Polycarbonate

Polycarbonates are plastics made from the group of synthetic polymers and the polyester family. Precise there are polymeric esters of carbonic acid with diols ( dihydric alcohols ). They can be prepared by polycondensation of phosgene ( a derivative of carbonic acid) with diols or by transesterification with carbonic acid diesters instead of the hazardous phosgene.

In 1953, the first industrially relevant polycarbonate was developed (abbreviation PC, code 7) by Hermann Schnell of Bayer AG. This was based on 2,2-bis (4- hydroxyphenyl ) propane (bisphenol A) and then (as well as other members of the group) marketed as Makrolon ®. Another internationally known brand is the manufacturer SABIC Lexan ®.

Synthesis

The most common polycarbonates are those which use bisphenol A as a diol component and phosgene.

As an alternative to bisphenol A diol also be used:

• Bisphenol S
• Tetramethyl bisphenol
• 1,1-bis ( 4-hydroxyphenyl ) -3,3,5-trimethylcyclohexane ( BPTMC )

Properties

Polycarbonates are generally amorphous and have a crystallite of less than 5%. They are characterized by high strength, impact strength, stiffness and hardness. Polycarbonates are largely resistant to the effects of weather and radiation. They are flammable, the flame goes out, however, after removal of the ignition source. In addition, polycarbonates are good insulators against electricity.

Polycarbonates are resistant to water, many mineral acids and aqueous solutions of neutral salts and oxidizing agents. Also, some non-polar organic solvents such as hydrocarbons and many oils and fats grab polycarbonates not. Fickle are polycarbonates, however, to some chlorinated hydrocarbons, such as dichloromethane. Also alkaline aqueous solutions, amines and ammonia attack polycarbonates.

Applications

Polycarbonates are transparent and colorless. However, they can be dyed.

Polycarbonate is relatively expensive. It is therefore used almost only where other plastics too soft, too fragile, too sensitive to scratching, not stable enough or are not transparent enough.

Applications are:

• Electric and equipment components
• Lenses and optical lenses
• Light covers
• Lenses of car headlights
• Seal rings in military vehicles (eg tanks )
• Airplane window
• Shields in special vehicles (eg police emergency vehicles )
• Burglar-proof glazing
• Underwater housings for cameras
• Glazing conservatories and greenhouses
• Solar Panels
• Covers, packaging, luggage cases
• Bodies in the function model
• Safety Helmets and visors
• Camping tableware
• Housing material for some SLRs, mobile phones and laptops
• Durable identification documents such as identity cards ( ID) and data pages in passports (so called Data Pages).
• Because of its good biocompatibility, it is used for a variety of medical disposable products.
• Tank sleeve with evaporators, also known as E-Cigarette
• Floor protection mats

The market share of the global polycarbonate plastic consumption is 2.2 million tons (2003 ) at about 1.3 percent.

Processing

Polycarbonates can be processed by all conventional methods for thermoplastics. In injection molding is required because of the high viscosity of the melt, a high injection pressure. The processing temperatures are 280-320 ° C and the extrusion 240-280 ° C. Before processing, however, the residual moisture must be brought to less than 0.01 percent by drying (4 to 24 hours at 120 ° C). Molding of polycarbonate is 0.6 to 0.8 percent. Polycarbonate has so good on no post-shrinkage. It can be with solvents such as dichloromethane and reaction resin adhesives glue and ultrasonic and hochfrequenzschweißbar.

Safety

American and Japanese studies suggest may from certain polycarbonates, the production of which the monomer bisphenol A was used, this will be released when heated again. Bisphenol A is suspected to cause serious health damage. Therefore is in the EU, the use of polycarbonate which contains bisphenol A, for example, as a material for baby bottles prohibited.

Recycling

The recycling code for polycarbonates is 07