What are Polycarbonates?
Polycarbonates are composed of long-chain linear polyesters of the chemical carbonic acid and dihydric phenols, like bisphenol A. Polycarbonates are unique group of thermoplastic polymers. They can be easily worked, molded, and also thermoformed, because of this characteristic, these polymers are widely used in the chemical industry. Their interesting characteristic (resistance to temperature, impact resistance and good optical properties) positions them in between commodity plastics and specialized engineering plastics. Polycarbonates do not have unique plastic identification code.
What are the properties of polycarbonates?
Before we start to list the properties of polycarbonate, it is probably good to explain why the properties of polycarbonates are the way they are. First, let us talk about the technical stuff. If you inspect the diagram above, you will see that there are two six-sided structures. They are called phenyl groups. You can also find two groups which are identified by the label CH3. They are the methyl groups. The existence of the phenyl group on the molecular chain plus the two methyl side groups leads to molecular stiffness in the polycarbonate. This stiffness gives large effect on the physical properties of polycarbonate. First, the attraction between the phenyl groups between different molecules leads to a lack of mobility on the individual molecules. This will result in very good thermal resistance but with a relatively high viscosity (i.e., lower melt flow) during polymer processing. This inflexibility and the absence of mobility will prevent polycarbonates from having a significant crystalline structure. The lack of crystalline structure (which refers to the amorphous nature of the polymer) will allow for light transparency.
Polycarbonate is transparent; it has also the ability to pass light nearly that of glass. It has great strength, toughness, resistance to heat, and an excellent dimensional stability and color stability. Flame retardants can also be used to polycarbonates.
Summary of the general properties can be summarized as follows:
• excellent physical properties
• excellent toughness
• very good heat resistance
• fair chemical resistance
• transparent to light
• moderately priced
• satisfactory processing
The properties of Polycarbonates compare to other materials
One of the greatest advantages of polycarbonate is its great impact strength. The following diagram shows the impact strength of polycarbonate compared to other commonly used plastics.
Polycarbonates have also some disadvantages. They only fair chemical resistance and they are attacked by many organic solvents. It is also a bit expensive when you compare it to other plastics. Polycarbonates are double the price of ABS plastic. In applications requiring lower heat and impact, ABS can be a bargain when you compared it to polycarbonate.
Glass-fiber reinforced polycarbonates
When you add glass fibers to polycarbonate, it significantly raises the tensile strength, flexural strength, flexural modulus, and the heat deflection temperature of polycarbonates. It also decreases the impact strength and tensile elongation. The higher the amount of glass fiber that is added to the polycarbonate, the greater is the effect on each of the mentioned property will be.
How are polycarbonates used?
Polycarbonates can be injection molded, blow molded, and they can also be extruded and it is an ideal engineering plastic that posses good electrical insulation, that is why polycarbonates are finding their way on electric meter housings. The price of polycarbonates is the limiting factor why they are not used mainly in engineering applications.
Other engineering applications for Polycarbonates include the following:
• equipment housing
• automotive parts
• lighting fixtures for CFL and Incandescent lamps
• non automotive vehicle windows
• structural parts
• medical supply parts and housings
• plastic lenses for eyeglasses and optics
How are Polycarbonate sold?
In general, the main distinguishing characteristic of the grade of polycarbonate is its melt flow. Changes in the melt flow will have an effect on other physical properties.
When we are specifying a grade for polycarbonates, it is required to know the conditions where this plastic will be used. You can find two major types of polycarbonates that are sold. First, we have Virgin polycarbonate which is a polycarbonate that has not been altered from the time of its original manufacturing until the time of purchase of the said product. We also have Polycarbonate regrind which comes from polycarbonates that are taken from the end-user. These new pellets can be compounded again with both virgin and other regrinded pellets to create a new product.
Potential hazards of Polycarbonates in food contact applications
Polycarbonate can be appealing to industry manufacturers and also to purchasers of food storage containers because of its clarity, toughness, light weight property, especially when you compared to silica glass. Polycarbonates can be seen in the market as single use and refillable plastic water bottles.
There are hundreds of studies that have researched the bioactivity of bisphenol-A leachates from polycarbonates. Bisphenol-A seems to be released from polycarbonate animal cages and into the water at room temperatures. It could be responsible for the enlargement of the reproductive organs of female mice.