A type of synthetic polymer produced artificially. It can be a viscous liquid or a solid that softens when heated, usually having a melting or softening temperature range when heated. It can exhibit plastic flow under external force, and some properties are similar to natural resins. The **important application of synthetic resin is the manufacture of plastics. To facilitate processing and improve performance, additives are often added, and sometimes it is directly used for processing and forming, hence it is often synonymous with plastics. Synthetic resins are also the basic raw materials for the production of synthetic fibers, coatings, adhesives, insulation materials, etc. There are many types of synthetic resins. According to the main chain structure, there are carbon chain, heterochain, and non-carbon chain synthetic resins; according to the characteristics of the synthesis reaction, there are addition-type and condensation-type synthetic resins. In practical applications, they are often classified into thermoplastic resins and thermosetting resins based on their thermal behavior. The raw materials for producing synthetic resins are abundant, initially mainly from coal tar products and calcium carbide, but now mainly from petroleum and natural gas products, such as ethylene, propylene, benzene, formaldehyde, and urea. The production methods for synthetic resins include bulk polymerization, suspension polymerization, emulsion polymerization, solution polymerization, melt polymerization, and interfacial condensation.
The **important application of synthetic resin is the manufacture of plastics. To facilitate processing and improve performance, additives are often added, and sometimes it is directly used for processing and forming, hence it is often synonymous with plastics. Synthetic resins are also the basic raw materials for the production of synthetic fibers, coatings, adhesives, insulation materials, etc.
There are many types of synthetic resins. According to the main chain structure, there are carbon chain, heterochain, and non-carbon chain synthetic resins; according to the characteristics of the synthesis reaction, there are addition-type and condensation-type synthetic resins. In practical applications, they are often classified into thermoplastic resins and thermosetting resins based on their thermal behavior. Among them, thermoplastic resins include polyethylene, polypropylene, polystyrene, polyvinyl chloride, etc. Thermosetting resins include phenolic resins, urea-formaldehyde resins, epoxy resins, fluororesins, unsaturated polyesters, and polyurethanes.
The development prospects of synthetic resins in China.
During the "11th Five-Year Plan" period, the rapid development of domestic industries such as electronic information, automobiles, and real estate, along with the upgrading of residents' consumption levels, will provide huge development space for the development of synthetic resins in China. It is expected that during the "11th Five-Year Plan" period, the demand for synthetic resins in China will continue to grow at a rate of about 10% as in the "10th Five-Year Plan" period. By 2010, the apparent consumption in the domestic market is expected to reach 64 million tons, an increase of about 26 million tons compared to the end of the "10th Five-Year Plan" period. It is expected that during the "11th Five-Year Plan" period, the domestic production of synthetic resins will grow at an average annual rate of 12%, and by 2010, the output is expected to reach 37 million tons, an increase of about 16 million tons compared to the end of the "10th Five-Year Plan" period.
Raw materials and methods of production.
The raw materials for producing synthetic resins are abundant, initially mainly from coal tar products and calcium carbide, but now mainly from petroleum and natural gas products, such as ethylene, propylene, benzene, formaldehyde, and urea. The production methods for synthetic resins include bulk polymerization, suspension polymerization, emulsion polymerization, solution polymerization, melt polymerization, and interfacial condensation.
Synthetic resin.
Synthetic resin is a polymer compound produced by combining low molecular raw materials—monomers (such as ethylene, propylene, vinyl chloride, etc.) through polymerization reactions into macromolecules. The commonly used polymerization methods in industry include bulk polymerization, suspension polymerization, emulsion polymerization, and solution polymerization.
Bulk polymerization.
Bulk polymerization is a polymerization process where monomers are polymerized under the action of initiators or heat, light, or radiation without adding other media. The characteristics are that the product is pure, does not require complex separation and purification, the operation is relatively simple, and the utilization rate of production equipment is high. It can directly produce quality products such as pipes and sheets, hence it is also called bulk polymerization. The disadvantage is that the viscosity of the material increases continuously with the progress of the polymerization reaction, making mixing and heat transfer difficult, and the temperature in the reactor is not easy to control. Bulk polymerization is often used in the production of polymethyl methacrylate (commonly known as acrylic), polystyrene, low-density polyethylene, polypropylene, polyester, and polyamide resins.
Suspension polymerization.
Suspension polymerization refers to the process where monomers are dispersed into droplets under the action of mechanical stirring or oscillation and dispersants, usually suspended in water. Therefore, it is also called bead polymerization. The characteristics are: there is a large amount of water in the reactor, the viscosity of the material is low, and heat transfer and control are easy; after polymerization, only simple separation, washing, and drying processes are needed to obtain resin products, which can be directly used for molding processing; the products are relatively pure and uniform. The disadvantage is that the production capacity and product purity of the reactor are not as good as bulk polymerization, and continuous production cannot be adopted. Suspension polymerization is widely used in industry. 75% of polyvinyl chloride resin is produced by suspension polymerization, and polystyrene is also mainly produced by suspension polymerization. The reactors are gradually becoming larger.
Emulsion polymerization.
Emulsion polymerization refers to the polymerization process where monomers form an emulsion in water with the help of emulsifiers under mechanical stirring or oscillation. The reaction product of emulsion polymerization is latex, which can be directly applied, or the latex can be destroyed and processed through washing, drying, etc., to obtain powdered or fibrous polymers. Emulsion polymerization can achieve high molecular weight polymers at relatively high reaction speeds, with low material viscosity, easy heat transfer and mixing, easy production control, and easy removal of residual monomers. The disadvantage of emulsion polymerization is that the emulsifiers added during the polymerization process affect the performance of the products. To obtain solid polymers, processes such as coagulation, separation, and washing are required. The production capacity of the reactor is lower than that of bulk polymerization.
Solution polymerization.
Solution polymerization is a polymerization reaction where monomers are dissolved in an appropriate solvent. The resulting polymers may sometimes dissolve in the solvent, belonging to typical solution polymerization, and the products can be used as coatings or adhesives. If the polymer does not dissolve in the solvent, it is called precipitation polymerization or slurry polymerization, and solid polymers need to undergo precipitation, filtration, washing, and drying to become finished products. In solution polymerization, both production operations and reaction temperatures are easy to control, but solvent recovery is required. Industrial solution polymerization can adopt continuous or batch methods, with large-scale production often using continuous methods, such as polypropylene.
Historical development.
Some tree secretions often form resins, but amber is a fossilized resin. Although shellac is also considered a resin, it is actually a deposit secreted by lac insects on trees. Shellac varnish, made from shellac, was initially used as a wood preservative, but with the invention of electric motors, it became one of the earliest insulating varnishes. However, by the 20th century, natural products could no longer meet the needs of electrification, prompting people to seek new, inexpensive substitutes. As early as 1872, German chemist A. Bayer first discovered that phenol and formaldehyde could quickly form reddish-brown hard lumps or viscous substances when heated under acidic conditions, but the experiment was halted because they could not be purified by classical methods. After the 20th century, phenol could be obtained in large quantities from coal tar, and formaldehyde was also produced in large quantities as a preservative, making the reaction products of the two more attractive, hoping to develop useful products. Despite many people spending enormous efforts on this, none achieved the expected results.
In 1904, Bakelite and his assistant also began this research, initially hoping to create an insulating varnish to replace natural resins. After three years of hard work, they not only produced insulating varnish but also created a true synthetic plastic material—Bakelite, which is well-known as "electric wood," "glue wood," or phenolic resin.
Once Bakelite was introduced, manufacturers quickly discovered that it could not only be used to make various electrical insulating products but also daily necessities. Edison used it to make records and soon claimed in advertisements that thousands of products had been made from Bakelite, thus heralding Bakelite's invention as the "alchemy" of the 20th century.
Phenolic resin, made from coal tar, ranked first in the production of synthetic resins before 1940, reaching over 200,000 tons annually. However, with the development of petrochemicals, the production of polymeric synthetic resins such as polyethylene, polypropylene, polyvinyl chloride, and polystyrene has also expanded. With the establishment of many large factories producing over 100,000 tons of these products annually, they have become the four most produced types of synthetic resins today. Synthetic resins, combined with additives, can be formed into plastic products through various molding methods. Today, there are dozens of types of plastics, with an annual production of about 120 million tons, and in our country, it exceeds 5 million tons. They have become basic materials for production, life, and national defense construction.
Synthetic resin is the main component of plastics, generally accounting for 40% to 100% of the plastic. Due to the high content and the fact that the properties of the resin often determine the properties of the plastic, people often regard resin as synonymous with plastic. For example, polyvinyl chloride resin is often confused with polyvinyl chloride plastic, and phenolic resin with phenolic plastic. In fact, resin and plastic are two different concepts. Resin is an unprocessed raw polymer that is not only used to make plastics but also serves as a raw material for coatings, adhesives, and synthetic fibers. Most plastics, except for a very small portion that contains 100% resin, require the addition of other substances in addition to the main component resin.