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The artificial synthesis of organic polymer materials is one of the major breakthroughs in modern science and technology. In the past, the metals, ceramics and other materials used by people were all natural materials directly taken from nature, or some natural materials were smelted and baked. The artificial synthetic material is a brand-new material created by human beings who get rid of the "gift" of nature and rely on their own wisdom.

Polymer compounds are compounds with very high molecular weight. A molecule often contains hundreds of thousands, tens of millions or even more atoms. These molecules are long and slender chains. The chains are entangled with each other, and the intermolecular attraction is very strong. Polymers have certain strength and elasticity. When the polymer is heated, the long chain is not easy to transfer heat, and there is a softening process before melting, so it has good plasticity, and it also has good electrical insulation. These special properties make polymer materials become modern new high-quality materials.

Organic polymer materials include plastics, rubbers, fibers, liquid crystal materials, etc.

   plastic

Plastics are everywhere in our daily life. Plastic bags, plastic shoes, plastic pots, etc., everything. In industry, plastics are widely used as pipes, casings and mechanical parts. All-plastic cars have also begun to appear in the rushing traffic on the road.

Plastic refers to a type of plastic polymer material with synthetic resin as the main component and some additives added. Plastics are entirely man-made materials, and a piece of natural plastic cannot be found in nature.

Resin is the raw material for producing plastic. Our common rosin is a natural resin. However, synthetic resins are used in the production of plastics, which polymerize low-molecular-weight compounds into high-molecular-weight compounds with thousands of molecular weights through various chemical reactions. Plastics are generally named after the synthetic resins that produce them.

The low molecular weight compounds that can be polymerized are called monomers. Their main components are carbon and hydrogen. Under certain conditions and the action of catalysts, the monomers polymerize into long chains with carbon atoms as the skeleton, which are called polymers.

The formed molecular chain can be a naturally curled linear long chain, or a branched chain composed of a long main chain and a short branched chain, or a structure in which the main chain is cross-linked into a network or body shape by the branched chain. The structure of the chain is different, the properties of the plastic are different, the degree of polymerization is different, the molecular weight of the polymer is different, and the properties of the synthetic resin are very different. Generally, as molecular weight increases, the compound changes from gas, liquid to solid, and increases in strength.

Plastics can be divided into thermoplastics and thermosetting plastics according to their properties. The molecular chains of thermoplastics are linear or branched chains, which generally become soft or viscous when heated, and can be plasticized and formed under heating conditions, and can be repeatedly deformed. The molecular chain of thermosetting plastics is in the form of a network. At the beginning of heating, it has fluidity. If it continues to heat, a chemical reaction will occur to form a network chain. At this time, the raw material is solidified, and it cannot be made plastic by heating.

Plastics can be divided into three categories according to actual use:

General-purpose plastics, these materials have large output, low price and wide uses, accounting for more than 3/4 of plastic output.

It includes five major varieties: polyolefin, polyvinyl chloride, polystyrene, phenolic resin and amino resin.

Engineering plastics, these materials have high strength and can withstand a certain high temperature and low temperature, and can replace metal to manufacture mechanical parts. Such plastics include polycarbonate, polyamide, and polyoxymethylene.

Special plastics with high temperature resistance, high price and low output, are only used in special occasions.

The reason why plastics develop so rapidly and is widely used is inseparable from its excellent performance.

The common advantages of plastics are:

It has good adjustability, and its performance can be changed by various physical and chemical means.

It is light in weight and has great advantages in aircraft and other aspects.

Excellent electrical properties, can be used as a good insulator, can also be made into semiconductors, conductors.

Resistant to general acid and alkali corrosion.

Easy to process and shape.

The surface of the finished product can be sprayed and electroplated with metal.

There are many varieties of plastics, each with its own characteristics, and different varieties can improve their properties by blending, blending, copolymerizing, strengthening and other methods to meet different requirements for use.

(1) The earliest synthetic plastics of ordinary plastics are phenolic resins. In 1907, American chemist Beckland condensed phenol and formaldehyde, and then added fillers such as wood powder. Phenolic resin is brittle, adding wood powder can significantly improve mechanical strength, adding mica powder can improve electrical insulation performance, adding asbestos powder can improve heat resistance. It is often used as a material for electrical products, so it is also called bakelite. Its products are opaque, hard and not afraid of hot water, and do not burn in flames. It is a good material for making many daily necessities.

In 1928, polyvinyl chloride plastic with certain plasticity was obtained by copolymerizing vinyl chloride and vinyl acetate. It has high corrosion resistance, insulation and certain mechanical strength. It is used in industry as corrosion-resistant equipment, such as valves, pipe fittings, etc.; in daily necessities as shoe soles, leather bags, raincoats, etc. Polyvinyl chloride is softened by heat, hardened by cold, and can be reused many times. It is one of the most common thermoplastics.

In 1930, Germany synthesized polystyrene. It has good insulation and is used as a high-frequency insulating part required for TV and radar. It is easy to form, brightly colored, and suitable for beautiful daily necessities.

After 1960, the output of various plastics jumped to the first place is polyolefin, mainly polyethylene and polypropylene. In 1953, the German chemist Ziegler invented the catalytic system of titanium tetrachloride-diethylaluminum, which can produce polyethylene at normal temperature and pressure, reducing the production cost by about 25% and increasing the catalytic efficiency by hundreds of times. , The electrical insulation, softness, corrosion resistance and mechanical strength of the produced products are very good, so they have been widely used. In 1955, Italian chemist Natta improved Ziegler's catalytic system to produce polypropylene plastic. It has good comprehensive performance, abundant raw materials and simple process, so it develops the fastest. It can be used to manufacture auto parts, TV parts and food packaging bags. Ziegler and Natta were awarded the 1963 Nobel Prize in Chemistry for their epoch-making contributions to the development of polymers.

(2) Engineering plastics Engineering plastics account for only about 20% of plastic products. Although the output is not as good as that of plastics, it has good mechanical strength, is easy to manufacture, resists atmospheric corrosion, will not rust, and can withstand high temperatures at a certain temperature, so it is becoming more and more popular. More and more to replace traditional metal materials.

Several varieties of engineering plastics commonly used are:

① Polycarbonate. It is a transparent thermoplastic developed in the 1960s. Its impact toughness is much better than that of plexiglass, and its transparency is 85% to 90% (92% for plexiglass), so it is widely used in the manufacture of windshields and canopies for supersonic aircraft. Because of its good electrical insulation and simple manufacturing process, it is widely used in the manufacture of capacitors.

②Nylon. Nylon is a general term for polyamide resin plastics, which are thermoplastics. Common varieties are nylon 610, nylon 6, nylon 1010, aromatic nylon and cast nylon.

Nylon has excellent wear resistance, oil resistance, high strength and excellent toughness, rigidity, creep resistance, etc. The used nylon material can also be melted and recycled.

In recent years, a large number of nylon materials have been used in the parts of various instruments, televisions, tape recorders, and radios.

Nylon plastics can also be sprayed and electroplated, making the parts more beautiful and durable. The operating temperature of nylon is between -60°C and 100°C.

③Polyoxymethylene engineering plastics. Polyoxymethylene engineering plastics have excellent comprehensive properties, their strength exceeds that of metals such as aluminum and zinc, and their lubrication and wear resistance are comparable to those of nylon. They can be molded by various methods, and are resistant to organic solvents and water. It is widely used as oil pipeline material. It also has unique resilience and can be made into plastic springs, shock-absorbing washers.

④ABS plastic. ABS resin can be obtained by processing styrene, acrylonitrile, butadiene and other raw materials by copolymerization or mixing method, and then processing to obtain ABS plastic. It not only maintains the crystal clear and transparent texture of styrene plastic, but also increases the strength, so it is widely used in the electronics industry. Recently, it is also used as a decorative material for the overall body of a car and the interior of an aircraft.

(3) High temperature-resistant plastics High-temperature-resistant plastics account for less than 5% of the total plastic products. They are cutting-edge products and are a hot topic of research in various countries. It is expected that the temperature of plastic products may reach 1000 ℃ by the end of this century.

High temperature plastics mainly include fluoroplastics, silicone polymers, aromatic heterocyclic plastics, etc.

Fluoroplastics refer to polytetrafluoroethylene, polychlorotrifluoroethylene, etc. PTFE is known as "the king of plastics". It is heat-resistant and cold-resistant. It can be used in the temperature range of -200°C to 250°C. It has good insulation and corrosion resistance. It is resistant to aqua regia and concentrated alkali corrosion. self-lubricating properties. It is often used as a wear-resistant material in the mechanical sector, and is widely used as a sealing material for pumps, valves, and pipe fittings in the chemical industry.

Silicone polymer is a general term for a series of materials such as silicone resin, silicone oil, and silicone rubber made of silicon. After it is polymerized into a polymer material, there are silicon-oxygen bonds in the molecular chain, so it has a polymer In addition to the plasticity, toughness and elasticity, it also has higher heat resistance, rigidity and hardness. Silicone oil is 100% transparent to visible light and can be coated on optical lenses to increase light transmittance and improve photo clarity. After the electric motor is treated with silicone resin, it can increase the horsepower and save 40% of silicon steel per motor. Artificial organs made of silicone polymers are implanted without rejection.

   synthetic rubber

Rubber is a natural polymer material. It is a material obtained by processing the sap of the rubber tree. Human beings have records about rubber balls as early as the 11th century. The main characteristics of rubber are its tensile and compressive elasticity, and thus have important uses in daily life, industry and national defense. A car needs 200 kg of rubber, a tank needs 800 kg of rubber, and a 30,000-ton warship needs 70 tons of rubber. It takes 6 to 8 years for a small rubber tree to tap rubber, and 20 kilograms of raw rubber can be harvested a year from an acre of fertile rubber trees. Natural rubber is far from meeting the demand. Therefore, people turn their attention to synthetic rubber.

In 1912, Germany synthesized methyl rubber for the first time using dimethyl butadiene as the monomer. But it has high cost and poor pressure resistance. In the early 1930s, the United States and the Soviet Union successfully developed sodium butadiene rubber, which has better performance than methyl rubber, but far less than natural rubber. So people intensified the modification experiment of sodium butadiene rubber. In 1937, styrene-butadiene rubber with similar properties to natural rubber was developed. In 1940, neoprene rubber with superior performance than natural rubber was developed. At present, people think that the most promising ones are butadiene rubber, isoprene rubber and ethylene propylene rubber.

Rubber is generally divided into general-purpose rubber and special rubber, but there is no clear boundary between the two.

(1) General-purpose rubber General-purpose rubber mainly refers to rubber used in tire manufacturing and civilian products, and its output accounts for more than 50% of synthetic rubber, mainly including styrene-butadiene rubber, isoprene rubber, ethylene-propylene rubber, and neoprene.

SBR is an old product in general rubber with a history of more than 50 years. It has better wear resistance, aging resistance and oxidation resistance, and has a more uniform texture than natural rubber. It can be mixed with natural rubber in any proportion.

It can be mixed with rubber, and a large amount of filler materials can also be added. After filling with 30% to 70% mineral oil, its cost is reduced by 20% and its life is increased by 20%. It can be used to produce various raincoats, rubber shoes, sponge products, etc.

Butadiene rubber is a fast-growing variety, which can be mixed with oil or a large amount of carbon black. Its performance is better than that of natural rubber, and the tires made of it are more than twice as durable as those made of natural rubber. Butadiene rubber is widely used in the production of V-belts, rubber springs, heat-resistant hoses, shoe soles, etc.

Ethylene-propylene rubber was only introduced in 1960, and its main raw materials are petroleum by-products ethylene and propylene. Its performance is similar to that of natural rubber. Oxidation resistance, aging resistance, good insulation performance, can be used in the range of -68 ℃ ~ 66 ℃, and light color, widely used in the production of cables and civil products.

Neoprene can be made from calcium carbide. Calcium carbide is smelted in an electric furnace with limestone and carbon, and calcium carbide is added with water to form acetylene, which is then polymerized into chloroprene rubber. It has the advantages that natural rubber does not have, such as corrosion resistance, aging resistance, non-flammability, insoluble in organic solvents such as gasoline, and is very valuable in military applications.

(2) Special rubber has high performance requirements as rubber for special purposes. If it needs to withstand high temperatures above 200 °C or low temperatures below -120 °C without changing its performance, or it has the characteristics of high insulation, radiation resistance and vacuum resistance. These aspects are the focus of everyone's attention.

The largest output of special rubber is nitrile rubber, which is produced by the copolymerization of butadiene and acrylonitrile in an aqueous emulsion. It is characterized by good heat resistance and oil resistance, and is mostly used as a material for fuel tanks and oil pipes. When filled with asbestos, it can be used as a car brake pad.

Silicone rubber is a new product. Its molecular chain is not composed of carbon atoms, but the skeleton of the molecule that is alternately connected by silicon atoms and oxygen atoms. It is both heat-resistant and cold-resistant, and can be used for a long time in the temperature range of -100°C to 300°C. It is an indispensable raw material for the aircraft and aerospace industries. It has good insulation and is widely used in the production of high-precision instrument components.

Fluorine rubber is not only resistant to low temperature, but also has good elasticity at low temperature. It is designed by material scientists according to the characteristics of fluoroplastics, which is expensive and low in output, and is only used in the military and aerospace industries.

(3) Liquid latex and adhesives Another common type of rubber products in our life is film products, such as medical gloves, air balloons, airships, raincoats, etc., which are all made of liquid latex.

Liquid latex is a latex that is directly polymerized with rubber monomers. Each synthetic rubber has a corresponding liquid latex, of which styrene-butadiene latex has the largest output. Liquid latex is easy to use. The vulcanizing agent is first added to the latex, and then the latex is coated on the fabric, baked to a certain temperature, and the latex is vulcanized and fixed into a film.

In addition to the production of film and sponge products, synthetic latex is also used in synthetic leather, non-woven fabrics, cold-proof cotton, ship bottom coatings and elastic cement platforms for rocket launches.

Liquid adhesive, also known as liquid rubber, is a low molecular weight polymer widely used to bond various metals, plastics, leather, books, etc.

fiber

Fiber materials include two categories: one is natural fibers, including plant fibers cotton, hemp, etc. and animal fibers, wool, silk, etc.; the other is chemical fibers, including man-made fibers and synthetic fibers.

my country's silk has long been known to the world. Since the 2nd century BC, my country's silk has been exported to Europe, Asia and Africa along the "Silk Road" that traverses Central Asia, which has promoted the development of my country's

exchanges and exchanges around the world. In the Northern Song Dynasty, the famous female textile innovator Huang Daopo improved the textile technology and made cotton spinning.

The weaving industry has developed in our country.

Natural fiber resources are limited. The annual output of lint per mu of fertile land is only about 50 kilograms, and a silkworm cocoon can only draw about 0.5 grams of raw silk. With the continuous increase of the world population, the demand for fibers is also increasing, but a large amount of fertile land cannot be used. To grow mulberry and cotton, because people want to grow grain to eat. The solution to the conflict between grain and cotton is to develop chemical fibers. The modern synthetic fiber industry uses petroleum and natural gas as raw materials, and the products have excellent performance and various patterns, which are deeply loved by consumers.

(1) Man-made fibers Man-made fibers are also called regenerated fibers, which are made of some substances that contain fibers themselves, such as wood, cottonseed linters, cotton stalks, bagasse, etc., or substances containing protein, such as soybeans, peanuts, corn, etc. Made of chemical treatment and a series of mechanical processes. Man-made fibers specifically refer to rayon, rayon, rayon, and the like.

The earliest man-made fiber is viscose fiber, which was processed by people in 1891 with wood, cotton lint, etc. as raw materials. The clothes made of it are comfortable to wear, have good air permeability, but have a large shrinkage rate, and are neither wear-resistant nor light-resistant.

Later, people developed cupro fibers, acetate fibers, etc., but the raw materials of man-made fibers were limited, and the product performance was not very good, so they gradually gave way to the rising star-synthetic fibers.

(2) Synthetic fibers Synthetic fibers are fibers that are chemically treated with substances that do not themselves contain cellulose or protein, such as coal, oil, natural gas, water, air, salt, limestone, etc. Synthetic fibers belong to the same polymer compound as rubber and plastic. The differences are as follows:

Most of the resins used as fibers are linear molecular chains with no or few branched chains.

This kind of resin can be dissolved in solvent and drawn into silk, or can be heated and melted to draw silk, but its structure is not destroyed when heated. The intermolecular cohesion of this type of resin is the largest among all polymers.

The first step in the production of synthetic fibers is spinning. The key to the spinning process is the spinneret, which is generally made of materials that are resistant to high temperature and wear. There are dozens to tens of thousands of diameters drilled on a spinneret

0.04～1mm hole. The molten fibers are ejected from the small holes and cooled to obtain very fine filaments, and the drawn filaments can be used to produce various products after being drawn and heat-set.

Synthetic fibers have a series of excellent properties that natural fibers do not have. It has high strength, wear resistance, insect resistance, light specific gravity, good warmth retention, and is generally resistant to acid and alkali corrosion.

Synthetic fibers are mainly composed of six major fibers:

①Polyamide fiber. In my country, it is called Nylon, which is the earliest synthetic fiber on the market. The main varieties are nylon 66, nylon 6, nylon 610 and so on. In 1940, the first batch of nylon stockings was launched, which shook the textile market. Nylon fiber is wear-resistant, strong, and has good resilience, but poor heat and light resistance. Nylon is mostly used to make socks, shirts, etc. It is industrially used as a cord and insulating material for heavy-duty automobile and aircraft tires, and is also used in the manufacture of cables, fishing nets, parachutes, high-grade carpets, etc.

②Polyester fiber. Also known as polyester (really good) in my country, it was synthesized in the United Kingdom as early as 1940, but industrial production was not realized until 1946. Polyester fiber has high strength and wear resistance, and the clothes made after blending are durable, wrinkle-resistant and easy to wash, so it has developed rapidly. By the early 1970s, the output ranked first in synthetic fibers.

③ Polyacrylonitrile fiber. In my country, it is also known as acrylic fiber and synthetic wool. It came out in 1950. It has good light resistance, heat preservation and elasticity, soft hand feeling, higher strength than wool, lower price than wool, not afraid of moths, sun-resistant and washable, suitable for making clothing materials, knitted outerwear , blankets, industrial fabrics, etc.

④Polyvinyl alcohol fiber. Also known as vinylon in my country, its performance is similar to that of cotton fiber, and its wear resistance is stronger than that of cotton fiber. It is the most absorbent of synthetic fibers, but has poor heat resistance and elasticity.

⑤Polypropylene fiber. Also known as polypropylene, it has a small specific gravity, high strength and light resistance.

⑥ PVC fiber. Also known as polyvinyl chloride, it has strong chemical resistance, good warmth retention, and is difficult to burn.

Synthetic fibers are mainly used in consumer goods, but some are also used in engineering technology. Aerospace, metallurgy, chemical industry and other departments require not only excellent comprehensive properties of fibers, but also high temperature resistance and strong corrosion resistance.

The emergence of synthetic fibers just filled this gap. After years of research, people have achieved a lot of results.

Aramid-1313 fiber can be used for a long time at 200℃, and its strength is twice that of strong nylon.

It was first used in the manufacture of space suits, and was also widely used as mountaineering rigging, high temperature filter bags, aircraft tire cords, etc.

Aramid-1414 fiber can be used for a long time at 290℃, and decompose at 560℃. Its strength is the champion among synthetic fibers, and its breaking strength is three times that of nylon. A fiber rope as thick as a finger can lift two Jiefang cars. Therefore, it is often used as a reinforcing fiber for composite materials, and is especially suitable for the production of radomes for aircraft and missiles.

Polyimide fiber can be used in the ultra-low temperature of -273℃, and can also work normally in the high temperature of 400℃, and can withstand the drastic changes of cold and heat without affecting the strength.

The fluorine fiber made by spinning polyvinyl fluoride can resist the corrosion of aqua regia. It can be used in the temperature range of -160 ℃ ~ 280 ℃, and it is very suitable to use its reinforced composite material as a self-lubricating bearing in aircraft.

(3) Synthetic leather and synthetic paper From the perspective of microstructure, both leather and paper belong to a flat fiber interwoven fabric. Leather fibers are strong collagen fibers that form a strong network structure through the action of tanning agents. The fibers of paper are plant fibers. During the papermaking process, these plant fibers are entangled with each other to form a network structure.

Synthetic leather is a resin film made by coating resin on a substrate cloth. But it has no micro-pores, does not perspirate, and is uncomfortable to wear. Later, people added polyurethane to the synthetic leather, and the polyurethane will produce micro pores during the solidification process. This synthetic leather has the same breathability as natural leather, but is much more durable than natural leather, and is popular because it can be upholstered in a variety of genuine leather finishes.

The strength of ordinary paper is generally not high, and it is easy to be eaten by insects, and it is not resistant to acid and alkali. People use man-made fibers as raw materials to make polymeric films, and then through the paper process, you can get synthetic paper. At present, there are tracing paper for tracing, coated paper for printing plates, and advertising paper that is not afraid of the sun and rain. The military maps and waterproof charts produced with this paper are resistant to folding and wrinkling, and are not afraid of water, and are very useful in the battlefield. convenient. If synthetic fiber is used as raw material, synthetic fiber paper can be made according to the traditional papermaking method. It has high strength, corrosion resistance, tear resistance, mildew resistance, and can be used as battery separator paper, which can not only improve battery life, but also improve battery performance.