. Go without a trace. Japanese electronics maker Sony Corp. has been packing MD disks with plastic paper made from corn for two years. The new packaging is as beautiful as the previous packaging, but it will not produce the "durable" adverse effects.
Scientists from the US Department of Agriculture recently announced that a new environmentally friendly food packaging material is expected to come out. This new material is made entirely of crushed strawberries and is very environmentally friendly and may replace traditional polyethylene plastics as a new material for food packaging. Tara McHuiy, a food expert from the U.S. Department of Agriculture, said that this newly developed food packaging material is no different from traditional products in terms of performance. Food packaging films made from it can also prevent the penetration of oxygen. To achieve the effect of food preservation. Since the ingredients of this new material are mainly derived from vegetables and fruits that are not suitable for consumption, it is a naturally decomposable and environmentally friendly material. In testing, packaging films made from this “magic†material not only served to preserve freshness, but also improved the taste of fruits such as bananas and apples. Tara McHugh said that in the near future, not only can strawberries be used as packaging materials, but even vegetables such as carrots and broccoli can be used as packaging materials. (to be continued)
2 Degradable plastic packaging materials