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Where does “waste plastic” come from? Where are you going?

Where does “waste plastic” come from? Where are you going?

Plastic waste will cause “white pollution” if it is discarded at will. There are environmental risks in non-standard treatment of plastic waste. So, how much do you know about the basic knowledge of waste plastics?

For a long time, different forms of disposable plastic products have been widely used in people’s lives. In recent years, with the development of e-commerce, express delivery, takeout and other new formats, the consumption of plastic lunch boxes, plastic packaging, etc. has increased rapidly, resulting in new resource and environmental pressure.

What is plastic?

Plastic is a kind of high molecular organic compound, which is the general term of thermoplastic materials such as filling, plasticizing and coloring, and belongs to a kind of high molecular organic polymer family.

What are the common plastics in life?

The common plastics materials in our life mainly include polyethylene (PE), polypropylene (PP), polystyrene (PS), polyvinyl chloride (PVC) and polyester (PET).

Their uses are as follows:

Polyethylene plastics (PE, including HDPE and LDPE) are commonly used as packaging materials;

Polypropylene plastics (PP) are commonly used as packaging materials and turnover boxes;

Polystyrene plastics (PS) are often used as foam liners and fast food lunchboxes.

PVC is often used as toys, containers, etc;

Polyester plastics (PET) are often used to make beverage bottles.

Where did all the waste plastics go?

After the plastics are discarded, there are four kinds of places to go: burning, landfill, recycling and abandoning.

Plastic is a kind of man-made material which is difficult to degrade and decomposes very slowly under natural conditions. When it enters the landfill, it will take about 200 to 400 years to degrade, which will reduce the capacity of landfill to treat waste; If burning directly, it will cause serious secondary pollution to the environment.

When burning plastics, not only a large amount of black smoke but also dioxins will be produced. Even in a professional waste incineration plant, it is necessary to strictly control the temperature (above 850 ° C), collect the fly ash after incineration, and finally solidify and landfill. Only in this way can the flue gas discharged from the incineration plant reach the EU 2000 standard and minimize environmental pollution.

Photo: there is a large amount of plastic waste in the garbage. Direct incineration of garbage is very easy to produce strong carcinogens dioxin.

Although there are many hazards of plastic waste, it is not “good for nothing”. Its destructive power is often bound with low recycling rate. Plastics can be recycled and reused as raw materials for heating and power generation. It is one of the most ideal disposal methods for waste plastics.

The environmental and economic value of recycled plastics is far greater than that of original plastics.

In the field of renewable resources, there is a public announcement: Recycling 1 ton of waste plastics = saving 6 tons of oil, which does not include a lot of water resources saved in the process of refining new materials. In general, plastics are relatively inert and difficult to be degraded in the natural environment, which brings huge burden and pressure to the ecological environment. It is an important way of ecological environment pollution to turn waste plastics into treasure. The environmental economic value of recycled plastics is far greater than that of original plastics.

Take PVC and polyester as examples

  1. Environmental and economic value of PVC recycling:

One ton of waste PVC collected and mechanically recycled will generate about 120 kg of carbon dioxide. These recycled materials can be directly used in products instead of raw materials. Environmental data from plastics Europe show that using raw materials (salt and oil) to produce 1 ton of pure PVC will produce 1900 kg of carbon dioxide. In this way, the use of recycled materials will save 94% of carbon dioxide emissions than the use of pure raw materials.

  1. Compared with primary polyester, recycled polyester has great environmental advantages

According to the EPA report, only one third of the primary energy is needed to produce recycled polyester, which reduces the emissions of sulfur dioxide and nitrogen dioxide by two thirds and 50%. The water consumption and carbon emissions are reduced by 10 times and 2.5 times, respectively. Another advantage is that it avoids the landfill of the same plastic.

The recycling of plastics not only saves social resources, but also saves production costs.

Recycled plastics worth higher price

Plastic is a very good material for recycling. Waste plastics can be used in all fields where plastics can be used. In foreign countries, the use of recycled plastics is considered to be an environmental behavior worthy of promotion and encouragement. We are willing to offer higher prices for such environmental protection products. The use of recycled plastics can not only reduce plastic pollution, but also make everyone fulfill the responsibility of recycling.

Waste plastics are produced everywhere in our life

The major sources of recycled plastics include plastic films (including plastic bags and agricultural films), plastic and woven fabrics, foam plastic products, plastic packaging boxes and containers, cable coating materials, daily plastic products, daily entertainment, health care, etc. Sheet and other plastic products are mainly used for plastic packaging. In addition, there are some other plastic packaging products (such as plastic pallets), agricultural plastic products (such as agricultural plastic water-saving equipment), decoration plastic products scrap rate is also high.

However, in recent years, the use of structural plastic building materials, such as plastic pipes and fittings, profiled materials, reinforced anti leakage geotechnical materials (including waterproof coiled materials), has increased greatly, and the actual service life is longer. At present, it is less than a large number of scrap period, so the waste amount of this part is not large.

According to the normal service life of household appliances of 10-15 years, the average number of TV sets to be scrapped is more than 5 million per year, the average number of washing machines is 5 million per year, and the average number of refrigerators is about 4 million per year. Therefore, China will eliminate more than 15 million waste household appliances every year. In recent years, electronic communication equipment, such as computers, mobile phones, VCDs, DVDs, records, compact discs, etc., have been upgraded rapidly, and the number of scrapped products has increased sharply every year, which has brought serious environmental problems.

Plastics are an important part of household electrical appliances, and the amount of renewable plastics produced is at least 150000 tons per year. If the amount of renewable plastics in discarded electronic communication equipment is taken into account, the figure is about 200000 tons. The main components of these recycled plastics are polypropylene (PP), polystyrene (PS), polyvinyl chloride (PVC), ABS and so on; Some thermosetting plastics, foamed polyurethane and glass fiber reinforced plastics are relatively difficult to recycle.

Reasonable disposal of recycled plastics is one of the important links in the recycling process of waste household appliances. Different kinds of plastics are used in different household appliances. The plastics used in the same product are different due to different manufacturers. Sometimes the additives, functional masterbatch or formula used are different due to the same kinds of plastics. This makes it difficult to recycle household appliances plastics. We should take them seriously and strive to recycle them effectively, Make it reduce environmental pressure and energy waste as much as possible.

The consumption of plastic accessories for electronic and electrical appliances has reached more than 1 million tons, which has been widely used in industrial supporting, information, transportation, aerospace and other fields, and the products are updated quickly. With this kind of products gradually entering a large number of scrap period, it has become an important source of waste plastics.

Recycled plastics are different forms of plastics that still have recycling value at the end of their service life. Almost all thermoplastics have recycling value.

Recycled plastics are produced in the production of synthetic resin, in the production and processing of plastic products and semi-finished products, in the process of plastic logistics and after consumer use. Generally, the plastics produced in the process of synthesis and processing are called pre consumer plastics; After circulation, consumption and use, the plastic is called post consumption plastic. Before consumption, the production of plastics is small, the quality is stable, and the recycling value is large. Generally, the plastics are properly treated in the production process and can be completely reused. What we call recycled plastics generally refers to the recyclable plastic products that lose use value after consumption and can be recycled. After recycling, centralization, classification and scientific and reasonable disposal, plastics can obtain recycling value and realize recycling.

The waste plastics industry, or the industrial chain, is closely related to the existing economic fields, and they depend on each other, survive together, and develop relatively synchronously.

The global recycling system is an inevitable part of the ecological chain of people’s daily life and economic life. Destroying any link will touch or destroy the ecological balance and progress.

What are the recycling technologies of waste plastics?

Step 1: classified collection

This is the first step in the treatment of waste plastics and provides convenience for subsequent use.

The waste plastics, such as leftover materials, substandard products and waste products, in the process of plastic production and processing are of single variety, no pollution and aging, and can be collected and treated separately.

Some of the waste plastics discharged in the circulation process can also be recycled separately, such as agricultural PVC film, PE film, PVC cable sheath material, etc.

Most of the waste plastics belong to mixed waste. In addition to the complex variety of plastics, they are also mixed with various pollutants, labels and various composite materials.

The second step: crushing and sorting

When crushing waste plastics, appropriate crushers should be selected according to their properties, such as single, double shaft or underwater crushers according to their hardness and softness. The crushing degree varies greatly according to the needs. The size of 50-100 mm is coarse crushing, the size of 10-20 mm is fine crushing, and the size of less than 1 mm is micro crushing.

There are many separation technologies, such as electrostatic method, magnetic method, screening method, wind method, specific gravity method, flotation method, color separation method, X-ray separation method, near infrared separation method, etc.

The third step: recycling

Waste plastics recycling technology mainly includes the following aspects:

  1. Direct recycling of mixed waste plastics

Polyolefin is the main component of mixed waste plastics, and its recycling technology has been widely studied, but the effect is not good.

  1. Processing into plastic raw materials

It is the most widely used recycling technology to process the collected single waste plastics into plastic raw materials. It is mainly used for thermoplastic resin. The recycled plastic raw materials can be used as raw materials for packaging, construction, agricultural and industrial appliances. Different manufacturers in the process of processing technology developed independently, can give the product unique performance.

  1. Processing into plastic products

By using the above technology of processing plastic raw materials, the same or different kinds of waste plastics are directly molded and processed into products. Generally, it is mostly thick wall products, such as plate or bar.

  1. Thermal power utilization

The waste plastics in municipal solid waste are separated and burned to generate steam or generate electricity. The technology has been relatively mature, combustion furnace has rotary furnace, fixed furnace, curing furnace; With the improvement of secondary combustion chamber and the progress of exhaust gas treatment technology, the exhaust gas emission of waste plastic incineration energy recovery system has reached a very high standard. In order to obtain economic benefits, the system of waste plastics incineration to recover heat and electric energy must form scale production.

  1. Fuel

The calorific value of waste plastics 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 crush the waste plastic into fine powder or micro powder, and then mix it into slurry to make fuel. If the waste plastic does not contain chlorine, the fuel can be used in cement kiln, etc.

  1. Heat decomposition to make oil

The oil can be used as fuel or raw material. There are two types of thermal decomposition devices, continuous and intermittent. The decomposition temperature can be divided into 400-500 ℃, 650-700 ℃, 900 ℃ (co decomposition with coal) and 1300-1500 ℃ (partial combustion gasification). The catalytic high-pressure hydride composition technology is also under study.