Polycarbonates (PC) are a group of thermoplastic polymers containing
carbonate groups in their chemical structures. Polycarbonates used in
engineering are strong, tough materials, and some grades are optically
transparent. They are easily worked, molded, and thermoformed. Because
of these properties, polycarbonates find many applications.
Polycarbonates do not have a unique resin identification code (RIC)
and are identified as "Other", 7 on the RIC list. Products made from
polycarbonate can contain the precursor monomer bisphenol A (BPA).
3 Properties and processing
4.1 Electronic components
4.2 Construction materials
4.3 Data storage
4.4 Automotive, aircraft, railway, and security components
4.5 Niche applications
4.5.1 Medical applications
6 Potential hazards in food contact applications
7 Environmental impact
7.2 Photo-oxidation of polycarbonate
7.3 Photo-aging reaction
7.4 Thermal degradation
7.5 Effect of fungi
8 See also
10 External links
Polycarbonates received their name because they are polymers
containing carbonate groups (−O−(C=O)−O−). A balance of useful
features, including temperature resistance, impact resistance and
optical properties, positions polycarbonates between commodity
plastics and engineering plastics.
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 the synthesis involves treatment of bisphenol A with
sodium hydroxide, which deprotonates the hydroxyl groups of the
(HOC6H4)2CMe2 + 2 NaOH → Na2(OC6H4)2CMe2 + 2 H2O
The diphenoxide (Na2(OC6H4)2CMe2) reacts with phosgene to give a
chloroformate, which subsequently is attacked by another phenoxide.
The net reaction from the diphenoxide is:
Na2(OC6H4)2CMe2 + COCl2 → 1/n [OC(OC6H4)2CMe2]n + 2 NaCl
In this way, approximately one billion kilograms of polycarbonate is
produced annually. Many other diols have been tested in place of
bisphenol A, e.g. 1,1-bis(4-hydroxyphenyl)cyclohexane and
dihydroxybenzophenone. The cyclohexane is used as a comonomer to
suppress crystallisation tendency of the BPA-derived product.
Tetrabromobisphenol A is used to enhance fire resistance.
Tetramethylcyclobutanediol has been developed as a replacement for
An alternative route to polycarbonates entails transesterification
from BPA and diphenyl carbonate:
(HOC6H4)2CMe2 + (C6H5O)2CO → 1/n [OC(OC6H4)2CMe2]n + 2 C6H5OH
The diphenyl carbonate was derived in part from carbon monoxide, this
route being greener than the phosgene method.
The ring-opening polymerization of cyclic carbonates has been
Properties and processing
Polycarbonate is a durable material. Although it has high
impact-resistance, it has low scratch-resistance. Therefore, a hard
coating is applied to polycarbonate eyewear lenses and polycarbonate
exterior automotive components. The characteristics of polycarbonate
compare to those of polymethyl methacrylate (PMMA, acrylic), but
polycarbonate is stronger and will hold up longer to extreme
Polycarbonate is highly transparent to visible light,
with better light transmission than many kinds of glass.
Polycarbonate has a glass transition temperature of about 147 °C
(297 °F), so it softens gradually above this point and flows
above about 155 °C (311 °F). Tools must be held at high
temperatures, generally above 80 °C (176 °F) to make
strain-free and stress-free products. Low molecular mass grades are
easier to mold than higher grades, but their strength is lower as a
result. The toughest grades have the highest molecular mass, but are
much more difficult to process.
Unlike most thermoplastics, polycarbonate can undergo large plastic
deformations without cracking or breaking. As a result, it can be
processed and formed at room temperature using sheet metal techniques,
such as bending on a brake. Even for sharp angle bends with a tight
radius, heating may not be necessary. This makes it valuable in
prototyping applications where transparent or electrically
non-conductive parts are needed, which cannot be made from sheet
metal. PMMA/Acrylic, which is similar in appearance to polycarbonate,
is brittle and cannot be bent at room temperature.
Main transformation techniques for polycarbonate resins:
extrusion into tubes, rods and other profiles including multiwall
extrusion with cylinders (calenders) into sheets (0.5–20 mm
(0.020–0.787 in)) and films (below 1 mm (0.039 in)),
which can be used directly or manufactured into other shapes using
thermoforming or secondary fabrication techniques, such as bending,
drilling, or routing. Due to its chemical properties it is not
conducive to laser-cutting.
injection molding into ready articles
Polycarbonate may become brittle when exposed to ionizing radiation
above 25 kGy (J/kg).
A bottle made from polycarbonate
Polycarbonate is mainly used for electronic applications that
capitalize on its collective safety features. Being a good electrical
insulator and having heat-resistant and flame-retardant properties, it
is used in various products associated with electrical and
telecommunications hardware. It can also serve as a dielectric in
high-stability capacitors. However, commercial manufacture of
polycarbonate capacitors mostly stopped after sole manufacturer Bayer
AG stopped making capacitor-grade polycarbonate film at the end of
Polycarbonate sheeting in a greenhouse
The second largest consumer of polycarbonates is the construction
industry, e.g. for domelights, flat or curved glazing, and sound
walls, which all use extruded flat solid or multiwall sheet, or
CDs and DVDs
A major application of polycarbonate is the production of Compact
Discs, DVDs, and Blu-ray Discs. These discs are produced by injection
molding polycarbonate into a mold cavity that has on one side a metal
stamper containing a negative image of the disc data, while the other
mold side is a mirrored surface.
Automotive, aircraft, railway, and security components
In the automotive industry, injection-molded polycarbonate can produce
very smooth surfaces that make it well-suited for sputter deposition
or evaporation deposition of aluminium without the need for a
base-coat. Decorative bezels and optical reflectors are commonly made
of polycarbonate. Due to its low weight and high impact resistance,
polycarbonate is the dominant material for making automotive headlamp
lenses. However, automotive headlamps require outer surface coatings
because of its low scratch resistance and susceptibility to
ultraviolet degradation (yellowing). The use of polycarbonate in
automotive applications is limited to low stress applications. Stress
from fasteners, plastic welding and molding render polycarbonate
susceptible to stress corrosion cracking when it comes in contact with
certain accelerants such as salt water and plastisol. It can be
laminated to make bullet-proof "glass", although "bullet-resistant" is
more accurate for the thinner windows, such as are used in
bullet-resistant windows in automobiles. The thicker barriers of
transparent plastic used in teller's windows and barriers in banks are
So-called "theft-proof" large plastic packaging for smaller items,
which cannot be opened by hand, is uniformly made from polycarbonate.
Lockheed Martin F-22 cockpit canopy
The cockpit canopy of the
Lockheed Martin F-22 Raptor
Lockheed Martin F-22 Raptor jet fighter is
made from a piece of high optical quality polycarbonate, and is the
largest piece of its type formed in the world.
Kereta Api Indonesia, the major railway operator in Indonesia, uses
polycarbonate solid sheet for their engine and passenger cars fleet
since 2016 due to high train stone throwing frequency.
Polycarbonate, being a versatile material with attractive processing
and physical properties, has attracted myriad smaller applications.
The use of injection molded drinking bottles, glasses and food
containers is common, but the use of BPA in the manufacture of
polycarbonate has stirred serious controversy (see Potential hazards
in food contact applications), leading to development and use of
"BPA-free" plastics in various formulations.
Laboratory safety goggles
Polycarbonate is commonly used in eye protection, as well as in other
projectile-resistant viewing and lighting applications that would
normally indicate the use of glass, but require much higher
Polycarbonate lenses also protect the eye from UV
light. Many kinds of lenses are manufactured from polycarbonate,
including automotive headlamp lenses, lighting lenses,
sunglass/eyeglass lenses, swimming goggles and SCUBA masks, and safety
glasses/goggles/visors including visors in sporting helmets/masks and
police riot gear (helmet visors, riot shields, etc.). Windscreens in
small motorized vehicles are commonly made of polycarbonate, such as
for motorcycles, ATVs, golf carts, and small planes and helicopters.
Typical products of sheet/film production include applications in
advertisement (signs, displays, poster protection). But also
applications as automotive safety glazing (ECE R 43).
The light weight of polycarbonate as opposed to glass has led to
development of electronic display screens that replace glass with
polycarbonate, for use in mobile and portable devices. Such displays
include newer e-ink and some LCD screens, though CRT, plasma screen
and other LCD technologies generally still require glass for its
higher melting temperature and its ability to be etched in finer
As more and more governments are restricting the use of glass in pubs
and clubs due to the increased incidence of glassings, polycarbonate
glasses are becoming popular for serving alcohol because of their
strength, durability, and glass-like feel.
Other miscellaneous items include durable, lightweight luggage,
MP3/digital audio player cases, ocarinas, computer cases, fountain
pens, riot shields, instrument panels, tealight candle containers and
blender jars. Many toys and hobby items are made from polycarbonate
parts, like fins, gyro mounts, and flybar locks in radio-controlled
helicopters, and transparent
LEGO (ABS is used for opaque
Polycarbonate resins are not suitable for long term exposure
to UV radiation. To overcome this the primary resin can have UV
Stabilisers added. These grades are sold as UV Stabilized
Polycarbonate to Injection Moulding and
Extrusion companies. Other
Polycarbonate sheet may have the anti-UV layer
added as a special coating or a coextrusion for enhanced weathering
Polycarbonate is also used as a printing substrate for nameplate and
other forms of industrial grade under printed products. The
polycarbonate provides a barrier to wear, the elements, and fading.
Many polycarbonate grades are used in medical applications and comply
with both ISO 10993-1 and USP Class VI standards (occasionally
referred to as PC-ISO). Class VI is the most stringent of the six USP
ratings. These grades can be sterilized using steam at 120 °C,
gamma radiation, or by the ethylene oxide (EtO) method. However,
scientific research indicates possible problems with
biocompatibility. Dow Chemical strictly limits all
its plastics with regard to medical applications. More
recently, scientists at the IBM Almaden Research Center have developed
aliphatic polycarbonates with improved biocompatibility and
degradability for nanomedicine applications.
Some major smartphone manufacturers use polycarbonate. Nokia has used
polycarbonate in their phones starting with the N9's unibody case in
2011. This practice continues with various phones in the Lumia series.
Samsung has started using polycarbonate with Galaxy S III's battery
cover in 2012. This practice continues with various phones in the
Galaxy series. Apple started using polycarbonate with the iPhone 5C's
unibody case in 2013.
Polycarbonates were first discovered in 1898 by Alfred Einhorn, a
German scientist working at the University of Munich. However,
after 30 years of laboratory research, this class of materials was
abandoned without commercialization. Research resumed in 1953, when
Hermann Schnell at
Bayer in Uerdingen, Germany patented the first
linear polycarbonate. The brand name "Merlon" was registered in 1955,
Later changed to Makrolon in the 1980s.
Also in 1953, and one week after the patent was submitted by Bayer,
Daniel Fox at
General Electric in Schenectady, New York, independently
submitted a closely related patent on a branched polycarbonate. Both
companies filed for U.S. patents in 1955, and agreed that the company
lacking priority would be granted a license to the technology.
Once patent priority was resolved, in Bayer's favor,
commercial production under the trade name Merlon in 1958 and GE began
production under the name Lexan in 1960. The production of Lexan was
taken over by
SABIC in 2007.
After 1970, the brownish original polycarbonate tint was improved to
Potential hazards in food contact applications
Bisphenol A and Endocrine disruptor
The use of polycarbonate containers for the purpose of food storage is
controversial. The basis of this controversy is their hydrolysis
(degradation by water, often referred to as leaching) occurring at
high temperature, releases bisphenol A:
1/n [OC(OC6H4)2CMe2]n + H2O → (HOC6H4)2CMe2 + CO2
More than 100 studies have explored the bioactivity of bisphenol A
derived from polycarbonates.
Bisphenol A appeared to be released from
polycarbonate animal cages into water at room temperature and it may
have been responsible for enlargement of the reproductive organs of
female mice. However, the animal cages used in the research were
fabricated from industrial grade polycarbonate, rather than FDA food
An analysis of the literature on bisphenol A leachate low-dose effects
by vom Saal and Hughes published in August 2005 seems to have found a
suggestive correlation between the source of funding and the
conclusion drawn. Industry-funded studies tend to find no significant
effects whereas government-funded studies tend to find significant
Sodium hypochlorite bleach and other alkali cleaners catalyze the
release of the bisphenol A from polycarbonate containers.
Alcohol is one recommended organic solvent for cleaning grease and
oils from polycarbonate.
Studies have shown that at high temperatures between 70 and
80 °C and high humidity, polycarbonates hydrolyzes to bisphenol
A (BPA). This condition is similar to that observed in most
incinerators. After about 30 days under such conditions, surface
crystals were formed. Measurements indicated that about 70% by mass of
the surface crystals were bisphenol A (BPA). BPA is a compound
that is currently on the list of potential environmental hazardous
chemicals. It is on the watch list of many countries, such as United
States and Germany.
−(−OC6H4)2C(CH3)2CO−)−n + H2O → (CH3)2C(C6H4OH)2 + CO2
The leaching of BPA from polycarbonate can also occur at environmental
temperature and normal pH (in landfills). The amount of leaching
increases as the material becomes older. A study found that the
decomposition of BPA in landfills (under anaerobic conditions) does
not occur. It will therefore be persistent in landfills.
Eventually, it will find its way into water bodies and contribute to
Photo-oxidation of polycarbonate
In the presence of UV light, oxidation of this polymer yields
compounds such as ketones, phenols, o-phenoxybenzoic acid, benzyl
alcohol and other unsaturated compounds. This has been suggested
through kinetic and spectral studies. The yellow color formed after
long exposure to sun can also be related to further oxidation of
phenolic end group
(OC6H4)2C(CH3)2CO)n + O2, R* → (OC6H4)2C(CH3CH2)CO)n
This product can be further oxidized to form smaller unsaturated
compounds. This can proceed by two different pathways, the products
formed depends on which mechanism takes place.
(OC6H4)2C(CH3CH2)CO + O2, H* → HO(OC6H4)OCO + CH3COCH2(OC6H4)OCO
(OC6H4)2C(CH3CH2)CO)n + O2, H* → OCO(OC6H4)CH2OH + OCO(OC6H4)COCH3
Photo-aging is another degradation route for polycarbonates.
Polycarbonate molecules (such as the aromatic ring) absorb UV
radiation. This absorbed energy causes cleavage of covalent bonds,
which initiates the photo-aging process. The reaction can be
propagated by side chain oxidation, ring oxidation or photo-fries
rearrangement. Products formed include phenyl salicylate,
dihydroxybenzophenone groups, and hydroxydiphenyl ether
n(C16H14O3) → C16H17O3 + C13H10O3
Polycarbonate phenyl salicylate 2,2-dihydroxybenzophenone
Waste polycarbonate will degrade at high temperatures to form solid,
liquid and gaseous pollutants. A study showed that the products were,
by mass, about 40–50% liquid, 14–16% gases, while 34–43%
remained as solid residue. Liquid products contained mainly phenol
derivatives (∼75%) and bisphenol (∼10%) also present.
Therefore, burning of these discs[clarification needed] is also not a
viable method of disposal.
Phenol derivatives are environmental pollutants, classified as
volatile organic compounds (VOC). Studies show that they are likely to
facilitate ground-level ozone formation and increase photo-chemical
smog. In aquatic bodies, they can potentially accumulate in
organisms. They are persistent in landfills, do not readily evaporate
and would remain in the atmosphere.
Effect of fungi
In 2001 a species of fungus, Geotrichum candidum, was found to consume
the polycarbonate found in compact discs (CD). This has prospects
CR-39, allyl diglycol carbonate (ADC) used for eyeglasses
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