The recycling value of plastic bags is low. In the process of use, plastic bags are not only scattered in urban streets, tourist areas, water bodies, highways and railways, but also potentially harmful. Plastic has a stable structure, is not easily degraded by natural microorganisms, and does not separate in the natural environment for a long time. This means that if the waste plastic garbage is not recycled, it will become a pollutant in the environment, permanently exist and accumulate, causing great harm to the environment.
First of all, it affects agricultural development. The accumulation of waste plastic products mixed in soil will affect the absorption of nutrients and water by crops, resulting in crop yield reduction.
Second, it poses a threat to the survival of animals. Waste plastic products discarded on land or in water are swallowed by animals as food, resulting in animal death. Last year, there were 20 herders near Qinghai Lake, nearly 1,000 sheep died and the economic loss was more than 300,000 yuan. Sheep like to eat oil residue wrapped in plastic bags, but they often eat together. Because the plastic they eat is difficult to digest in the stomach for a long time, the stomach is crowded, they can't eat any more, and finally they can only starve to death. Such things are common in zoos, pastoral areas, rural areas and oceans.
Thirdly, waste plastics will not only occupy a lot of land with landfill, but also the occupied land will not be restored for a long time, which will affect the sustainable use of land. Waste plastic products entering domestic garbage will not degrade for 200 years if they are buried.
It does great harm to the land, changes its pH value, affects the absorption of nutrients and water by crops, and leads to agriculture.
As for plastic products discarded in water or on land, it will not only affect the environment, but also lead to death if swallowed passively. This destroys the ecological balance.
Fourth, decompose toxic substances at high temperature. Plastic products are not toxic substances, but because of their recyclability.
The equipment used is not perfect, the process is simple, and many manufacturers do not have legal business licenses, which leads to duplication.
When the temperature of plastic products reaches 65℃, toxic substances will precipitate and penetrate into food, causing harm to important parts of human body such as liver, kidney, reproductive system and central nervous system.
I. Classification of plastics
There are many kinds of plastics, so far there are about 300 kinds of plastics put into production in the world. There are many ways to classify plastics, and there are two commonly used methods:
1, according to the different properties of plastics after heating, it can be divided into thermoplastic and thermosetting plastics.
The molecular structure of thermoplastics is linear, which softens or melts when heated, can be shaped into a certain shape, and then hardens after cooling. It becomes soft when heated to a certain extent, and becomes hard after cooling. This process can be repeated many times. Such as polyvinyl chloride, polyethylene, polystyrene, etc. Thermoplastic molding process is relatively simple, can be produced continuously, and has quite high mechanical strength, so it develops rapidly.
The molecular structure of thermosetting plastics is a kind of bulk structure, which can be softened by heating and shaped into a certain shape. However, after heating to a certain extent or adding a small amount of curing agent, it will harden and set, and will not soften and deform after reheating. Thermosetting plastics, such as phenolic plastics, amino plastics, epoxy resins, etc. Can't be recycled after processing and molding. Thermosetting plastics are complicated in molding process and difficult to produce continuously, but they are good in heat resistance, difficult to deform and relatively low in price.
2. According to the different uses of plastics, they can be divided into general plastics and engineering plastics.
General plastics refer to plastics with large output, low price and wide application range, mainly including polyolefin, polyvinyl chloride, polystyrene, phenolic plastics and aminoplastics. Many products used in people's daily life are made of these general plastics.
Engineering plastics can be used as engineering structural materials instead of metals to manufacture machine parts. Such as polyamide, polycarbonate, polyoxymethylene, ABS resin, polytetrafluoroethylene, polyester, polysulfone, polyimide and the like. Engineering plastics have the characteristics of low density, high chemical stability, good mechanical properties, excellent electrical insulation and easy processing and molding. , widely used in automobiles, electrical appliances, chemicals, machinery, instrumentation and other industries, as well as aerospace, rockets, missiles and so on.
Second, the composition of plastic
The plastic we usually use is not a pure substance, it is made of many materials. Polymer (or synthetic resin) is the main component of plastic. In addition, in order to improve the properties of plastics, various auxiliary materials, such as fillers, plasticizers, lubricants, stabilizers, colorants, etc. , must be added to the polymer to become a plastic with good performance.
1, synthetic resin
Synthetic resin is the most important component in plastics, and its content in plastics is generally 40% ~ 100%. Because of its large content and the nature of resin often determines the nature of plastic, people often regard resin as synonymous with plastic. For example, PVC resin and PVC plastic, phenolic resin and phenolic plastic are confused. In fact, resin and plastic are two different concepts. Resin is a kind of raw material polymer, which is not only used to make plastics, but also used as raw material for coatings, adhesives and synthetic fibers. Except a few plastics contain 100% resin, most plastics need to add other substances besides the main component resin.
Step 2 pack
Fillers, also called fillers, can improve the strength and heat resistance of plastics and reduce costs. For example, adding wood flour to phenolic resin can greatly reduce the cost, make phenolic plastic one of the cheapest plastics, and significantly improve the mechanical strength. Fillers can be divided into two categories: organic fillers, such as wood flour, rags, paper and various fabric fibers; Inorganic fillers, such as glass fiber, diatomite, asbestos and carbon black.
3. Plasticizer
Plasticizers can increase the plasticity and softness of plastics, reduce brittleness, and make plastics easy to process and shape. Plasticizer is generally an organic compound with high boiling point, which can be mixed with resin, non-toxic and tasteless, and stable to light and heat. Phthalates are the most commonly used. For example, in the production of PVC plastics, if more plasticizer is added, and if no plasticizer is added or less plasticizer is added (dosage
4. Stabilizer
In order to prevent synthetic resin from being damaged by light and thermal decomposition during processing and use, and to prolong its service life, stabilizers should be added to plastics. Commonly used are stearate and epoxy resin.
5. Colorants
Colorants can make plastics have various bright and beautiful colors. Organic dyes and inorganic pigments are usually used as colorants.
6. Lubricants
The function of lubricant is to prevent the plastic from sticking to the metal mold during molding, and at the same time, it can make the plastic surface smooth and beautiful. Commonly used lubricants include stearic acid and its calcium and magnesium salts.
In addition to the above additives, flame retardants, foaming agents, antistatic agents, etc. can also be added to plastics to meet different use requirements.