Thermoplastics were produced after thermosetting plastics
In 1835, French chemist Henri Victor Regnault (1810-1878) was studying Dutch liquid and mixed it with potassium hydroxide. The action of ethanol solution produces a colorless and anesthetic gas, which is vinyl chloride (CH2=CHCl).
The Dutch liquid was discovered by Dutch chemist Johann Rudolph Deiman (1743-1808) and others at the end of the 18th century. It is still used in chemical laboratories to dehydrate ethanol with sulfuric acid to produce ethylene (CH2=CH2). , and let it react with chlorine to form an oily liquid, called Dutch liquid, that is, chlorinated ethylene (CH2ClCH2Cl), also known as ethylene dichloride or ethylene dichloride.
Ethylene chloride reacts with potassium hydroxide to form vinyl chloride, potassium chloride and water:
CH2ClCH2Cl KOH══CH2CHCl KCl H2O In 1872, German chemist Eugen Baumann, 1846-1896) published a report on the study of vinyl chloride, stating that if it was placed in a sealed glass tube and exposed to sunlight, it would transform into a white solid powder. He believed that this was an isomer of vinyl chloride, and studied some properties of this substance. It is acid-resistant, heat-resistant, very tough and not easy to wear. It generates a strong charge when rubbed against silk and melts at high temperatures. It turns into a black object and releases hydrogen chloride gas. Bowman did not realize that the solid product was polyvinyl chloride, but only provided information for those who later produced polyvinyl chloride.
In 1912, Russian chemist Ostrom Myslensky (Иван Иванович Остромысленский, 1880-1939) prepared polyvinyl chloride and called it Cauprene Chlorid. This word today can be translated as "polypentene rubber chloride." He had no concept of polymers at that time. Ostromeslensky named it this way because he thought that the polyvinyl chloride he produced was like an insoluble, difficult-to-process, and difficult-to-handle rubber. We do have difficulties with PVC because PVC breaks down very easily at processing temperatures.
Later, between 1912 and 1915, German chemist Fritz Klatte applied for several patents for the preparation of polyvinyl chloride. He pointed out that the polymer produced by exposing vinyl chloride to sunlight or arc light can be dissolved in chlorobenzene (C6H5Cl). The solution will form a gel after cooling, and a transparent, soft and non-flammable film will be left after the solvent evaporates. Some compounds can be added to the solution of chlorobenzene to enhance the toughness of the product. These compounds include camphor, benzene, toluene, naphthalene phosphates and carbonates, etc.
Obviously, these substances are added as plasticizers to plasticize polyvinyl chloride. Before PVC is plasticized, it is hard and brittle and glassy.
In 1926, Waldo L. Semon, a chemistry professor at Kent State University in the United States, proposed the use of tricresyl phosphate ((CH3C6H4)3PO4) to plasticize polyvinyl chloride, and achieved success.
Then, in 1928, the American Carbon Compound and Carbon Chemical Company, DuPont Company, and the German Farben Company each obtained patents. According to their patents, they produced vinyl chloride and vinyl acetate polymers. This is because the homopolymer of a monomer of vinyl chloride can only be processed in the molten state and is easily decomposed at the melting temperature, while the polymer can be processed at lower temperatures. Adding vinyl acetate to vinyl chloride for polymerization also plays a plasticizing effect on polyvinyl chloride.
Today, there are two types of PVC products: soft and hard. Soft polyvinyl chloride products are made because plasticizers are added to the ingredients, while hard polyvinyl chloride products are made without plasticizers.
The density of hard polyvinyl chloride plastic is very small, half lighter than the lightest metal aluminum. Its tensile strength is equivalent to that of rubber. It has good water resistance, oil resistance and chemical resistance, so it is used to make chemicals. Sewage and detoxification towers for industrial waste gases such as textiles and textiles, as well as transportation pipelines for normal temperature gases and liquids. PVC also has excellent electrical insulation properties, so it is often used in the electrical industry and telecommunications industry. Lightning arresters made from rigid polyvinyl chloride rods work well.
Soft polyvinyl chloride is widely used in industry, agriculture, medicine and health, and daily necessities. It can be used as cable material in industry; in agriculture, polyvinyl chloride film can be used to raise seedlings, which can increase crop yields; in medicine, it can be used as a blood transfusion film instead of glass bottles to store plasma, reducing losses caused by transportation and other reasons, and it is also easy to carry. Most plastic products in daily life are made of PVC, such as plastic sandals, raincoats, sheets, toys, artificial leather gloves and artificial leather bags, etc.
Chemists discovered that vinyl chloride can be obtained by reacting acetylene with hydrogen chloride:
Acetylene can be obtained from petrochemical processing, so the conditions are met for mass production of polyvinyl chloride.
Polyvinyl chloride was developed in the mid-1930s. Its output was once the highest among various plastics, but later the output of polyethylene and polypropylene exceeded that of polyvinyl chloride.
The plastic that appeared almost at the same time was polystyrene.
The monomer of polystyrene, styrene (C6H5CH=CH2), exists in some natural plants. In 1827, French pharmacist J.F. Bonastre obtained styrene when he distilled liquid styrax resin. The styrax tree is native to Asia Minor and is a deciduous tree. The aromatic resin it secretes has been transported from Arabia to India and China since ancient times.
The molecular formula of styrene is C6H5CH=CH2. It is a colorless, flammable and aromatic liquid. In 1869, the French chemist Bertello made it by dehydrogenating styrene (C6H5C2H5), which has become a method of producing styrene in industry today. This method is based on the reaction of ethylene and benzene in the presence of aluminum trichloride (AlCl3) when heated to about 95°C to generate ethyl phenylbenzene. Phenyl ethane decomposes thermally at 630°C to produce styrene and hydrogen:
Chemists have long observed that styrene polymerizes slowly when placed and polymerizes rapidly when exposed to sunlight or in the presence of metallic sodium. In 1839, German chemist E. Simon first produced polystyrene. The German company Farben was the first to produce polystyrene.
J. A． Brydson. Plastics materials． London: Newnes-Butterworths, 1975.
Because polystyrene is low in cost, has good molding properties, is easy to color, is transparent and hard, has low water absorption, and especially has excellent electrical properties, it has developed rapidly and can be made into televisions, Radar and other insulating components.
Plastics such as polyvinyl chloride, polystyrene, and polyethylene are all thermoplastics. They soften when heated and can be molded into certain shapes. They harden after cooling, remain soft when reheated, and change again after cooling. hard. They are different from thermosetting plastics. Thermosetting plastics become soft when first heated and can be molded into a certain shape. However, they harden and shape after being heated for a certain period of time or after adding a curing agent. They will not soften when reheated and will not dissolve when placed in a solvent. . Phenolic plastics, urea-formaldehyde plastics, etc. are all thermosetting plastics. They cannot be recycled, so those who purchase waste products do not accept or purchase these thermosetting plastics. This has to do with their molecular structure.
The molecular structure of resin can generally be divided into three categories. The first type is linear (Figure 38-1), the second type is branched (Figure 38-2), and the third type is It is mesh type (Figure 38-3). If the molecular structure of synthetic resin is linear or branched, it is a thermoplastic plastic; if it is a mesh type, it is a thermosetting plastic.