Curing Agents and Hardeners for Adhesives: Amines, Polyamides, Anhydrides and Latent Cures

Epoxy curing agents are the reactive half of every epoxy adhesive: amines, polyamides, anhydrides, polythiols and latent hardeners open the epoxide ring and turn a liquid resin into a crosslinked thermoset. Curing agents are one of 15 raw-material families among the adhesive chemicals that industrial adhesives are formulated from. The hardener, not the resin, decides whether a bond cures at room temperature or in an oven, how long the mix stays workable and how high its glass transition climbs.

This page compares ten curing agent families in one selection table, each with its cure mode, a dosing value with its basis and its CAS numbers. Amine hardeners are dosed by stoichiometry: DETA needs 10.9 phr with an EEW 190 epoxy resin, calculated from its AHEW of 20.6 g/eq, while dicyandiamide runs at about 8 phr with about 3 phr urea accelerator in a published one-part example. The EU hazard picture splits sharply: IPDA carries Annex VI 612-067-00-9, 2-methylimidazole is a Candidate List SVHC, diuron is Carc. 1B since 1 September 2025 and MDA has been past its Annex XIV sunset date since 2014. In the US, 21 CFR 175.105(c)(5) names cyanoguanidine, IPDA, DETA, TETA and amine-based polyamides for food-packaging adhesives.

Sources and checks: identities and hazard classifications are read at ECHA and the issuing regulator, standards at the body that publishes them, and grade values at the data sheet named next to them; methodology and fact-checking explains each step.

What Is an Epoxy Curing Agent?#

An epoxy curing agent, also called a hardener, is a compound that reacts with or catalyzes the epoxide groups of an epoxy resin so that the resin crosslinks into an infusible network. Co-reactive hardeners join that network near stoichiometry, while catalytic agents trigger homopolymerization of the resin at a few phr (parts per hundred resin).

Resin and hardener are two different raw materials. The epoxy resin (Part A) carries the epoxide groups; the hardener (Part B) carries the reactive hydrogens or the catalytic nitrogen that opens them. What can serve as a hardener for epoxy resin? Ten families do: aliphatic and cycloaliphatic amines, polyamides and amidoamines, phenalkamines, polyetheramines, aromatic amines, anhydrides, dicyandiamide, imidazoles, polythiols and the accelerators that speed them up.

The hardener sets three properties the resin cannot set alone: cure temperature, pot life and the glass transition of the cured bond. A liquid bisphenol A resin cured with an aliphatic amine bonds at room temperature, while the same resin with dicyandiamide stays liquid for months and cures only in an oven. Resin and curing agent together make up epoxy adhesives in one-part and two-part form.

How Does Epoxy Cure? Amine Addition, Anhydride Esterification and Catalytic Homopolymerization#

Epoxy cures when a nucleophile opens the three-membered epoxide ring: a primary or secondary amine N-H adds once per active hydrogen, and the new hydroxyl group autocatalyzes the next addition. One epoxide reacts per active hydrogen, so a primary amine with two hydrogens links two epoxide groups. Standard liquid epoxy resin contains low levels of hydrolyzed glycol end groups that raise its reactivity toward amines (Burton, "Acceleration of Epoxy Resin Systems", 2013).

Anhydrides follow a different route. A hydroxyl group or a catalyst opens the anhydride to a half-ester acid, and that acid reacts with an epoxide; because epoxide homopolymerization competes, the optimum anhydride-to-epoxide ratio stays below 1.0. Imidazoles and tertiary amines start an anionic homopolymerization through their pyridine-type or tertiary nitrogen, and a tertiary amine turns a thiol into a thiolate that opens the epoxide fast, even at low temperature.

Dicyandiamide adds latency to these routes. It is insoluble in the resin at room temperature, then dissolves on heating and reacts through its amine hydrogens and its nitrile group, with catalytic homopolymerization alongside. Epoxy cure is one chemical-reaction route among the ways in which adhesives cure, set out under how adhesives cure.

Co-Reactive Hardeners vs Catalytic Curing Agents#

Co-reactive hardeners (amines, polyamides, phenalkamines, anhydrides, polythiols and, in part, dicyandiamide) are dosed by equivalents; catalytic agents (tertiary amines, imidazoles) are dosed at a few phr. A co-reactive hardener becomes part of the network, so the rule is one amine hydrogen per epoxide group, and an off-ratio mix leaves unreacted groups behind.

Accelerators sit between the two classes. They work by adding or quickly creating hydroxyl groups, by raising the exotherm temperature, or both (Burton 2013). Non-reactive accelerators need no change to the stoichiometry. Reactive accelerators with N-H groups must be counted, with an AHEW of 81.1 g/eq for APDEA and 53.09 g/eq for DMDPTA in the same source.

Types of Epoxy Hardeners: One Selection Table for Every Curing Agent Family#

The selection table below sets out ten epoxy curing agent families in four groups: amine-based hardeners, fatty and cardanol-based hardeners, heat-activated curing agents, and fast-cure hardeners with their accelerators.

Each request is passed straight to independent companies of that trade, and no company pays AdhesiveAdditives.com to be named or to receive requests; the editorial policy explains how.

Every dosing cell is a value of the named grade or source, or a calculation from molecular weight, and none of them is a class limit. Every hardener in the table cures the epoxy members of the thermoset adhesive resins family, from liquid bisphenol A resin to novolac and cycloaliphatic grades.

Amine-Based Curing Agents: Aliphatic, Cycloaliphatic, Polyether and Aromatic Amines#

Aliphatic amines (DETA, TETA) cure at room temperature, cycloaliphatic amines (IPDA, DCH) cure slower to a higher Tg, polyetheramines give long pot life and flexibility, and aromatic amines react only hot. The full names are DETA (diethylenetriamine), TETA (triethylenetetramine), IPDA (isophorone diamine) and DCH (1,2-diaminocyclohexane). DETA is not DEA and not DETDA, and IPDA is not the isocyanate IPDI.

Polyetheramines carry their primary amine groups on secondary carbons of a polypropylene oxide chain, and that hindrance gives long pot life and low exotherm; flexibility rises with molecular weight. Aromatic amines such as DDS (4,4'-diaminodiphenyl sulfone) and DETDA (diethyltoluenediamine) are weak nucleophiles that build high-Tg networks for aerospace film adhesives and prepregs. Amine blush is the surface defect of primary amines: with carbon dioxide and water they form carbamate salts, and amine adducts resist this.

Fatty and Cardanol-Based Curing Agents: Polyamides, Amidoamines and Phenalkamines#

Polyamide hardeners are dimer-fatty-acid polyamines whose fatty backbone flexibilizes the bond and makes the mix ratio forgiving; phenalkamines are cardanol Mannich bases that cure cold and on damp surfaces. Residual primary and secondary amines of the polyamide react with the epoxide, and the fatty chain also aids wetting. Open containers of polyamide absorb moisture and carbon dioxide. In phenalkamines, the phenolic hydroxyl of cardanol accelerates the amine-epoxy reaction and the C15 side chain gives water tolerance. These curing polyamides are not the thermoplastic polyamide resins used in hot melts.

Heat-Activated Curing Agents: Anhydrides, Dicyandiamide and Imidazoles#

Anhydrides need heat and a catalyst and give long pot life and low exotherm, while dicyandiamide is insoluble at room temperature, which makes one-part adhesives storable. In the Huntsman example of the selection table, the accelerated anhydride system reaches a Tg onset of 180 to 190 °C (356 to 374 °F) (TDS 2009). Anhydrides are moisture-sensitive, so their containers stay closed.

Imidazoles work both as catalytic hardeners and as accelerators. The pyridine-type nitrogen starts anionic homopolymerization, and the same nitrogen accelerates anhydride and dicyandiamide cure. Substitution at N-1 or C-2, salts and adducts tune how latent an imidazole stays in the resin.

Fast-Cure Hardeners and Cure Accelerators: Polythiols, Tertiary Amines and Urones#

Polythiols cure epoxy fast at ambient and low temperature once a tertiary amine such as DMP-30 (2,4,6-tris(dimethylaminomethyl)phenol) turns the thiol into thiolate; urones release dimethylamine on heating and accelerate dicyandiamide. This thiolate route serves five-minute repair and fixture adhesives. Ester-linked thiols such as PETMP (pentaerythritol tetrakis(3-mercaptopropionate)) are sensitive to hydrolysis. Urones such as diuron are substituted ureas, and BDMA (benzyldimethylamine) is a second tertiary amine accelerator.

How to Choose a Curing Agent: Cure Temperature, Pot Life and Glass Transition#

Choose an epoxy curing agent by the cure temperature the line can supply first, then by the pot life the process needs and the glass transition the bond must keep in service. The eight selection cases below map each requirement to a hardener family.

1. Forgiving general-purpose two-part adhesive: polyamide.
2. Fast ambient cure: DETA, TETA or their adducts.
3. Clear bond with higher Tg: IPDA or DCH.
4. Damp or cold surfaces: phenalkamine, or cycloaliphatic amine adducts.
5. Long pot life and flexibility: polyetheramine plus accelerator.
6. Five-minute fixture: polythiol plus DMP-30.
7. One-part oven cure: micronized dicyandiamide plus urone or imidazole adduct.
8. High Tg and electrical duty: anhydride plus imidazole.

Pot life depends on the mixed mass, because the exotherm heats a large batch faster than a small one. Henkel's data sheet for LOCTITE EA 9394 AERO (Rev. 7/2015) gives a pot life of 90 min for a 450 g mass and states that no more than 450 g should be mixed at once. How pot life is measured, and why it depends on mass, is covered under pot life.

Accelerators shorten pot life too, and an excess of them costs performance. Excess tertiary amine gives odor, yellowing, brittleness and a lower Tg (Burton 2013), so an accelerator level is set by test, not by the stoichiometry.

Matching the Curing Agent to Cure Schedule and Service Temperature#

Room-temperature hardeners reach their properties in days and heat-cure hardeners in minutes at oven temperature; a cycloaliphatic amine raises Tg by amine choice alone. The selection table shows DCH reaching a Tg 18 °C above IPDA with the same resin, 176 °C (348.8 °F) against 158 °C (316.4 °F).

A glass transition is not a service temperature. The EA 9394 AERO data sheet gives a Tg of 78 °C (172.4 °F) dry and 68 °C (154.4 °F) wet, yet rates the adhesive to 177 °C (350 °F), defined as the temperature at which 6.9 MPa (1,000 psi) lap shear is retained. A data sheet service temperature is a strength criterion, not the glass transition; the difference is explained under service temperature and glass transition.

Dicyandiamide sets the cure window of one-part adhesives. Unaccelerated, its cure peaks near 200 °C (392 °F) and completes within 30 min; urea accelerators lower the cure to about 150 °C (302 °F) (Pasatta 2022). That window decides whether a part can go through an existing oven.

How Much Curing Agent Goes Into a Two-Part or One-Part Epoxy Adhesive?#

A stoichiometric hardener is dosed at phr = AHEW × 100 / EEW, so DETA with an EEW 190 resin needs 10.9 phr (calculated), while catalytic and latent curing agents are dosed by recipe at a few phr. AHEW is the amine hydrogen equivalent weight and EEW the epoxide equivalent weight of the resin.

The mix ratio of a two-part adhesive follows from this calculation. Versamid 140 is the forgiving case: its BASF data sheet of May 2014 allows 50 to 70 phr with an EEW 190 epoxy resin. Two-part epoxy adhesives meter Part B to this ratio at the mixing head, and two-part epoxy adhesives cover the metering in detail.

One-part adhesives carry the hardener inside the resin. A latent hardener such as micronized dicyandiamide stays dispersed and unreacted until heat dissolves or activates it, so no metering step exists.

Stoichiometric Hardeners: AHEW, EEW and the phr Rule#

AHEW is the amine's molecular weight divided by its active hydrogens: DETA 103.2 / 5 = 20.6 g/eq. The table below applies the same arithmetic to five amines at an EEW of 190.

Blends change the EEW. In the worked example of Dow's Epoxy Resins Product Overview Guide (Form 296-01864-0213), 100 parts of an EEW 189 resin, 100 parts of an EEW 240 resin, 30 parts of a diluent of EEW 130 and 230 parts filler give a blend EEW of 391, so DETA is dosed at 5.27 parts per hundred of filled formulation. Blends of several resins and hardeners are solved from hardener AHEW and resin EEW in the mix ratio calculator.

Amine value is not AHEW. A tertiary nitrogen counts in the amine value but carries no active hydrogen, so phr is never computed from amine value. For a monoanhydride the equivalent weight equals the molecular weight, 152 to 178 g/eq, and the anhydride-to-epoxide ratio is set below the theoretical 1.0.

Loadings of Catalytic Curing Agents, DICY and Accelerators#

Latent agents run at about 5 to 10 phr; a published example uses about 8 phr dicyandiamide with about 3 phr urea accelerator (Pasatta 2022). Dicyandiamide is 2-cyanoguanidine, C2H4N4, with a molar mass of 84.08 g/mol.

Tertiary amines and imidazoles run lower. Burton (2013) screened DMP-30 at 3 to 5 phr, and the anhydride system in the selection table uses 0.5 part accelerator per 100 parts resin; imidazoles sit at catalytic levels, far below stoichiometric amine levels.

Stoichiometric work with dicyandiamide uses an equivalent weight of 21.02 g/eq (84.08 / 4). Latent systems cure in about 5 to 60 min hot and store for weeks to one year, and an epoxy and dicyandiamide mix without urea showed no viscosity rise in 60 weeks at room temperature (Pasatta 2022). Cure schedules of DICY-cured one-part heat-cure epoxy adhesives depend on the accelerator.

How Are Epoxy Curing Agents Regulated?#

Amine and anhydride curing agents such as IPDA, BDMA and MTHPA carry harmonized CLP classifications as corrosives or sensitizers, and three curing agents have stricter EU status. Of these, 2-methylimidazole (2-MI) is a Candidate List SVHC, diuron is Carc. 1B since 1 September 2025, and MDA (4,4'-methylenedianiline) needs REACH authorization.

The table below compares the CLP Annex VI entries and the Candidate List and Annex XIV status of each family.

California's Proposition 65 list (OEHHA, 2026-07-31) names three of these substances for cancer: 2-methylimidazole since 2012-06-22, diuron since 2002-05-31 and MDA since 1988-01-01. DETA, TETA, IPDA and MXDA are not listed.

CLP Hazard Classes, Sensitization and SVHC Status of Curing Agents#

IPDA (CAS 2855-13-2) carries Annex VI 612-067-00-9 (ATP17, Reg. (EU) 2021/849, applicable since 17 December 2022): H302, H314, H318 and Skin Sens. 1A H317; MTHPA, MHHPA and HHPA carry Resp. Sens. 1 H334. These anhydrides (methyltetrahydrophthalic, hexahydromethylphthalic and hexahydrophthalic anhydride) add Eye Dam. 1 H318 and Skin Sens. 1 H317.

The resin side of a two-part kit carries its own label element. Epoxy mixtures with constituents of average molecular weight 700 or less carry EUH205 (CLP Annex II section 2.5), and EUH205 wording on the resin side is part of hazard labeling for adhesives. For the two CMR accelerators, CLP Annex I Tables 3.6.2 and 3.7.2 (consolidated text of 2026-07-01) classify a mixture Carc. 1B from 0.1 % diuron and Repr. 1B from 0.3 % 2-methylimidazole, since neither entry has a specific concentration limit. REACH Annex XVII lists diuron in Appendix 2 (entry 28) and 2-methylimidazole in Appendix 6 (entry 30), so neither may be supplied to the general public in mixtures above the classification limit.

Sensitization reaches beyond the resin. In the IVDK patch-test data of 2008 to 2022, 22.7 % of patients positive to the bisphenol A diglycidyl ether resin also reacted to MXDA, and testing the resin alone missed 1.9 % of patients sensitized to diluents or hardeners (Reissig et al., Contact Dermatitis, 2026).

US Food-Packaging Adhesive Listings for Curing Agents#

21 CFR 175.105(c)(5) names four curing agents and one polyamide class for food-packaging adhesives, used behind a functional barrier or within the limits for dry, fatty and aqueous food (eCFR, up to date as of 2026-10-30). The curing-agent names in the listing are set out below.

• cyanoguanidine (dicyandiamide)
• 3-(aminomethyl)-3,5,5-trimethylcyclohexylamine (IPDA)
• diethylenetriamine and triethylenetetramine, each listed by name
• polyamides from dimerized vegetable oil or azelaic acids with DETA, ethylenediamine, hexamethylenediamine, tetraethylenepentamine, TETA or poly(oxypropylene)diamine of molecular weight 2010 or 440

The conditions matter as much as the names. With fatty and aqueous food, a listed adhesive may contact the food only as the trace amount at seams and at the edge exposure between packaging laminates, and the container label reads "food-packaging adhesive". Conditions of use, labeling and EU rules for food-contact adhesives are set out on the regulation page.

21 CFR 175.300(b)(3)(viii)(b) is a separate listing for resinous and polymeric coatings, not for adhesives. It names MXDA (at most 3 % of the resin), DMP-30 and the phenalkamine 68413-28-5 among its curing agents. MTHPA, MHHPA and NMA have no named listing in either section.

Sourcing Curing Agents: Specifications, Producers and Distributors#

Epoxy curing agents are bought against a sales specification of AHEW or equivalent weight, amine value and viscosity, from producers such as Westlake Epoxy, which bought the former Hexion epoxy business in February 2022 for about USD 1.2 billion. Huntsman Advanced Materials (epoxy, MDI and structural adhesives) appears in the ASI Top 20 2026 ranking published on 2026-07-07, and the Versamid polyamide brand is now sold by Huntsman.

Ownership changes rename grades, so an RFQ states the incumbent grade family with its old and new producer names. Producers and distributors of curing agents are listed among adhesive raw material suppliers for curatives.

What a Curing Agent Specification Must State#

A curing agent specification states equivalent weight with its basis, amine value, viscosity at 25 °C (77 °F) and color, plus form and the number of qualification lots. A data sheet gives typical product values; the sales specification and the certificate of analysis give the contractual limits. The five fields of a curing agent specification are listed below.

1. State the AHEW or equivalent weight and its basis.
2. State the amine value with its test method.
3. State the viscosity at 25 °C (77 °F).
4. State the color and the physical form, such as liquid or micronized powder.
5. State the sample size and the number of qualification lots.