An epoxy adhesive is a reactive thermoset adhesive in which an epoxy resin, counted as 100 parts, crosslinks with a hardener dosed by stoichiometry or with a latent hardener released by heat. Among industrial adhesive chemicals it is built from three groups: the epoxy resin, the hardener and modifiers such as diluents, tougheners, fillers and silanes. The resin side is set first, and every other part is dosed against it.
Four sub-chemistries follow from that base: two-part room-temperature epoxies, one-part heat-cure epoxies, toughened crash-durable grades and high-temperature epoxies. They differ in hardener, cure route, modifier and service limit.
An amine hardener is dosed so that each amine hydrogen meets one epoxide group: diethylenetriamine (DETA) needs 10.9 parts per 100 parts of a resin with an epoxide equivalent weight (EEW) of 189 g/eq. A published one-part formula cured 28 min at 180 °C (356 °F) reaches 20.6 MPa lap shear on CR340 steel, and 20 wt % of a polyurethane toughener raises impact wedge peel energy from 4.1 J to 25.8 J. Raising the cure temperature from 60 to 120 °C lifts the glass transition temperature (Tg) of one laboratory epoxy from 66.3 to 116.9 °C, while one aerospace paste is rated to 177 °C (350 °F) with a Tg of 78 °C. On the regulatory side, liquid bisphenol A epoxy resin carries CLP Annex VI entry 603-074-00-8, epoxy mixtures carry EUH205, bisphenol A is prohibited in EU food-contact adhesives under Regulation (EU) 2024/3190, and 21 CFR 175.105(c)(5) names the epoxy resins, cyanoguanidine and several amines used in US 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 Adhesive?#
An epoxy adhesive is an adhesive whose network forms when the oxirane rings of an epoxy resin open and add to an active-hydrogen hardener, an anhydride or a latent hardener, or homopolymerize under an ionic catalyst. The product of that reaction is a crosslinked thermoset that does not melt again. Active-hydrogen hardeners include amines, polyamides, amidoamines and thiols; latent hardeners include dicyandiamide and dihydrazides; ionic catalysts include imidazoles, tertiary amines and cationic photoinitiators.
"Epoxy resin" names the uncured raw material, and "epoxy adhesive" names the formulated two-component or one-component product that contains it, so the resin is one ingredient of the adhesive. Epoxide adhesive and structural epoxy are synonyms. The abbreviation "EP" is avoided on this page because it also stands for ethylene-propylene.
How Do Epoxy Adhesives Bond and Cure?#
Epoxy adhesives bond because the cured network carries hydroxyl and ether groups that interact with oxide surfaces, and they cure by ring-opening addition or homopolymerization. Each epoxide ring that opens leaves a hydroxyl group behind, so the polar groups that hold the bond are produced by the cure itself. Oxide layers on aluminum and steel are such surfaces.
Hardeners act in two ways. Co-reactive hardeners such as amines, polyamides, anhydrides and polythiols join the network and are dosed near stoichiometry, while catalytic agents such as tertiary amines and imidazoles trigger homopolymerization of the resin at a few phr. Chemical reaction is one of four routes covered under how adhesives cure, next to evaporation, cooling and radiation.
Accelerators speed both routes. In B. Burton's paper "Acceleration of Epoxy Resin Systems", accelerators work by adding or quickly creating hydroxyl groups, by raising the exotherm temperature, or by both.
Cure Routes: Room-Temperature Amine Cure and Latent Heat Cure#
Epoxy adhesives cure by two routes: amine addition at room temperature after Part A and Part B are mixed, or latent heat cure of a one-part paste in an oven. In the two-part route the amine, polyamide, amidoamine or thiol hardener reacts as soon as the parts are metered and mixed. Heat accelerates that reaction and raises the final glass transition temperature (Tg), so a warm post-cure raises the Tg reached at room temperature.
In the one-part route a latent hardener, micronized dicyandiamide (DICY), dihydrazides or encapsulated or adduct imidazoles, stays dormant until heat dissolves or activates it. Unaccelerated DICY in bisphenol A diglycidyl ether shows its peak exotherm at 180 °C (356 °F) by DSC at 20 °C/min, with virtually no cure at 130 °C (266 °F) (US patent 4,459,398 A, filed 1983-05-27). A urea accelerator brings the cure down to about 150 °C (302 °F), and latent systems cure in about 5 to 60 min hot while storing for weeks to one year (Pasatta, Polymer Innovation Blog, 2022).
What Are Epoxy Adhesives Made Of?#
Epoxy adhesives are made of an epoxy resin as the network former, a hardener or latent curative as the crosslinker, and modifiers: reactive diluents for viscosity, tougheners for fracture energy, fillers and thixotropes for rheology, and silanes for adhesion. The table below compares the seven raw-material functions, the substances that fill them and the published share of each with its basis.
| Function | Family hub | Substances | Share (basis, source) |
|---|---|---|---|
| Base resin | thermoset adhesive resins | bisphenol A epoxy resin, bisphenol F epoxy resin, epoxy novolac resin, multifunctional glycidyl amine epoxies, cycloaliphatic epoxy resin | resin = 100 parts, the basis of every phr value |
| Room-temperature hardener | curing agents and hardeners | amine hardeners (DETA, triethylenetetramine TETA, isophorone diamine IPDA), polyamide hardeners, phenalkamine hardeners, polyetheramine hardeners, polythiol hardeners | stoichiometric, phr = amine hydrogen equivalent weight (AHEW) × 100 / EEW; DETA 10.9 phr with an EEW 189 resin (calculated from AHEW 20.6 g/eq); Versamid 140 50 to 70 phr with an EEW 190 resin (BASF TDS May 2014) |
| Heat-cure and latent hardener | (same hub) | dicyandiamide, anhydride hardeners, aromatic amine hardeners, imidazole curing agents | DICY about 8 phr with about 3 phr urea (Pasatta 2022); anhydride example 100 resin : 140 hardener : 0.5 accelerator by weight (Huntsman LY 5210 / Aradur 917 / DY 070, TDS 2009) |
| Accelerator | (same hub) | epoxy accelerators (DMP-30, BDMA, urones) | DMP-30 3 to 5 phr in accelerator screening (Burton) |
| Reactive diluent, toughener | functional additives for adhesives | epoxy reactive diluents, epoxy tougheners | HELOXY Modifier 8 at most about 20 % of the resin portion (Westlake TDS, read 2026-11-02); carboxyl-terminated butadiene-acrylonitrile (CTBN) or phenol-terminated polyurethane (PTPU) 5 to 30 wt % studied (Chae et al. 2020); core-shell rubber 2 to 6 wt % (Glaskova-Kuzmina et al. 2022) |
| Filler, thixotrope | fillers and rheology modifiers | calcium carbonate, fumed silica | CaCO3 22 wt % in the Chae et al. 2020 one-part formula (calculated); fumed silica: no level in the sources read |
| Adhesion promoter | adhesion promoters and silane coupling agents | 3-glycidoxypropyltrimethoxysilane (GPTMS) | 1.0 pbw typical use level in epoxy applications such as filled encapsulants (Momentive Silquest A-186 and A-187 bulletin, 02/11) |
Base Resins: The Network Formers of Epoxy Adhesives#
Liquid bisphenol A epoxy resin is the base resin of both one-part and two-part epoxy adhesives, with bisphenol F resin for lower viscosity and epoxy novolac for higher crosslink density. Each resin is specified by its epoxide equivalent weight (EEW), the grams of resin that carry one epoxide group, and by its viscosity. The table lists published grade values from one producer guide.
| Resin type | Grade (producer, data sheet) | EEW (g/eq) | Viscosity or softening point | Note |
|---|---|---|---|---|
| Liquid bisphenol A (LER) | D.E.R. 331 (Dow Epoxy Resins Product Overview Guide, Form 296-01864-0213) | 182 to 192 | 11,000 to 14,000 mPa·s at 25 °C | low-viscosity grades D.E.R. 383 and 330 crystallize at room temperature; heating to 50 to 55 °C (122 to 131 °F) restores the liquid |
| Bisphenol F (BPF) | D.E.R. 354 (same guide) | 167 to 174 | 3,400 to 4,200 mPa·s at 25 °C | functionality about 2 |
| Epoxy novolac | D.E.N. 425 to 439 (same guide) | 169 to 210 | not compared | functionality 2.5 to 3.8 |
| Solid bisphenol A, type 1 | D.E.R. 661 (same guide) | 500 to 560 | softening 75 to 85 °C | solid types run up to type 9 |
| Solid bisphenol A, type 9 | (same guide) | 2,500 to 5,500 | not stated | highest molecular weight in the range |
The monomer of liquid bisphenol A resin is bisphenol A diglycidyl ether, written DGEBA in papers and BADGE in regulation. A lower EEW means more epoxide groups per gram, so the hardener demand rises as the EEW falls. Bisphenol F resin lowers viscosity without a diluent, and novolac resins with more than two epoxide groups per molecule raise crosslink density and Tg.
Standard liquid resin carries low levels of hydrolyzed glycol end groups. Those end groups raise reactivity toward amines and viscosity and hinder crystallization, according to Burton's acceleration paper. Glycidyl amine resins such as tetraglycidyl diaminodiphenylmethane (TGDDM) and triglycidyl p-aminophenol (TGPAP) carry three or four epoxide groups and form the base of aerospace film and paste adhesives.
Hardeners and Latent Curatives#
Room-temperature epoxy hardeners are aliphatic and cycloaliphatic amines, polyamides, polyetheramines and polythiols, and heat-cure curatives are dicyandiamide, anhydrides, aromatic amines and imidazoles. Each amine hardener is characterized by its amine hydrogen equivalent weight (AHEW), the molecular weight divided by the number of active N-H hydrogens. Polyamides give a forgiving ratio, polyetheramines a long pot life with an accelerator, and polythiols a fast cure with a tertiary amine catalyst.
The table compares published results for three hardener systems with their source.
| Hardener system | Grade (producer, data sheet date) | Published result |
|---|---|---|
| Isophorone diamine (IPDA) vs 1,2-diaminocyclohexane (DCH) with a liquid bisphenol A resin | IPDA and DCH-99 with EPON 828 (INVISTA page, read 2026-11-02) | Tg 158 °C vs 176 °C (DSC, second run) |
| Anhydride, accelerated | LY 5210 / Aradur 917 / DY 070 at 100:140:0.5 (Huntsman TDS 2009) | Tg onset 180 to 190 °C after 4 h at 100 °C + 1 h at 140 °C + 3 h at 180 °C |
| Tertiary amine accelerator with amine curatives | DMP-30 (Burton, "Acceleration of Epoxy Resin Systems") | odor, yellowing, brittleness and Tg loss in excess |
Dicyandiamide counts 21.02 g/eq in stoichiometry (molecular weight 84.08 g/mol divided by 4).
Modifiers: Diluents, Tougheners, Fillers and Silanes#
Epoxy adhesive modifiers are reactive diluents that cut viscosity, tougheners that raise fracture energy, fillers and thixotropes that set rheology and bond line, and silanes that improve adhesion. Glycidyl ether diluents such as C12-14 alkyl glycidyl ether and 1,4-butanediol diglycidyl ether carry epoxide groups and enter the network. The HELOXY Modifier 8 data sheet treats the shift in blend EEW as negligible below 10 phr, so small diluent additions need no new hardener calculation.
Tougheners are carboxyl-terminated butadiene-acrylonitrile rubber (CTBN), phenol-terminated polyurethane (PTPU) and core-shell rubber (CSR). Core-shell rubber is supplied as masterbatches of 25 to 40 wt % rubber in DGEBA (Glaskova-Kuzmina et al., Polymers, 2022), so the masterbatch also adds epoxide groups to the blend. Calcium carbonate and fumed silica set rheology, cost and bond-line thickness. Free aminosilane belongs on the hardener side: in Gelest's coupling-agent brochure, 50 parts bisphenol A epoxy with 5 parts aminopropyltriethoxysilane and 50 parts toluene rises in viscosity over 14 days, while a ketimine-blocked aminosilane stays stable.
Epoxy Adhesive Formulation#
Epoxy adhesive formulation fixes the resin at 100 parts and doses every amine hardener by stoichiometry, phr = AHEW × 100 / EEW, so that each amine hydrogen meets one epoxide group. Off-ratio mixing in either direction leaves a soft or brittle bond, the first failure mode recorded for epoxy adhesives. Latent and catalytic curatives follow their own dosage rules, which is why the two starting formulas below use different bases.
How Hardener Mix Ratio Follows Stoichiometry#
The hardener mix ratio equals AHEW × 100 / EEW parts per 100 parts resin, with AHEW equal to the amine's molecular weight divided by its active N-H count. Diethylenetriamine (DETA, 103.17 g/mol) carries 5 active hydrogens, so its AHEW is 20.6 g/eq. With a resin of EEW 189, DETA needs 10.9 phr (calculated from AHEW 20.6 g/eq), and the same result holds at EEW 190.
Blends need a combined EEW before the ratio is set. The blend EEW is the total weight divided by the sum of weight over EEW for each epoxy-bearing part, so only epoxy-bearing parts enter the denominator while fillers enter the total weight. The epoxy mix ratio calculator runs this arithmetic for resin, diluent and filler lists.
Accelerators with N-H groups count as hardener. Burton gives an AHEW of 81.1 g/eq for APDEA and 53.09 g/eq for DMDPTA, while non-reactive accelerators need no recalculation. Amine value is not AHEW: a tertiary nitrogen counts in the amine value but carries no active hydrogen, so phr is never calculated from amine value.
Two Published Starting Formulas#
Two complete epoxy adhesive formulas are published with every part: a one-part heat-cure paste by Chae et al. (2020) and a two-part filled system from a producer guide's worked example. The tables give each part as published and as wt %, calculated here from the published parts.
One-part heat-cure formula (Chae et al., Polymers 2020, 12, 1549):
| Component (grade as published) | Function | Parts (g) | wt % (calculated) |
|---|---|---|---|
| DGEBA, YD-128 (EEW 187) | base resin | 30 | 48 |
| Core-shell rubber masterbatch, Kaneka MX-154 (40 wt % CSR in DGEBA, EEW 301) | toughener and resin | 15 | 24 |
| Dicyandiamide, Dyhard 100 | latent hardener | 3.12 | 5 |
| N,N-dimethyl-N'-phenylurea | accelerator | 0.39 | 1 |
| Calcium carbonate, Omyacarb 10 | filler | 14 | 22 |
| Sum | 62.51 | 100 |
Two-part formula (Dow Epoxy Resins Product Overview Guide, Form 296-01864-0213, worked example):
| Component | Side | Parts | wt % of mixed adhesive (calculated) |
|---|---|---|---|
| D.E.R. 331 (EEW 189) | Part A | 100 | 21 |
| D.E.R. 337 (EEW 240) | Part A | 100 | 21 |
| 1,4-Butanediol diglycidyl ether (EEW 130) | Part A | 30 | 6 |
| Filler | Part A | 230 | 47 |
| DETA | Part B | 24.2 | 5 |
| Sum | 484.2 | 100 |
The one-part paste cures 28 min at 180 °C and reaches 20.6 MPa lap shear on CR340 steel, a paper value measured in the ISO 4587:2003 geometry as used by the authors. Its DICY works out at about 7 parts per 100 parts of the epoxy-bearing components (3.12 of 45, calculated), and the formula also carries 1 wt % dimer acid-modified epoxy whose basis the paper does not state, so it is left out of the wt % column.
The two-part example sets Part A at 460 parts with a blend EEW of 391, and the guide then doses DETA at 20.6 × 100 / 391 = 5.27 parts per hundred of filled Part A, which gives the 24.2 parts of Part B. Both formulas are published examples, not recommendations for a product.
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Properties of Epoxy Adhesives#
Epoxy adhesive properties follow from a crosslinked network: strength and heat resistance rise with the degree of cure and the glass transition temperature, while the unmodified network fails by brittle cleavage under impact. Neat epoxy conducts heat at 0.15 to 0.25 W/(m K), a literature value reported by Chung and Lin (2016), so heat transfer through a bond line depends on its fillers. The two sections below quantify the cure and toughness sides.
How Cure Temperature Sets Strength and Heat Resistance#
A higher cure temperature raises both the degree of cure and the glass transition temperature of an epoxy adhesive, and an undercured bond keeps a Tg below its service temperature. The table gives laboratory values for one fast epoxy cured isothermally (PMC13120039); its uncured Tg is -37.2 °C.
| Isothermal cure temperature | Degree of cure | Tg after cure |
|---|---|---|
| 60 °C (140 °F) | 0.805 | 66.3 °C |
| 80 °C (176 °F) | 0.918 | 101.7 °C |
| 100 °C (212 °F) | 0.963 | 109.3 °C |
| 120 °C (248 °F) | 0.976 | 116.9 °C |
A data sheet service temperature is a retained-strength criterion, not a Tg. Henkel's LOCTITE EA 9394 AERO data sheet (Rev. 7/2015) rates the paste to 177 °C (350 °F), defined as the temperature at which it retains 6.9 MPa (1,000 psi) lap shear by ASTM D1002, against 28.9 MPa (4,200 psi) at 25 °C on phosphoric acid anodized 2024-T3 aluminum. The same sheet gives a Tg of 78 °C dry and 68 °C wet, so the rated service temperature lies 99 °C above the dry glass transition temperature of that grade.
Brittleness and How Rubber Phases Offset It#
An epoxy network without toughener fails by brittle cleavage under impact, and a dispersed rubber phase offsets it by concentrating stress and triggering shear yielding. With 2 to 6 wt % core-shell rubber, fracture toughness rises by 60 to 108 %, tensile strength and modulus fall by 10 to 20 %, and Tg rises by 10 to 20 °C (Glaskova-Kuzmina et al. 2022, paper values).
Chae et al. (2020) tested the same trade-off on CR340 steel after 28 min at 180 °C. Impact wedge peel energy at 2 m/s rises from 4.1 J for the control to 5.8 J with the best CTBN level and to 25.8 J with 20 wt % PTPU, while lap shear rises from 20.6 MPa to 32.3 MPa. Tg falls by about 4 °C per 5 wt % CTBN and about 8 °C per 5 wt % PTPU, and the CTBN adhesives show unstable crack growth.
Which Substrates Do Epoxy Adhesives Bond?#
Epoxy adhesives bond five substrate groups: aluminum, steel, composites, ceramics and, after surface treatment, many plastics. The five groups are listed below.
- Aluminum, etched or phosphoric acid anodized for durable structural joints.
- Steel, such as the CR340 grade used in published one-part tests.
- Composites, such as glass-fiber reinforced thermoplastics after plasma treatment.
- Ceramics.
- Plastics, after surface treatment.
Epoxy adhesives work on metal, and metal bonding is their core industrial use: the published one-part formula above was tested on steel, and the aerospace paste on anodized aluminum. Oxide surfaces give the hydroxyl groups of the cured network a polar partner.
The question of the strongest adhesive for metal to metal joints belongs to the comparison of structural adhesives, because epoxy, acrylic and polyurethane chemistries all bond metal in place of fasteners. The page on structural adhesives compares them by joint design rather than by a ranking.
Metal Epoxy Bonding and Surface Preparation#
Metal epoxy bonds last when the metal surface is prepared, and on aluminum durability depends on etching or phosphoric acid anodizing as described in ASTM D3933-98(2025). That ASTM guide covers phosphoric acid anodizing of aluminum for structural adhesive bonding and is active.
Adhesive failure from poor surface preparation is one of the five failure modes recorded for epoxy adhesives. In a laboratory study, atmospheric-pressure plasma raised the lap shear of glass-fiber reinforced polyphenylene sulfide bonded with epoxy from 3.76 MPa untreated to 3.93, 4.24 and 4.69 MPa, a gain of 24.8 %, and moved the failure from partially adhesive to substrate break (PMC12115051).
Abrasion, etching, anodizing, plasma, corona, flame and primers are the treatment routes for metals and plastics. Their parameters belong to surface preparation for bonding, which also owns the anodizing guide.
How Epoxy Adhesives Are Mixed, Applied and Cured#
A two-part epoxy adhesive is applied by metering Part A and Part B at the producer's ratio, mixing within the pot life of the mixed mass and curing on a time-temperature schedule. A one-part epoxy is dispensed as supplied and cured in an oven. Pot life depends on the mass mixed, because a larger mass holds more reaction heat: the BASF Versamid 140 data sheet (May 2014) gives 2 h for 200 g at 25 °C (77 °F) and a minimum application temperature of 15 °C (59 °F).
Four process faults recur with two-part systems. Off-ratio mixing leaves a soft or brittle bond, and a large mixed mass overheats from its own exotherm; Henkel's EA 9394 AERO sheet therefore limits a single mix to 450 g. Amine blush forms when primary amines react with carbon dioxide and water to carbamate salts at the surface, which hurts appearance and the adhesion of a following layer. A crystallized Part A has to be warmed back to a clear liquid before metering, as shown in the base resin table.
One-part epoxies skip metering but need oven time at temperature. The published one-part paste above cures 28 min at 180 °C, and a lower oven temperature without accelerator leaves the paste undercured. Pot-life measurement methods are listed in the test table below.
How Are Epoxy Adhesives Tested?#
Epoxy adhesives are tested for lap shear strength, peel resistance, impact and fracture energy, pot life and, on the resin side, epoxy content, and their metal lap shear method, ASTM D1002-10(2019), is active. The table lists each property with its standard, edition and status.
| Property | Standard and edition | Status | Method page |
|---|---|---|---|
| Lap shear, metal | ASTM D1002-10(2019); ISO 4587:2003 | active; valid | lap shear testing |
| T-peel | ASTM D1876-08(2023); ISO 11339:2022 | active; valid | T-peel testing |
| Floating roller peel | ASTM D3167-10(2025) | active | peel testing (same page) |
| Impact wedge peel | ISO 11343:2019, 2 m/s | current | impact wedge peel testing |
| Mode I fracture | ASTM D3433-99(2020); ISO 25217:2009 | active; valid | fracture testing (same page) |
| Pot life | ISO 10364:2024 (fourth edition); EN 14022:2010 | current; withdrawn 2018-03-16 | pot life of industrial adhesives |
| Epoxy content of the resin | ASTM D1652-11(2019), 0.1 to 26 % epoxide; ISO 3001:1999 | active; valid | resin specification |
Every result in these tests is a product value tied to substrate, surface preparation, cure schedule and method, so two data sheets compare only when all four match. The lap shear values on this page name their substrate and cure for that reason.
Regulation of Epoxy Adhesives#
Three rule sets govern epoxy adhesives: CLP classification of their resins, diluents, hardeners and accelerators, EU food-contact rules on bisphenol A and bisphenol A diglycidyl ether, and the US listing of epoxy components in 21 CFR 175.105. The table gives the CLP Annex VI line, or its absence, for the main raw materials (Regulation (EC) No 1272/2008, consolidated text of 2026-07-01).
| Substance | CAS (EC) | Hazard line |
|---|---|---|
| Liquid epoxy resin, bisphenol A-epichlorohydrin, MW ≤ 700 | 25068-38-6 (EC 500-033-5) | Annex VI 603-074-00-8: Skin Irrit. 2 H315, Eye Irrit. 2 H319, Skin Sens. 1 H317, Aquatic Chronic 2 H411; SCL H315, H319 at C ≥ 5 % |
| Bisphenol A diglycidyl ether (BADGE) | 1675-54-3 (EC 216-823-5) | Annex VI 603-073-00-2: H315, H319, H317 |
| Bisphenol F epoxy resin | 9003-36-5 (EC 500-006-8) | No Annex VI entry |
| Epoxy phenol novolac resin | 28064-14-4 (ECHA list number 608-164-0) | No Annex VI entry |
| Dicyandiamide | 461-58-5 (EC 207-312-8) | No Annex VI entry |
| Isophorone diamine (IPDA) | 2855-13-2 (EC 220-666-8) | Annex VI 612-067-00-9 (ATP17, Reg. (EU) 2021/849, applicable 2022-12-17): H302, H314, H318, Skin Sens. 1A H317 |
| C12-14 alkyl glycidyl ether | 68609-97-2 (EC 271-846-8) | Annex VI 603-103-00-4: H315, H317 |
| 1,4-Butanediol diglycidyl ether | 2425-79-8 (EC 219-371-7) | Annex VI 603-072-00-7: H332, H312, H315, H319, H317 |
| Diuron (urone accelerator) | 330-54-1 (EC 206-354-4) | Annex VI 006-015-00-9 (ATP21, Reg. (EU) 2024/197, applicable 2025-09-01): Carc. 1B H350, STOT RE 2 H373, H400, H410 |
| 2-Methylimidazole | 693-98-1 (EC 211-765-7) | Annex VI 613-330-00-0 (ATP14, applicable 2021-09-09): Repr. 1B H360Df; Candidate List since 2020-06-25 |
| 4,4'-Methylenedianiline (MDA) | 101-77-9 (EC 202-974-4) | Annex VI 612-051-00-1: Carc. 1B H350, Muta. 2 H341, STOT SE 1 H370, STOT RE 2 H373, H317, H411; REACH Annex XIV entry 2, sunset date 2014-08-21 |
Hazard Classification of Epoxy Adhesive Raw Materials#
Liquid bisphenol A epoxy resin carries CLP Annex VI entry 603-074-00-8, including the harmonized environmental class H411, while its monomer BADGE (603-073-00-2) carries the same skin and eye codes without H411. Both entries set a specific concentration limit of 5 % for skin and eye irritation (H315, H319). The two CAS numbers are never interchanged: 25068-38-6 is the oligomeric resin, 1675-54-3 the monomer.
Mixtures that contain epoxy constituents with an average molecular weight of 700 or less carry EUH205, "Contains epoxy constituents. May produce an allergic reaction.", unless they are already labeled as sensitizing (CLP Annex II, section 2.5). The phrase and its label rules are covered under hazard labeling for adhesives, next to the EUH204 statement of isocyanate mixtures.
Hardeners and accelerators drive the stricter labels. IPDA carries Skin Sens. 1A since ATP17, and diuron carries Carc. 1B since 2025-09-01 with no specific concentration limit, so a mixture with 0.1 % or more diuron is classified Carc. 1B. 2-Methylimidazole is Repr. 1B and a Candidate List substance, and REACH Annex XVII Appendix 2 (diuron) and Appendix 6 (2-methylimidazole) bar supplying either to the general public in mixtures above the classification limit. MDA has needed an authorization in the EU since its sunset date, so it is no longer a current curative choice there.
Food-Contact Epoxy Adhesives: BPA, BADGE and US Listings#
Regulation (EU) 2024/3190 prohibits bisphenol A in the manufacture of food-contact adhesives (Article 3) with no derogation for adhesives, and Regulation (EC) 1895/2005 still limits BADGE migration to 9 mg/kg. Regulation 2024/3190 entered into force on 2025-01-20 and was corrected by Regulation (EU) 2026/250 (in force 2026-02-23). Single-use final articles made with bisphenol A could be first placed on the market until 2026-07-20, and listed exceptions run until 2028-01-20. Under Article 4, materials made with another bisphenol derivative, such as BADGE-based epoxy, must contain no residual bisphenol A at a detection limit of 1 µg/kg.
Regulation 1895/2005 sets the BADGE limit as the sum of BADGE, BADGE.H2O and BADGE.2H2O, adds 1 mg/kg for the sum of its three chlorohydrins, and prohibits BFDGE and NOGE in food-contact adhesives. It stays in force next to 2024/3190, which repeals only Regulation (EU) 2018/213. BADGE itself is not a hazardous bisphenol under 2024/3190.
In the US, 21 CFR 175.105(c)(5) names epichlorohydrin-4,4'-isopropylidenediphenol resin, epichlorohydrin-phenolformaldehyde resin, cyanoguanidine, DETA, TETA, IPDA and polyamides of dimerized vegetable oil acids with listed amines (eCFR, up to date as of 2026-10-30). A listed component may be used only behind a functional barrier or, for fatty and aqueous food, in no more than the trace amount at seams and edge exposure, and the container label reads "food-packaging adhesive". No adhesive is cleared as such; the jurisdiction's listing and its conditions of use decide, as set out for food-contact adhesives.
How to Choose an Epoxy Adhesive#
Choose an epoxy adhesive by cure route first (room temperature or oven), then by load case (static shear or impact), service temperature against the cured Tg, and food-contact status. The table matches six requirements to an epoxy type with the published evidence behind each.
| Requirement | Epoxy type | Evidence |
|---|---|---|
| Cure without an oven | two-part amine or polyamide | Versamid 140 system: pot life 2 h on 200 g at 25 °C, minimum application 15 °C (BASF TDS May 2014) |
| Single component, oven on the line | one-part DICY plus urea | cure down to about 150 °C with urea (Pasatta 2022); 28 min at 180 °C in Chae et al. 2020 |
| Impact and peel loads | toughened | impact wedge peel 25.8 J at 20 wt % PTPU vs 4.1 J control (Chae et al. 2020, paper values) |
| Higher service temperature | high-temperature, elevated cure | Tg 116.9 °C after 120 °C cure vs 66.3 °C after 60 °C cure (laboratory, PMC13120039); service temperature defined by retained lap shear (LOCTITE EA 9394 AERO, Henkel TDS Rev. 7/2015, 6.9 MPa) |
| EU food-contact adhesive | manufactured without bisphenol A | Regulation (EU) 2024/3190 Art. 3; BADGE SML 9 mg/kg under (EC) 1895/2005 |
| US food packaging | components named in 21 CFR 175.105(c)(5) | functional barrier or (a)(2) limits |
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.
Limits of Epoxy Adhesives#
Epoxy adhesives have five limits, each tied to cure or surface. The five limits are listed below.
- Off-ratio mixing, which leaves a soft or brittle bond.
- Undercure, which leaves the Tg below the service temperature.
- Amine blush in humid conditions, from carbamate salts on the surface.
- Adhesive failure on untreated plastics and poorly prepared surfaces.
- Brittle cleavage under impact without a toughener.
Epoxy Adhesive Sub-Chemistries Compared#
Epoxy adhesives come in four sub-chemistries: two-part room-temperature epoxies, one-part heat-cure epoxies, toughened crash-durable grades and high-temperature epoxies. The table compares their resin and hardener, cure, key published data and main uses.
| Type | Resin and hardener | Cure | Key data (basis) | Main uses |
|---|---|---|---|---|
| two-part epoxy adhesives | LER or BPF resin; amine, polyamide or thiol hardener | room temperature after metered mixing; heat accelerates | Versamid 140 50 to 70 phr with EEW 190 resin (BASF TDS May 2014) | metal and composite assembly |
| one-part heat-cure epoxy adhesives | LER with micronized DICY and urone | oven; about 150 °C with urea (Pasatta 2022) | 20.6 MPa lap shear, CR340 steel, 28 min at 180 °C (Chae et al. 2020, paper value) | automotive body-shop steel and aluminum |
| toughened epoxy adhesives | host system plus CTBN, core-shell rubber or PU prepolymer | as the host system | core-shell rubber 2 to 6 wt %: fracture toughness +60 to 108 % (paper values) | crash-durable joints |
| high-temperature epoxy adhesives | novolac or glycidyl amine resins; aromatic or cycloaliphatic amines, anhydrides, DICY | elevated cure or post-cure | service limit set by Tg and a retained-strength criterion (EA 9394 AERO, 6.9 MPa) | aerospace film and paste |
Three of the four types start from liquid bisphenol A or F resin and differ in hardener and modifier. Toughening is an add-on to either cure route, while the high-temperature type also moves to novolac or glycidyl amine resins to raise crosslink density.
Epoxy Adhesives in Industry and Research#
Epoxy adhesives serve metal, composite and electronics assembly, and current research quantifies toughening, cure and occupational sensitization. Their place among the other types of adhesives by chemistry follows from the thermoset network, and the sections below cover uses, comparisons, data sheets and exposure research.
Where Are Industrial Epoxy Adhesives Used?#
Industrial epoxy adhesives are used in three sectors: automotive body shops, aerospace structures and electronics. The three sectors are listed below with the epoxy type each uses.
- Automotive adhesives: one-part heat-cure epoxies for body-shop steel and aluminum.
- Aerospace and composite adhesives: film and paste adhesives on multifunctional glycidyl amine resins.
- Electronics adhesives: anhydride plus imidazole systems for high Tg and electrical use.
Each sector page names the substrates and process limits behind these choices.
Epoxy Compared With Polyurethane, Cyanoacrylate and Acrylic Adhesives#
Epoxy differs from polyurethane, cyanoacrylate and acrylic adhesives in label and surface demand: epoxy mixtures carry EUH205, isocyanate mixtures EUH204, and Henkel and ITW data sheets describe MMA structural acrylics as needing little or no surface preparation. The three comparisons are listed below.
- Epoxy vs polyurethane adhesives: EUH205 against EUH204 labeling.
- Epoxy vs cyanoacrylate: two-part or oven cure against moisture cure.
- Epoxy vs acrylic (MMA) structural adhesives: surface preparation demand.
What Should an Epoxy Adhesive Data Sheet State?#
An epoxy adhesive data sheet states typical product values tied to substrate, surface preparation, cure schedule and test method, and the producer behind the grade. Producer names change: the former Hexion epoxy business has belonged to Westlake since February 2022. ASTM D2471-99, the gel time and peak exotherm method, was withdrawn in 2008 with no replacement and is still cited on data sheets.
Suppliers compare fairly only on the same fields, which the guide to adhesive manufacturers and suppliers uses for qualification. The six fields every epoxy data sheet should carry are listed below.
- Mix ratio by weight and by volume.
- Pot life with the mixed mass and temperature.
- Cure schedule as time at temperature.
- Lap shear with method, substrate and preparation.
- Service temperature with its definition.
- Hazard statements and food-contact listing.
Occupational Sensitization to Epoxy Raw Materials#
Sensitization to bisphenol A diglycidyl ether (DGEBA) among occupational dermatitis patients fell from 4.2 % in 2008 to 2010 to 2.9 % in 2020 to 2022 in IVDK patch-test data (Reissig et al., Contact Dermatitis, 2026). Plastics processors showed the highest adjusted odds ratio, 11.7. DGEBA-positive patients were co-sensitized to hexanediol diglycidyl ether (43.6 %), 1,4-butanediol diglycidyl ether (35.7 %), phenyl glycidyl ether (30.8 %) and m-xylylenediamine (22.7 %), and testing DGEBA alone missed 1.9 % of patients sensitized to diluents or hardeners.