Epoxy resins are common in many industries, and disposing of them under RCRA rules can be complicated. Epoxy-based resins are two-part solutions created by combining an epoxy with a hardener or “cureative.” When combined, these materials create a “thermoset plastic” material that is moldable for a short time before setting or curing into an inert solid form. Epoxy resins have a vast number of applications: they are used as paints or coatings on machinery and automobiles, as structural adhesives in products from airplanes to golf clubs, as electrical insulation in circuit boards, and much more.
While there are a variety of epoxy materials, each with particular characteristics and uses, disposing of epoxy resins of any kind raises a common problem. Before use, the epoxy itself is typically a flammable liquid. The hardener or cureative is a non-flammable liquid, but may be corrosive or toxic. When mixed, the epoxy and the hardener yield an inert, solid plastic that may not display the hazardous characteristics of either of its two parts.
When disposing of a two-part epoxy, one of three scenarios will apply:
If disposing of an unused two-part epoxy before mixing it, Part A (the epoxy) is usually a D001 ignitable hazardous waste, and Part B (hardener) may be a D002 corrosive. Either chemical may be on the P- or U-list of chemical product wastes.
If the epoxy is mixed, fully cured, and used as an adhesive, coating, or to form a mold, it is a used product and cannot be assigned a P or U waste code. Luckily, the inert solid plastic that results once the epoxy fully solidifies will very rarely exhibit any hazardous waste characteristic.
The third scenario is the most complicated. The epoxy is mixed, some portion of it is used, and the excess becomes a solid waste before it fully solidifies.
After the epoxy components are mixed, they begin to harden or cure. A mixed but not yet fully solid epoxy solution, when destined for disposal, is a solid waste, and waste codes must be applied at the time the waste is generated. (40 CFR 261.3) Even though the chemical reaction has begun, the unused mixture is still an unused commercial chemical product (40 CFR 261.33) and the applicable P or U codes would apply, along with any hazardous waste characteristics. None of the F or K listings for specific and non-specific sources of hazardous waste will apply to mixed epoxy solutions.
The Epoxy Is Fully Cured. Now What?
Once it has completed curing, the epoxy will no longer exhibit the hazardous waste characteristics of ignitability (D001) or corrosivity (D002). [40 CFR 261.21-261.22] Once the waste no longer exhibits any regulated characteristics, it is no longer subject to regulation as hazardous waste. [40 CFR 261.3(d)-(g)]
If, however, the hazardous waste was assigned a P (acute) or U (toxic) hazardous waste code, those chemical product codes still apply. Listed hazardous waste codes apply until the waste is de-listed via petition (40 CFR 260, Subpart C) or treated to Part 268 standards.
Lastly, even though the hardened epoxy no longer exhibits the hazardous waste characteristic of ignitability (D001) or corrosivity (D002), it did exhibit those characteristics at the time the waste was generated. Therefore, the treatment standards (40 CFR Part 268) associated with these characteristics are still applicable—even though the characteristics and waste codes themselves are gone.
What About Toxicity?
None of this discussion touched on the characteristic of toxicity. [40 CFR 261.24] Certain epoxy compounds do have toxic heavy metals or complex organic compounds incorporated into their matrix. If they do, and either the unused components or the hardened epoxy contains a TCLP level of one or more toxicity constituents, then the epoxy has to be managed as toxicity characteristic hazardous waste.
Lastly, if you have unused epoxy and the unused chemicals would be hazardous wastes (by characteristic or listing), then you can’t get rid of it by intentionally mixing the components to create an inert solid. Doing so is waste treatment and requires a permit. [40 CFR 260.10-definition of "treatment"]
The U.S. EPA requires all hazardous waste personnel to complete training annually. Learn to identify the hazardous waste generated at your facility, manage and store it in full compliance with RCRA, and ensure proper disposal at the upcoming Hazardous/Toxic Waste Management Workshops!