Polycarbonate is a versatile, tough plastic used for a variety of applications, from bulletproof windows to compact disks (CDs). The main advantage of polycarbonate over other types of plastic is unbeatable strength combined with light weight. While acrylic is 17% stronger than glass, polycarbonate is nearly unbreakable. Bulletproof windows and enclosures as seen inside banks or at drive-throughs are often made of polycarbonate. Add to this the advantage that polycarbonate is just one-third the weight of acrylic, or one-sixth as heavy as glass, and the only drawback is that it is more expensive than either acrylic or glass.
Compact disks and digital versatile discs (DVDs) are perhaps the most readily recognized examples of polycarbonate. If you've ever archived files on a writable CD, then later tried to break it before throwing it away, you know just how tough polycarbonate can be!
Polycarbonate lenses are also used in quality sunglasses that incorporate filters to block ultra-violet (UV) rays and near-UV rays. The lenses can also be polarized to block glare, and their high impact resistance makes them perfect for sports. Many sunglasses manufacturers choose polycarbonate because it can be easily shaped without problems like cracking or splitting, resulting in extremely lightweight, distortion-free, fashionable glasses that feature all of the health benefits doctors recommend.
Polycarbonate is also used in the electronics industry. Apple's original iMac featured polycarbonate mixed with clear colors for a transparent computer case. Many cell phones, pagers, and laptops also use clear or opaque polycarbonate in their casings.
Other uses for polycarbonate include greenhouse enclosures, automobile headlights, outdoor fixtures, and medical industry applications, though the list is virtually endless. Somewhat less toxic than polyvinyl chloride (PVC) to produce, polycarbonate nevertheless requires toxic chemicals in its production phase. It is, however, recyclable and environmentally preferable to PVC in applications for which either material can be used.
Polycarbonate roofing panels are a durable, long-lasting solution for your exterior roofing needs. Whether your covering a deck, strengthening your roof in critical places, building a carport to keep your automobiles safe from the elements, or just covering a tool shed, it behooves you to consider going with...
More on Polycarbonate
Polycarbonates, commonly known by the trademarked name Lexan, are a particular group of thermoplastic polymers. They are easily worked, moulded, and thermoformed. Because of these properties, polycarbonates find many applications. Polycarbonates do not have a unique plastic identification code and are identified as Other, 7.
Structure of Polycarbonate
Polycarbonates received their name because they are polymers containing carbonate groups (-O-(C=O)-O-). Most polycarbonates of commercial interest are derived from rigid monomers, and the mechanical properties. Their interesting features (temperature resistance, impact resistance and optical properties) position them between commodity plastics and engineering plastics.
Properties and processing of Polycarbonate
Polycarbonate derived from BPA is a very durable material. Although it has high impact-resistance, it has low scratch-resistance and so a hard coating is applied to polycarbonate eyewear lenses and polycarbonate exterior automotive components. The characteristics of polycarbonate are quite like those of polymethyl methacrylate (PMMA, acrylic), but polycarbonate is stronger, usable in a wider temperature range but more expensive. This polymer is highly transparent to visible light and has better light transmission characteristics than many kinds of glass.
Polycarbonate has a glass transition temperature of about 150 °C (302 °F), so it softens gradually above this point and flows above about 300 °C (572 °F). Injection moulding is more difficult than other common thermoplastics owing to its non-Newtonian fluid flow behaviour. Tools must be held at high temperatures, generally above 80 °C (176 °F) to make strain- and stress-free products. Low molecular mass grades are easier to mould 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 forming bends on a brake. Even for sharp angle bends with a tight radius, no heating is generally necessary. This makes it valuable in prototyping applications where transparent or electrically non-conductive parts are needed, which cannot be made from sheet metal. Note that PMMA/Plexiglas, 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
- extrusion with cylinders into sheets (0.5-15 mm (0.020-0.59 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, routing, laser cutting etc.
- injection molding into ready articles
Applications of Polycarbonate
Polycarbonate Electronic components
Polycarbonate is mainly used for electronic applications that capitalize on its collective safety features. Being a good electrical insulator and having heat and flame resistant properties, it is used in myriad products associated with electrical and telecommunications hardware. They are used as dielectric in high stability capacitors.
Polycarbonate Construction materials
The second largest consumer of polycarbonates is the construction industry, e.g. for domelights, flat or curved glazing, and sound walls.
Polycarbonate Data storage
A major application of polycarbonate is the production of compact discs, DVDs, and Blu-ray Discs. The blanks are produced by injection molding. Typical products of sheet/film production include applications in advertisement (signs, displays, poster protection).
Polycarbonate Automotive and aircraft components
In the automotive industry, injection moulded polycarbonate can produce very smooth surfaces that make it well suited for direct (without the need for a basecoat) metalised parts such as decorative bezels and optical reflectors. Its uniform mould shrinkage results in parts with greater accuracy than those made of polypropylene. However, due to its susceptibility to environmental stress cracking, its use is limited to low stress applications. It can be laminated to make bullet-proof "glass", although "bullet-resistant" would be more accurate.
The cockpit canopy of the 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.
Polycarbonate Niche applications
Polycarbonate, being a versatile material with attractive processing and physical properties, has attracted myriad smaller applications. The use of injection molded drinking bottles and glasses and food containers has stirred serious controversy (see below). Many kinds of lab equipment, such research animal enclosures
Many kinds of lenses are manufactured from polycarbonate, including automotive headlamp lenses, lighting lenses, sunglass/eyeglass, lenses, and safety glasses. Other miscellaneous items: MP3/Digital audio player cases, Ocarinas, computer cases, riot shields, visors, instrument panels. Many toys and hobby items are made from polycarbonate parts, e.g. fins, gyro mounts, and flybar locks for use with radio-controlled helicopters.
For use in applications exposed to weathering or UV-radiation, a special surface treatment is needed. This either can be a coating (e.g. for improved abrasion resistance), or a coextrusion for enhanced weathering resistance.
Polycarbonate Medical applications
Some 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.
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