In the world, polymer products are the youngest materials. They are not only used in various industrial fields, but also have entered all families, and their output tends to exceed that of metal materials, which will be the most active material pillar in 2 1 century. Polymer materials can be seen everywhere around us. In our understanding, polymer materials are materials based on polymer compounds. Polymer materials are classified into rubber, fiber, plastic, polymer adhesive, polymer coating and polymer-based composite materials according to their characteristics. Today I want to study the characteristics, advantages and disadvantages of various polymer materials as the main line.
From the chemical knowledge we have learned before, we can know that polymer materials are actually organic compounds, and organic compounds are compounds of carbon. In addition to carbon atoms, other elements are mainly hydrogen, oxygen, nitrogen and so on. Stable structures can be formed between carbon atoms and between carbon atoms and atoms of other elements. Carbon atoms are tetravalent, and each monovalent bond can connect a hydrogen atom. Therefore, a large number of organic compounds with different structures can be formed. The total number of organic compounds is close to10 million, far exceeding the sum of other elemental compounds, and new organic compounds are constantly being synthesized. Thus, due to the formation of different special structures, organic compounds have unique functions. Some organic structures (also called functional groups) can be substituted in the polymer. In order to change the characteristics of polymers. The molecular weight of polymers is huge, reaching at least 10,000, or millions to millions, so people call them polymers, macromolecules or polymers. Polymer materials include three kinds of synthetic materials, namely plastic, synthetic fiber and synthetic rubber (called resin before processing).
1. rubber
Rubber is a linear flexible polymer. Rubber is an elastic hydrocarbon isoprene polymerization, which exists in the form of emulsion when it is unprocessed. Rubber emulsion can be obtained from the juice of some plants, or it can be artificial. It is also one of the most common polymer materials. The valence between molecular chains is small, and molecular chains are flexible. Under the action of external force, great deformation can occur, and it can be restored to its original state quickly after removing external force. Rubber is a completely amorphous polymer with low glass transition temperature (T g) and high molecular weight, exceeding several hundred thousand. Because the molecular chain of rubber can be crosslinked, crosslinked rubber has the ability of rapid recovery and good physical and mechanical properties and chemical stability when it is deformed by external force. Therefore, rubber is the basic raw material of rubber industry, which is widely used to manufacture rubber products such as tires, hoses, tapes and cables.
Rubber is divided into natural rubber and synthetic rubber according to raw materials.
From the structure of rubber, it is not difficult to find that the general structure of unvulcanized rubber is analyzed from the linear structure. Because of its large molecular weight, it is fine spherical without external force. When external force is applied and removed, the entanglement degree of fine particles changes, and the molecular chain rebounds, resulting in a strong recovery tendency, which is the origin of rubber's high elasticity.
Rubber has good comprehensive properties and is widely used. Mainly includes: ① natural rubber. Made of rubber latex with three leaves, it has good elasticity, high strength and comprehensive performance. ② Isoprene rubber. The full name is cis-1, 4- polyisoprene rubber, which is a high cis-synthetic rubber made of isoprene. Because its structure and performance are similar to natural rubber, it is also called synthetic natural rubber. ③ Styrene-butadiene rubber. Short for SBR, it has good comprehensive properties and chemical stability. ④ Butadiene rubber. Compared with other general rubber, vulcanized cis-polybutadiene rubber has excellent cold resistance, wear resistance and elasticity, less heat generation under dynamic load and good aging resistance, and is easy to be used with natural rubber, chloroprene rubber and nitrile rubber.
Then we will introduce special rubber. Special rubber refers to rubber with some special properties. Mainly includes: ① chloroprene rubber. CR for short is polymerized from chloroprene. It has good comprehensive properties, such as oil resistance, flame retardancy, oxidation resistance and ozone resistance. However, it has high density, easy crystallization and hardening at room temperature, poor storage and poor cold resistance. ② Nitrile rubber. NBR for short is polymerized from butadiene and acrylonitrile. Good oil resistance and aging resistance, and can be used in air at 120℃ or oil at 150℃ for a long time. In addition, it also has water resistance, air tightness and excellent bonding performance. ③ Silicone rubber. The main chain consists of silicon atoms and oxygen atoms alternately, and the silicon atoms have organic groups. High and low temperature resistance, ozone resistance and good electrical insulation. (4) fluororubber. Synthetic rubber with fluorine atoms in its molecular structure. It is usually expressed by the number of fluorine atoms of fluorine-containing units in * * * polymers, such as fluororubber 23, which is a * * * polymer of vinylidene fluoride and chlorotrifluoroethylene. Fluorine rubber is resistant to high temperature, oil and chemical corrosion. (5) polysulfide rubber. It is formed by condensation polymerization of dihalides of alkali metals or alkaline earth metals and polysulfides. It has excellent oil resistance and solvent resistance, but its strength is not high, its aging resistance and processability are not good, and its smell is unpleasant. It is mainly used with nitrile rubber. In addition, there are polyurethane rubber, chlorohydrin rubber, acrylate rubber and so on.
2. Plastic
As we all know, plastic can be used anywhere because of its portability and cheapness. Let's take a look at the characteristics and uses of plastics.
Plastic is a synthetic polymer compound, which can change its shape freely. Plastic is a substance polymerized from monomer raw materials through synthesis or condensation reaction, and is composed of synthetic resin, filler, plasticizer, stabilizer, lubricant, pigment and other additives. Its main component is synthetic resin.
The broad definition of plastics refers to materials with plastic behavior. The so-called plasticity refers to the deformation when an external force is applied, and it can still maintain its state when the external force is cancelled. The elastic modulus of plastic is between rubber and fiber, and it can be deformed to some extent when stressed. Soft plastic is close to rubber, and hard plastic is close to fiber. In a narrow sense, plastic is defined as a material with resin (or directly polymerized with monomer during processing) as the main component and additives such as plasticizer, filler, lubricant and colorant as the auxiliary components, which can flow and form during processing.
Compared with other materials, plastics have the following characteristics.
Chemical corrosion resistance
< 2 > shiny, partially transparent or translucent.
< 3 > most of them are good insulators.
< 4 > light and strong
(5) Easy processing, mass production and low price.
↓6↓ It has a wide range of uses, diverse functions, easy coloring and local high temperature resistance.
Plastics are divided into general-purpose plastics and engineering plastics, which are mainly defined by the universality of use. For example, PE and PP are cheap and can be produced on many different types of machines. Engineering plastics are more expensive, but the stability and physical properties of raw materials are much better. Generally speaking, they have both rigidity and toughness.
Most plastics have strong corrosion resistance and do not react with acid and alkali. Plastic manufacturing cost is low. Durable, waterproof, lightweight, easy to shape into different shapes. It is a good insulator. Plastics can be used to prepare fuel oil and gas, which can reduce the consumption of crude oil.
However, it also has many disadvantages, for example, when recycling waste plastics, it is difficult to classify and uneconomical. Plastic is easy to burn, and when it burns, it will produce toxic gases. Plastics are products extracted from petroleum, and petroleum resources are limited.
According to the different physical and chemical characteristics of various plastics, plastics can be divided into thermosetting plastics and thermoplastic plastics.
Plastic molding refers to the process of making final plastic products from polymers produced by synthetic resin manufacturers. Processing methods (usually referring to one-time processing of plastics) include compression molding (compression molding), extrusion molding (extrusion molding), injection molding (injection molding), blow molding (hollow molding), calendering and so on.
After long-term struggle and opening to the outside world, China plastics industry has formed a relatively complete industrial system and become a basic material industry that keeps pace with steel, cement and wood. As a new material, its application field has far exceeded the above three materials. Since the beginning of 2 1 century, China plastics industry has made remarkable achievements and achieved a historic leap. As one of the pillar industries of light industry, the plastic industry has maintained a growth rate of more than 10% in recent years. While maintaining a rapid development speed, its economic benefits have also been improved. The total output value of enterprises above designated size in plastic products industry ranks third in light industry 19, and the product sales rate is 97.8%, which is higher than the average level of light industry. From the production of synthetic resin, plastic machinery and plastic products, the development of plastic industry in China is strong.
The development of plastic technology is changing with each passing day. Developing new materials with brand-new applications, improving the performance of existing materials market and improving the performance of special applications are several important directions of new material development and application innovation.
1 is a new type of bioplastics with high thermal conductivity. This bioplastic not only has good thermal conductivity, but also has the advantages of light weight, easy molding and little environmental pollution. It can be used to produce light and thin frames for computers, mobile phones and other electronic products.
Color-changing plastic film combines natural optical effect and artificial optical effect, which is actually a new method to make objects change color accurately.
3 plastic blood, researchers at the University of Sheffield in the United Kingdom have developed an artificial "plastic blood" that looks like a sticky paste. As long as it is soluble in water, it can be given to patients and used as a blood substitute in the first aid process.
New bullet-proof plastic, this new material will be temporarily deformed after being hit by bullets, but it will soon return to its original state and can continue to be used. In addition, this new material can evenly distribute the impact of bullets, thus reducing the harm to human body.
Plastic that can reduce car noise. This material is mainly used for automobile body and wheel well liner, producing barrier layer, which can absorb the sound in the cabin and reduce the noise by 25%~30%.
With the continuous exploration of science and technology and the continuous development of material research, it is believed that more and more new plastic products will come out, and then they will be able to better benefit mankind.
3. fiber
Fiber: After a certain mechanical processing (drawing, stretching, setting, etc.), the polymer forms thin and soft filaments. ) to form fibers. Fiber has the characteristics of large elastic modulus, small deformation, high strength, strong crystallization ability and small molecular weight, generally tens of thousands.
Fibers are generally divided into natural fibers, man-made fibers and synthetic fibers.
Natural fibers refer to fibers grown or formed in nature, including plant fibers (natural cellulose fibers), animal fibers (natural protein fibers) and mineral fibers.
Man-made fiber is a kind of fiber that can be used for textile like cotton, wool and silk. It is made of natural polymer compound-cellulose or protein as raw materials (such as wood, cotton wool, straw, bagasse and other fibers or protein such as milk, soybeans and peanuts) through a series of chemical treatments and mechanical processing. Such as rayon, rayon, etc.
The chemical composition of synthetic fiber is completely different from that of natural fiber. It is an organic substance extracted from petroleum, coal, natural gas, limestone, agricultural and sideline products and other substances that do not contain cellulose or protein, and then made into fibers through chemical synthesis and mechanical processing. Such as polyester, nylon, acrylic fiber, polypropylene fiber and chlorine fiber.
Fiber is a natural or synthetic filamentous substance. In modern life, the application of optical fiber is everywhere, involving many high technologies. Missiles need to be protected from high temperature, dams need to be protected from collapse, cement needs to be protected from cracking, and blood vessels and nerves need to be repaired, all of which are inseparable from the "recreation" of fibers.
Comfortable clothes, cold protection and sun protection are our initial requirements for clothes, and now this requirement is easy to achieve. Clothing made of seaweed carbon fiber can make human molecules rub for a long time to generate thermal reaction and promote blood circulation, so it can store heat and keep warm. Clothes made of anti-ultraviolet fiber can reduce the trouble of holding umbrellas in summer.
The greater role of fiber has long been more than just daily wear. Viscose-based carbon fiber helps missiles put on "heat protection clothes" and can withstand tens of thousands of degrees of high temperature; Inorganic ceramic fibers have good oxidation resistance, high chemical stability, corrosion resistance and electrical insulation, and are used in aerospace and military fields. Polyimide fiber can be used as high-temperature fire protection clothing, racing fire protection clothing, armored protective clothing and flight clothing; Carbon nanotubes can be used as electromagnetic wave absorbing materials, and can be used to make invisible materials, electromagnetic shielding materials, electromagnetic radiation pollution protection materials and "darkroom" (wave absorbing) materials.
Fiber is also a good helper for environmental protection. Polylactic acid, as a completely biodegradable plastic, has attracted more and more attention. Polylactic acid can be made into agricultural film, paper substitute, paper plastic film, packaging film, food container, domestic garbage bag, pesticide and fertilizer slow-release material, cosmetic additive and so on.
Fiber has been widely used in medicine. Medical textiles made of chitin fiber have antibacterial, deodorizing, anti-inflammatory, antipruritic, moisturizing and anti-drying, skin care and other functions, so they can be made into various hemostatic cotton, bandages, gauze, etc., which are naturally degraded after being discarded and do not pollute the environment. Polyacrylamide hydrogel can control drug release; Surgical suture made of polylactic acid or chitosan fiber will automatically degrade and absorb after wound healing, so patients do not need surgery to remove the suture.
In the field of architecture, anti-seepage and anti-crack fibers can enhance the strength and anti-seepage performance of concrete. Combining fiber technology with concrete technology to develop polypropylene fiber can improve the performance of concrete and the quality of civil engineering. It can exert crack resistance, impermeability, impact resistance and bending resistance for dams, airports, highways and other projects, and has been used in large-scale projects such as the National Grand Theatre, the roof apron of the command center of Shanghai Public Security Bureau, and the hongkou football stadium of Shanghai.
With the development of biotechnology, the characteristics of some fibers can come in handy. Muscle-like fibers can be made into "artificial muscles" and "human organs". Polyacrylamide is biocompatible and has always been a good substitute for human tissues. Polyacrylamide hydrogel can contract and expand regularly, which can simulate the movement of human muscles.
Collagen is the most common protein in human body, which exists in heart, eyeball, blood vessels, skin, cartilage and bones, and provides strength support for these human tissues. Synthetic nanofibers can form a gel similar to colloid at the fracture site, guide bone minerals to form a structural arrangement similar to natural bone around collagen fibers, and repair bones invisibly.
Spider silk has always been imitated and made by human beings. The diameter of natural spider silk is about 4 microns, its traction strength is five times that of steel, and it also has excellent waterproof and telescopic function. If we make an artificial spider silk with the characteristics of natural spider silk, it will have a wide range of uses. It can be used not only as an ideal material for parachutes and car seat belts, but also as a surgical suture that can be easily absorbed by the human body.
Fiber filling can effectively improve the strength and stiffness of plastics. Fiber reinforced plastics are rigid structural materials.
Fiber reinforced plastics have two main components. The matrix is thermosetting plastic or thermoplastic plastic, and is filled with fiber materials. Generally, the strength of the matrix is low, while the fiber filler has high rigidity but is fragile. In the reinforced plastic obtained by compounding the two, the fiber bears great load stress, and the matrix resin supports the fiber to transmit external load through the shear stress at the interface with the fiber.
The use of glass fiber is dominant in reinforced plastics, and there are many varieties. Alkali-free glass (E-glass) is a kind of common fiber with low alkali metal oxide content, which has excellent chemical stability and electrical insulation. High strength glass fiber (S glass) contains magnesium aluminum silicate and other components, and its strength is higher than that of E glass fiber 10%-50%. Due to the difference in chemical composition and production technology, there are various glass fibers with high modulus, medium alkali and high alkali. Carbon fiber has great rigidity and excellent corrosion resistance, and is often used to reinforce thermosetting plastics.
At present, the international research on organic polymer materials is constantly strengthening and deepening. On the one hand, the important general organic polymer materials are constantly improved and popularized, so that their properties are constantly improved and their application scope is constantly expanded. For example, plastics are usually used as insulating materials, but in recent years, in order to meet the needs of the electronic industry, conductive plastics with excellent conductivity have been developed. Conductive plastics have been used to make batteries, etc. It is expected to be widely used in industry. On the other hand, the research on special functional materials closely related to human beings is also constantly strengthened, and some progress has been made, such as bionic polymer materials and polymer intelligent materials. This kind of polymer material shows potential application prospects in aerospace, architecture, robotics, bionics and medicine. In a word, the application scope of organic polymer materials is gradually expanding, and polymer materials will have an increasing impact on people's production and life.
References: material net, new organic polymer materials, composite materials magazine, medical polymer materials, rubber reference materials, plastic processing applications, physical chemistry, Baidu Encyclopedia, high-performance fibers.
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