Polycarbonate

Polycarbonate
Repeating chemical structure unit of Polycarbonate made from bisphenol A Transmission spectrum of Polycarbonate
Physical properties
Density (ρ)	1.20-1.22 g/cm3
Abbe number (V)	34.0
Refractive index (n)	1.584–1.586
Flammability	V0-V2
Limiting oxygen index	25–27%
Water absorption—Equilibrium (ASTM)	0.16–0.35%
Water absorption—over 24 hours	0.1%
Radiation resistance	Fair
Ultraviolet (1–380 nm) resistance	Fair
Mechanical properties
Young's modulus (E)	2.0–2.4 GPa
Tensile strength (σt)	55–75 MPa
Elongation (ε) at break	80–150%
Compressive strength (σc)	>80 MPa
Poisson's ratio (ν)	0.37
Hardness—Rockwell	M70
Izod impact strength	600–850 J/m
Notch test	20–35 kJ/m2
Abrasive resistance ASTM D1044	10–15 mg/1000 cycles
Coefficient of friction (μ)	0.31
Speed of sound	2270 m/s
Thermal properties
Glass transition temperature (Tg)	147 °C (297 °F)
Heat deflection temperature	0.45 MPa: 140 °C (284 °F) 1.8 MPa: 128–138 °C (262–280 °F)
Vicat softening point at 50 N	145–150 °C (293–302 °F)[1]
Upper working temperature	115–130 °C (239–266 °F)
Lower working temperature	−40 °C (−40 °F)[2]
Thermal conductivity (k) at 23 °C	0.19–0.22 W/(m·K)
Thermal diffusivity (a) at 25 °C	0.144 mm²/s[3]
Linear thermal expansion coefficient (α)	65–70 × 10−6/K
Specific heat capacity (c)	1.2–1.3 kJ/(kg·K)
Electrical properties
Dielectric constant (εr) at 1 MHz	2.9
Permittivity (ε)	2.568 × 10−11 F/m
Relative permeability (μr) at 1 MHz	0.866(2)
Permeability (μ) at 1 MHz	1.089(2) μN/A2
Dissipation factor at 1 MHz	0.01
Surface resistivity	1015 Ω/sq
Volume resistivity (ρ)	1012–1014 Ω·m
Chemical resistance
Acids—concentrated	Poor
Acids—dilute	Good
Alcohols	Good
Alkalis	Good-Poor
Aromatic hydrocarbons	Poor
Greases and oils	Good-fair
Halogenated hydrocarbons	Good-poor
Halogens	Poor
Ketones	Poor
Gas permeation at 20 °C
Nitrogen	10–25 cm3·mm/(m2·day·Bar)
Oxygen	70–130 cm3·mm/(m2·day·Bar)
Carbon dioxide	400–800 cm3·mm/(m2·day·Bar)
Water vapour	1–2 gram·mm/(m2·day) @ 85%–0% RH gradient
Economics
Price	2.6–2.8 €/kg[4]

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).

Structure[edit]

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.

Production[edit]

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 bisphenol A.^[5]

(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 (one million tonnes) 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 BPA.^[5]

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.^[5]

The ring-opening polymerization of cyclic carbonates has been investigated.^[6]

Properties and processing[edit]

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 temperature. Polycarbonate is highly transparent to visible light, with better light transmission than many kinds of glass.^{[citation needed]}

Polycarbonate has a glass transition temperature of about 147 °C (297 °F; 420 K),^[7] so it softens gradually above this point and flows above about 155 °C (311 °F; 428 K).^[8] Tools must be held at high temperatures, generally above 80 °C (176 °F; 353 K) 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.^{[citation needed]}

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.^{[citation needed]}

Main transformation techniques for polycarbonate resins:

• extrusion into tubes, rods and other profiles including multiwall^{[citation needed]}
• extrusion with cylinders (calenders) into sheets (0.5–20 mm (0.020–0.787 in; 20–787 thou)) and films (below 1 mm (0.039 in; 39 thou)), 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.^{[citation needed]}
• injection molding into ready articles^{[citation needed]}

Polycarbonate may become brittle when exposed to ionizing radiation above 25 kGy (J/kg).^[9]

Applications[edit]

Electronic components[edit]

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.^[5] However, commercial manufacture of polycarbonate capacitors mostly stopped after sole manufacturer Bayer AG stopped making capacitor-grade polycarbonate film at the end of year 2000.^[10][11]

Construction materials[edit]

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 corrugated sheet.

Data storage[edit]

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[edit]

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 also polycarbonate.

The third generation Mazda MX-5 was offered with a Power Retractable Hard Top (PRHT) variant that uses a folding hardtop made of polycarbonate, which added only 36 kg (79 lb) to the weight of a comparably equipped soft top without diminishing trunk space when retracted.^[12]

So-called "theft-proof" large plastic packaging for smaller items, which cannot be opened by hand, is uniformly made from polycarbonate.

The cockpit canopy of the 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.^[13][14]

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.^[15]

Niche applications[edit]

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.

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 impact-resistance. 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).^[5] 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 detail.

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.^[16][17]

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,^[18] and transparent LEGO (ABS is used for opaque pieces).^[19]

Standard 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 applications including Polycarbonate sheet may have the anti-UV layer added as a special coating or a coextrusion for enhanced weathering resistance.

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.

Medical applications[edit]

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.^[20] However, scientific research indicates possible problems with biocompatibility.^{[citation needed]} Dow Chemical strictly limits all its plastics with regard to medical applications.^[21][22] More recently, scientists at the IBM Almaden Research Center have developed aliphatic polycarbonates with improved biocompatibility and degradability for nanomedicine applications.^[23]

Phones[edit]

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.