Plastic-based monomers as the raw material, by polyaddition or polycondensation reaction of polymerization of the polymer compound (Macromolecules), only moderate deformation resistance, between the fibers and rubber between the synthetic resin and the filler, plasticizer, stabilizer It is composed of additives such as agents, lubricants and colorants. plastic pollution
The main component of plastic is resin. Resin and various additives that have not yet mixed with a polymer compound. The term resin was originally named after the lipids secreted by plants and animals, such as rosin and shellac.
Resin accounts for about 40% to 100% of the total weight of the plastic. The basic properties of plastics are mainly determined by the nature of the resin, but additives also play an important role. Some plastics are basically composed of synthetic resins, with or without additives, such as plexiglass, polystyrene, and the like.
The plastic raw material is defined as a synthetic or natural high molecular polymer which can be kneaded into various shapes to finally maintain the shape of the material or plastic material.
Plastic is an important organic synthetic polymer material and is widely used. However, the “white pollution” caused by waste plastics is becoming more and more serious.
If we can understand the composition and classification of plastics in detail, it will not only help us scientifically use plastic products, but also facilitate the classification and recycling of plastics, and effectively control and reduce “White pollution“. Plastic Pollution
Most plastics are light, chemically stable and will not rust,
Good impact resistance.
Has good transparency and wear resistance.
Good insulation and low thermal conductivity.
Generally, the moldability and colorability are good, and the processing cost is low.
Most plastics have poor heat resistance, large thermal expansion rate, and are easy to burn.
Poor dimensional stability, easy to deform.
Most plastics have poor low-temperature resistance, become brittle at low temperatures, and are prone to aging.
Some plastics are readily soluble in solvents.
Plastics can be distinguished between thermoset and thermoplastic. The former cannot be reshaped and the latter can be reproduced.
The physical elongation of thermoplasticity is relatively large, generally ranging from 50% to 500%. The force does not change completely linearly at different elongations. Plastic Pollution
The different properties of plastics determine their use in the industry. With the advancement of technology, plastic modification has not stopped research.
It is hoped that in the near future, plastics can be modified to have a wider range of applications, and even replace steel and other materials and no longer pollute the environment.
There are basically two types: the first one is a linear structure, the polymer compound having such a structure is called a linear polymer compound, the second is a bulk structure, and the polymer compound having such a structure is called a bulk polymer.
Some polymers have a branched chain called a branched polymer, which is a linear structure. Some polymers have to cross-link between molecules, but cross-linking is less. It is called a network structure and belongs to a body structure. Plastic Pollution
Two different structures exhibit two opposite properties. Linear structure, heating can be melted, hardness and brittleness are small.
The body structure has a large hardness and brittleness. Plastics are made of two kinds of polymers. Thermoplastics are made of linear polymers, and thermosets are made of bulk polymers.
<1> Chemical resistance
<2> Glossy, partially transparent or translucent
<3> Most of them are good insulators
<4> Light and strong
<5> Easy processing, mass production, and low price
<6> Wide range of uses, many effects, easy coloring, and partial high-temperature resistance
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- Most plastics have strong corrosion resistance and do not react with acids and bases.
- Plastic manufacturing costs are low.
- Durable, waterproof and lightweight.
- Easy to be molded into different shapes.
- It is a good insulator.
- Plastics can be used to prepare fuel oils and fuel gases, which can reduce crude oil consumption.
When recycling used plastics, classification is very difficult and economically uneconomical.
Plastics are easy to burn and produce toxic gases when burned. For example, when polystyrene is burned, toluene is produced.
A small amount of this substance may cause blindness, inhalation, and vomiting, etc. PVC combustion may also produce hydrogen chloride toxic gas.
In addition to burning, it is a high-temperature environment, which may cause the plastic to decompose toxic components, such as benzene.
Plastics are made from petroleum refined products, and petroleum resources are limited.
Plastics buried under the ground for hundreds of years, thousands of years or even tens of thousands of years will not rot.
The heat resistance of plastics is poor and easy to age.
Due to the inability of plastics to degrade naturally, it has become the number one enemy of mankind and has also led to the tragedy of many animal deaths.
For example, monkeys, baboons, dolphins and other animals in the zoo will accidentally swallow the No. 1 plastic bottle that the tourists left behind.
They will die in pain because they are not digested. Looking at the beautiful and pure sea, they will look closer, but they are full. Plastic Pollution
A variety of plastic garbage that cannot be contained in the ocean and a variety of plastics that cannot be digested have been found in the intestines of many dead seabird samples.
Plastic Pollution: World Problem
The pollution of plastic waste produced by the petrochemical industry is a global environmental problem. Most plastics are discarded after they are used in one-off use.
So far, the academic community believes that plastic products will not be decomposed due to their stable physical and chemical structure and may be tens to hundreds of years in the natural environment.
Professor Yang Jun introduced that in 2013, global consumption of 299 million tons of plastics, of which polystyrene plastics accounted for 7%, consumes about 21 million tons per year.
Common plastic lunch boxes, coffee cups and other materials that can withstand boiling water temperature are polystyrenes. Authoritative surveys have shown that polystyrene is only degraded in the range of 0.01%-3% in soil, sludge, rot waste, or manure microbial communities for 4 months.
Every year, 40 million tons of waste plastics are accumulated in the environment. About 2 million tons of discarded plastics are thrown into the environment every year in China.
Taking farmland agricultural film as an example, the annual output of agricultural film in China is up to one million tons, and it is increasing at a rate of 10% per year. Plastic Pollution
No matter what kind of crop is covered, all the coated soil has residual film. According to statistics, the annual residual amount of agricultural film in China is as high as 350,000 tons, and the residual film rate is 42%.
A large amount of residual film remains in the farmland layer of 0-30 cm in farmland. That is to say, nearly half of the agricultural film remains in the soil, which is a great hidden danger in food safety.
“Plastic is completely assimilated by microorganisms in the soil, degraded into CO2 and water to achieve inorganic mineralization, which may take 200-400 years, resulting in accumulation in the environment.” Professor Yang Jun told the Yangcheng Evening News reporter.
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Physical and chemical classification
According to the different physical and chemical properties of various plastics, plastics can be divided into two types: thermosetting plastics and thermoplastics.
Thermoplastics: refers to plastics that melt after heating, can flow to the mold after cooling, and then melt after heating; then use heating and cooling to make a reversible change (liquid-solid state), The so-called physical change.
General-purpose thermoplastics have a continuous use temperature below 100 ° C. Polyethylene, polyvinyl chloride, polypropylene, and polystyrene are called four general-purpose plastics.
Thermoplastic plastics are also classified into hydrocarbons, vinyl containing polar genes, engineering, and cellulose. It becomes soft when heated, hardens when cooled, and can be softened and hardened repeatedly to maintain a certain shape. Plastic Pollution
It is soluble in certain solvents and has meltable and soluble properties. Thermoplastics have excellent electrical insulation properties, in particular, polytetrafluoroethylene (PTFE), polystyrene (PS), polyethylene (PE), polypropylene (PP) having a low dielectric constant and dielectric loss, should Use as high frequency and high voltage insulation materials.
Thermoplastics are easy to shape, but have low heat resistance and are prone to creep. The degree of creep varies with load, ambient temperature, solvent, and humidity.
In order to overcome these weaknesses of thermoplastics and meet the needs of applications in space technology, new energy development, etc. countries are developing melt-formable heat-resistant resins such as polyetheretherketone (PEEK) and polyethersulfone (PES), polyaryl sulfone (PASU), polyphenylene sulfide (PPS), and the like.
The composite materials using them as matrix resins have high mechanical properties and chemical resistance, can be thermoformed and welded, and the interlaminar shear strength better than epoxy resin.
If polyetheretherketone is used as a matrix resin and a carbon fiber composite material, the fatigue resistance exceeds that of epoxy/carbon fiber.
It has good impact resistance, good creep resistance at room temperature, good processability, continuous use at 240 ~ 270 ° C, is an ideal high-temperature resistant insulation material.
The composite material made of polyethersulfone as matrix resin and carbon fiber has high strength and hardness at 200 ° C, and can maintain good impact resistance at -100 ° C, non-toxic, non-combustible, least smoke, radiation resistance Well, it is expected to be used as a key component of the spacecraft, and it can be molded into a radome . Plastic Pollution
Formaldehyde cross-linking plastics include phenolic plastics, aminoplasts (such as urea-formaldehyde- melamine -formaldehyde, etc.).
Other crosslinked plastics include unsaturated polyesters, epoxy resins, phthalyl acrylate resins, and the like.
(2) Thermosetting plastics
Thermosetting plastics are plastics that cure or have insoluble (melting) properties under heat or other conditions, such as phenolic plastics, epoxy plastics, and the like.
Thermosetting plastics are divided into two types: formaldehyde cross-linking type and another cross-linking type. After hot working, a cured product having infusibility and insolubilization is formed, and the resin molecules thereof are crosslinked into a network structure by a linear structure.
If you strengthen the heat, it will break down and destroy. Typical thermosetting plastics are phenolic, epoxy, amino, unsaturated polyester, furan, polysiloxane, and newer polystyrene polyphthalate plastics.
They have the advantages of high heat resistance, heat deformation and the like. The disadvantage is that the mechanical strength is generally not high, but the mechanical strength can be improved by adding a filler to form a laminate or a molded material.
Thermosetting plastics made of phenolic resin as the main raw material, such as phenolic molded plastic (commonly known as Bakelite), are characterized by being durable, dimensionally stable, and resistant to other chemicals other than strong alkali.
Various fillers and additives can be added depending on the application and requirements. For varieties requiring high insulation properties, mica or glass fiber can be used as the filler; for heat-resistant varieties, asbestos or other heat-resistant fillers can be used; for earthquake-resistant varieties, various suitable fibers or rubber can be used as fillers. Plastic Pollution
And some toughening agents to make high toughness materials. In addition, modified phenolic resins such as aniline, epoxy, polyvinyl chloride, polyamide, polyvinyl acetal can also be used to meet the requirements of different applications.
The phenolic resin can also be made into a phenolic laminate, which is characterized by high mechanical strength, good electrical properties, corrosion resistance, and easy processing, and is widely used in low-voltage electrical equipment.
The aminoplast are urea formaldehyde, melamine formaldehyde, urea melamine formaldehyde and the like. They have the advantages of hard texture, scratch resistance, colorlessness, translucency, etc.
The coloring materials can be made into brightly colored products, commonly known as electric jade. Because it is resistant to oil and is not affected by weak bases and organic solvents (but not acid resistant), it can be used at 70 ° C for a long time and can withstand 110 ~ 120 ° C for a short period of time.
It can be used in electrical products. Melamine formaldehyde plastic has higher hardness than urea formaldehyde plastic, has better water resistance, heat resistance and arc resistance, and can be used as arc-resistant insulation material.
There are many kinds of thermosetting plastics made of epoxy resin as the main raw material, and about 90% of them are based on bisphenol A epoxy resin. It has excellent adhesiveness, electrical insulation, heat resistance and chemical stability, small shrinkage and water absorption, and good mechanical strength.
Both unsaturated polyester and epoxy resin can be made into FRP with excellent mechanical strength. For example, FRP with unsaturated polyester has good mechanical properties and low density (only 1/5 to 1/4 of steel and 1/2 of aluminum), which is easy to process into various electrical parts.
Plastics made from dipropylene phthalate resins are superior to phenolic and amino thermosets in electrical and mechanical properties. It has low hygroscopicity, stable product size, good molding performance, acid and alkali resistance, boiling water and some organic solvents.
Molding compounds are suitable for the manufacture of structurally complex parts that are both temperature resistant and highly insulating. It can be used for a long time in the temperature range of -60 to 180 °C, and the heat resistance grade can reach F grade to H grade, which is higher than the heat resistance of phenolic and aminoplast.
Silicone plastics in the form of polysiloxane structures are widely used in electronics and electrical engineering. The silicone laminated plastic multi-glass cloth as a reinforcing material, a silicone molded plastic over glass fiber and asbestos as filler for the manufacture of high temperature, high or submersible motors, appliances, electronic equipment parts and the like.
This type of plastic is characterized by a small dielectric constant and tg δ value is less affected by frequency, and is resistant to corona and arc in the electrical and electronic industries. Even if the discharge causes decomposition, the product is silica rather than conductive carbon black.
These materials have outstanding heat resistance and can be used continuously at 250 °C. The main disadvantages of polysiloxanes are low mechanical strength, low tackiness, and poor oil resistance. Plastic Pollution
Many modified silicone polymers have been developed, such as polyester modified silicone plastics, which are used in electrical engineering. Some plastics are both thermoplastic and thermoset plastics.
For example, polyvinyl chloride, generally thermoplastic, Japan has developed a new type of liquid polyvinyl chloride is thermosetting, molding temperature is 60 ~ 140 ° C; the United States a plastic called Lundex, both thermoplastic processing Features, but also the physical properties of thermoset plastics.
1 hydrocarbon plastic. It is a non-polar plastic, which has crystallinity and non-crystallinity. The crystalline hydrocarbon plastics include polyethylene, polypropylene, etc., and the non-crystalline hydrocarbon plastics include polyphenylene.
2 vinyl-based plastics containing polar genes. Most of the fluorine-containing plastics are amorphous transparent bodies, including polyvinyl chloride, polytetrafluoroethylene, polyvinyl acetate and the like. Most of the vinyl monomers can be polymerized using a free radical catalyst.
3 thermoplastic engineering plastics. It mainly includes polyoxymethylene, polyamide, polycarbonate, ABS, polyphenylene ether, polyethylene terephthalate, polysulfone, polyethersulfone, polyimide, polyphenylene sulfide and the like. Polytetrafluoroethylene. Modified polypropylene and the like are also included in this range.
4 thermoplastic cellulose plastics. It mainly includes cellulose acetate, cellulose acetate butyrate, sputum, cellophane and so on.
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