Polycarbonate is a synthetic polymer in terms of chemistry, it can be considered a complex polyester of carbonic acid and phenols. As you know, s alts of carbonic acid are called carbonates, hence the name of the popular polymer today, formed from two parts - poly (which means a lot) and carbonate.
A little chemistry
Polycarbonate macromolecule has a linear structure. In general, its formula can be written as follows:
H-[-O-R-O-(C=O)-O-R-] -OH.
Depending on the type of substituent R, all polycarbonates can be divided into aromatic, fatty-aromatic and aliphatic. The most used of them today is the first group. Trade names of aromatic polycarbonates may be different, but they are united by similar values of physical and mechanical parameters, such as high light transmission, low specific gravity, relatively high melting point. Polycarbonates with these properties contain many benzene rings (aromatic substituents).
Advantages of polycarbonates
- Strength. One of the most famous properties and significant advantage of polycarbonate is its high resistance to mechanical shocks.
- Transparency. Due to their high light transmission, polycarbonates have successfully replaced silicate glass in many areas of life and production, since they also have a relatively low weight.
- Thermal resistance. The values of melting (softening) temperatures of polycarbonates differ somewhat from each other depending on the structural features of the macromolecule, but, as a rule, it exceeds 200 °C.
- Thermoplasticity. Polycarbonate is a type of polymer that can be remelted many times. At the same time, after hardening, it will restore its properties.
- Sustainability. Due to the previous property, polycarbonate products can be recycled.
- Fire safety. The ignition temperature significantly exceeds the melting point of polycarbonate, it is about 570 ° C.
- Chemical resistance. Thanks to this property, the material is successfully used in various aggressive environments.
Flaws
It is worth noting that polycarbonate has all of the above advantages only if its constituent macromolecules have a molecular weight of more than 25,000. Otherwise, itvery fragile and has a much lower melting point. Polycarbonate, manufactured in violation of technology, may contain a rather high number of molecules with a reduced molecular weight, which negatively affects its strength and performance characteristics.
Another significant disadvantage of polycarbonates is their low resistance to ultraviolet radiation. However, today there are technologies that can protect the polymer from direct exposure to UV rays. This is usually done with protective films that are fused to the polycarbonate during the manufacturing phase of the product. Another limiting factor in the use of polycarbonate is its high thermal expansion.
Physical and mechanical properties
- Refractive index - 1.5850.
- Density (at 25° C) - 1.20g/cm3.
- Glass transition temperature - 150 °C.
- Softening temperature 220-230 °C.
- Decomposition temperature >320 °C.
- Frost resistance, °C < -100
- Tensile strength - 65-70 MPa.
- Bending strength - 95 MPa.
- Specific heat capacity - 1090-1255J/(g K).
- Thermal conductivity is 0.20 W/(m K).
- Coefficient of linear thermal expansion -1(5-6) 10-5 °C.
- Brinell hardness - (784-980) 105 Pa.
Cellular and monolithic polycarbonate
Cellular polycarbonate is a panel of several layers of plastic, between which there are longitudinal ribsrigidity. In the context of such a leaf vaguely resembles a honeycomb, for which it got its name. Such sheets can be easily bent in a cold state, reaching the smallest possible bending radius. Cellular polycarbonate is most often used for the construction of decorative partitions and the construction of transparent roofs.
Monolithic polycarbonate has higher impact resistance and transparency. A significant advantage is the high heat resistance of monolithic polycarbonate, the melting point is quite high, which allows it to be used without fear at temperatures reaching 120 ° C. Also, its important property is frost resistance, which allows the use of products made of this type of plastic at temperatures down to minus 50 ° С.
Using polycarbonate
Construction. Due to its high transparency and lightness, polycarbonate helps architects to realize their most daring projects. At the same time, the weight of the structure, relative to traditionally used glass, can significantly reduce the load on the foundations, and therefore save on materials. Moreover, polycarbonate also has thermal insulation properties, if we talk about its cellular variety. Translucent structures are made from it for swimming pools and stadiums, parking lots and supermarkets, transitions between buildings and winter gardens. This material is also popular with gardeners. Increasingly, polycarbonate is used for greenhouses. Its melting point is significantly higher than atmospheric even in the hottest summer, and therefore significantsolar heat cannot harm this polymer
- Electronics. Cases and protective coatings for laptops, smartphones, players, home computers and much more are made from polycarbonate. Thanks to this polymer, touch screen technology was able to reach the masses. It is used to produce biometric passports.
- Advertising. Polycarbonate is used to create light structures, signboards, scoreboards, three-dimensional letters and much more. All this can have very intricate extraordinary forms. Also, their sheets of monolithic plastic are used to make anti-vandal protection of advertising structures.
- Optical discs. Since the 1980s, polycarbonate has been used to create the backing of CDs. Today it is also used to make high-capacity DVDs.
- Automobile and aircraft industry. For the construction of aircraft, the latest materials are traditionally used, which have high strength and lightness, which is also characteristic of polycarbonate. It is used to make the domes of the cockpits of fighters and glass for the helmets of astronauts and pilots. For cars, polycarbonate is used not only for glass, but also for headlights and sunroofs.
- Medicine. A very important field of application of polycarbonate has become the manufacture of medical instruments. This became possible due to such advantages of the material as non-toxicity and high biocompatibility, as well as the lack of an immune response of the body to this plastic. And thanks to its strength and transparency, it competed with glass and metal alloys. products and equipment,made using this material are used to monitor the tissues and fluids of the human body. In addition, the high melting temperatures of polycarbonates allow them to be subjected to the most modern sterilization methods - heat, radiation, UV rays.
- Optics. In the 2000s, polycarbonate lenses began to be made for industrial protective goggles, which protected the eyes during various work. Such products are dozens of times stronger than other plastic lenses; in the event of a blow to them, they do not spread fragments, they are even harder to scratch. Gradually, polycarbonate was also used for everyday spectacle lenses. Due to their safety qualities, such lenses are very often used for children's glasses, motorcycle helmet glasses.
- Other areas. Today, polycarbonate has become so firmly established in our lives that residents of not only megacities, but also remote villages, daily encounter products, of which this plastic is a part. Ballpoint pens, flashlights, computer mice, irons and kettles, corks for wine bottles, furniture parts, containers for drinking liquids and even packaging film are made from it.
