From 1930s to 1950s, the plastics industry developed vigorously, and some commonly used plastics such as PVC, polystyrene, polyethylene and polypropylene were industrialized one after another.
The monomer ethylene CH2=CH2 of polyethylene was prepared by Dutch chemists as early as the end of 18. In the 1920s and 1930s, petroleum cracking appeared and ethylene was produced in large quantities.
Polymerizing ethylene gas into solid polyethylene and transforming thousands of simple molecules into connected macromolecules is a kind of chemical magic, which is the result of chemists' research on the influence of high pressure on chemical reactions.
At the beginning of the 20th century, after the successful application of high-pressure synthetic ammonia and oil hydrogenation, chemists became interested in the study of using high pressure in chemical reactions. A. Mitchill, a Dutch chemistry professor, tried to trial-produce organic dyes at 3000 atmospheres, and later increased it to 20000 atmospheres. 193 1 year, British Imperial Chemical Industry Company designed a device to study the reaction effect of binary and ternary organic systems at 3000 atmospheres. Chemists E.W. Fossett and Gibson participated in this research. 1933, they made the mixture of ethylene and benzaldehyde (C6H5CHO) react at 170℃ and 1400 atmospheric pressure, and found a thin layer of white wax on the inner wall of the reactor. So they repeated the experiment with only ethylene, and the reaction was so violent that the equipment broke, producing hydrogen, methane and free carbon, but not polyethylene.
By1935,65438+February, several other chemists of Imperial Chemical Industry Company, such as perrin, J.G.patton and E.G.Williams, had updated their equipment at 180℃ and 1000 ~. After the test started, the pressure gradually decreased due to the poor sealing of the reactor, but the result was unexpected, and 8 grams of polyethylene was obtained. After careful and repeated research, chemist J.C.Swallow thinks that the success of the experiment is accidental. Due to the poor sealing of the reactor, some ethylene leaked, but a small amount of oxygen was introduced, which played a catalytic role in ethylene polymerization.
Chance and other chemists involved in the experiment applied for a patent at 1936 * * at the same time, and it was approved at 1937 on September 6. Imperial Chemical Industry Company built a 50-liter reactor at 1939 for trial production. By the end of 1939, the polyethylene output will reach 100 tons.
During World War II (1939- 1945), polyethylene began to be used as military material to produce high-frequency radar cables. In this way, the manufacturing technology of high-pressure polyethylene was transferred from Imperial Chemical Industry Company in Britain to Dupont Company and Union Carbide Company in the United States. 1943, the two companies began to produce polyethylene.
After the beginning of World War II, Germany and Japan, as axis countries, also studied and produced polyethylene, but the progress was slow. By 1944, that is, towards the end of World War II, the Franco-German company in Germany had reached the production scale of 5- 10 tons per month. After the war, Batischer aniline and soda ash plants in the Federal Republic of Germany introduced British technology to build factories for production.
As early as during the war, Japan discovered this kind of flexible ash on the radar feeder of the American B29 bomber that was shot down, which attracted attention. Later, it was found to be polyethylene in the patent of British Imperial Chemical Industry Company. At that time, several researchers from Kyoto University, Osaka University and Tokushima University who were engaged in high-pressure chemistry research in Japan accepted the entrustment of the Japanese military authorities and organized a polyethylene research group. However, due to the technical conditions and material level of Japan at that time, the research encountered many difficulties and spent a lot of energy. It was not until 1944 that 6.3 grams of polyethylene products were produced. The war ended when they designed a pilot plant with a daily output of 20 kilograms. After the war, the research and development work was stopped for a period of time, but because polyethylene can replace lead as cable coating material and can be used as insulation material of submarine cables, the voice of re-developing polyethylene in Japan is once again high. The experimental device of 195 1- 1953 Nissan 10 kg was continuously studied. By 1955, Japan also imported patents from British Imperial Chemical Industry Company, and started industrial production on 1958. During the same period, Mitsubishi Petrochemical Company of Japan purchased the patents of Batischer aniline and soda ash plant in Germany, and also realized industrialization.
The production of high-pressure polyethylene requires high equipment and is difficult to operate, which urges chemists and engineers to study low-pressure production. In the 1950s, during the period of 1953- 1954, chemists in the United States and Germany applied for technical patents for ethylene low-pressure polymerization. Chemist Standard oil Co A. zletz proposed that molybdenum oxide be dissolved in hydrocarbons and ethylene be polymerized at 230~270℃ and 40~80 atmospheric pressure. Phillips Petrouemco chemists J.P.Hogan and R.L.Banks proposed to use chromium oxide as a catalyst, at 130~ 160℃ and1.4 ~ 3.5 MPa (1ATM = 65438. Germany Max? Karl Ziegler (1898- 1973), a chemist at Max Planck Institute, proposed that triethylaluminum (Al(C2H5)3) and titanium tetrachloride (TiCl4) were used as catalysts, and the reaction was carried out at a temperature higher than 50℃ and an atmospheric pressure higher than 10. At the end of 1953, a very noticeable thing happened. Under the condition of excluding air, triethylaluminum and titanium tetrachloride were simultaneously poured into about 2 liters of hydrocarbon similar to gasoline, and ethylene was introduced at 100, 20 and 5 atmospheres, even at normal pressure, and then the ethylene gas was quickly absorbed. After one hour, the solid matter settled and passed through. At this time, it is impossible to stir. Add some ethanol to remove the catalyst, and the product turns white. After filtration and drying, white powdery polyethylene was obtained.
So companies all over the world have bought Ziegler patents and put them into industrial production.
Low pressure polyethylene and high pressure polyethylene are not exactly the same in physical properties. High pressure polyethylene has low density, also called low density polyethylene; Low-pressure polyethylene has a high density, also known as high-density polyethylene.
High pressure polyethylene has low density, light weight, softness, impact resistance and good transparency. Widely used in film production, crop cultivation and packaging of daily necessities such as food, medicine and clothing. It is impermeable to water, but breathable. Goldfish and water are packed in polyethylene film bags, and the goldfish will not die after sealing the bags. The strength, hardness and solvent resistance of low-pressure polyethylene are better than that of high-pressure polyethylene, and the container can be boiled and disinfected. Polyethylene covered wire is widely used in the military because of its good insulation performance, non-hardening at MINUS 50℃ and high friction strength. Nowadays, many polyethylene bottles, pots, medicine bottles, sprayers and funnels have entered the market. Polyethylene can also be made into single fiber, which is similar to fireproof tape except rope making.
Ethylene, the raw material of polyethylene, is rich in sources and can be made from petroleum cracking. The manufacturing process of polyethylene is short, and no plasticizer is used when processing film products, so it develops rapidly and occupies the first place in plastic output.
Propylene, a homologue of ethylene, was first obtained from 1849- 1850 by a German chemist J.W. Nold through a red-hot tube. Like ethylene, it is a colorless and sweet gas. With the development of petrochemical industry, propylene, like ethylene, can be obtained in large quantities from petroleum pyrolysis gas. After ethylene is synthesized into polyethylene for various purposes under high pressure and low pressure, chemists naturally think that propylene will be as useful as polyethylene after polymerization. Polypropylene is a paste-like viscous liquid, which can't be a solid substance, and its melting point is very low, about 75℃, so it is useless in industry and has to be burned.
After Ziegler made the catalyst for ethylene low-pressure polymerization, both industrial production and academic theory attracted the attention of all parties. It spread to universities and research institutions in various enterprise departments at an extremely fast speed. Giulio Natta (1903- 1979), a chemistry professor in Politecnico di Milano, first accepted this academic influence. He found that solid polypropylene with good crystallization and high melting point can be obtained by using titanium trichloride (TiCl3) instead of titanium tetrachloride in Ziegler catalyst for propylene polymerization. After studying the molecular structure of polypropylene, he determined that the modified catalyst would make polypropylene molecules arrange regularly, thus making polypropylene have good properties. He called this modified catalyst isotactic catalyst, and the polypropylene polymerized with this catalyst is isotactic polypropylene.
After polymerization, there is a side methyl group on each link of polypropylene long chain molecule.
Judging from the spatial arrangement position of polypropylene macromolecules, there are the following three arrangements:
All the side groups in (1) polypropylene macromolecules are located on one side of the main chain plane.
(2) The side groups in polypropylene macromolecules regularly alternate on both sides of the main chain plane.
(3) The side groups in polypropylene macromolecules are randomly distributed on both sides of the plane formed by the main chain.
The first is isotactic polypropylene, the second is syndiotactic polypropylene and the third is atactic polypropylene.
Isotactic polypropylene is a white crystalline powder with a melting point of 165~ 170℃ and good tensile strength. It can be molded, formed into a film or stretched into filaments. Its fabric is light, strong, wear-resistant and elastic.
1957, the Italian company Monte Catini first established a factory to produce isotactic polypropylene under the trade name meraklon. Then the American Hercules Company started production at 1959 under the trade name of Hekulan. After polyethylene, China also built a factory to produce polypropylene under the trade name of polypropylene.
Polypropylene clothing, underwear, socks, gloves, furniture cloth and curtains have entered people's homes. The main industrial applications of polypropylene fiber are ropes, fishing nets, canvas, hoses and packaging materials. Because of its good corrosion resistance, it is also used as industrial filter cloth and work clothes.
Turning two cheap colorless gases, ethylene and propylene, into white solids and making them into various shapes of fibers, films and articles is a chemical invention and a catalyst provided by Ziegler and Natta. Both of them won the 1963 Nobel Prize in chemistry. Unfortunately, neither of them attended the award ceremony. Ziegler thought that Natta had stolen his research results and refused to attend. Nata is paralyzed in bed and can't go.