The product class identified as Diethylenetriamine (DETA) Epoxy Hardener & Polyamide Resin Feedstock is described by the linear structure H₂NCH₂CH₂NHCH₂CH₂NH₂. The molecule contains two primary amine groups, one secondary amine group, and five amine hydrogens. The molecular weight is 103.17 g/mol, resulting in an amine hydrogen equivalent weight of 20.6 g/eq. This low equivalent weight permits high crosslink density in epoxy networks but also creates a severe exotherm and short pot life. Typical density values range from 0.950 g/cm³ to 0.958 g/cm³ at 20 °C by ASTM D4052. Dynamic viscosity at 25 °C is in the 6.5–7.5 mPa·s band by ASTM D7042. Flash point under closed cup conditions is 94–102 °C by ASTM D93, and vapour pressure at 25 °C is below 0.1 mmHg under OECD TG 104. DETA is hygroscopic and miscible with water, alcohols, and many organic polar solvents. These properties support its use as a fast ambient-cure epoxy hardener and as a nitrogen-functional monomer for reactive polyamide resins based on dimerized fatty acids.

Property	Typical envelope	Test basis
CAS registry	111-40-0	—
Molecular weight	103.17 g/mol	Calculated from H₂NCH₂CH₂NHCH₂CH₂NH₂
Amine hydrogen equivalent weight	20.6 g/eq	Active hydrogen basis
Density at 20 °C	0.950–0.958 g/cm³	ASTM D4052
Dynamic viscosity at 25 °C	6.5–7.5 mPa·s	ASTM D7042
Flash point, closed cup	94–102 °C	ASTM D93
Vapour pressure at 25 °C	<0.1 mmHg	OECD TG 104

Why Does a Stoichiometric Deviation Beyond 12 phr Depress Wet Adhesion in DETA-Cured Epoxy Systems?

For a standard bisphenol A diglycidyl ether with an epoxide equivalent weight of 190 g/eq, the theoretical DETA dosage is calculated as 20.6 g/eq × 100 g/190 g/eq = 10.86 phr. Practical formulations use 8–12 phr. Below 8 phr, amine-starved networks retain unreacted oxirane and show incomplete crosslinking. Above 12 phr, residual primary amine groups increase equilibrium water uptake and can function as hydrophilic defects in immersion service. Comparative immersion testing under ISO 2812-1:2017 shows earlier blister formation in 12 phr DETA films than in polyamide adduct systems when both are applied to abrasive-blasted steel. The gel time of a 100 g mass at 25 °C measured by the Techne gel timer is normally 20–40 min, while a 250 g mass can exceed 180 °C due to exothermic advancement. Production meter-mix lines therefore use cooled static mixers and direct dispensing into shallow moulds to limit thermal runaway.

Differential scanning calorimetry at 10 °C/min by ASTM E2041 for a 10.86 phr DETA/DGEBA mixture typically shows reaction onset near 25–40 °C and a peak exotherm at 110–130 °C. The primary amine hydrogens react preferentially; secondary amine addition becomes kinetically significant after roughly 50–60% conversion. This two-stage consumption produces a tightly crosslinked amorphous network. Thin-film cure of a 200 μm solvent-free film at 25 °C reaches tack-free time below 2 h by ISO 9117 pendulum damping, while full hardness development generally requires 7 days. At 5 °C, tack-free time extends beyond 8 h. Adding unmodified DETA above 15 phr is generally avoided because the exotherm can exceed 220 °C in a 1 kg batch and because unreacted amine plasticises the coating. Acid accelerators such as salicylic acid are not recommended unless process controls can manage the additional exothermic salt formation; premature gelation in static mixers is a known failure mode when accelerator concentrations exceed 2 wt%.

In high-humidity spray booths, DETA-rich clear coats are often withdrawn from service because primary amine groups react with atmospheric carbon dioxide and water to form carbamate salts. The visual defect is amine blush, a waxy surface layer that appears when evaporative cooling drops the paint surface below the dew point. The application limit used in many coating specifications is a dew point margin of at least 3 °C and relative humidity below 60–70%; dew point is measured by ISO 8502-4:2017. If the blush layer is not removed by solvent wiping or sanding, recoat pull-off adhesion by ISO 4624:2016 often falls below 2 MPa. To reduce direct handling exposure and carbamation risk, DETA is frequently converted to an epoxy-amine adduct by reaction with excess DGEBA at 60–80 °C under nitrogen. The adduct increases the amine hydrogen equivalent weight to 80–120 g/eq and lowers free DETA vapour pressure. Benzyl alcohol is sometimes added at 5–10 wt% to extend open time, but it remains in the cured film and can act as a plasticiser. Closed mixing vessels with nitrogen blankets and molecular-sieve breather vents are standard for bulk DETA storage on coating production lines.

When DETA Is Condensed with Dimer Acid Above 200 °C, Polyamide Molecular Weight Growth Follows a Two-Stage Viscosity Curve

Dimerized tall oil fatty acid and DETA are charged to a glass-lined batch reactor at 1.6–2.2 mol DETA per mole of dimer acid. The condensation reaction liberates water and proceeds through an amidation stage that is water-removal limited below 180 °C. Between 180 °C and 220 °C, the degree of polymerization follows an approximately linear increase with distillate mass. Above 230 °C, free DETA can cyclize to imidazoline; this side reaction consumes amine sites and reduces final amine value. In a 10,000 L glass-lined reactor fitted with a packed column and reflux splitter, the heating profile is staged at 2 °C/min from 180 °C to 225 °C to avoid gel formation. Nitrogen sparge is maintained at 0.2–0.5 reactor volumes per minute to strip water; vacuum below 50 mbar is applied only after the acid value falls below 5 mg KOH/g. The resulting reactive polyamide typically shows an amine value of 330–400 mg KOH/g by ASTM D2074 and a Brookfield viscosity at 40 °C of 30–80 Pa·s. Dimer acid batch-to-batch variation in monomer/dimer/trimer distribution shifts final viscosity independently of amine value; on-line acid value feedback and feed-ratio adjustment are used to keep the product within a narrow qualification window.

The polyamide resins produced from DETA are used as flexibilised epoxy hardeners in marine and industrial maintenance primers. A typical letdown for a solid DGEBA resin with an epoxide equivalent weight of 500–550 g/eq uses 40–80 phr reactive polyamide. Compared with unmodified DETA, the polyamide reduces blush potential and improves wetting on mechanically prepared steel. The operational boundary is that thin-film cure below 5 °C slows substantially; a 200 μm film can require more than 72 h for through-cure. For hot-melt adhesives, DETA-derived polyamides with softening points between 100 °C and 160 °C are applied by slot-die or roll coating. Open time is influenced by amide chain morphology; published data for this specific configuration is limited. In printing ink pigment chips, a twin-screw extruder with an L/D ratio of 48:1 is operated from 120 °C to 160 °C. Free DETA in the polyamide resin should be kept below 2 wt% because off-gassing during extrusion creates odour and can form carbamate deposits on vent ports.

Regulatory status and supply-chain qualification thresholds

DETA is registered under REACH (EC) No 1907/2006 for EU import or manufacture above 1 tonne/year. Hazard communication follows CLP (EC) No 1272/2008; supplier safety data sheets classify the substance as corrosive and skin sensitising. For transport, DETA is assigned to UN 2079, class 8, packing group II. Storage incompatibilities include strong oxidizers, mineral acids, and low-molecular-weight epoxy resins unless handled under closed-loop temperature control. No direct food-contact approval is implied for the neat amine; a specific polyamide resin grade must be assessed under the relevant food-contact regulation before use. Qualification of DETA as a polyamide feedstock typically includes amine value by ASTM D2074, acid value by ASTM D1980, dynamic viscosity by ASTM D2196, and colour by ASTM D1209. The primary/secondary/tertiary amine distribution can also be determined by ISO 9702 for epoxy-hardener quality systems. Acceptance windows are set in supplier quality agreements because the required limits differ for liquid epoxy hardeners and solid polyamide resins.

Standard or regulation	Scope	Qualification parameter
REACH (EC) No 1907/2006	EU chemical registration and supply	Registration number for tonnage band
CLP (EC) No 1272/2008	Classification, labelling and packaging	Corrosive and sensitising hazard statements
ASTM D2074	Amine value of fatty polyamides	Potentiometric titration
ISO 9702	Amine group nitrogen content	Primary/secondary/tertiary amine split
ISO 8502-4:2017	Surface preparation and dew point assessment	Minimum 3 °C dew point margin
ASTM D93	Flash point by closed cup	94–102 °C