Engineering Thermoplastic
Polycarbonate — Polycarbonate
Polycarbonate (PC) is an amorphous engineering thermoplastic combining exceptional impact strength with optical clarity. It is virtually unbreakable and widely used where glass-like transparency and toughness are required.
Summary
Polycarbonate (PC) is a high-performance, amorphous engineering thermoplastic renowned for its exceptional impact resistance, optical clarity, and high heat deflection temperatures. Often used as a lightweight, shatterproof alternative to glass, it maintains its mechanical properties over a broad temperature range. While sensitive to certain chemicals and UV radiation in its base form, it can be stabilized and alloyed to suit demanding automotive, medical, and electronic applications. Its versatility is further enhanced by its compatibility with high-precision injection moulding and extrusion.
PCMakrolonLexanPanliteCalibre
Manufacturers
5
Grades
6
Applications
6
Equivalents
3
Technical description
Polycarbonate is an amorphous engineering thermoplastic characterized by an unusual combination of high stiffness, high impact strength (even at low temperatures), and excellent transparency. In its natural state, it is a clear, straw-colored resin that can be tinted to optical perfection or made opaque with pigments. The material exhibits a high glass transition temperature (Tg) of approximately 147°C (297°F), allowing it to retain structural integrity in high-heat environments where many other transparent plastics, such as PMMA or Polystyrene, would soften and deform.
From a mechanical standpoint, Polycarbonate is unique because of its ductility. Unlike most transparent plastics that fail in a brittle manner, PC typically undergoes plastic deformation before failure, absorbing a massive amount of energy. Typical values for notched Izod impact strength range from 600 to 900 J/m (ASTM D256), which is significantly higher than most other engineering resins. It also possesses a high refractive index (1.586), allowing for thinner lenses in eyewear. However, its high viscosity means it requires significant pressure and temperature during processing, and its notched sensitivity means that sharp geometric transitions must be avoided in design to prevent premature mechanical failure.
Chemically, PC is a polyester of carbonic acid. The aromatic rings in the backbone provide heat resistance and rigidity, while the carbonate groups provide some polar character. This polar nature makes PC susceptible to certain solvents, particularly ketones, esters, and aromatic hydrocarbons, which can cause 'crazing'—the formation of microscopic cracks that weaken the part. It also has a moderate moisture absorption rate (0.15% to 0.35% at equilibrium), but because the moisture reacts chemically with the polymer chain at processing temperatures (hydrolysis), extremely strict drying protocols are mandatory for successful manufacturing.
History
Polycarbonate was discovered nearly simultaneously and independently in 1953 by two researchers working on opposite sides of the Atlantic. Dr. Hermann Schnell at Bayer AG in Germany filed for a patent on the material just days before Dr. Daniel Fox at General Electric (GE) in the United States made a similar discovery while working on a new wire insulation material. This led to a period of cross-licensing and competition that defined the early days of the material's commercialization. Bayer marketed their product under the trade name Makrolon, while GE introduced their version as Lexan.
Initially, polycarbonate was seen as a niche material due to its high production cost. However, throughout the 1960s and 70s, its unique properties—specifically its ability to replace glass in safety applications and its use in heavy-duty electrical components—drove rapid adoption. The 1980s saw the explosion of PC in the digital data storage market with the rise of the Compact Disc, a market Lexan and Makrolon dominated for decades. Today, while the ownership of the original GE Plastics division has shifted to SABIC, the legacy of these two chemical pioneers remains at the heart of the global polycarbonate industry.
Chemical structure
Polycarbonate is a thermoplastic polymer characterized by the presence of carbonate groups (-O-(C=O)-O-) in its long molecular chain. The most prevalent type of PC is synthesized from Bisphenol A (BPA) and phosgene. During the polymerization process, the monomers are linked via ester groups, leading to a long-chain linear polyester structure. The bulky phenyl rings in the backbone of the BPA-polycarbonate molecule are responsible for the high glass transition temperature (Tg) and the stiffness of the material, as they restrict the rotation of the polymer chain.
Morphologically, polycarbonate is predominantly an amorphous polymer. This lack of a crystalline structure is the fundamental reason for its exceptional optical transparency and low, predictable shrinkage during processing. While it is possible to induce some semi-crystallinity through prolonged heating at high temperatures (annealing) or solvent exposure, such occurrences are generally avoided as they lead to embrittlement and loss of transparency. The high molecular weight and the specific arrangement of the aromatic rings contribute to the material's legendary toughness, which allows it to absorb significant energy before failure.
Polymer family
Polycarbonate belongs to the family of engineering thermoplastics. Specifically, it is classified as a clear, amorphous polyester. In the broader hierarchy of polymers, it sits above commodity plastics like PE and PVC, but generally below high-performance 'super-plastics' like PEEK or PEI in terms of thermal resistance. However, it occupies a unique 'goldilocks' zone in the material world, offering a combination of transparency, impact strength, and heat resistance that few other materials can match at a comparable price point, which is why it remains one of the most widely used engineering resins globally.
How it's made
The primary commercial route for producing polycarbonate is the interfacial polymerization process. In this method, Bisphenol A (BPA) is dissolved in a caustic soda solution to form a sodium salt. This aqueous phase is then mixed with an organic solvent (typically dichloromethane) containing phosgene gas. The reaction occurs at the interface of the two liquids, where the BPA and phosgene combine to form the polymer chain. Catalysts are added to speed up the reaction, and chain terminators are used to control the molecular weight.
An alternative, more environmentally friendly method is the 'melt transesterification' or non-phosgene process. In this route, BPA is reacted with diphenyl carbonate (DPC) at high temperatures and under a vacuum. This process eliminates the use of highly toxic phosgene gas and chlorinated solvents, producing phenol as a byproduct that can be recycled. While the melt process can sometimes result in a slightly more yellowed product compared to the interfacial method, advancements in catalyst technology have significantly closed the quality gap, leading to its increased adoption by major producers.
Advantages
- ●Exceptional impact resistance, often described as 'bulletproof' and virtually unbreakable compared to glass or acrylic.
- ●High optical clarity with light transmission rates typically exceeding 88-90% in clear grades.
- ●Excellent dimensional stability and low mold shrinkage (0.5%–0.7%), allowing for high-precision tolerances.
- ●Wide operating temperature range, maintaining mechanical properties from -40°C to 120°C (up to 140°C for high-heat grades).
- ●Inherent flame retardancy in many grades, frequently achieving UL94 V-0 ratings at thin gauges.
- ●Good electrical insulation properties with high dielectric strength, suitable for electronic housings.
- ●Good creep resistance, allowing the material to maintain its shape under long-term mechanical stress.
- ●Biocompatibility in specific medical grades (ISO 10993), making it suitable for surgical instruments and blood oxygenators.
- ●Ease of sterilization via ethylene oxide (EtO) or gamma radiation (though yellowing may occur with radiation).
- ●High ductitility, allowing for cold-forming or 'metal-like' bending in thin-gauge sheets.
Disadvantages
- ●Susceptible to stress cracking (crazing) when exposed to certain chemicals like alkalis and hydrocarbons.
- ●Relatively poor scratch resistance, requiring hard-coating for applications like eyewear or automotive glazing.
- ●Sensitivity to hydrolytic degradation; it must be dried to less than 0.02% moisture before processing to avoid loss of properties.
- ●High processing temperatures are required (280°C - 320°C), which can lead to material yellowing if residence times are long.
- ●Limited UV resistance in its natural state, necessitating the use of UV stabilizers or cap-layers for outdoor use.
- ●Contains Bisphenol A (BPA), raising regulatory and health concerns in food-contact and infant applications.
- ●Higher cost compared to commodity resins like Polypropylene or Polystyrene.
When to choose it
Polycarbonate should be the first choice when a project requires a combination of high impact resistance and optical clarity. It is the gold standard for safety glazing, riot gear, and protective eyewear where human safety depends on the material not shattering. It is also the ideal selection for components that must withstand both low-temperature impact (down to -40°C) and high-temperature service (near 120°C), a range that few other transparent plastics can cover.
Choose PC when dimensional stability is critical. Because it is amorphous and has a very low and predictable shrink rate, it is perfect for high-precision parts مانند internal camera components or complex electronic housings. It is also the preferred material for high-voltage electrical components that require transparency for inspection, as it offers excellent dielectric strength and can be formulated to meet stringent UL94 V-0 flame retardancy standards without sacrificing too much of its mechanical performance.
When to avoid it
Avoid using polycarbonate in applications involving continuous exposure to strong alkalis, such as industrial-strength cleaning agents or certain detergents, as these will cause rapid chemical degradation and cracking. It should also be avoided in applications requiring high scratch resistance without the use of secondary hard-coatings, as the material is relatively soft (measured on the Rockwell R scale) and MARs easily.
Furthermore, PC is not the ideal choice for high-speed friction and wear applications, as it has a high coefficient of friction and can gall against other surfaces. For components requiring 'bearing and wear' properties, materials like POM (Acetal) or Nylon are generally superior. Lastly, in the food and beverage industry, there is a push to avoid BPA-containing PC for products specifically aimed at infants or where stringent 'BPA-free' marketing is required; in these cases, Copolyesters like Tritan are often used as substitutes despite having lower heat resistance.
Physical Properties
- Density
- 1.20 g/cm³
- Water Absorption (24h)
- 0.15 %
- Transparency
- Transparent (88% light transmission)
- Shrinkage
- 0.5 – 0.8 %
Mechanical Properties
- Young's Modulus
- 2.3 – 2.4 GPa
- Tensile Strength
- 60 – 70 MPa
- Flexural Strength
- 90 – 100 MPa
- Impact Strength (Izod)
- 600 – 900 J/m
- Hardness (Rockwell M)
- 70
- Elongation at Break
- 100 – 150 %
Thermal Properties
- Glass Transition Temperature
- 147 °C
- Continuous Service Temperature
- 115 – 130 °C
- Heat Deflection Temperature
- 130 – 140 °C
- Thermal Conductivity
- 0.20 W/m·K
- CTE
- 65 – 70 × 10⁻⁶ /K
Electrical Properties
- Dielectric Constant
- 2.9 – 3.0
- Volume Resistivity
- 10¹⁶ Ω·cm
- Dielectric Strength
- 15 kV/mm
Chemical Resistance
- Acids (dilute)
- Good
- Bases
- Poor
- Alcohols
- Fair
- Oils
- Good
- Gasoline
- Fair
- Acetone
- Poor (attacks)
- UV Resistance
- Poor (unless coated)
Sustainability
- Recyclability
- Recyclable
- Recycling Code
- 7
- Bio-based Content
- 0 – 50 % (bio grades)
- Carbon Footprint
- ~5 kg CO₂e / kg
Process compatibility
Injection moulding
The primary method for PC. High pressures and temperatures (280-320C) required. Mold must be heated (80-120C) for best surface finish.
Extrusion
Common for producing sheets, films, and profiles. High melt strength of certain grades is ideal.
Blow moulding
Used for large water carboys and containers. Requires specific high-melt-strength (low MFR) grades.
Thermoforming
Excellent for large signs and aircraft parts. Sheets must be predried before heating to avoid bubbles.
CNC machining
Machines well but generates heat quickly. Use sharp tools and appropriate cooling to avoid melting and stress.
3D printing
FDM is common but difficult due to warping/bed adhesion issues. Requires enclosures. SLA resins for PC-like properties exist.
Bonding
Solvent bonding (using Methylene Chloride) is very effective. Adhesive bonding with epoxies or cyanoacrylates is also common.
Painting
Compatible with many coatings but solvent choice is critical to avoid stress cracking of the substrate.
Laser cutting
Possible but problematic for thick sections. Tends to char, discolour, and produce sticky residue. Thin films work better.
Rotomoulding
Rarely used for PC due to high melt viscosity and degradation risks at the long cycle times required.
Manufacturing compatibility
Injection MoldingExtrusionBlow MoldingThermoformingCNC MachiningLaser CuttingBonding
Applications
Automotive and Transportation
Headlight lenses, panoramic sunroofs, and interior instrument clusters where impact resistance and clarity are vital.
Medical Devices
Blood oxygenators, dialysis filter housings, surgical staplers, and intravenous connectors requiring sterilization.
Architecture and Construction
Multi-wall roofing sheets, skylights, and security glazing for banks or high-risk storefronts.
Electronics and Electrical
Laptop housings, smartphone frames, light socket connectors, and transparent fuse box covers.
Personal Protective Equipment (PPE)
Riot shields for law enforcement, safety goggles, welding helmets, and motorcycle visor systems.
Aerospace and Defense
Aircraft cabin windows, interior lighting covers, and canopy systems for military jets.
Consumer Goods
Reusable water bottles, suitcases (hardside luggage), and high-end kitchen appliances like blender jars.
Data Storage and Optics
Compact discs (CDs), DVDs, and Blu-ray discs, though this market has declined in favor of digital streaming.
Lighting and Signage
LED diffusers, street light globes, and illuminated outdoor signage requiring UV stability and impact protection.
Industrial Machinery
Machine safety guards and sight glasses for pressurized tanks where monitoring of fluids is necessary.
Environmental impact
The environmental profile of polycarbonate is complex. On one hand, its extreme durability and long service life contribute to resource efficiency by reducing the need for frequent replacements. In sectors like automotive and aerospace, its lightweight nature directly contributes to fuel efficiency and reduced CO2 emissions compared to glass or metal components. However, the production of polycarbonate is energy-intensive and traditionally relies on phosgene, a highly toxic gas, and Bisphenol A (BPA), an endocrine disruptor that has faced significant regulatory scrutiny, particularly in the European Union and for food-contact applications.
Modern environmental efforts focus on reducing the footprint of PC through bio-attributed feedstocks and improved recycling loops. Some manufacturers, such as Covestro and SABIC, have introduced 'mass balance' PC grades where a portion of the raw materials is derived from bio-waste or circular feedstocks. Additionally, while PC is a fossil-fuel-based plastic, its high value and purity in specific streams (like water carboys or optical discs) make it an attractive candidate for high-quality recycled content, though the mechanical properties of recycled PC are sensitive to the number of heat cycles the material has undergone.
Recycling
Polycarbonate is identified by the Resin Identification Code (RIC) '7', which serves as the 'Other' category. This often complicates curbside recycling, as it is mixed with various other resins. However, in industrial and closed-loop settings, PC is highly recyclable. Mechanical recycling involves grinding clean scrap into regrind, which can then be re-pelletized and blended with virgin resin. Because PC is an amorphous engineering plastic, its properties—particularly molecular weight—degrade with each heat cycle (thermal history). Typically, a 20% regrind limit is recommended for structural parts to maintain impact integrity.
Chemical recycling, or advanced recycling, is a growing field for polycarbonate. Depolymerization processes can break the polymer back down into its constituent monomers, BPA and DPC (or phenol), which can then be purified and used to create 'virgin-quality' resin again. This is particularly useful for contaminated or multi-layer waste that cannot be mechanically recycled. Major players like SABIC and Covestro are increasingly offering 'Certified Circular Polycarbonate' based on these mass-balance and chemical recycling techniques.
Available grades
PC OpticalPC FRPC GF10PC GF30PC MedicalPC UV
Manufacturers
Equivalent materials
Compare Polycarbonate with…
Frequently asked questions
Does polycarbonate require drying before injection moulding?▾
Yes, polycarbonate is extremely hygroscopic. It must be dried in a desiccant dryer to a moisture content of <0.02% (typically 3-4 hours at 120°C) before processing. Failure to do so causes hydrolysis, resulting in bubbles, silver streaks (splay), and a dramatic loss of impact strength.
How does PC compare to Acrylic (PMMA) in optical applications?▾
PC is naturally clear with ~90% transmission, while PMMA is even clearer at ~92%. However, PC is much tougher (virtually unbreakable) but softer and more prone to scratches. PMMA is brittle but more UV stable and scratch-resistant.
Is polycarbonate suitable for long-term outdoor exposure?▾
Standard PC is not very UV resistant and will yellow and become brittle within months of direct exposure. For outdoor use, 'UV stabilized' grades or sheets with a co-extruded UV-protective layer must be specified.
What chemicals should be avoided when cleaning polycarbonate parts?▾
PC is sensitive to many chemicals. Avoid cleaners containing ammonia, strong alkalis, or aromatic hydrocarbons. Always use a 'polycarbonate-safe' cleaner or mild soap and water to prevent stress cracking.
Can you blend polycarbonate with other resins like ABS?▾
Yes, several manufacturers offer PC/ABS blends. This combines the high heat and impact resistance of PC with the improved processability and lower cost of ABS. It is a standard material for automotive interiors and electronics.
What is the maximum service temperature for polycarbonate?▾
Unfilled PC usually begins to soften around 145°C-150°C (Glass Transition Temperature). For continuous use under load, 120°C is a safe ceiling, though specialized high-heat grades (like Covestro Apec) can reach 200°C.
Is polycarbonate sensitive to notch effects?▾
While PC is generally strong, it is notch-sensitive. Sharp internal corners create stress concentrators that can cause a part to fail under impact. Engineers should always use generous radii (0.5mm minimum) in part design.