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Polycarbonates are a particular group of thermoplastic polyesters. They are easily worked, molded, and thermoformed; as such, these plastics are very widely used in modern manufacturing. Their interesting features (temperature resistance, impact resistance and optical properties) positions them between commodity plastics and engineering plastics.
Chemistry Polycarbonates got their name because they are polymers having functional groups linked together by carbonate groups (-O-(C=O)-O-) in a long molecular chain. Also carbon monoxide was used as a C1-synthon on an industrial scale to produce diphenyl carbonate, being later trans-esterificated with a diphenolic derivative affording poly(aromatic carbonate)s. Taking into consideration the C1-synthon we can divide polycarbonates into poly(aromatic carbonate)s and poly(aliphatic carbonate)s. The second one, poly(aliphatic carbonate)s are a product of the reaction of carbon dioxide with epoxides, what owing to the thermodynamical stability of carbon dioxide requires the use of catalyst. The working systems are based on porphyrins, alkoxides, carboxylates, salens and beta-diiminates as organic, chelating ligands and aluminium, zinc, cobalt and chromium as the metal centres. Poly(aliphatic carbonate)s display promising characteristics, have a better biodegradability than the aromatic ones and could be employed to develop other specialty polymers. The most common type of polycarbonate plastic is one made from Bisphenol A, in which groups from Bisphenol A are linked together by carbonate groups in a polymer chain. This polycarbonate is characterized as a very durable material, and can be laminated to make bullet-proof "glass", though “bullet-resistant” would be more accurate. Although polycarbonate has high impact-resistance, it has low scratch-resistance and so a hard coating is applied to polycarbonate eyewear lenses. The characteristics of polycarbonate are quite like those of polymethyl methacrylate (PMMA; acrylic), but polycarbonate is stronger and more expensive. This polymer is highly transparent to visible light and has better light transmission characteristics than many kinds of glass. CR-39 is a specific polycarbonate material - although it is usually referred to as CR-39 plastic - with good optical and mechanical properties, frequently used for eyeglass lenses. Polycarbonate has Applications Main transformation techniques for Polycarbonate resins are: Polycarbonate is becoming more common in housewares as well as laboratories and in industry, mainly where at least two of its three main features are required: high impact resistance, temperature resistance and optical properties. Typical injected applications are lighting lenses sunglass/eyeglass lenses, compact discs, DVDs, automotive headlamp lenses, Nalgene bottles. It is also used for animal enclosures and cages used in research... Typical sheet/film applications are: domelights, flat or curved glazing, sound walls, Remark 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. Most common resins are LEXAN® from General Electric, CALIBRE® from DOW Chemicals, MAKROLON® from Bayer and PANLITE® from Teijin Chemical Limited. As being based on bisphenol A, and phenol based on benzene, pricing is much depending on phenol and benzene pricing. Potential hazards in food contact applications Polycarbonate may be appealing to fabricators and purchasers of food storage containers due to its clarity and toughness. Polycarbonate has been described as lightweight and highly break resistant particularly when compared to silica glass. Polycarbonate may be seen in the form of single use and refillable plastic water bottles. More than 100 studies have explored the bioactivity of bisphenol A leachates from polycarbonates. Bisphenol A appeared to be released from polycarbonate animal cages into water at room temperature and that it may have been responsible for enlargement of the reproductive organs of female mice.• 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 while government funded studies tend to find significant effects.• One point of agreement among those studying polycarbonate water and food storage containers may be that using sodium hypochlorite bleach and other alkali cleaners to clean polycarbonate is not recommended, as they catalyze the release of the Bisphenol-A. The tendency of polycarbonate to release bisphenol A was discovered after a lab tech used strong cleaners on polycarbonate lab containers. Endocrine disruption later observed on lab rats was traced to exposure from the cleaned containers. Synthesis
Interaction with other chemicals (1) At room temperature. At temperatures above 60°C hydrolysis is more present, degrading the plastic. Degradation depends on time and temperature. Using Sodium hypochlorite Bleach and other alkali cleaners on polycarbonate is not recommended as they cause the release of Bisphenol-A, a known endocrine disrupter. | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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