For a long time, different forms of disposable plastic products have been widely used in residents’ lives. In recent years, with the development of new formats such as e-commerce, express delivery, and takeaway, the consumption of plastic lunch boxes and plastic packaging has risen rapidly, resulting in new Resource and environmental pressure. The random disposal of plastic waste will cause “white pollution”, and there are environmental risks in the improper handling of plastic waste. So, how much do you know about the basics of waste plastics?
01 What is plastic? Plastic is a kind of high molecular organic compound, which is the general term for filled, plasticized, colored and other thermoplastic forming materials, and belongs to a family of high molecular organic polymers.
02 Classification of plastics According to the characteristics of the plastic after molding, it can be divided into two kinds of material plastics: thermoplastic and thermosetting. Thermoplastic is a kind of chain linear molecular structure, which softens after being heated and can replicate the product many times. The thermosetting plastic has a network molecular structure, which becomes permanent deformation after being processed by heat and cannot be repeatedly processed and copied.
03 What are the common plastics in life?
Common plastic products in daily life mainly include: polyethylene (PE), polypropylene (PP), polystyrene (PS), polyvinyl chloride (PVC) and polyester (PET). Their uses are:
Polyethylene plastics (PE, including HDPE and LDPE) are often used as packaging materials; Polypropylene plastic (PP) is often used as packaging materials and turnover boxes, etc.; Polystyrene plastic (PS) is often used as foam cushions and fast food lunch boxes, etc.; Polyvinyl chloride plastic (PVC) is often used as toys, containers, etc.; Polyester plastic (PET) is often used to make beverage bottles, etc.
Plastic is everywhere
04 Where did all the waste plastic go? After plastic is discarded, there are four places to go-incineration, landfill, recycling, and natural environment. A research report published in Science Advances by Roland Geyer and Jenna R. Jambeck in 2017 pointed out that as of 2015, humans had produced 8.3 billion tons of plastic products in the past 70 years, of which 6.3 billion tons were discarded. About 9% of them are recycled, 12% are incinerated, and 79% are landfilled or discarded.
Plastics are man-made substances that are difficult to degrade and decompose extremely slowly under natural conditions. When it enters the landfill, it takes about 200 to 400 years to degrade, which will reduce the ability of the landfill to dispose of waste; if it is directly incinerated, it will cause serious secondary pollution to the environment. When plastic is burned, not only a large amount of black smoke is produced, but also dioxins are produced. Even in a professional waste incineration plant, it is necessary to strictly control the temperature (above 850°C), and collect the fly ash after incineration, and finally solidify it for landfill. Only in this way can the flue gas emitted by the incineration plant meet the EU 2000 standard , To minimize environmental pollution.
The garbage contains a lot of plastic garbage, and direct incineration is easy to produce dioxin, a strong carcinogen
If they are abandoned to the natural environment, in addition to causing visual pollution to people, they will also cause many potential hazards to the environment: for example, 1. affect agricultural development. The degradation time of plastic products currently used in our country usually takes 200 years. Waste agricultural films and plastic bags in the farmland are left in the field for a long time. Waste plastic products are mixed in the soil and accumulate continuously, which will affect the absorption of water and nutrients by crops and inhibit the production of crops. Development, resulting in reduced crop yields and deterioration of the soil environment. 2. A threat to the survival of animals. Waste plastic products discarded on land or in water bodies are swallowed as food by animals, leading to their deaths.
Whales that died by accidentally eating 80 plastic bags (weighing 8 kg)
Although plastic waste is harmful, it is not “heinous”. Its destructive power is often tied to low recycling rate. Plastics can be recycled and reused as raw materials for making plastics, materials for heat generation and power generation, turning waste into treasure. This is the most ideal disposal method for waste plastics.
05 What are the recycling technologies for waste plastics?
The first step: separate collection.
This is the first step in the treatment of waste plastics, which facilitates its subsequent use.
Plastics discarded during the production and processing of plastics, such as leftovers, foreign products and waste products, have a single variety, no pollution and aging, and can be collected and processed separately.
Part of the waste plastic discharged in the circulation process can also be recycled separately, such as agricultural PVC film, PE film, and PVC cable sheathing materials.
Most waste plastics are mixed wastes. In addition to the complex varieties of plastics, they are also mixed with various pollutants, labels and various composite materials.
The second step: crushing and sorting.
When the waste plastic is crushed, a suitable crusher should be selected according to its nature, such as a single, double-shaft or underwater crusher according to its hardness. The degree of crushing varies greatly according to needs. The size of 50-100mm is coarse crushing, the size of 10-20mm is fine crushing, and the size below 1mm is fine crushing.
There are multiple separation techniques, such as electrostatic method, magnetic method, sieving method, wind method, specific gravity method, flotation method, color separation method, X-ray separation method, near-infrared separation method, etc.
The third step: resource recycling.
Waste plastic recycling technology mainly includes the following aspects:
1. Direct recycling of mixed waste plastics
The mixed waste plastics are mainly polyolefins, and its recycling technology has been extensively studied, but the results are not great.
2. Processing into plastic raw materials
Reprocessing the collected relatively simple waste plastics into plastic raw materials is the most widely used recycling technology, mainly used for thermoplastic resins. The recycled plastic raw materials can be used as raw materials for packaging, construction, agricultural and industrial appliances. Different manufacturers use independently developed technology in the processing process, which can give products unique performance.
3. Processing into plastic products
Using the above-mentioned technology for processing plastic raw materials, the same or different waste plastics are directly formed into products. Generally, they are thick bi products, such as plates or bars.
4. Thermal power utilization
The waste plastics in the municipal waste are sorted out and burned to generate steam or generate electricity. The technology is relatively mature. The combustion furnaces include rotary furnaces, fixed furnaces, and vulcanizing furnaces. The improvement of the secondary combustion chamber and the progress of tail gas treatment technology have made the tail gas emissions of the waste plastic incineration energy recovery system reach a high standard. The waste plastics incineration recovery heat and electric energy system must form a large-scale production in order to obtain economic benefits.
5. Fueling
The calorific value of waste plastic can be 25.08MJ/KG, which is an ideal fuel. It can be made into solid fuel with uniform heat, but the chlorine content should be controlled below 0.4%. The common method is to pulverize waste plastics into fine powder or micronized powder, and then blend into a slurry for fuel. If the waste plastic does not contain chlorine, the fuel can be used in cement kilns, etc.
6. Thermal decomposition to make oil
Research in this area is currently relatively active, and the obtained oil can be used as fuel or crude raw material. There are two types of thermal decomposition devices: continuous and discontinuous. The decomposition temperature is 400-500℃, 650-700℃, 900℃ (co-decomposition with coal) and 1300-1500℃ (partial combustion gasification). Technologies such as hydrogenation decomposition are also under study.
06 What can we do for Mother Earth?
1.Please minimize the use of disposable plastic products, such as plastic tableware, plastic bags, etc. These disposable plastic products are not only unfavorable to environmental protection, but also a waste of resources.
2.Please actively participate in garbage classification, put waste plastics in recyclables collection containers, or deliver them to the two-network integration service site. do you know? For every ton of waste plastics recycled, 6 tons of oil can be saved and 3 tons of carbon dioxide can be reduced. In addition, I have a small reminder that I have to tell everyone: clean, dry, and uncontaminated waste plastics can be recycled, but some contaminated and mixed with other garbage are not recyclable! For example, contaminated plastic bags (film), disposable fast food boxes for takeaways, and contaminated express packaging bags should be put in dry garbage.
Post time: Nov-09-2020