Today, degradable plastics are mainly divided into two types: photodegradable plastics and biodegradable plastics. Photodegradable plastics are materials that degrade automatically under the action of light. The reaction mechanism is that the plastic absorbs ultraviolet rays from sunlight, which reduces the bond energy in the plastic. Polymeric long chain breaks. Large molecules become small molecules. Finally, it is completely oxidized by air. Photodegradable materials are mainly divided into two categories: one is photodegradable materials of metal oxides or organometallic oxides. The other is polyaromatic hydrocarbons containing sensitizing olefins. Photodegradable materials are easily oxidized when photosensitive groups or photosensitizers are activated under light conditions. Under atmospheric conditions, the activity of photosensitizers, the wavelength of light, and the structure of the polymer all affect the degradation rate. Therefore, it is difficult to industrialize and industrialize photodegradable materials. Like our PLA lunch box, it belongs to biodegradable plastic.
Raw plastics are one of the most important products in the chemical industry. Due to the advantages of plastics with strong functionality, good processability, and easy large-scale production, they continue to create new applications and continue to replace other traditional materials. In 2019, global plastics output has reached 400 million tons, and it is the most important material for building human society. Traditional materials such as wood, stone, glass, and metal will decompose into various forms after a period of time and return to the natural cycle, but plastics are completely man-made, and most of them are difficult to decompose after hundreds of years. It has formed the "white pollution" problem that society is very concerned about. In order to not only enjoy the performance and cost advantages of plastics but also alleviate the harm of waste plastics to the environment, degradable plastics came into being. The development of degradable plastics has been slow in the early stage. The main reason is that the production cost is high and the implementation policy is not strong enough. However, since China banned the import of foreign waste in 2018, the industry trend has changed significantly. In the past, although overseas developed countries produced a large amount of plastic waste, by exporting to China and other regions, the huge external cost was solved with a small cash cost; while China has borne additional external costs, and the burden is getting heavier and heavier. . In order to solve the serious waste problem, China has begun to ban the import of foreign garbage.
The processing cost of developed countries has suddenly increased significantly, so we can see that European countries have successively introduced mandatory policies for plastics since 2018, and domestic policies have become more and more strict. Therefore, we believe that degradable plastics have entered an industry outbreak period, while Polylactic acid (PLA) and PBAT are among the most promising materials.
There are four main treatment methods for plastic waste: discarding, landfilling, incineration, and recycling. The processing costs of these four methods increase in turn. Among them, the cost of discarding is zero, and the cost of landfilling is also very low. The cost of incineration per ton is about 300 yuan. The cost of regeneration is almost the same as the cost of producing new materials. Plastic recycling realizes the cycle of product-recycled material-product, so there is almost no pollution, carbon emissions are very small, and other methods will cause harm to the air, ocean, groundwater, organisms, etc. It can be said that the lower the processing cost, The the external costs incurred are higher. At present, about 25% of the waste plastics in the world can be recycled, but the application of plastic recycling is relatively limited. Many products cannot be converted into recycled materials after use, so the proportion of recycling is not much room for improvement. In order to reduce the external cost of plastic waste, new recycling methods must be developed.
Degradable plastics can be converted into fertilizers, carbon dioxide, and water through composting. After planting sugar or starchy crops, they can be converted into organic molecules for the production of polymer materials through fermentation or chemical processing. Such a degradable cycle, like a recycling cycle, can greatly reduce the environmental impact of waste plastics. In addition, degradable plastics can be divided into bio-based and petrochemical-based based on raw materials. For example, the main raw materials such as PLA, PHA, and PBS are crops, and the main raw materials such as PBAT and PCL are crude oil. The production of degradable plastics from petrochemical raw materials will not enter the degradable cycle. The production of carbon dioxide emissions can also break society's inherent perception of the large carbon emissions of petrochemical products.