The "degradable plastic" defined by the national standard is not a good way to solve the problem of plastic grunge. Although the environmental impact of biodegradable plastics is less than non-degradable plastic, it still leads to many environmental issues, so it can only see it as a substitute for alleviating plastic problems, rather than a solution of plastic problems. Although we can have expectations for technology development, in accordance with the current level of science and technology, only reduce consumption can minimize the impact of plastic products on the environment. To completely compare biological degradation plastics and traditional plastics, we may wish to disassemble the lifecycle of plastics.
1. Common degradable plastics
It is currently discussed that biodegradable plastics, which use renewable biological resources, such as crops, microorganisms, etc., and some use fossil resources. The most commonly used commercial biodegradable plastic is PHA (polyhydroxy fatty acid ester) and PLA (polylactic acid), which are respectively subjected to microorganisms (feeding by crop) and corn as the main raw material.
2, degradable plastic production
2.. Since the current source of biodegradable plastic raw materials is crops (corn, sugar cane, etc.), rather than fossil fuels, so from raw materials, biodegradable plastics can save approximately half of fossil fuel than traditional plastics. If the world's traditional plastics are replaced by biodegradable plastics, it can save approximately 3.49 million barrel fuels per day, accounting for about 4% fossil fuel consumption in the world.
2.2. Traditional plastics that consume less energy than characteristics during biodegradable plastic production process. In the production process of biodegradable plastic, it is generally 2500-45 million coke energy, and the most common PLA requires 44.7 million volute energy. The traditional plastics need to consume 7300-86 million coke energy per kilogram, which is much higher than that of biodegradable plastics. If the global non-degradable plastic is replaced with a biodegradable plastic, it can save 1-2.2 × 1019 joule energy every year according to the 2019 global plastic production. It accounted for 1.7-3.8% of the global energy consumption of 5.8 × 1020 Joules in 2019.
2.3. In terms of production cost, the price of biodegradable plastics is now slightly higher than traditional plastic (between 1-2 times), but according to the development speed of the industry, the price will continue to decline in the near future.
2.4. Production of 1 kg of biodegradable PLA plastics requires approximately 2.65 kilograms of corn, producing 1 kg of biodegradable PHA plastic takes approximately 3.7 kg of corn. According to the 2019 data, if all traditional plastics are replaced into PLA, approximately 975 million tons of corn are consumed each year; if all traditional plastics are replaced into PHA, approximately 1.36 billion tons of corn are consumed each year. At the same time, 2018/2019 global corn production is 1.09 billion tons, close to the cost of replacement plastics. Moreover, with more corn, or cultivated land is used to plant raw materials such as biodegradable plastics, the prices of corn and other crops will naturally rise, thus continuing to threaten food guarantees in the low food area. It can be seen that biodegradable plastics is a major threat to global food supply, and it is difficult to fully alternative traditional plastics before the technology has been achieved.
2.5. During the raw material planting process of biodegradable plastic, a large amount of fertilizer and insecticide are used, where the toxic substance will penetrate into the water, and the safety of drinking water is safe, wildlife safety, and soil safety.
3, degradable plastic recycling
3.1. Because the production of biodegradable plastics is too small, there is still lack of systematic, large-scale recovery methods. To give a simple example, when the garbage classification is proposed in Shanghai, many people need to shake the kitchen waste garbage when they are throwing garbage, and it is easy to stain your hands. So creating a creative wetting garbage bag, people want to throw the biodegradable garbage bag and wet garbage into wet trash. However, the garbage treatment department quickly sounded, indicating that although "degradable garbage bag" will most degrade, but it still has indiscriminated, even toxic and harmful ingredients, will affect the treatment of wet rubbish. Also, such garbage bag degradation speed is much slower than the kitchen waste, and cannot be treated synchronously. It can only be treated as dry waste incineration. Although biodegradable plastics can be degraded by biodegradation, it does not mean that they will ultimately break the recovery treatment, which is degraded.
3.2. When creative degradation plastics are not effectively recovered, they will decompose a large amount of greenhouse gas-methane in an aerobic environment.
3.3. When creative degradation plastics are not effectively recovered, after entering the marine environment, it is greatly reduced by sufficient microorganisms and oxygen, and biodegradation efficiency. Because it is not possible to degrade in time, these degradable plastics still have a great probability to harm the marine organisms before the degradation is completed.
4 comparison of overall carbon emissions
Because of the different raw materials, biodegradable plastics are less than traditional plastics in the entire life cycle. Because the raw materials of biodegradable plastic are mainly plants, their degradation is less than the carbon dioxide in the plant growth, so the carbon dioxide emissions of biodegradable plastics are mainly derived from mechanical emissions during production and transportation. The traditional plastic per kilogram of traditional plastics will release 2.5-3.4 kilograms of carbon dioxide in its complete life cycle, and biodegradable plastic will release 1.8 kg of carbon dioxide per kilogram of biodegradable plastics. If traditional plastic is replaced with biodegradable plastics, depending on the species, the world will release 0-830 million tons of carbon dioxide every year (consider the life cycle of the entire product). This order is approximately 2.3% compared to about 36 billion tons of carbon emissions per year [17].
5 potential threat
When the environmental impact of degradable plastic (oil consumption, carbon emissions, energy consumption, agricultural pollution, etc.) still exists, and that degradable plastics will still cause environmental issues. If we are in this time, due to mistakes, it is harmless, and a large amount of "degradable" plastic product is used, the overall environmental impact (the impact of unit plastic products × plastic products) may It will be greater than the era of traditional plastics. Not to mention the definition of degradation of plastics, it is still blurred. When it is "degradable plastic", "only needs a long time to degrade in the ideal environment", the environmental hazard Only increasing.
In summary, if you use a biodegradable plastic to replace the traditional plastic, 4% fossil fuel can be saved, reducing 2.3% carbon emissions worldwide, saving 2% of the world's energy consumption. Even if we use biodegradable plastics to replace all disposable plastics (approximately half of global plastics production), it can reach half of the results. At the same time, at the same time, replacement of disposable plastic products to degrade plastics can consume more than half of corn production, and cause risk from methane, pesticides, fertilizers, can't degrade in time. Therefore, it is necessary to emphasize that "degradable" does not explain that this plastic product can be simply harmless, which will still trigger a series of energy consumption, carbon emissions, food shortages, and so on. According to the current level of technology, "degradable plastic" is a way to slow the problem, it is not a way to solve the problem, and it is impossible to use degradable plastic products due to the word "degradable". If we all completely abandon the use of disposable products, it will not cause pollution and consumption of those fuel, energy, carbon emissions, etc., etc. Therefore, under the existing technological conditions, the use of conventional plastics is replaced with degradable / stacui plastics, and the use of a disposable plastic article is better.
