Post 480 by Gautam Shah
Polycarbonate is a tough plastic valued for its transparency. It has very high impact resistance combined with light weight. It is, 1/3 the weight of acrylic, and 1/6 of glass. Acrylic is 17% stronger than glass, where as polycarbonate is nearly unbreakable, being 400 times stronger than glass. It is very ductile, self extinguishing and flame retardant plastic. It remains dimensionally stable in prolonged sunlight exposure. Polycarbonate is more expensive than Glass or Acrylic. It is recyclable and environmentally preferable to PVC. Polycarbonate is attacked by many organic solvents. It is also fairly expensive compared to other plastics.
Polycarbonates were first discovered in 1898, but remained without commercial exploitation for 30 years. In the post war period research resumed in 1953, with Bayer patenting the first linear polycarbonate. One week after this GE USA independently synthesized a branched polycarbonate and filed a conflicting patent. After the patent priority resolution, Bayer began commercial production under the trade name Makrolon in 1958. and GE began production under the name Lexan in 1960. After 1970, the original brownish polycarbonate tint was improved to glass-clear.
Polycarbonate is a versatile plastic, which can be injection moulded, extruded, blow moulded and thermo formed. Unlike most thermoplastics, polycarbonate can undergo large plastic deformations without cracking or breaking. It can, as a result be reshaped at room temperature by using techniques for sheet metal working. This makes it valuable for model or prototype making applications. It can be joined mechanically, solvent bonded, and welded with skill. Virgin polycarbonate is the original polymer, whereas re-ground polycarbonate is waste that has been prilled or formed into pellets. The properties do not change much after such prilling.
Polycarbonate is an amorphous thermoplastic of long-chain linear polyesters of carbonic acid and dihydric phenols. They are called polycarbonate because functional groups of polymers are linked by carbonate groups. An amorphous (non crystalline) polymer has a glass like, transparent appearance due to the random orientation and intertwined nature of its molecules like spaghetti. Polycarbonate has a glass transition temperature of about 147 °C and so begins to soften gradually above this point. It begins to flow at about 155 °C. Working tools or forming nozzles are held at above 80 °C temperature to get a product with a clean surface. The toughest grades have the higher molecular mass, but are more difficult to process.
The prime uses of Polycarbonate relate to its transparency, toughness, lightness of weight, and exterior durability. Some of the uses are unbreakable openings’ ‘glasses’, roof domes, greenhouse enclosures, police riot shields, vandal-proof light shields, partitions in taxis, non rattling ‘glass’ for bus and tram sliding windows, bullet and temper-proof covers for the valuables and exhibits. Its easy form-ability allows its use for transparent gift and jewellery boxes, utensil covers, bodies of gadgets like hair dryers, housing for electric meters, switch covers, funerary caskets, safety helmets, and computer parts.
Polycarbonate has excellent transparency, durability, and high a refractive index, and so is used to make eyeglasses. A thin polycarbonate formed to required curvature makes it very light in weight eyeglasses for spectacles. The clarity, scratch resistance and ability to take on transparent colours makes it suitable for inspection glasses in industries, air craft interior fittings, mines lights, high voltage switches, sockets, back-lit advertising display boards, see-through floors and bottom lit dance floors.
During the last decade polycarbonate is being used for making CDs and DVDs. Polycarbonate like ABS plastic can receive sputter deposition or evaporation deposition of aluminium without the need for a base-coat. Polycarbonate composites are used for marine utilities like boats, frigates. The addition of glass fibres to polycarbonate increases the tensile strength, flexural strength, flexural modulus, and heat deflection temperature.