Several main biodegradable materials have their own advantages and disadvantages
The new century will face two major problems, one is the resource problem (energy problem); Second, environmental pollution.
Due to the massive exploitation of oil resources and the rapid increase in the consumption of oil products, oil resources are becoming increasingly exhausted (there is still 70 years of exploitation time), and environmental pollution is becoming increasingly serious. In particular, the "white pollution" caused by the massive use of non degradable plastics by people is shocking. The "CDM plan" (i.e. the clean development technology plan) implemented by the United Nations aims to reduce emissions and reduce environmental pollution worldwide. Therefore, looking for new resources for sustainable development and exploring and studying environmentally friendly materials have become an important topic for human survival and development. Natural polymer materials such as starch and cellulose are obtained by photosynthesis of plants. They are extremely rich in resources, widely exist in fruits and stems of plants, have sustainability, and are easy to degrade in the natural environment. They are ideal materials to solve the above problems. Because natural polymer materials have good biodegradability and resource sustainability, the research and application of biodegradable materials have attracted great attention of governments all over the world.
The wide use of plastic products has brought people a lot of convenience and great wealth, but plastic waste has also brought people a lot of trouble, but also brought disaster. Plastic waste, also known as "white pollution", is a major "public hazard" in the world today, and has become an important factor threatening the ecological environment. Therefore, how to solve the problem of "white pollution" is a public topic highly valued by governments all over the world and all people of insight from all walks of life.
At present, some countries regard degradable plastics as the fourth important application material after metal materials, inorganic materials and polymer materials, and it has become the focus of research and development in developed industrial countries. Especially in recent years, biodegradable plastics have developed rapidly in the world. Its products have been widely used in the field of packaging. But at present, no enterprise in the world can provide an effective, durable and acceptable degradable plastic. Only the United States, Britain, Italy and Japan can produce fully degradable plastics to monopolize the international market of billions of dollars. There are four major brands of fully biodegradable plastics in international products: novon in the United States, mater Bi in Italy, blopodt in the United Kingdom and blonde in Japan. Only mater Bi in Italy has truly formed industrial production. The product still has shortcomings, and the price of the product is as high as more than 7000 US dollars / ton, which is difficult to promote and apply on a large scale.
As a packaging material, the output of plastic products in China has ranked fourth in the world in just 20 years. In 2000, the total waste of plastic products in China exceeded 50million tons. There were 500000 plastic lunch boxes used in Shanghai fast food industry and 500000 in Beijing every day. The cost of treating garbage pollution in the fast food industry is 10 times the production price. The annual cost is 300-400 million yuan. According to statistics, the consumption of fast food boxes in China is 10billion, with an annual growth rate of at least 15%. The output of plastic products used for packaging household appliances and instruments is 60 ~ 100 times that of tableware. The cost of treating environmental pollution across the country is shocking. The annual investment in environmental protection is about 100billion yuan, up to 80billion yuan from 1989 to 1995 and 450 billion yuan from 1996 to 2000, which seriously restricts China's economic development. The difficult degradability of plastic packaging products and the serious harm of its "white pollution" have caused immeasurable losses to society and the environment, and a large amount of land for burying garbage is wasted every year. The environmental pollution centered on the city is increasing, and it is spreading to the countryside, and the environmental pollution is increasing. If it is not controlled and stopped, it will have a great adverse impact on our future generations and the earth we live on. This aspect has attracted the attention of governments all over the world, actively taking measures to stop it, and seeking new alternatives to solve the problem of environmental pollution. Faced with this situation, the State Council passed the "decision on several issues of environmental protection" and other documents. The state also formulated 171 national and industrial standards for environmental protection, and newly promulgated more than 500 local environmental protection regulations. China is a signatory to the Montreal decision and the Vienna Declaration, and the document clearly stipulates the limited use period of EPS foam.
From the perspective of the international market, it is difficult for plastic product packaging, especially plastic food packaging, to enter the international market. After China's entry into WTO, how to protect domestic national industries and expand exports depends largely on the development of product packaging technology. In recent years, China's refrigerators, televisions and other products exported to Europe and the United States have received high fines because the internal packaging materials do not meet the requirements of foreign exports, which not only suffer economic losses, but also affect China's international image. The United States, Japan, Germany and other developed countries have explicitly banned the use of disposable plastic tableware, and have also begun to intensify efforts to ban plastic products packaged in household appliances and instruments. Since 1989, Denmark, the Netherlands, the United States, Britain, France, Italy, Japan and other countries have made corresponding provisions while restricting or banning ordinary non degradable plastic packaging. The European community proposed in 1991 to stop using non degradable plastic packaging by January 2001. In China, following the environmental protection law, the law of the people's Republic of China on the prevention and control of environmental pollution by solid waste has been implemented on April 1st, 1996. Therefore, eradicating the public nuisance of "white pollution" is the consensus of people all over the world.
In the mid-1980s, scientific and technological workers around the world have done a lot of exploratory work from the recycling of plastic products to seeking new materials to replace non degradable plastics.
Comparison of several main degradation materials
According to different degradation methods, at present, it is mainly divided into five categories: Double degradable plastics; Paper Products; Grass fiber; Polypropylene; Fully biodegradable packaging materials.
1. Double degradable plastic: adding starch to plastic is called biodegradable plastic, adding photodegradation initiator is called photodegradable plastic, and adding starch and photodegradation initiator at the same time is called Double degradable plastic. Double degradable plastics can only be degraded into small fragments or powder because they cannot be completely degraded into molecular state. The damage to the ecological environment cannot be weakened at all, but even worse; Photosensitizers in photodegradable plastics and double degradable plastics have varying degrees of toxicity, and some are even carcinogens. In 1995, FDA (the abbreviation of the roed and Drug Administration) expressly stipulated that photodegradable plastics should not be used in contact with food packaging. Photodegradation initiators are mostly composed of anthracene, phenanthrene, cyclopentadienyl, benzophenone, alkyl amine, anthraquinone and their derivatives. Which of these compounds is toxic and will cause cancer after long exposure. These compounds produce free radicals under light, and free radicals will have a great impact on human body in aging, pathogenic factors and other aspects, which is well-known, and cause great harm to the natural environment.
2. Polypropylene: polypropylene was gradually formed in the Chinese market after the former State Economic and Trade Commission issued the No. 6 order "prohibiting disposable foamed plastic tableware". Because the "foamed plastics" prohibited by the former State Economic and Trade Commission did not prohibit "non foamed plastics" products, some people took advantage of the loopholes in national policies. The toxicity of polypropylene has attracted the attention of the student nutrition meal Office of the Beijing municipal government. Beijing has begun to prohibit the use of polypropylene tableware among primary and secondary school students.
3. Straw fiber packaging materials: the application of straw fiber packaging materials is limited due to the difficulty in solving the problems of color, sanitation and energy consumption. In December, 1999, organized by the former State Economic and Trade Commission and issued by the State Bureau of technical supervision, the standard for packaging materials focused on the color, hygiene and heavy metals of packaging materials, which limited the application of such materials in the market. Moreover, the strength problem of straw fiber packaging materials has not been solved, so it can not be used as shockproof packaging for household appliances and instruments, and the cost is high.
4. Paper product packaging materials: because paper product packaging materials require a large amount of pulp, and a large amount of wood pulp is added according to different requirements (for example, 85-100% of wood pulp is required to be added to the instant noodle bowl in order to maintain the strength and straightness of the instant noodle bowl), the early pollution of the pulp used in paper products is very serious, and the impact of wood pulp on natural resources is also considerable. Therefore, its application is limited. Paper products and packaging products were widely used in the United States in the 1980s, and now they have been basically replaced by starch biodegradable materials.
5. Fully biodegradable packaging materials: in the early 1990s, China and developed countries such as the United States, Germany, Japan and South Korea successively carried out research on biodegradable packaging materials using starch as raw materials, and achieved gratifying results. As a naturally degradable material, biodegradable polymers play a unique role in environmental protection, and their research and development have also developed rapidly. The so-called biodegradable materials must be materials that can be completely digested by microorganisms and only produce natural by-products (carbon dioxide, methane, water, biomass, etc.). Starch is the fruit of annual plants, which can be rice starch, corn starch, potato starch, sweet potato starch, cassava starch, etc. As a disposable packaging material, starch has no pollution in the process of production and use, and can be used as feed, feeding fish and other animals, or as fertilizer after degradation.