Before reading this article, first observe your surroundings, as well as your body and hands, and I think you can find some plastic products. At least mobile phone in your hand has a lot of plastic parts, and if clothes you are wearing are made of chemical fiber, they are also plastic. Plastic has penetrated all aspects of our lives, without plastic our modern civilization will cease to exist. And more and more plastics are creating a lot of environmental problems because they are not properly disposed of. But outside of practitioners, vast majority of population knows little about plastic. Today I will introduce you to some basic knowledge about plastic.
01 How many types of plastic are there?
There is no exact number of types of plastic, but theoretically there are thousands of them. Moreover, scientists and research departments of chemical companies are constantly inventing new types of plastics. The national standard "GB/T 16288-2008 Labeling of plastic products" lists 140 kinds of plastics, covering most of plastics widely used at present. The most common in our daily life are following: PET, PE (including HDPE and LDPE), PP, PS, PVC, PC, ABS, EVA, EPS, etc., as well as chemical fibers commonly used in clothing industry. (nylon, polyester) etc.
The image is taken from official website of UNPE (United Nations Environment Program)Most of beverage bottles are made of PET, plastic bags are mainly of polyethylene, express lunch boxes are mainly of polypropylene, and some of them PVC; both PET and PE bottles for protective products are available; CDs are made of polycarbonate.
02 Where did plastic go?
Once plastic has been used, there are four uses for it: incineration, landfill, recycling, and being left in wild lakes and seas. About 9% is recycled, 12% is incinerated, and 79% ends up in landfill or environment. (Data provided by United Nations Environment Program UNEP). Plastics will release carcinogenic dioxins if temperature is not properly controlled during incineration. This is one of reasons for maximum possible separation of wet waste, because presence of wet waste makes it very difficult to control temperature. Even if strict temperature control can be ensured, fly ash from an incinerator must be collected, finally solidified, and disposed of in a landfill. Burial does not lead to disappearance of plastic. Since traditional plastics are not biodegradable, it will take at least 500 years for them to disappear into landfills.
The ideal method of disposal is recycling. The most ideal is same level of recycling as recycling of beverage bottles into new food-grade PET particles that are still used to make beverage bottles. This cycle goes on and on, forming a vicious cycle. But in most cases, its quality is downgraded and recycled. For example, particles recycled from beverage bottles are used to make chemical fiber and clothing, while recycled chemical fiber clothing is used to make greenhouse quilted quilts. Recycling extends life cycle of plastic and reduces amount of plastic waste generated. But it still ends up as waste.
Sources of land-based plastic waste entering sea in 2010: Jambeck et al. Science, 2015 And worst is accidental release, which is especially common in rural areas and poorly managed scenic areas. Most of this plastic waste that has not been properly collected and treated will end up in waterways and eventually end up in sea.
Color tint represents proportion of plastic waste that is not properly disposed of; size of circle corresponds to weight of plastic waste that ends up in ocean. The image is taken from UNEP official website. Data taken from Jambeck et al. Science. In 2015, scientists collected and analyzed samples from 57 rivers. It is estimated that more than 90% of plastic waste enters ocean via rivers. passes through 10 rivers - 8 are in Asia, 2 are in Africa and 4 of 8 rivers in Asia are in China.
The image is taken from UNEP official website, and data is obtained from Center for Environmental Research. Helmholtz in Leipzig, Germany and published in Environmental Science & Technology
After plastic enters ocean, some of it quickly sinks to bottom and some of it floats to surface. Some of them were accidentally eaten by marine life, resulting in death. Others decompose into microplastics, which move with ocean currents to all corners of world. Microplastics have been found in Arctic and Antarctic, in marine life and in our drinking water.
03 Which plastics can be recycled
Plastic can be divided into thermoplastic and thermoset. Theoretically, all thermoplastics can be recycled, and vast majority of plastics we come into contact with in everyday life are thermoplastics. Thus, from a technical point of view, most of plastic in everyday use is recyclable. But in fact, ability to recycle a certain type of plastic depends on whether it meets conditions of purity, concentration and large quantity, and whether the price is enough to cover labor, storage, logistics and other costs.
Picture nets such as takeaway lunch boxes are mostly made from polypropylene, and those used for food packaging should be of a higher quality. But because it is stained with oil and food residue, it is difficult to clean, which is not conducive to recycling.
Beverage bottles, toiletries bottles, and edible oil barrels are relatively easy to recycle among everyday plastics.