Comprehensive Guide on Polycarbonate (PC)

olycarbonate (PC) is a transparent thermoplastic with carbonate functional groups. Its high strength makes it resistant to impact and fracture. It is lightweight so an excellent alternative to glass. PC is melted and forced into a mold with high pressure to give it the desired shape. It is widely used owing to its eco-friendly processing and recyclability.

What is polycarbonate (PC)?

Polycarbonate is a high-performance tough, amorphous, and transparent thermoplastic polymer. It has organic functional groups linked together by carbonate groups (–O–(C=O)–O–). It offers a unique combination of properties. PC is popularly used as an engineering plastic owing to its unique features that include:

• High impact strength
• High dimensional stability
• Good electrical properties amongst others

The characteristics of polycarbonate are similar to polymethyl methacrylate (PMMA, acrylic). But PC is more expensive, stronger, and used in a wider temperature range. It has a melting point of 155°C.

As PC shows excellent compatibility with certain polymers, it is widely used in blends, such as PC/ABS, PC/ PET, and PC/PMMA. Some of the common applications are compact disc, safety helmets, bullet-proof glass, car headlamp lenses, baby feeding bottles, roofing, glazing, etc.

DID YOU KNOW?
Polycarbonate was first prepared in 1953 by Dr.H.Schnell of Bayer AG, Germany, and by D.W. Fox of General Electric Company, USA.

How PC is manufactured?

Polycarbonates are manufactured by condensation polymerization of bisphenol A (BPA; C₁₅H₁₆O₂) and phosgene (COCl₂).

What are the properties of polycarbonate?

PC is an ideal material well known for its versatile characteristics. It is widely used in the industry for its eco-friendly processing and recyclability. It comprises a unique set of chemical and physical properties. This makes it suitable over glass, PMMA, and PE. The key properties of polycarbonates include:

• Toughness – Polycarbonate maintains a toughness value between -20°C to 140°C. They are virtually unbreakable.
• High Impact Strength – PC has a high strength that makes it resistant to impact and fracture. It provides safety and comfort in applications that demand high reliability and performance. The polymer has a density of 1.2 – 1.22
• Transmittance – PC is an extremely clear plastic that can transmit over 90% of light as good as glass. Polycarbonate sheets are available in a wide range of shades. These sheets can be customizable depending on an end-user application.
• Lightweight – This feature allows virtually unlimited possibilities for OEMs to design as compared with glass. The property increases efficiency and makes the installation process easier. It also reduces overall transportation costs.
• Protection from UV Radiations – Polycarbonates can be designed to block ultraviolet radiation. They provide 100% protection from harmful UV rays.
• Optical Nature – For having an amorphous structure, PC offers excellent optical properties. The refractive index of clear polycarbonate is 1.584.
• Chemical Resistance – Good chemical resistance against diluted acids, aliphatic hydrocarbons, and alcohols. It shows moderate resistance against oils and greases. PC is readily attacked by diluted alkalis, aromatic, and halogenated hydrocarbons. Manufacturers recommend cleaning PC using agents which do not affect their chemical nature. It is sensitive to abrasive alkaline cleaners.
• Heat Resistance – Polycarbonates have high heat resistance. They are thermally stable up to 135°C. Further heat resistance can be improved by adding flame retardants without impacting material properties.

TIP: In case you have specific requirements, try using the “key feature” facet to narrow down your search to find your Polycarbonate grade of interest.

What are the strengths and limitations of high heat PC grades?

Strengths	Limitations
Highly transparent and offers light transmission as good as glass.High toughness even down to -20°CHigh mechanical retention up to 140°CIntrinsically flame retardantOffers good electrical insulation properties that are not influenced by water or temperaturePossesses good abrasion resistanceCan withstand repeated steam sterilizations	Easily attacked by hydrocarbons and basesPost prolonged exposure to water at over 60°C, their mechanical properties start to degradeProper drying is required before processingLow fatigue enduranceYellowing tendency post exposure to UV

How additives or thermoplastic blends optimize material properties?

Addition of additives

The creep resistance of polycarbonates can be improved by up to 28 MPa by adding 5-40% fillers at 210°F temperature. These fillers include glass- or carbon-fiber reinforcements. Reinforced grades, when compared to standard PC grades, have better:

• tensile modulus,
• flexural strength, and
• tensile strength.

Adding additives can improve flame retardancy, thermal stability, UV light, and color stability. They also improve several other properties. Coated polycarbonate sheets also show better weatherability, and mar- and chemical resistance.

• Stabilizers based on benzotriazole are useful to stabilize PC against UV light. They also protect from UV degradation.
• Phosphorous acid esters-based stabilizers improve the thermal stability of polycarbonate.
• Flame retardants such as halogenated, phosphorous-based, and silicone-based are widely used as additives. They help to attain the required UL performance, increase LOI, and reduce the heat of combustion for PC products.

Thermoplastic blends

Polycarbonate blends are successful commercially. They provide the right balance between performance and productivity.

PC/Polyester Blends: Suitable for applications that require high chemical resistance. PC/PBT blends offer higher chemical resistance than PC/PET blends. This is due to PBT’s higher crystalline behavior. PET blended grades offer superior heat resistance.

PC/ABS Blends: PC’s toughness and high heat resistance combine the ductility and processability of ABS. This provides an excellent combination of properties. View PC/ABS blends here »

How is PC processed?

The common methods to produce polycarbonate parts are:

• Extrusion
• Injection molding
• Blow molding
• Thermoforming

PC is melted and forced into a mold with high pressure to give it the desired shape. Drying before processing i.e., 2-4 hr at 120°C is highly recommended. Target moisture content should be a maximum of 0.02%.

In order to avoid material degradation, the ideal maximum residence time is between 6-12 minutes depending on the selected melt temperature. Two major techniques involved in polycarbonate processing are injection molding and extrusion.

Injection Molding

Injection molding is the most common method to produce polycarbonates and their blends. Polycarbonate is highly viscous. It is usually processed at high temperatures 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 and plates. Since polycarbonate is a poor-flowing plastic, the 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, %
PC	280-320	80-100	0.5-0.8
High Heat PC	310-340	100-150	0.8-0.9
Filled PC	310-330	80-130	0.3-0.5
PC/ABS	240-280	70-100	0.5-0.7
PC/PBT	250-270	60-80	0.8-1.0
PC/PET	260-280	60-80	0.6-0.8

Typical Settings for Injection-Molding Various Polycarbonate Resins

Extrusion

In the extrusion 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. Recommendations:

• Extrusion Temperature: 230-260°C
• L/D ratio of 20-25 is recommended

3D Printing

Polycarbonate is the strongest thermoplastic material. It is an interesting choice as a 3D Printing filament. PC is known for maintaining temperature resistance. It does not shatter like plexiglass.

• Machine bendable at a 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. These include solvent bonding, adhesive bonding, or mechanical fastening. It is imperative to understand the quality requirements for adhesive bonding processes according to regulatory standard DIN 2304-1.

Is PC safe for use?

Polycarbonate plastic is a perfect material for baby bottles, refillable water bottles, sippy cups, and other food and beverage containers. Though the safety of PC came under scrutiny as it is made with bisphenol A (BPA).

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 analysis have shown that:

• The potential human exposure to BPA from PC products in contact with foods and beverages is low. 
• They pose no known risk to human health.

Several regulatory authorities worldwide are US FDA, European Commission’s Scientific Committee on Food, and UK Food Standards Agency. They have recognized the 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. This leads to the development of “BPA-free” polycarbonate products.

Is PC recyclable?

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.

What are the developments in bio-based polycarbonate?

Many companies have developed bio-based polycarbonate. This version is poised to act as a drop-in substitute for its synthetic counterpart in several end-use industries. Bio-PC has a similar molecular structure with enhanced durability. But there are certain limitations w.r.t production cost.

In the last few years, several new developments were seen in this segment. They include:

DURABIO™ by Mitsubishi Chemical Corporation – It is a bio-based engineering plastic. It is made from plant-derived isosorbide monomer. Its transparency and optical homogeneity surpass those of BPA-based conventional polycarbonate resin.

POLYSORB® Isosorbide by Roquette – It is a plant-based alternative solution to BPA. It can be used as a monomer in polycarbonate synthesis. Isosorbide-based polycarbonates can be used to provide enhanced chemical, UV, and scratch resistance in the construction and automotive industries amongst others.

LEXAN™ PC resin based on Certified Renewable Feedstock by SABIC – It is a latest polycarbonate solution based on ISCC PLUS certified feedstock. Part of its TRUCIRCLE™ initiative of circular solutions, SABIC shows significant reductions in carbon footprint (up to 50%) and fossil depletion impacts (up to 35%) during polycarbonate resin production based on renewable feedstock.

Recently, a breakthrough has been made at the Korea Research Institute of Chemical Technology (KRICT) in this field. The researchers have created a bio-polycarbonate made largely from glucose. Unlike earlier bio-polymers, the team claims that this new bio-polycarbonate has the strength and durability to match its petrochemical counterpart, paving the way for commercialization.

Reference：omnexus