Cured Epoxy resins in their most simple form are built by mixing the starting components epoxy resin and hardener in a specific mixing (stoichiometric) ratio to produce a thermoset polymer. The most widely commercialised resin of its kind is created by reacting Bisphenol A (BPA) and epichlorohydrin in a 2-step process, which results in its pure form as the basic monomer unit of an epoxy resin called BADGE – or DGEBA – short for BisphenolADiGlycidylEther. However most liquid epoxy resins contain also higher molecular weight fractions like dimer, trimer or oligomer species in varying content, depending on the reaction conditions. BADGE is then mixed with hardeners and/or other reactive substances in a process called “curing” or “hardening” to constitute the final epoxy-based polymer.
The selection of the reactants, the mixing ratio, and the curing process itself will determine many properties of the cured epoxy resin, like its adhesion to other materials, its mechanical strength, its thermal and chemical resistance or its dielectric strength.
Media’s attention has been drawn to experimental studies on BPA since the 90s, driving public and political concerns because coverage often focuses only on research showing negative effects and tends to excessively exaggerate the risks. The quoted animal toxicity studies commonly use high exposure concentrations, unlikely to occur in real life, and small cohorts (number of test animals with the same characteristics). The replicability of “experimental” studies is questionable, and so are the conclusions and the statistical relevance of the results.
NGOs have also campaigned to ban BPA with emotional messages and politically driven restrictions based on the precautionary principle. However, the truth is that only minute residual traces of BPA are left in epoxy resin. These traces, also known as technical impurities, will either react during the curing process or will be embedded and thus immobilised into the cured resin matrix.
This process also prevents a release during service life. At the end of the use period, incineration in refuse incineration plants, cement kilns or steel foundries (recycling of coated steel) is a common disposal form. The recycling of epoxy-based polymers is due to their highly crosslinked thermoset nature a challenge and is today still in its infancy. Grinding of cured epoxy polymers to powder and subsequent use as a filler is a possibility but represents only a low value downgrading recycling option.
Solubility in water: 300mg/l
Solubility in water: 7mg/l
Bisphenol A (BPA)
BPA is a starting substance for BADGE – also described as an intermediate -. However, BADGE is a completely different molecule with its own unique properties, not just an aggregate of BPA + epichlorohydrin. BPA is one of the most scrutinised substances.
The Consortium Linking Academic and Regulatory Insights on BPA Toxicity (CLARITY-BPA) program was developed to study the full range of potential health effects from exposure to BPA. The program was initiated by NIEHS, NTP, and the U.S. Food and Drug Administration (FDA) to provide data that can be used for regulatory decisions to provide comprehensive Clarity on the real risk and health effects, particularly concerning reprotoxicity and endocrine disrupting properties of exposure to BPA.
CLARITY-BPA has two components:
- Core Study : A two-year guideline-compliant study of potential BPA toxicity in rats, which was conducted according to federal regulatory and statutory guidelines for toxicity testing.
- Grantee Studies : Studies conducted by university researchers but testing a range of additional endpoints. The Grantee Studies used animals raised in the same conditions and exposed to the same doses of BPA as the Core Study.
These two components combined produced a robust study design that united standard research practices used by regulators with innovative studies conducted at universities.
One key strength was identical BPA exposure conditions for both components of the study, which were generated by the same facility in the FDA’s National Center for Toxicological Research (NCTR). A second strength was that grantees received blinded Core Study samples, meaning they did not know whether samples had been dosed with BPA or how much, to minimise the potential for bias.
The results of the core study were published in September 2018. In a statement released in conjunction with the report, Dr. Stephen Ostroff, Deputy Commissioner for Foods and Veterinary Medicine at the U.S. Food and Drug Administration (FDA) noted: “Our initial review supports our determination that currently authorised uses of BPA continue to be safe for consumers.”
A report integrating findings from the Core Study and Grantee Studies is expected from NTP in fall 2019.
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REACH is a comprehensive regulatory framework adopted by the European Union in June 2007 to improve the protection of human health and the environment from the risks that can be posed by chemicals, while enhancing the competitiveness of the EU chemicals industry.
REACH applies to all chemical substances: those used in industrial processes but also in our day-to-day lives. Therefore, the regulation has an impact on most companies across the EU.
To comply with REACH, companies must identify and manage the risks linked to the substances they manufacture and market in the EU. They must demonstrate how a substance can be safely used, and they must communicate the risk management measures to the users.
If the risks cannot be adequately managed, authorities can restrict the use of a substance in different ways. In the long run, the most hazardous substances, the so-called substances of very high concern, should be replaced with less hazardous alternatives.
- Epoxy precursors and non-polymeric epoxy building blocks are REACH registered.
- All registration dossiers are regularly updated.
- Several epoxy building blocks are subject to the so-called Community Rolling Action Plan (CoRAP), a deeper probing substance evaluation organized by ECHA to scrutinize potential hazard concerns which may not have been fully addressed in the registration dossier. Depending on the results of the substance evaluation, a substance may be cleared of all concerns, or alternatively may be subject to further regulatory measures like harmonized classification and labeling (CLH), SVHC identification, and ultimately restriction and/or authorization.
- Industry has a vital interest to provide up-to-date hazard and safe-use information.
- BADGE is registered under REACH: 100-1,000 kt/a.
- 2015 aggregated volume EU 291kt.
- 83% industrial, 16% professional (flooring), rest consumer (disappearing).
- Classification: Skin Irrit. 2 // Eye Irrit. 2 // Skin Sens. 1 // Aquatic Chronic 2.
CoRAP 2015 ongoing:
- Human health/suspected CMR: Transgenic rodent assay completed. The results indicate no mutagenic activity in somatic cells of duodenum, stomach or liver.
- Exposure/wide dispersive use, consumer use, aggregated tonnage.
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BPA- have been proposed for prioritisation by ECHA in 2018, which in the future could potentially lead to inclusion into Annex XIV, i.e. authorisation. Please note that BPA is used as a monomer in the manufacturing of epoxy resins, which is an intermediate use.
- Envisioned Scope: small percentage of hardeners containing elevated amounts of BPA as a curing accelerator and co-curing agent.
UBA, restriction dossier proposal expected during the 2nd half of 2019.
- Envisioned Scope: unclear for the time being.
- Aim: reduce environmental concentration of BPA, predominantly in surface waters.
- Studies show contribution of epoxy and polycarbonate to BPA concentration in the environment is only ca. 1%.
Authorisation or restrictions for BPA will have no impact on epoxy polymers or BADGE, as BPA is used only as an intermediate to create BADGE. Once reacted with epichlorohydrin, the BPA has transformed into a new substance – BADGE. Intermediate uses are exempt from authorisation hence Epoxy resins are not affected by the inclusion into Annex XIV.
BADGE REACH registered CAS-Nr. Changed
Following on a recent decision by the European Chemicals Agency (ECHA), and in accordance with the REACH regulation (EC) No. 1907/2006, it is necessary to modify the “chemical identifiers”, (Chemical Name, CAS Number, EC Number), for a range of low molecular weight Bisphenol A based epoxy resins.
Accordingly, several epoxy resin products can no longer be described as “Reaction products of Bisphenol-A and Epichlorohydrin” and the new “chemical identifiers” shown below will be assigned:
New substance ID
Old substance ID
4,4′-Isopropylidenediphenol, oligomeric reaction products with 1-chloro-2,3-epoxypropane
REACH registration number
The ERC members have initiated a transition project and will gradually update their Safety Data Sheets (SDS) and labels of all the affected epoxy resin products over the next 12-18 months.
Please note that while there is no impact on the product properties or classification, on receipt of an updated SDS you may need to update your own SDS and/or update existing product notifications and certifications.
German WGK (Rigoletto) database
The request to assign the CAS No. 1675-54-3 for Bisphenol-A-diglycidylether (BADGE) to the existing Water Hazard Class (WGK) under the assignment no.2007 and the CAS no. 25068-38-6 was submitted to UBA. UBA is currently processing this request on update of the Rigoletto database.
Other epoxy building blocks