Due to its chemical properties it is not conducive to laser-cutting. 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.extrusion into tubes, rods and other profiles including multiwall.Main transformation techniques for polycarbonate resins: PMMA/Acrylic, which is similar in appearance to polycarbonate, is brittle and cannot be bent at room temperature. This makes it valuable in prototyping applications where transparent or electrically non-conductive parts are needed, which cannot be made from sheet metal. Even for sharp angle bends with a tight radius, heating may not be necessary. As a result, it can be processed and formed at room temperature using sheet metal techniques, such as bending on a brake. Unlike most thermoplastics, polycarbonate can undergo large plastic deformations without cracking or breaking. The toughest grades have the highest molecular mass, but are more difficult to process. Low molecular mass grades are easier to mold than higher grades, but their strength is lower as a result. Tools must be held at high temperatures, generally above 80 ☌ (176 ☏) to make strain-free and stress-free products. Polycarbonate has a glass transition temperature of about 147 ☌ (297 ☏), so it softens gradually above this point and flows above about 155 ☌ (311 ☏). Thermally processed material is usually totally amorphous, and as a result is highly transparent to visible light, with better light transmission than many kinds of glass. The characteristics of polycarbonate compare to those of polymethyl methacrylate (PMMA, acrylic), but polycarbonate is stronger and will hold up longer to extreme temperature. Therefore, a hard coating is applied to polycarbonate eyewear lenses and polycarbonate exterior automotive components. Although it has high impact-resistance, it has low scratch-resistance. (HOC 6H 4) 2CMe 2 + (C 6H 5O) 2CO → 1/n n + 2 C 6H 5OH Properties and processing Transesterification route Īn alternative route to polycarbonates entails transesterification from BPA and diphenyl carbonate: Tetramethylcyclobutanediol has been developed as a replacement for BPA. Tetrabromobisphenol A is used to enhance fire resistance. The cyclohexane is used as a comonomer to suppress crystallisation tendency of the BPA-derived product. 1,1-bis(4-hydroxyphenyl)cyclohexane and dihydroxybenzophenone. Many other diols have been tested in place of bisphenol A, e.g. In this way, approximately one billion kilograms of polycarbonate is produced annually. Na 2(OC 6H 4) 2CMe 2 + COCl 2 → 1/n n + 2 NaCl The net reaction from the diphenoxide is: The di phenoxide (Na 2(OC 6H 4) 2CMe 2) reacts with phosgene to give a chloroformate, which subsequently is attacked by another phenoxide. The first step of the synthesis involves treatment of bisphenol A with sodium hydroxide, which deprotonates the hydroxyl groups of the bisphenol A. The overall reaction can be written as follows: The main polycarbonate material is produced by the reaction of bisphenol A (BPA) and phosgene COClĢ. A balance of useful features, including temperature resistance, impact resistance and optical properties, positions polycarbonates between commodity plastics and engineering plastics. Polycarbonates received their name because they are polymers containing carbonate groups (−O−(C=O)−O−). The unique O=C bond is short (1.173 Å in the depicted example), while the C-O bonds are more ether-like (the bond distances of 1.326 Å for the example depicted). This molecule reflects a subunit of a typical polycarbonate derived from bis(phenol-A).Ĭarbonate esters have planar OC(OC) 2 cores, which confers rigidity. Structure of dicarbonate (PhOC(O)OC 6H 4 ) 2CMe 2 derived from bis(phenol-A) and two equivalents of phenol. Products made from polycarbonate can contain the precursor monomer bisphenol A (BPA). Polycarbonates do not have a unique resin identification code (RIC) and are identified as "Other", 7 on the RIC list. Because of these properties, polycarbonates find many applications. They are easily worked, molded, and thermoformed. Polycarbonates used in engineering are strong, tough materials, and some grades are optically transparent. Polycarbonates ( PC) are a group of thermoplastic polymers containing carbonate groups in their chemical structures.
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