Polycarbonate (PC)

What is Polycarbonate

Polycarbonate (PC) is an amorphous thermoplastic whose polymer chain contains repeating carbonate linkages. The dominant commercial form is bisphenol A polycarbonate, made by joining bisphenol A units through carbonate groups into a rigid, transparent backbone. Because the polymer is amorphous rather than semi-crystalline, it has no sharp crystalline melting point, transmits light with very little haze, and softens progressively above its glass transition temperature of roughly 147 to 150 degrees Celsius. That amorphous structure is the root of both its clarity and its low molding shrinkage, typically 0.5 to 0.7 percent for unfilled grades.

The defining engineering property of polycarbonate is impact resistance. Unfilled grades reach notched Izod impact strength in the range of about 600 to 850 joules per meter at room temperature, far above acrylic, polystyrene, or most other transparent plastics, and they remain ductile down to roughly minus 40 degrees Celsius. Combined with light transmission near 88 to 90 percent and a refractive index of about 1.585, this lets one material serve as both a structural and an optical part: safety glazing, machine guards, automotive headlamp lenses, and riot shields all exploit the same combination of toughness and transparency.

Polycarbonate was developed independently and almost simultaneously in the mid-1950s. Hermann Schnell at Bayer in Germany patented bisphenol A polycarbonate in 1953, with Bayer commercializing it under the Makrolon trade name from 1958. Daniel Fox at General Electric in the United States arrived at the same polymer around the same period, and GE commercialized it as Lexan from 1960. Two industrial synthesis routes coexist today: the interfacial phosgenation process, in which bisphenol A reacts with phosgene at a water and solvent interface, and the melt transesterification (non-phosgene) process, in which bisphenol A reacts with diphenyl carbonate. The melt route avoids phosgene and chlorinated solvents and is the preferred technology for most newly built plants.

In market terms polycarbonate is one of the largest-volume engineering thermoplastics. Global demand is on the order of 6 to 7 million tonnes per year, with a market value in the region of 25 to 28 billion US dollars in the mid-2020s. Supply has shifted heavily toward Asia, and Chinese capacity alone now exceeds 4 million tonnes per year, a substantial share of world output. The principal end uses are electrical and electronics housings, optical media and lenses, automotive lighting and glazing, construction sheet and glazing, medical devices, and safety equipment.

The application history tracks the polymer's two strengths. Optical clarity made polycarbonate the substrate of choice for the compact disc, DVD, and Blu-ray, an enormous volume application through the 2000s that drove optical-grade resin development. Impact resistance put it into police riot shields, machine guards, bank-teller screens, and bullet-resistant laminates. Automotive headlamp lenses moved from glass to hard-coated polycarbonate for weight and design freedom, and full polycarbonate automotive glazing is now used for fixed windows and panoramic roofs. In construction, multi-wall sheet glazes greenhouses, stadium roofs, and walkways where glass weight or breakage is unacceptable. These are not marketing examples; each one selected polycarbonate because a measurable property, transparency or impact or both, beat the alternatives.

Two synthesis routes matter to buyers for more than chemistry trivia. Interfacial-phosgenation resin and melt-transesterification resin can differ slightly in end-group chemistry, residual chloride, and color, which affects optical and electrical grades at the margins; some optical and high-purity grades are specified by route. The melt route also leaves no residual solvent, an advantage for some food and medical applications. For most structural and enclosure parts the route is invisible in the datasheet, but it can appear in supplier qualification documents for sensitive applications.

It is important to separate the polymer from the part. A polycarbonate datasheet describes a specific grade: a base resin plus a defined molecular weight (read indirectly through melt flow rate), plus an additive package that may include UV stabilizers, flame retardants, mold-release agents, colorants, and glass or carbon reinforcement. Two parts both labeled polycarbonate can differ by an order of magnitude in stiffness, by a full flammability class, and by years of outdoor service life. The rest of this guide is organized around that grade-level view, because the procurement decision is always a grade decision, never a polymer decision.

Grade Families and Forms

Manufacturers organize polycarbonate into grade families defined by their additive package and intended application, then offer each family across multiple physical forms: injection-molding and extrusion pellets, solid and multi-wall sheet, film, rod, and tube. Both Covestro (Makrolon) and SABIC (Lexan) publish families that map onto the categories below. Selecting the right family first, then the right form, then the right melt flow, is the fastest path through a supplier catalog.

General purpose and optical grades are unmodified or lightly modified clear resins, supplied as pellets for injection molding or as cast and extruded blanks for machining. Optical-quality variants control gel count, birefringence, and yellowness index tightly, which is why the same chemistry served decades of CD, DVD, and Blu-ray substrate production and continues to serve camera, automotive, and lighting lenses. These grades are clear but not UV-stable on their own and will yellow outdoors without protection.

UV-stabilized glazing sheet is the construction and signage workhorse. A co-extruded UV-absorbing cap layer on one or both faces protects the bulk polymer, and these products typically carry a 10-year warranty against breakage and excessive yellowing. Solid sheet is used where full transparency and impact strength matter; twin-wall and multi-wall sheet trade some clarity for thermal insulation and lower weight in greenhouse and roofing glazing. The UV-protected face must face the weather, a detail that is easy to install backward.

Flame-retardant grades add a halogen-free or halogenated FR package to reach UL 94 V-2, V-0, or 5VA ratings at a specified thickness, and many also meet rail standard EN 45545-2 or aircraft interior FAR 25.853. They dominate electrical and electronic enclosures, luminaire bodies, and transport interiors. Because the FR rating is thickness-dependent, the family alone is not a specification; the UL Yellow Card thickness governs.

Glass-fiber reinforced grades trade transparency for stiffness and dimensional stability, covered in Chapter 4. Food and medical grades use certified base resins with controlled extractables and documented FDA, EU 10/2011, or USP Class VI compliance for bottles, housings, and sterilizable devices, though BPA migration concerns increasingly push new designs toward alternative chemistries.

Forms also drive selection. The same resin family is sold as injection-molding pellets, extrusion-grade pellets, cast and extruded sheet, machinable rod and tube, thin film for membrane switches and labels, and multi-wall structural sheet. Form changes the achievable property set: extruded solid sheet preserves near-full transparency and impact strength, twin-wall and triple-wall sheet add insulation and stiffness-to-weight at the cost of clarity, and machined stock from cast blank avoids the molding-induced stresses that can later craze. Buyers should specify form, thickness, and surface finish alongside the grade, because a glazing sheet datasheet and a molding-pellet datasheet for nominally the same grade family report different numbers measured on different specimens.

Mechanical and Thermal Properties

The numbers below describe standard unfilled bisphenol A polycarbonate measured by the common ISO and ASTM methods. They are typical mid-range values; any specific grade datasheet takes precedence, because molecular weight, additives, and reinforcement shift these figures substantially. Reinforced and FR grades are addressed in Chapter 4.

Mechanical behavior. Polycarbonate yields rather than shattering. Under tensile load it reaches a yield point near 60 to 70 MPa, then necks and draws to elongations often above 100 percent, dissipating energy as plastic deformation. This ductility, not raw strength, is what makes it the impact material of choice: a 3 mm sheet can stop a thrown object that would crack acrylic or glass. The tradeoff is a relatively soft, scratch-prone surface (Rockwell M70), which is why optical and glazing parts are usually hard-coated.

Thermal behavior. Being amorphous, polycarbonate has a glass transition near 147 to 150 degrees Celsius and no crystalline melt point. Its practical continuous-use temperature is around 115 to 125 degrees Celsius, and heat deflection temperature under a 1.8 MPa load sits near 128 to 138 degrees Celsius. The coefficient of thermal expansion is high at roughly 65 to 70 micrometers per meter per Kelvin, about ten times that of steel, so large glazing panels and long molded parts need expansion gaps and slotted fasteners. The polymer is also notably notch-sensitive and prone to environmental stress cracking when exposed to certain solvents, oils, and alkaline cleaners under stress.

Optical and electrical behavior. Light transmission of 88 to 90 percent through a 3 mm section, a refractive index near 1.585, and high Abbe-limited but usable clarity make polycarbonate a workhorse lens and glazing material. Electrically it is a good insulator: volume resistivity above 10^15 ohm-centimeter, dielectric constant around 2.9 to 3.0 at 1 MHz, and dielectric strength on the order of 15 to 35 kV/mm depending on thickness and test geometry. These properties, together with V-rated flame retardancy in FR grades, underpin its dominance in electrical enclosures.

Chemical resistance and stress cracking. Polycarbonate resists water, dilute acids, and many oils, but it is vulnerable where many engineers underestimate it. Strong alkalis, amines, ketones, esters, and chlorinated and aromatic solvents attack or dissolve it, and a wide range of otherwise mild substances cause environmental stress cracking: under sustained tensile stress, contact with certain oils, plasticizers, adhesives, threadlockers, and aggressive cleaning agents initiates fine cracks that propagate and embrittle the part. Molded-in residual stress and sharp internal corners compound the risk. This is the single most common in-service failure mode for polycarbonate, and it is why a compatibility check against the real contact media and cleaning regime, not just the nominal process fluid, belongs in every selection.

Additives, Reinforcement, and Standards

Most of what distinguishes one polycarbonate part from another lives in the additive and reinforcement package, not the base polymer. This chapter covers the four additive systems engineers specify most often, then the standards that let a datasheet be compared like-for-like.

UV stabilization. Bare polycarbonate absorbs ultraviolet light in the 290 to 400 nm band, which photo-oxidizes the bisphenol A backbone and causes yellowing, surface chalking, and gradual loss of impact strength. Protection takes two forms: a co-extruded UV-absorbing cap layer on sheet products, or UV absorbers compounded into molding resin. UV-protected glazing sheet from major makers typically carries a 10-year warranty against breakage and excessive yellowing, but the protection only works on the treated face.

Flame retardancy. FR packages move standard PC from its native UL 94 V-2 or HB rating up to V-0 or 5VA at a stated thickness. The rating is intrinsically thickness-dependent, so a grade may be V-0 at 1.5 mm yet only V-2 at 0.8 mm; the governing number is the minimum rated thickness on the UL Yellow Card. Transport applications layer additional standards on top, such as EN 45545-2 for European rail interiors and FAR 25.853 for aircraft cabins.

Glass and carbon reinforcement. Short glass fiber at 10 to 40 percent by weight is the most common structural modification. It raises stiffness and strength, cuts thermal expansion, and improves creep resistance, at the cost of transparency, ductility, and mold wear. Carbon-fiber grades go further on stiffness and add static dissipation. The table contrasts unfilled PC with a typical 30 percent glass-filled grade.

Blends and copolymers. Polycarbonate is frequently alloyed to tune cost and performance. PC/ABS blends improve flow, lower cost, and ease processing for automotive interiors and electronics; PC/PBT and PC/PET blends add chemical resistance. These are distinct datasheet families and should not be specified by the bare PC name.

Mold-release and other additives. Internal mold-release agents ease ejection of thin-wall and complex parts; impact modifiers shift the ductile-to-brittle transition lower for cold-service parts; optical brighteners and tints tune appearance; and anti-static or laser-marking additives serve electronics. Each additive trades against another property, so an additive-loaded grade is a deliberate compromise rather than a free upgrade, which is why generic substitution between grades that merely share a base resin is risky.

Governing standards. Three documents let polycarbonate grades be compared and procured consistently. ISO 7391 (Plastics, Polycarbonate (PC) moulding and extrusion materials) defines the designation system and the basis for specifications, with Part 2 covering specimen preparation and property determination; ISO 21305 is its successor in the current ISO structure. ASTM D3935 is the United States material specification for unfilled and reinforced polycarbonate and polycarbonate copolymer for injection molding, blow molding, and extrusion. UL 94 governs flammability classification, and supporting test methods such as ISO 1133 (melt flow), ISO 75 (heat deflection), ISO 180 (Izod impact), and ASTM D1003 (haze and transmission) define how individual datasheet numbers are measured. Specifying the standard and test method alongside each value is what makes two suppliers' datasheets genuinely comparable.

Key Specification Parameters

A polycarbonate datasheet can list dozens of values, but a handful drive most selection and processing decisions. Reading them correctly, and knowing which test method produced each number, prevents the common mistake of comparing grades across incompatible test bases.

Melt flow rate (MFR/MVR). Measured per ISO 1133 or ASTM D1238, MFR is the practical proxy for molecular weight and the single most important processing parameter. Low-MFR grades (around 3 to 6 g/10 min) carry higher molecular weight and toughness, suited to thick-wall, high-impact parts; high-MFR grades (above 20 g/10 min) fill thin walls and long-flow optical parts more easily but sacrifice some impact strength. Matching MFR to wall thickness and flow length is step one of grade selection.

Impact strength and ductility. Quote notched Izod or Charpy with the test temperature, because polycarbonate's value depends strongly on notch radius and temperature. A high room-temperature figure does not guarantee performance at minus 30 degrees Celsius or behind a sharp internal corner. For glazing and guards, multi-rate or falling-dart impact data is more representative than a single notched value.

Heat resistance. Three distinct numbers describe thermal limits: glass transition temperature (about 147 to 150 degrees Celsius), heat deflection temperature under load (about 128 to 138 degrees Celsius at 1.8 MPa, higher at 0.45 MPa), and the manufacturer's rated continuous-use temperature (about 115 to 125 degrees Celsius). They are not interchangeable; HDT under load is the right figure for a part that must hold shape under stress at temperature.

Flammability. The specification is the UL 94 class plus the thickness it was achieved at, optionally with a glow-wire (IEC 60695) or limiting oxygen index value. A grade named V-0 without a stated thickness is incompletely specified.

Optical and weathering. For transparent parts, the relevant numbers are light transmission and haze per ASTM D1003, yellowness index per ASTM E313, and any UV warranty terms. For outdoor parts, demand the UV protection method (cap layer versus compounded absorber) and the warranty duration explicitly.

Processing-linked parameters. Several datasheet figures exist only to be respected at the machine. Drying conditions (120 degrees Celsius, 2 to 4 hours, dew point minus 30 degrees Celsius) are mandatory because residual moisture degrades molecular weight during melting. The recommended melt temperature window of roughly 280 to 320 degrees Celsius and mold temperature of 80 to 120 degrees Celsius govern surface finish, internal stress, and impact retention; running too cold leaves frozen-in stress that later crazes, while running too hot accelerates degradation and yellowing. Mold shrinkage near 0.5 to 0.7 percent for unfilled grades, and anisotropic shrinkage in glass-filled grades, must be designed into tooling. These parameters are not optional fine print; ignoring them turns a good grade into a brittle part.

• MFR/MVR (ISO 1133): processing window and molecular weight proxy, match to wall thickness.
• Notched Izod/Charpy (ISO 180/179): always paired with test temperature and notch geometry.
• HDT (ISO 75): load-bearing thermal limit, quote at the relevant load.
• UL 94 class + thickness: the only complete way to state flame retardancy.
• Light transmission and haze (ASTM D1003): for optical and glazing grades.
• Certifications: FDA / EU 10/2011 food contact, USP Class VI medical, EN 45545-2 rail, as applicable.

Selection Decision Factors

Polycarbonate selection goes wrong most often when engineers pick a base resin and bolt on requirements afterward, instead of letting the dominant constraint drive the grade family from the start. The ordered sequence below works as a reusable RFQ template.

1. Define the dominant constraint: transparency, impact, flame retardancy, structural stiffness, or chemical and food contact. This single decision selects the grade family (general purpose, glazing, FR, glass-filled, or certified) before any number is chosen.
2. Set the thermal envelope: maximum continuous service temperature and any load present at temperature. Compare against rated continuous-use temperature and HDT under the relevant load, not against the glass transition temperature.
3. Quantify impact requirements: specify notched impact at the lowest service temperature and the worst notch geometry, and prefer falling-dart data for sheet and guards. Confirm low-temperature ductility if the part sees sub-zero service.
4. Fix flammability: state the required UL 94 class and the minimum wall thickness, plus any transport standard (EN 45545-2, FAR 25.853) or glow-wire requirement. Verify on the UL Yellow Card, not the grade name.
5. Address weathering and UV: for outdoor parts, require an explicit UV protection method and warranty term, and specify a hard coat where abrasion or chemical contact is expected.
6. Check chemical compatibility: polycarbonate is vulnerable to environmental stress cracking from many solvents, fuels, and alkaline cleaners under load. Verify against the actual contact media and cleaning agents before committing.
7. Match processing to geometry: select MFR for the wall thickness and flow length, confirm drying requirements (120 degrees Celsius, 2 to 4 hours, dew point minus 30 degrees Celsius), and account for mold wear with abrasive glass-filled grades.
8. Confirm certifications and total cost: validate food, medical, optical, or transport approvals against the destination market, then weigh resin price against scrap, coating, and warranty exposure across the part's life.

A frequently overlooked dimension is supply and serviceability: grade availability in the destination region, color and form (pellet, sheet, multi-wall) lead times, the maker's UL file and regulatory documentation, and the existence of a qualified second source. Major suppliers including Covestro (Makrolon), SABIC (Lexan), Trinseo (Calibre), Mitsubishi Engineering-Plastics (Iupilon), Teijin (Panlite), Idemitsu (Tarflon), and large Chinese producers such as Wanhua Chemical and Luxi Chemical offer overlapping grade ranges, which makes dual-sourcing on equivalent ISO 7391 datasheet properties practical for high-volume parts.