A GUIDE TO POLYCARBONATE IN GENERAL
Material Safety Data Sheet
What is polycarbonate?
Polycarbonates are long-chain
linear polyesters of carbonic acid and dihydric phenols, such
as bisphenol A.
What are the properties of polycarbonate?
Before starting to list properties of polycarbonate, it is probably
wise to explain why the properties are the way they are. First,
the technical stuff. Take a look at the above diagram. In it,
you will see two six-sided structures. These are called phenyl
groups. You will also see two groups identified by the label CH3.
These are methyl groups. The presence of the phenyl groups on
the molecular chain and the two methyl side groups contribute
to molecular stiffness in the polycarbonate. This stiffness has
a large effect on the properties of polycarbonate. First, attraction
between of the phenyl groups between different molecules contributes
to a lack of mobility of the individual molecules. This results
in good thermal resistance but relatively high viscosity (i.e.,
low melt flow) during processing. The inflexibility and the lack
of mobility prevent polycarbonate from developing a significant
crystalline structure. This lack of crystalline structure (the
amorphous nature of the polymer) allows for light transparency.
Now for the clearer, less technical version of the properties.
Polycarbonate is naturally transparent, with the ability to transmit
light nearly that of glass. It has high strength, toughness, heat
resistance, and excellent dimensional and color stability. Flame
retardants can be added to polycarbonate without significant loss
The general properties can be summarized as follows:
- excellent physical properties
- excellent toughness
- very good heat resistance
- fair chemical resistance
- moderate to high price
- fair processing
How do these properties compare to other materials?
One of the biggest advantages of polycarbonate is its impact strength.
The following diagram compares the impact strength of polycarbonate
to other commonly sold plastics.
Polycarbonate does have its disadvantages. It has only fair chemical
resistance and is attacked by many organic solvents. It is also
fairly expensive compared to other plastics. It has been as much
as double the price of ABS. In applications where lower heat and
impact are needed, ABS can be quite a bargain compared to polycarbonate.
What is a glass fiber reinforced grade of polycarbonate?
The addition of glass fibers to polycarbonate significantly increases
the tensile strength, flexural strength, flexural modulus, and
heat deflection temperature of the polycarbonate while causing
a decrease in the impact strength and tensile elongation. (See
Glossary of Plastic Properties for an explanation of each term.)
The greater the amount of glass fiber added to the polycarbonate,
the greater the effect on each property will be.
How is polycarbonate used?
It can be injection molded, blow molded, and extruded and is an
ideal engineering plastic with good electrical insulating properties,
finding applications in electric meter housings and covers, casket
hardware, portable tool housings, safety helmets, computer parts,
and vandal-proof windows and light globes. The price of polycarbonate
restricts its use to mainly engineering applications.
Other engineering applications include the following:
- equipment housings
- exterior automotive components
- outdoor lighting fixtures
- nameplates and bezels
- non automotive vehicle windows
- brackets and structural parts
- medical supply components
- plastic lenses for eyeglasses
How is polycarbonate sold?
In general, the primary distinguishing characteristic of a grade
of polycarbonate is its melt flow. The only exceptions are glass
fiber reinforced grades, which are sold based on the percentage
of glass fiber used in the production of the plastic. Other properties
(such as UV stabilization, mold release, impact modification,
and flame retardancy) typically differentiate grades of the same
melt flow or percentage of glass fiber. Changes in melt flow have
an effect on other physical properties.
When specifying a grade of polycarbonate, it is necessary to know
the conditions under which it will be used. In the following diagram,
you can see the effect of temperature on izod impact strength for
three different grades of polycarbonate.
Lastly, there are two major types of polycarbonate sold. Virgin
polycarbonate is polycarbonate which has not been altered from
the time of original manufacturing to the purchase of the product.
Polycarbonate regrind comes from polycarbonate that is taken from
an end-user and ground into pellets. These new pellets can be
compounded again with other material (both virgin and other regrind
pellets) to produce a new product. The nature of polycarbonate
is such that its properties do not deteriorate significantly after
being reground if dried properly prior to processing.
What is UL approval?
UL (Underwriters Laboratories) performs various tests on products
sold in the United States. One such test, UL94, is used to measure
the resistance of plastics to a flame source. For polycarbonate,
the test will normally result in a mark of V-0, V-1, V-2. V-0
is the most flame retardant and V-2 is the least flame retardant
of the marks typically given to polycarbonate. If the material
does not pass the test for V-0, V-1, or V-2; then the product
is not UL approved. UL approval is given for a particular product
at a measured thickness which is reported with the rating. Hence,
saying that a given product is V-2 is insufficient information
without also specifying at what thickness the rating is valid.
UL approval is required for certain applications of polycarbonate.
|Maximum time any one specimen can burn after removal of 2nd application of flame
|Maximum glowing time permitted for any one sample after removal of 2nd application of flame
|Total flaming combustion time allowed
(maximum) for the 10 flame applications
|Ignition of cotton from dripping, flaming particles
|Flaming combustion up to the holding clamp
- Shall not have a burning rate exceeding 1.5 inch/minute over a 3 inch span for specimens having a thickness of 0.120 inch and above.
- Shall not have a burning rate exceeding 3.0 inch/minute over a 3 inch span for specimens having a thickness of under 0.120 inch.
- Shall cease to burn before the flame reaches the 4 inch reference mark but shall not comply with 94 V-0, V-1, or V-2 requirements.
The second part of the UL94 test determines the Relative Thermal
Index (RTI) of the material. The RTI is the temperature at which
a specific property will decrease to half of its original value
after 60,000 hours of exposure at that temperature. If a material
has not been tested, the generic RTI for the material is assigned.
The generic RTI for polycarbonate is 80°C. PTS Tristar polycarbonate
grades have elevated RTI as shown below.
UL information for PTS Polycarbonate
What is FDA certification?
Materials that are used in applications that are in contact with
food require FDA certification.
What is UV stabilization?
UV stabilizers are added to polycarbonate to help protect the
material from the effects of exposure to the Sun. Radiation from
the Sun, especially in the UV portion of the spectrum, degrades
the properties of polycarbonate. The addition of UV stabilizers
allows the material to sustain exposure to the Sun for a longer
period of time.
What is mold release?
Adding a mold release agent to polycarbonate makes processing
easier. It acts in a way similar to a lubricant in the injection