Polycarbonate ( PC ) is a group of thermoplastic polymers containing carbonate groups in their chemical structure. The polycarbonate used in engineering is a strong and difficult material, and some optically transparent values. They are easy to do, printed, and thermoform. Due to these properties, polycarbonate finds many applications. Polycarbonate has no unique resin identification code (RIC) and is identified as "Other", 7 on the RIC list. Products made of polycarbonate may contain bisphenol A (BPA) monomer precursors.
Video Polycarbonate
Structure
Polycarbonate receives their name because they are polymers containing carbonate groups (-O- (C = O) -O-). The balance of useful features, including temperature resistance, impact resistance and optical properties, position polycarbonate between commodity plastic and engineering plastics.
Maps Polycarbonate
Production
The main polycarbonate material is produced by the reaction of bisphenol A (BPA) and phosgene COCl
2 . The overall reaction can be written as follows:
The first step of synthesis involves the treatment of bisphenol A with sodium hydroxide, which deprotonates the hydroxyl group of bisphenol A.
- (HOC 6 2 2 CMe 2 2 NaOH -> Na 2 2 H 2 2 2 O
Diphenoxide (Na 2 ) 2 CMe 2 ) reacts with phosgene to produce chloroformate, which is then attacked by other phenoxides. The net reaction of diphenoxide is:
- Na 2 (OC 6 H 4 ) 2 CMe 2 COCl 2 -> 1/n [OC (OC 6 4 ) 2 CMe 2 ] n 2 NaCl
In this way, about one billion kilograms of polycarbonate is produced each year. Many other diols have been tested in place of bisphenol A, eg. 1,1-bis (4-hydroxyphenyl) cyclohexane and dihydroxybenzophenone. Cyclohexane is used as a comonomer to suppress the tendency of crystallization of CPA-derived products. Tetrabromobisphenol A is used to improve fire resistance. Tetramethylcyclobutanediol has been developed as a substitute for BPA.
Rute alternatif untuk polycarbonate melibatkan transesterifikasi dari BPA dan diphenyl carbonate: 2 CMe 2 (C 6 H 5 O) 2 CO -> 1/n [OC < 2 CMe 2 ] n
Diphenyl carbonate comes partly from carbon monoxide, this route becomes greener than the phosgene method.
The cyclic carbonate-opening ring polymerization has been investigated.
Properties and processing
Polycarbonate is a durable material. Despite its high impact resistance, it has a low scratch resistance. Therefore, a hard layer is applied to polycarbonate eyeglass lenses and exterior polycarbonate automotive components. Characteristics of polycarbonate are compared with polymethyl methacrylate (PMMA, acrylic), but polycarbonates are stronger and will last longer for extreme temperatures. Polycarbonate is highly transparent for visible light, with better light transmission than many types of glass.
Polycarbonate has a glass transition temperature of about 147 Â ° C (297 Â ° F), thus gradually softening above this point and flowing above about 155 Â ° C (311 Â ° F). Equipment should be held at high temperatures, generally above 80 ° C (176 ° F) to make the product stress free and stress free. Low molecular mass values ​​are more easily formed than higher grades, but their strength is lower as a result. The heaviest values ​​have the highest molecular mass, but are much more difficult to process.
Unlike most thermoplastics, polycarbonates can undergo major plastic deformation without cracking or breaking. As a result, it can be processed and shaped at room temperature using a sheet metal technique, such as bending the brakes. Even for sharp corner corners with tight radius, heating may not be necessary. This makes it valuable in prototyping applications where transparent or electrically non-conductive parts are required, which can not be made from sheet metal. PMMA/Acrylic, which is similar to polycarbonate, is brittle and can not be bent at room temperature.
The main transformation technique for polycarbonate resin:
- extrusion into tubes, trunks and other profiles including multiwall
- extrusion with cylinder (calendar) into sheet (0,5-20 mm (0,020-0,787 in)) and film (below 1 mm (0,039 in)), which can be used directly or produced to another form using thermoforming or secondary fabrication techniques, such as bending, drilling, or routing. Due to its chemical nature is not conducive to laser cutting.
- injection molds into ready goods
Polycarbonate can become brittle when exposed to ionizing radiation above 25 kGy (J/kg).
Apps
Electronic components
Polycarbonate is mainly used for electronic applications that utilize its collective safety features. Being a good electrical insulator and having heat resistant and fire retardant properties, it is used in various products related to electrical and telecommunication hardware. It can also function as a dielectric in high stability capacitors. However, the commercial manufacture of polycarbonate capacitors largely stopped after a single producer of Bayer AG ceased making polycarbonate film grade capacitors at the end of 2000.
Construction materials
The second largest consumer of polycarbonate is the construction industry, for example for mastery, flat or curved glass, and sound walls, all of which use flat or multiwall sheets of extrusion, or corrugated sheets.
Data storage
The main applications of polycarbonate are the production of Compact Discs, DVDs, and Blu-ray Discs. These discs are produced by molding a polycarbonate injection into a mold cavity having one side of a metal stamp containing a negative image of the disc data, while the other side of the mold is the mirror surface.
Automotive, aircraft, rail and security components
In the automotive industry, injection molded polycarbonates can produce very fine surfaces that make it particularly suitable for sputter deposition or aluminum evaporation deposition without the need for a base layer. The decorative bezel and optical reflector are generally made of polycarbonate. Due to its low weight and high impact resistance, polycarbonate is the dominant material for making automotive headlamp lenses. However, automotive headlights require external surface coatings due to their low scratch resistance and susceptibility to ultraviolet (yellowing) degradation. The use of polycarbonate in automotive applications is limited to low stress applications. Stress from fasteners, plastic welding and molding make polycarbonate susceptible to crack corrosion stress when in contact with certain accelerators such as brine and plastisol. It can be laminated to make bullet-proof "glass", though "bulletproof" is more accurate for thinner windows, as used on bullet-proof windows in cars. The thick barrier of transparent plastic used in the window of the cashier and the barrier in the bank is also polycarbonate.
Large plastic packaging called "anti-thief" for smaller items, which can not be opened by hand, is uniformly made of polycarbonate.
Lockheed Martin F-22 Raptor fighter jet canopy is made from a piece of high-quality optical polycarbonate, and is the largest part of its kind formed in the world.
Kereta Api Indonesia, the main rail operator in Indonesia, uses polycarbonate solid sheets for engines and passenger car fleets since 2016 because of the high frequency of rock-throw stops.
Niche Apps
Polycarbonate, being a versatile material with attractive processing and physical properties, has attracted many smaller applications. The use of injection-fed bottles, glasses, and food containers is common, but the use of BPA in polycarbonate production has caused serious controversy (see Hazards in food contact applications), leading to the development and use of plastic "BPA-free" various formulations.
Polycarbonate is commonly used in eye protection, as well as other projectile-resistant display and lighting applications that typically indicate the use of glass, but require much higher impact resistance. Polycarbonate lenses also protect the eyes from UV rays. Many types of lenses are manufactured from polycarbonate, including automotive headlamp lenses, lighting lenses, sunglasses/glasses, swimming goggles and SCUBA masks, and safety glasses/visors/visors including visors in helmet/sport masks and police anti-riot equipment helmets, anti-riot shields, etc.). Windscreens on small motor vehicles are generally made of polycarbonate, such as for motorcycles, ATVs, golf carts, and small planes and helicopters.
Typical products of sheet/film production include applications in advertisements (marks, displays, poster protection). But also the application as an automotive safety glass (ECE R 43).
The light weight of polycarbonate compared to glass has led to the development of an electronic display screen that replaces glass with polycarbonate, for use in mobile and portable devices. The displays include newer e-ink and multiple LCD screens, although CRTs, plasma screens and other LCD technologies in general still require glass for higher melting temperatures and the ability to engrave in finer detail.
As more governments limit the use of glass in pubs and clubs due to the increasing incidence of glass, polycarbonate glasses are becoming popular for presenting alcohols due to strength, durability, and a glassy feel.
Other miscellaneous items include durable and lightweight baggage, MP3/digital audio player case, ocarinas, computer case, pen, anti-riot shield, instrument panel, tealight candle container and blender jar. Many toys and hobby items are made of polycarbonate parts, such as fins, gyro holder, and flybar locks on radio controlled helicopters, and transparent LEGOs (ABS used for frosted pieces).
Standard Polycarbonate resins are not suitable for long-term exposure to UV radiation. To overcome this the main resin can have UV Stabilizer added. This value is sold as UV Stabilized Polycarbonate to Injection Molding and Extrusion company. Other applications including Polycarbonate sheets may have an anti-UV coating added as a special coating or coextrusion to improve the weathering resistance.
Polycarbonate is also used as a printing substrate for nameplate and other forms of industrial grade under printed products. Polycarbonate provides a barrier for wear, element, and fading.
Medical applications
Many polycarbonate grades are used in medical applications and conform to ISO 10993-1 and USP Class VI standards (sometimes referred to as PC-ISO). Class VI is the most stringent of the six USP rankings. These values ​​can be sterilized using steam at 120 ° C, gamma radiation, or with ethylene oxide (EtO). However, scientific research suggests possible problems with biocompatibility. Dow Chemical strictly limits all plastics with respect to medical applications. More recently, scientists at IBM's Almaden Research Center have developed aliphatic polycarbonates with improved biocompatibility and degradability for nano-drug applications.
Phone
Some large smart phone manufacturers use polycarbonate. Nokia has used polycarbonate on their phones starting with the N9 unibody case in 2011. This practice continues with various phones in the Lumia series. Samsung has begun using polycarbonate with the Galaxy S III battery cover in 2012. This practice continues with various phones in the Galaxy series. Apple began using polycarbonate with the unibody case of iPhone 5C in 2013.
History
Polycarbonate was first discovered in 1898 by Alfred Einhorn, a German scientist working at the University of Munich. However, after 30 years of laboratory research, this material class was abandoned without commercialization. The study continued in 1953, when Hermann Schnell at Bayer in Uerdingen, Germany patented the first linear polycarbonate. The brand name "Merlon" was registered in 1955, later converted to Makrolon in the 1980s.
Also in 1953, and one week after the patent filed by Bayer, Daniel Fox at General Electric in Schenectady, New York, independently filed a closely related patent on branched polycarbonate. The two companies filed for a US patent in 1955, and agreed that less priority companies would be licensed for the technology. Once the patent priority was completed, with Bayer's help, Bayer commenced commercial production under the Merlon trade name in 1958 and GE started production under the name Lexan in 1960. Lexan's production was taken over by SABIC in 2007.
After 1970, the original brown polycarbonate color was upgraded to "clear glass."
Potential hazards in food contact apps
The use of polycarbonate containers for food storage purposes is controversial. The basis of this controversy is their hydrolysis (degradation by water, often referred to as leaching) occurs at high temperatures, releasing bisphenol A:
- 1/n [OC (OC 6 H 4 ) 2 CMe 2 ] < sub> n H 2 O -> (HOC 6 4 ) 2 CMe 2 CO 2
More than 100 studies have explored the bioactivity of bisphenol A derived from polycarbonate. Bisphenol A appears to be released from the polycarbonate animal enclosure into water at room temperature and may be responsible for the enlargement of female reproductive organs. However, the animal enclosures used in this study were made from industrial grade polycarbonate, rather than FDA food grade polycarbonate.
The literature analysis of bisphenol A low-dose leachate effect by Saal and Hughes vom published in August 2005 appears to have found a suggestive correlation between the funding sources and the conclusions drawn. Industry-funded studies tend not to find a significant effect whereas government-funded studies tend to find significant effects.
Sodium hypochlorite bleach and other alkaline cleaners catalyze the release of bisphenol A from the polycarbonate container. Alcohol is one of the recommended organic solvents for cleaning fat and oil from polycarbonate.
Environmental impact
Disposal
Studies have shown that at high temperatures between 70 and 80 ° C and high humidity, polycarbonate is hydrolyzed to bisphenol A (BPA). This condition is similar to that observed in most incinerators. After about 30 days under such conditions, surface crystals are formed. Measurements show that about 70% of the mass of the surface crystals is bisphenol A (BPA). BPA is a compound that is currently on the list of potentially harmful environmental hazards. It's in the watchlist of many countries, such as the United States and Germany.
- - (- OC 6 H 4 ) 2 C (CH 3 ) 2 CO -) - n H 2 O -> (CH 3 ) 2 C (C 6 H 4 OH) 2 CO 2
The removal of BPA from polycarbonate can also occur at ambient temperature and normal pH (in landfills). The number of washes increases with age. A study found that decomposition of BPA in landfills (under anaerobic conditions) did not occur. It will therefore be persistent in the final dump. Eventually, it will find its way into the body of water and contribute to water pollution.
Photo-oxidation polycarbonate
In the presence of UV light, the oxidation of this polymer produces compounds such as ketones, phenols, o-phenoxybenzoic acids, benzyl alcohols and other unsaturated compounds. This has been suggested through kinetic and spectral studies. The yellow color that is formed after exposure to sunlight can also be attributed to further oxidation of the phenolic end group
- ( 4 4 ) 2 C (CH 3 ) 2 CO) n O 2 , R * -> (OC 6 H 4 ) 2 C (CH 3 CH 2 ) CO) n
This product can be further oxidized to form a smaller unsaturated compound. This can be continued with two different paths, the product formed depending on which mechanisms occur.
- Path A
- (OC 6 H 4 ) 2 CH (CH 3 CH 2 ) CO O 2 , H * -> HO (OC 6 OCO CH 3 COCH 2 (OC 6 H 4 ) OCO
- Path B
- (OC 6 H 4 ) 2 CH (CH 3 CH 2 ) CO n O 2 , H * -> OCO (OC 6 H 4 ) CH 2 OH OCO (OC 6 4 ) COCH 3
Photo-oxidation reactions.
Photo-aging reactions
Photo-aging is another degradation route for polycarbonate. Polycarbonate molecules (such as aromatic rings) absorb UV radiation. This absorbed energy leads to the cleavage of the covalent bond, which initiates the photo-aging process. The reaction may be propagated by side chain oxidation, oxidation ring rings or photo-frying. The products formed include phenyl salicylate, dihydroxybenzophenone groups, and hydroxydiphenyl ether groups.
- n (C 16 H 14 O 3 ) -> C 16 H 17 < < /dd>
Polycarbonate phenyl salicylate 2,2-dihydroxybenzophenone
Degradasi thermal
Polycarbonate waste will be degraded at high temperatures to form solid, liquid and gas pollutants. A study showed that the product, with mass, was about 40-50% liquid, 14-16% gas, while 34-43% remained as a solid residue. Liquid products mainly contain phenol derivatives (~ 75%) and bisphenol (~ 10%) are also present. Therefore, burning these discs is also not a proper disposal method.
Phenol derivatives are environmental pollutants, classified as volatile organic compounds (VOCs). Studies show that they are likely to facilitate the formation of ozone in the soil surface and increase the chemical photo-smoke haze. In aquatic bodies, they are potentially accumulated in organisms. They survive in landfills, not volatile and will remain in the atmosphere.
Mushroom effect
In 2001 a species of fungus, Geotrichum candidum , was found to consume polycarbonate found on compact discs (CDs). It has prospects for bioremediation.
See also
- CR-39, allyl diglycol carbonate (ADC) is used for glasses
- Organic electronics
- Mobile phone accessories
- Thermoplastic polyurethane
- Steam polishing
References
External links
Source of the article : Wikipedia
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