Why do we talk about biodegradable bags?
The word plastic is derived from the Greek word "plastikos", which means a substance that can be shaped into any shape. In addition to being cheap, plastics have good properties, especially durable. In the past half-century, the output of plastics has increased by 20 times (from 15 million tons in 1964 to 359 million tons in 2018), and is expected to double again in the next 20 years.
Currently, about 50% of the plastics produced are disposable plastics. The "one-time-use" culture has contributed to the waste of plastic resources. In addition, improper waste management leads to a large number of waste plastics entering the natural environment. Plastic waste can stay in nature for a long time. For example, plastic bottles are at least 450 years, which poses a serious threat to our planet: the accumulation of plastic in the soil makes the soil fertility decline; the accidental ingestion of plastic by land and marine life causes health problems and even death; Plastics in marine organisms can eventually reach the human table through the food chain...
Although plastics were only produced and used on a large scale around 1950, the reality that plastics are difficult to degrade and output has grown too fast has forced mankind to face an environmental problem that may last for centuries. Since the 1980s, scientists have begun to investigate whether plastics can degrade and disappear through the action of microorganisms in an environment where microorganisms are active. This kind of plastic, which is more easily transformed by microorganisms than ordinary plastic, is exactly what this report describes-biodegradable plastic.
In recent years, biodegradable plastics have entered a golden period of development, and their market share has grown steadily. Related reports that have been well-received frequently appear. However, there is currently insufficient public understanding of biodegradable plastics, especially the limitations of this material and the potential negative effects.
It should be noted that "biodegradable" is a relatively general term. The same kind of biodegradable material is under controlled conditions such as industrial composting or household composting, and in natural environments such as uncontrolled soil and seawater. The biodegradability varies. Biodegradable plastics also need to be recycled and properly disposed in a specific way, and should not be discarded at will.
What is biodegradable plastic?
When we want to understand biodegradable plastics, we often encounter the following concepts:
Biodegradable plastics, compostable plastics, fossil-based plastics, bio-based plastics, bioplastics and oxygen-degradable plastics.
Biodegradable plastics refer to plastics that can degrade under the action of microorganisms such as bacteria, fungi, and algae. Under ideal conditions, biodegradable plastics can be completely degraded by microorganisms after being discarded, generating harmless substances such as carbon dioxide and water.
Compostable plastic is one of the biodegradable plastics. According to the definition of the American Society for Testing and Materials (ASTM), compostable plastic refers to degradation under the condition of composting ①. The degradation rate is the same as other compostable materials, and it does not leave behind. Plastic with visible or toxic residues. At present, compostable plastics are the most mature and widely used among biodegradable plastics, because the composting process is more controllable, thus ensuring that the materials are completely degraded.
According to the different sources of plastic raw materials (fossil resources ② or biomass resources ③), plastics are divided into "fossil-based plastic" (fossil-based plastic) and "bio-based plastic" (bio-based plastic). Whether plastic is biodegradable or not does not necessarily have to do with what kind of raw material the plastic is made of. Currently, only very few fossil-based plastics are biodegradable. In the production of biodegradable plastics, the use of fossil raw materials such as oil and natural gas accounts for about 25%.
The concept of “bioplastics” is broad, meaning that plastics are derived from biomass resources and/or are biodegradable.
In addition, there is a controversial "oxo-degradable plastic" (oxo-degradable plastic). Compared with other ordinary plastics, oxygen-degradable plastics contain additives that promote oxidation, which can promote the oxidation and decomposition of plastics into fragments. However, if there is no subsequent biodegradation, this material cannot be completely degraded, and will only become plastic particles. The European Parliament passed the European Union Directive (EU) 2019/904 in June 2019, which prohibits the circulation of disposable plastic products made of oxygen-degradable plastics in the EU member states.
①A method of processing organic waste under aerobic conditions, which can produce organic fertilizer.
② Mainly refers to coal, oil, and natural gas.
③Renewable organic matter, such as crops.
④ Tiny plastic particles less than 5 mm in length.
What are the current standards for biodegradable plastics?
The standardization work of biodegradable plastics was carried out relatively late. In the early stage, certain modifications were mainly based on foreign advanced standards, or foreign standards were directly used equivalently. At present, the standards for biodegradable plastics are still relatively backward, and there are problems of aging, missing, and lagging.
For example, under controlled composting conditions, the domestic standards GB/T 19277.1-2011 and GB/T 19277.2-2013 for measuring the biodegradability of plastics are equivalent to the international standards ISO 14855-1:2005 and ISO 14855-2:2007, respectively. Translated. These two international standards have been replaced by ISO 14855-1:2012 and ISO 14855-2:2018, respectively, and China has not updated accordingly.
As another example, the standard method for measuring the anaerobic biodegradability of plastics is currently only measured in aqueous culture fluids (GB/T 32106-2015), and it can also be measured in urban sewage sludge and other environments internationally.
Therefore, China should speed up the establishment of a standard system for biodegradable plastics, so as to guide enterprises to produce biodegradable plastic products that meet the specifications.
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