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What is Polycarbonate?
Polycarbonate (PC) is a high-performance tough, amorphous and transparent thermoplastic polymer which has an organic functional groups linked together by carbonate groups (–O–(C=O)–O–) and offers a unique combination of properties. It is used as an engineering plastics thanks to its:
High impact strength
- High dimensional stability
- Good electrical properties, amongst several others
The polymer shows excellent mechanical properties (Density: 1.2 – 1.22 g/cm3), maintains toughness upto 140°C and down to -20°C. The characteristics of polycarbonate are quite like those of polymethyl methacrylate (PMMA, acrylic), but polycarbonate is stronger, usable in a wider temperature range (Melting point: 155°C) but more expensive. PC shows excellent compatibility with certain polymers. Therefore, it is widely used in blends such as PC/ABS, PC/ PET, PC/PMMA…
Polycarbonate was first prepared in 1953 by Dr.H.Schnell of Bayer AG, Germany and by D.W. Fox of General Electric Company, USA.
PC is a good material of choice in industry due to its versatile characteristics, eco-friendly processing and recyclability. They have the unique set of chemical and physical properties making them suitable over glass, PMMA, PE, etc.
- Toughness and High Impact Strength – Polycarbonate has high strength that makes it resistant to impact and fracture and hence provides safety and comfort in application demanding high reliability & performance. They are virtually unbreakable.
- Transmittance – PC is an extremely clear plastic and can transmit over 90% of light as good as glass. PC sheets are available in a wide range of shades which can be customized depending on the end-user application.
- Lightweight – The benefits allows provides OEMs virtually unlimited possibilities for design compared with glass. The property allows increased efficiency, makes installation process easier and reduces overall transportation costs.
- Protection from UV Radiations – Polycarbonates can be designed to block ultraviolet radiation and provide 100% protection from the sun’s harmful UV rays.
- Optical Nature – Thanks to its amorphous structure, PC offers excellent optical properties. Refractive index of clear polycarbonate is 1.584.
- Chemical Resistance – Polycarbonate exhibits good chemical resistance against diluted acids, aliphatic hydrocarbons and alcohols; moderate chemical resistance against oils and greases. PC is readily attacked by diluted alkalis, aromatic and halogenated hydrocarbons. Manufacturers recommend to clean PC sheets with certain cleaning agents which do not affect its chemical nature. It is sensitive to abrasive alkaline cleaners.
- Heat Resistance – Polycarbonates offers good heat resistance and are thermally stable upto 135°C. Further heat resistance can be improved by adding flame retardants without impacting material properties.
|Highly transparent and offer light transmission as good as glass||Easily attacked by hydrocarbons & bases|
|High toughness even down to -20°C||Post prolonged exposure to water at over 60°C, their mechanical properties start to degrade|
|High mechanical retention up to 140°C||Proper drying is required before processing|
|Intrinsically flame retardant||Low fatigue endurance|
|Offers good electrical insulation properties that are not influenced by water or temperature||Yellowing tendency post exposure to UV|
|Possess good abrasion resistance|
|Can withstand repeated steam sterilizations|
- Other Properties:
- Good electrical insulation properties, not influenced by water or temperature
- Good abrasion resistance
- Resistant to repeated steam sterilization
- More efficient than other engineering thermoplastics
Limitations of Polycarbonates
There are also certain limitations associated with polycarbonate plastics:
- Low fatigue endurance
- Mechanical properties degrade after prolonged exposure to water at over 60°C
- Attacked by hydrocarbons and bases
- Proper drying before processing is needed
- Yellows after long exposure to UV
Use of Additives or Thermoplastic Blends for
Polycarbonates’ creep resistance can be further improved with addition of glass- or carbon-fiber reinforcements. 5-40% of GF reinforcements can improve creep resistance upto 28 MPa at temperature as high as 210°F. Reinforced grades have better tensile modulus, flexural- & tensile strength as compared to standard PC grades.
Additives are also added to improve flame retardancy, thermal stability, UV light and color stability and several other properties. Coated polycarbonates sheets also show better weatherability, mar and chemical resistance.
- Stabilizers based on benzotriazole are useful for stabilization of PC against UV light and protects from UV degradation.
- Phosphorous acid esters-based stabilizers are known to be effective in improving thermal stability of polycarbonate
- Several flame retardants (halogenated, phosphorous-based, silicone-based) are widely used to achieve necessary UL performance, increase LOI and reduce the heat of combustion for PC products
Polycarbonate blends are successful commercially for providing right balance between performance and productivity.
PC/Polyester Blends: These alloys are suitable for applications where high chemical resistance is required. PC/PBT Blends offer higher chemical resistance than PC/PET Blends due to PBT’s higher crystalline behavior. While PET blended grades offer superior heat resistance.
PC/ABS Blends: PC’s toughness and high heat resistance combined with ABS ductility and processability provide an excellent combination of properties.
Applications of PC
As discussed above, these characteristics provide design freedom to product designers, engineers and OEMs and make polycarbonates an ideal material for use in several applications such as:
Polycarbonates and its blends are used in appliances such as refrigerators, air conditioners, coffee machines, food mixers, washing machines, hair dryers steam iron water tanks etc. because they offer shape freedom through a wide range of mechanical properties. It also enhances robustness and visual appeal of product.
Being lightweight and transparent, PC is used to make eye-catching design as well as enhance vehicle efficiency by reducing weight without affecting durability & improve aerodynamics of vehicle. Thanks to its high heat resistance it is used in light housing, headlamp bezel & lenses. PC blends are used in car interior and exterior body parts as well due to their rigidity and excellent creep resistance.
|Building & Construction:
PC is known as a suitable alternative to glass in a number of glazing applications such as agricultural houses, industry or public building, facades, security windows, shelters and skylights due to the high impact strength, transparency, resistance to UV light and weatherability.
PC has very low birefringence, internal stress and due to its high dimensional accuracy, it is used to manufacture CDs/DVDs. Also, its high transparency allows to design innovative products for everyday life such as safety goggles, ophthalmic lenses, large-volume water bottles, etc. It’s also optically clear, which makes it ideal for things like shatterproof sunglasses, face shields, protective glasses or even as a component in bullet-proof windows.
|Electrical & Electronics:
In E&E market, PC is used in many applications such as circuit breakers, electrical housing, lighting applications, domestic switches, plug & sockets, switchgears, relays, connectors, EVs, battery packaging material, etc. The strength of polycarbonate helps prevent the housing units from breaking and polycarbonate films help prevent scratches on the screens.
Polycarbonates are majorly used in medical applications, thanks to the excellent combination of properties such as clarity, heat resistance, dimensional stability and toughness. PC can be sterilized by ethylene oxide, high energy radiation and limited autoclave cycles. Typical medical applications include surgical instruments, drug delivery systems, hemodialysis membranes, blood reservoirs, blood filters etc. where polycarbonates have been able to replace glass and metal.
Because of its heat resistance and shatter resistance, polycarbonate is used in applications for direct contact with foods and beverages. Food storage containers made from PC are reusable, help preserve freshness, protect foods from contamination and can be conveniently used in the refrigerator and microwave.
|Other applications include:
How PC is Manufactured?
Polycarbonates are manufactured by condensation polymerization of bisphenol A (BPA; C15H16O2) and phosgene (COCl2).
Methods Used to Produce Polycarbonate Parts
Polycarbonate can be processed by extrusion, injection molding, blow molding, thermoforming etc.
It is melted and forced into a mold with high pressure to give it the desired shape. Drying before processing is highly recommended: 2-4 hr at 120°C. Target moisture content should be a maximum of 0.02%.
In order to avoid material degradation, the ideal maximum residence time is between 6 and 12 minutes, depending on the selected melt temperature. There are two major techniques involved in polycarbonate processing: injection molding and extrusion (mentioned below).
Injection molding is most often used method to produce parts made from polycarbonates and its blends. Since polycarbonate is highly viscous, it is usually processed at high temperature to reduce its viscosity. In this process, the hot polymer melt is pressed through into a mold with high pressure. The mold when cools, gives the molten polymer its desired shape and characteristics. This process is generally used to manufacture polycarbonate bottles, plates, etc. Since polycarbonate is a poor-flowing plastic, wall thickness should not be too thin.
Certain guidelines that need to be followed while processing polycarbonate by injection molding are mentioned below:
|Resin||Melt Temperature, °C||Mold Temperature, °C||Molding Shrinkage, %|
|High Heat PC||310-340||100-150||0.8-0.9|
In this process, the polymer melt is passed through a cavity which helps in giving it the final shape. The melt when cooled attains and maintains the shape acquired. This process is used to manufacture polycarbonate sheets, profiles and long pipes. Some recommendations for processing polycarbonate with this technique are listed below:
- Extrusion Temperature: 230-260°C
- L/D ratio of 20-25 is recommended
Polycarbonate is a strongest thermoplastic material and an interesting choice as a 3D Printing filament. It is a really strong material while still maintaining temperature resistance. Polycarbonate does not shatter like plexiglass.
- Machine bendable at room temperature
- Printing temperature from 260 – 300°C
- Recommended printing bed temperature of 90°C or higher
- Print speeds : 30mm/s is ideal, can go up to 60 or 80mm/s
Polycarbonate material can be bonded using several techniques including solvent bonding, adhesive bonding or mechanical fastening… Better understand the quality requirements for Adhesive bonding process according to regulatory standard DIN 2304-1.
Is Polycarbonate Safe for Use? How to Recycle PC?
Polycarbonate plastic is a perfect material for baby bottles, refillable water bottles, sippy cups, and many other food and beverage containers. However, safety of PC came under scrutiny because it is made with bisphenol A (BPA) and research & government agencies worldwide continue to study the potential for low levels of BPA to migrate from polycarbonate products (material degradation in contact with water) into foods and beverages. These analyses have shown that potential human exposure to BPA from polycarbonate products in contact with foods and beverages is very low and poses no known risk to human health.
Several regulatory authorities worldwide, few to name US FDA, European Commission’s Scientific Committee on Food, UK Food Standards Agency, have recognized safe use of PC for food contact applications but there are some studies as well which showed BPA to be a hazardous risk to health and hence, leading to development of “BPA-free” polycarbonate products.
All applications made for Polycarbonate plastic is 100% recyclable and identified by recycling code “7”. One of the methods are chemical recycling where scrapped PC is reacted with phenol to produce monomers which are purified for further polymerization.
Researchers are also working to develop new processes for recycling polycarbonates into another type of plastic—one that does not release bisphenol A (BPA) into the environment when it is used or dumped into a landfill.
Polycarbonate Properties and Their Values
As discussed above, polycarbonate offers a unique combination of properties: high impact strength, high dimensional stability, good electrical properties, amongst several others. Glass filled grades of polycarbonate show good chemical and moisture resistance too. From physical properties, dimensional stability, electrical performances to fire and thermal properties, find out every possible attribute with its values here.