Polycarbonate (PC) is one of the engineering plastics with the best overall balance of properties, combining high transparency, high impact strength, excellent heat resistance, and dimensional stability. In electrical and electronic, automotive, medical, and industrial equipment applications, PC is used for transparent windows and protective face shields, as well as extensively for housings and structural parts. When an application involves live components or must meet safety certification requirements, the flame retardancy of PC becomes a key consideration that cannot be avoided.
Many people believe that PC is inherently flame-retardant and requires no additional modification. This is only partly true. Pure PC is indeed more difficult to ignite than materials such as ABS and PP, but its UL94 rating is usually only V-2. Flame retardants are still required for PC to achieve V-0 consistently. Moreover, adding flame retardants changes the transparency, impact strength, heat resistance, and processing performance of PC. These changes directly affect product design and mold development.
This article begins with the combustion characteristics of PC and systematically reviews the UL94 ratings achievable with PC, halogenated and halogen-free flame-retardant solutions, and the effects of flame retardants on performance. It also lists common commercial flame-retardant PC grades to help manufacturing customers avoid unnecessary problems during material selection.
I. Combustion Characteristics of PC: Naturally Char-Forming, but Not Inherently V-0
The molecular backbone of PC contains numerous aromatic rings and carbonate groups. During combustion, the surface of PC carbonizes rapidly and forms a dense char layer. This layer insulates the underlying material from heat and oxygen, slowing further decomposition. This char-forming characteristic gives PC a degree of self-extinguishing behavior, and its burning rate is significantly lower than that of ABS, PP, and PMMA.
However, the inherent flame retardancy of pure PC is not sufficient to achieve V-0 consistently. The reasons are as follows:
- Although PC forms char during combustion, it continues to burn for a period of time, and its afterflame time may exceed the 10-second limit required for V-0;
- PC produces molten drips during combustion. Although these drips generally do not continue burning, they may ignite the cotton placed below, causing failure in the V-0 dripping test;
- The flame-retardant performance of PC is strongly affected by the wall thickness of the molded part. Thin-wall parts (<1.5 mm) have more difficulty achieving a high flame-retardancy rating than thick-wall parts.
Therefore, pure PC is generally rated UL94 V-2. Some thick-wall parts may achieve V-1, but consistently passing V-0 is difficult. Products such as electrical and electronic housings, chargers, and connectors that require V-0 certification must use a flame-retardant-modified PC grade.
II. UL94 Ratings Achievable with PC
1. V-2 Rating: Pure PC and Lightly Flame-Retardant PC
Pure PC exhibits a degree of self-extinguishing behavior in the vertical burning test. Its afterflame time is generally short, but molten drips may ignite the cotton, so it is classified as V-2. For many non-critical flame-retardant applications, V-2 is sufficient.
Typical applications:
- Transparent windows, protective covers, instrument-panel lenses, and other products that require high transparency but only a general flame-retardancy rating;
- Products that do not come into direct contact with exposed live components;
- Parts with relatively thick walls (>2.0 mm), for which pure PC is sufficient.
Note: A V-2 rating is not guaranteed for every pure PC grade. Combustion behavior varies among PC brands. If an explicit V-2 listing on a UL Yellow Card is required, select a UL-certified grade.
2. V-0 Rating: The Standard Choice for Flame-Retardant PC
To enable PC to achieve V-0 consistently, flame retardants must be added, usually halogen-free phosphate ester flame retardants or halogenated brominated flame retardants. Flame-retardant PC is used extensively in electrical and electronic applications:
- Charger housings and power-adapter housings;
- Laptop housings and tablet housings (often as an alloy with ABS);
- Internal structural components of televisions;
- Heat-dissipation components and housings for LED lighting;
- Industrial control-equipment panels.
Key characteristic:
After achieving V-0, flame-retardant PC can still retain relatively high impact strength and heat resistance. This is its core advantage over flame-retardant ABS and flame-retardant PP.
III. Flame-Retardant Systems for PC: Primarily Halogen-Free, Supplemented by Halogenated Systems
1. Halogen-Free Flame-Retardant PC: Phosphate Ester Flame Retardants
Halogen-free flame-retardant technology for PC is highly mature. Most mainstream halogen-free flame-retardant PC grades use phosphate ester flame retardants, such as resorcinol bis(diphenyl phosphate) (RDP) and bisphenol A bis(diphenyl phosphate) (BDP).
Mechanism of action:
- At high temperatures, phosphate esters decompose and release phosphoric acid, promoting char formation on the PC surface and creating a denser char layer;
- At the same time, they release noncombustible gases that dilute the concentration of combustible gases;
- Some phosphate esters also act as plasticizers, improving the flowability of PC.
Advantages:
- Environmentally friendly and halogen-free; complies with RoHS, REACH, and halogen-free standards;
- Relatively high flame-retardant efficiency with a moderate additive loading (typically 5%–15%);
- Relatively little effect on transparency; some grades can remain translucent or even transparent;
- Improves flowability and facilitates the molding of thin-wall parts.
Disadvantages:
- Phosphate ester flame retardants reduce the heat resistance of PC, and the HDT may decrease from 130°C to 115–125°C;
- Impact strength decreases, particularly low-temperature impact strength;
- Phosphate esters may migrate to the surface under hydrolytic conditions, affecting the long-term stability of molded parts;
- The cost is higher than that of pure PC but generally lower than that of halogenated flame-retardant PC.
Typical applications:
Chargers, adapters, laptop housings, internal television components, and LED lighting.
2. Halogenated Flame-Retardant PC: Brominated Flame Retardants
Halogenated flame-retardant PC generally uses brominated polycarbonate copolymers or brominated epoxy resins as flame retardants. Unlike ABS, halogenated flame-retardant PC accounts for a relatively small share of the market because halogen-free flame-retardant technology for PC is already highly mature and environmental trends increasingly favor halogen-free solutions.
Advantages:
- High flame-retardant efficiency, allowing the additive loading to be kept relatively low;
- Good retention of heat resistance, with a smaller decrease in HDT than in phosphate ester systems;
- Some grades can achieve a 5VA rating and are suitable for more stringent fire-safety requirements.
Disadvantages:
- Produces smoke and corrosive gases during combustion;
- Does not meet halogen-free requirements and is subject to export restrictions;
- Higher cost and a limited selection of grades.
Typical applications:
Flame-retardant PC components with extremely high heat-resistance requirements and certain industrial-equipment housings.
IV. Overall Effects of Flame Retardants on PC Performance
| Performance Property | Pure PC (V-2) | Halogen-Free Flame-Retardant PC (V-0) | Halogenated Flame-Retardant PC (V-0) |
| Notched impact strength | 60–90 kJ/m² | 30–60 kJ/m² | 40–70 kJ/m² |
| Heat deflection temperature (1.82 MPa) | 125–135°C | 110–125°C | 120–130°C |
| Tensile strength | 60–70 MPa | 55–65 MPa | 55–65 MPa |
| Light transmittance (3 mm) | 88%–91% | Translucent to opaque, depending on grade | Generally opaque |
| Melt flow index (300°C/1.2 kg) | 5–15 | 8–20 (plasticized by phosphate ester) | 5–12 |
| Color options | Transparent or any color | Transparent/translucent/black/white | Primarily dark colors |
| Processing window | Wide | Relatively wide, but moisture must be controlled | Relatively narrow; attention to degradation required |
Processing precautions:
- More stringent drying requirements:
Phosphate esters in halogen-free flame-retardant PC are hygroscopic. Before processing, the material must be dried at 120°C for 3–4 hours, with moisture content controlled below 0.02%. Otherwise, molded parts may develop silver streaks and bubbles, and hydrolysis may even cause a severe loss of properties.
- Processing-temperature control:
Phosphate ester flame retardants may decompose at excessively high temperatures, producing gases and black specks. A barrel-temperature range of 270–300°C is recommended, and prolonged residence time should be avoided.
- Mold temperature:
A mold temperature of 80–100°C is recommended to obtain good surface quality and dimensional stability. Controlling internal stress in flame-retardant PC is equally important, particularly for structural parts with snap-fits or screw bosses.
- Screw speed and back pressure:
Use a moderate screw speed (50–100 rpm), and do not set the back pressure too high, to prevent excessive shear from decomposing the flame retardant.
- Mold corrosion:
Halogen-free flame-retardant PC is generally only mildly corrosive to molds, but some brominated flame retardants may release trace amounts of acidic gases. Mold maintenance should be monitored during long-term production.
V. Reference List of Common Commercial Flame-Retardant PC Grades
Some common commercial flame-retardant PC grades are listed below for material-selection reference. Specific properties should be confirmed using each brand’s official TDS and UL Yellow Card.
| Brand | Typical Grade | UL94 Rating | Flame-Retardant System | Features and Typical Applications |
| SABIC | Lexan 940 | V-0 | Halogen-free phosphate ester | General-purpose flame-retardant PC for electronic housings; translucent option available |
| SABIC | Lexan 941 | V-0 | Halogen-free phosphate ester | High flow; suitable for thin-wall charger housings |
| SABIC | Lexan 943 | V-0 | Halogen-free phosphate ester | Transparent flame-retardant PC for windows/panels |
| Covestro | Makrolon 6485 | V-0 | Halogen-free phosphate ester | Flame-retardant PC for electrical and electronic housings |
| Covestro | Makrolon 6555 | V-0 | Halogen-free phosphate ester | High-flow flame-retardant grade for thin-wall parts |
| Chimei | PC-6600 | V-0 | Halogen-free phosphate ester | General-purpose flame-retardant grade for housings |
| Chimei | PC-6700 | V-2 | Halogen-free | Lightly flame-retardant with good toughness |
| LG Chem | Lupoy GN1006F | V-0 | Halogen-free phosphate ester | Flame-retardant PC for appliance housings |
| Formosa | AC3830 | V-0 | Halogen-free | Flame-retardant PC for electronic housings |
| Mitsubishi | Iupilon EFR Series | V-0 | Halogen-free | Flame-retardant PC for industrial components |
Selection tips:
- There are relatively few transparent V-0 flame-retardant PC grades, and they are expensive, such as SABIC Lexan 943. If a product must be both transparent and flame-retardant, grade availability should be confirmed in advance;
- For thin-wall parts (<1.2 mm), give priority to high-flow flame-retardant grades such as Makrolon 6555;
- If the product will be used in a high-temperature, high-humidity environment for an extended period, the hydrolytic stability of the phosphate ester flame retardant must be considered;
- The market supply of halogenated flame-retardant PC grades is limited. If a halogen-free solution cannot meet the heat-resistance requirement, ask the supplier whether brominated flame-retardant PC or a PC/ABS alloy can be used instead.
VI. Material-Selection Recommendations
When is pure PC (V-2) sufficient?
The product has no V-0 certification requirement;
The product does not come into direct contact with exposed live components;
High transparency and high impact strength must be retained;
The product has relatively thick walls and only modest flame-retardancy requirements.
When must flame-retardant PC (V-0) be selected?
The product contains live components and safety standards require V-0;
Charger, adapter, and power-module housings;
Export products that must obtain UL certification;
The customer’s specification explicitly requires V-0.
Halogenated or halogen-free?
Among flame-retardant PC solutions, halogen-free systems are now overwhelmingly mainstream. Unless the customer has special requirements, or the product has extremely high heat-resistance requirements that cannot be met by a halogen-free solution, halogen-free flame-retardant PC should be selected first.
How should you choose between flame-retardant PC and PC/ABS?
Flame-retardant PC offers better heat resistance and higher impact strength, making it suitable for high-temperature environments and applications requiring high toughness;
Flame-retardant PC/ABS has a lower cost and better processing flowability, making it suitable for large thin-wall housings;
If the product requires chemical resistance (for example, contact with cleaning agents), flame-retardant PC/ABS may be more sensitive than pure PC, so immersion testing is required.
Conclusion
PC has an inherent flame-retardancy advantage over ABS and PP, but the statement that PC is inherently flame-retardant is not entirely accurate. Pure PC can generally achieve only V-2. To pass V-0 certification consistently, a flame-retardant-modified grade must be selected. Halogen-free flame-retardant PC is the mainstream solution in the current market and offers a good balance among environmental performance, transparency, and processability, but its negative effects on heat resistance and low-temperature impact strength must be considered.
We have long supplied flame-retardant PC resin from brands such as SABIC, Covestro, Chimei, and LG. We offer multiple V-0/V-2 options, together with TDS documents, UL Yellow Cards, and RoHS/REACH declarations.
If you are developing a flame-retardant electronic housing, charger, or industrial panel, please contact us. Based on your product structure, certification requirements, and target cost, we will recommend the most suitable grade and arrange sample testing.
