Is Polycarbonate Toxic? Separating the Monomer, the Polymer and the Migrant requires a division of the question into free bisphenol A (BPA) monomer, the aromatic polycarbonate macromolecule, and the low-molecular-mass species that move from a finished article into food, water, or biological fluid. Polycarbonate is synthesised by condensation of BPA (CAS 80-05-7) with phosgene in an interfacial process or with diphenyl carbonate in a melt transesterification process. The repeat unit has a molar mass of 254.3 g/mol, whereas commercial injection-moulding and extrusion grades typically exhibit weight-average molecular mass from 28,000 g/mol to 80,000 g/mol. The difference in molecular size between monomer and polymer controls absorption, metabolism, and the applicable regulatory limit.

Free BPA Monomer Is a Residual Process Variable with Endocrine Activity

Free BPA is 2,2-bis(4-hydroxyphenyl)propane with a molecular mass of 228.29 g/mol and an octanol-water partition coefficient log Kow of 3.32. It is not classified primarily as an acute oral toxicant; the regulatory concern is oestrogen-receptor-mediated activity at very low exposure concentrations. The European Food Safety Authority re-evaluation published in 2023 established a tolerable daily intake of 0.2 ng/kg body weight per day, replacing the 2015 temporary tolerable daily intake of 4 µg/kg body weight per day. Under REACH, BPA was included on the Candidate List in 2017 as a substance of very high concern for endocrine-disrupting properties relevant to human health.

Residual free BPA in polycarbonate resin must be distinguished from BPA generated later by hydrolytic or thermal chain scission. Interfacial polymerisation is conducted in a methylene chloride-water system containing sodium hydroxide; the resin solution is washed and steam-stripped before pelletising. Incomplete washing or reduced stripper vacuum leaves unreacted BPA in the pellet. Melt transesterification uses diphenyl carbonate at high temperature and vacuum; finishing reactors and vent ports remove unreacted BPA, phenol, and cyclic oligomers. Food-contact polycarbonate resin specifications generally require free BPA below 50 µg/g, although published data for this specific configuration is limited.

The polycarbonate matrix itself is a high-molecular-weight aromatic carbonate with a glass transition temperature of approximately 147°C, a density of 1.20 g/cm³, and tensile yield strength of 60–70 MPa under ASTM D638. In bacterial reverse-mutation testing under OECD TG 471 and in vitro mammalian tests under ISO 10993-3, extracts from cured polycarbonate do not show genotoxic responses at the limit concentrations. The polymer is practically insoluble in water and simulated gastrointestinal fluids; because the molecular mass is far above the threshold for passive transepithelial uptake, systemic absorption of the intact polymer is negligible. The bulk polymer therefore does not present the endocrine-active mechanism associated with BPA.

That polymer-directed conclusion does not apply after the carbonate linkage is broken. Hydrolytic and thermal chain scission reduces molecular mass and liberates BPA or short-chain hydroxyl-terminated oligomers at the part surface. The relevant risk from a polycarbonate article is a migrant risk. Material that has been converted to low-molecular-mass phenolic species at the surface can transfer into liquids, and the species may be detected analytically as free BPA or as BPA after hydrolysis. Migration testing is therefore performed on the finished part rather than on virgin pellets.

What Migrates from Polycarbonate Under Food Contact Conditions?

European migration testing for polycarbonate food-contact articles is performed according to the EN 1186 series using food simulants A (10% ethanol), B (3% acetic acid), C (50% ethanol), and D2 (vegetable oil). Specific migration of BPA is measured by high-performance liquid chromatography with fluorescence detection, or by LC-MS/MS, following CEN/TS 13130-13. The governing European instrument for plastic food-contact articles is Regulation (EU) No 10/2011, as amended by Regulation (EU) 2018/213. The specific migration limit for BPA is 0.05 mg/kg food under this regime. Regulation (EU) No 321/2011 separately prohibits BPA in polycarbonate infant feeding bottles. In the United States, 21 CFR 177.1580 covers polycarbonate resins and does not codify a numerical BPA migration limit; the clearance defines authorised use conditions and extractive specifications.

Migration is not a single-value property of polycarbonate. The free residual monomer contributes to the initial migrant pool, but hydrolytic degradation during service generates additional BPA at the surface. Published aqueous migration data for new polycarbonate bottles at 100°C for 1 h generally remain below 50 µg/L, the numerical equivalent of the EU SML for aqueous simulants, but older bottles and those exposed to alkaline detergent have shown higher values; published data for this specific configuration is limited. The independent variable is not total resin charge but the surface area-to-volume ratio under test, the thermal history, and the extent of hydrolysis.

Reported BPA migration values also depend on analytical preparation. If the procedure includes hydrolysis of the aqueous or food simulant before chromatography, the result can include BPA derived from low-molecular-mass carbonate oligomers. If only free BPA is measured, the value may be lower. CEN/TS 13130-13 therefore describes specific procedures for BPA in food simulants; LC-MS/MS provides the sensitivity needed for the 0.05 mg/kg SML when dilute food samples are analysed. Laboratories that omit the hydrolysis step may under-report the total hydrolysable migrant pool.

When Hydrolytic Degradation Accelerates Monomer Liberation in Aqueous Service

Hydrolysis is the principal non-toxicological mechanism that converts polycarbonate into its monomeric building block. The carbonate group reacts with water to produce chain scission; when both carbonate bonds adjacent to the same BPA unit are hydrolysed, BPA is released. Under neutral or acidic conditions the reaction is slow at ambient temperature but accelerates at 121°C steam-sterilisation temperature. Under alkaline conditions, such as 2% sodium hydroxide solution or aggressive dishwasher detergent, the rate increases sharply because hydroxide ion attacks the carbonate carbon. Polycarbonate should not be autoclaved repeatedly or cleaned with high-pH agents if long service life is required. Published data for this specific configuration is limited, but the polymer-migrant boundary is usually characterised by measuring molecular-weight retention and free BPA after accelerated ageing.

A steam autoclave at 121°C for 30 min repeated over 50 cycles can produce measurable reductions in melt viscosity and impact strength; some studies report an increase in surface free BPA after repeated autoclaving, although absolute quantities remain below the EU migration limit in intact, dry-moulded parts. In contact with 3% acetic acid at 70°C for 2 h, compliant polycarbonate articles are expected to release BPA below 0.05 mg/kg. Polycarbonate food-contact uses are therefore not prohibited in Europe for general food service, but authorised use requires migration testing appropriate to the intended contact temperature and simulant.

For polycarbonate in medical device housings, connectors, and ports, the migration question is treated as an extractables-and-leachables problem under ISO 10993-18 rather than a food-contact SML. Ethylene oxide sterilisation at 55°C with an ethylene oxide concentration of 600 mg/L does not generate BPA; gamma irradiation at 25 kGy, however, can induce radical-mediated discoloration and molecular-weight reduction without necessarily liberating free BPA unless residual moisture is present. Polycarbonate medical parts therefore require resin selection and moulding conditions that avoid excessive residual water, which would otherwise convert sterilisation energy into hydrolysis.

In drinking-water-contact applications, polycarbonate sight glasses and covers are evaluated under NSF/ANSI 61 for extraction of BPA and other contaminants into aggressive test waters. The pass/fail criterion is set by product-specific extraction studies; published data for this specific configuration is limited. Hot chlorinated water accelerates surface crazing and carbonate hydrolysis, so the upper continuous-service temperature should be verified against the certified use conditions rather than assumed from room-temperature data.

Processing Conditions That Control the Monomer-to-Migrant Transition

Injection moulding and extrusion conditions are the primary production-scale variables separating a low-migrant polycarbonate part from a degraded one. Polycarbonate pellets must be dried to a moisture content below 0.02% by weight before melt processing. A closed-loop desiccant dryer at 120°C for 4 h is standard; hopper residence time and dew point control below −30°C prevent re-absorption. When the melt is processed between 280°C and 320°C, hydrolytic scission is minimal. A general-purpose screw with a 32:1 L/D ratio, coupled with vacuum venting at −0.08 MPa relative pressure, removes low-molecular-mass species before the metering zone. A vent system that loses vacuum below −0.06 MPa cannot strip residual BPA effectively; this is a recognised production fault in pelletised compound.

Barrel residence time is an equally critical boundary. At melt temperatures above 360°C or residence times beyond 10 min, thermal degradation of the carbonate bond begins to generate BPA, phenol, and carbon dioxide. This can be detected as a rise in the yellow index, a drop in intrinsic viscosity, and an increase in surface oligomer content. Mould temperatures are typically 80°C to 120°C to control stress and part dimensions; they do not drive monomer formation directly but affect cooling stress and therefore long-term crack resistance in hot water service.

No amine-based stabilisers or mould-release agents should be used in polycarbonate food-contact formulations because residual amine functionality can attack the carbonate linkage at melt temperatures and increase monomer formation. This incompatibility is a batch-to-batch process parameter controlled by raw-material purity rather than by an additive concentration that can be rectified later.

For high-temperature beverage dispensing, the intended-use temperature must not exceed the simulant condition established in the migration test, because BPA migration increases with temperature. In institutional warewashing, repeated exposure to alkaline detergents at 80°C and rinse sanitising at 82°C for 30 s must be included in repeated-use migration testing under EN 1186; otherwise the part cannot be declared compliant for that use.