Epoxy Resin Supplier & Manufacturer: E-51 / E-44 Liquid & Solid Grades

E-51 and E-44 grades are bisphenol A diglycidyl ether resins differentiated primarily by epoxide equivalent weight, viscosity, and softening point. Incoming lots are released under GB/T 13657 and tested for epoxide equivalent weight by ISO 3001:1999 or ASTM D1652. E-51 typically shows an epoxide equivalent weight of 184–195 g/eq and viscosity at 25 °C of 10000–16000 mPa·s when measured by ISO 3219. E-44 typically shows an epoxide equivalent weight of 210–240 g/eq and a softening point of 12–20 °C by ASTM E28. The E-51 grade is supplied as a liquid, while E-44 may be supplied as a high-viscosity liquid or a solid depending on ambient storage and transport temperature. Manufacturing sites producing these resins by bisphenol A–epichlorohydrin condensation are typically certified under ISO 9001:2015 and package E-51 in 220 L epoxy-lined steel drums, whereas solid E-44 is packed in 25 kg multi-wall bags with polyethylene liners.

How does ambient moisture affect cure stoichiometry in E-51 and E-44 systems?

Resin and curing agents are conditioned at 23 °C ± 2 °C and relative humidity below 50 % according to ISO 291. When substrate relative humidity exceeds 60 %, amine-cured E-51 or E-44 systems can develop surface carbamate blush from reaction of atmospheric carbon dioxide with primary amine hydrogens. This side reaction consumes active hydrogen and alters stoichiometry in the top 50–100 µm of the film. Water absorption after 24 h immersion in distilled water, tested by ASTM D570, commonly falls between 0.2 % and 0.5 % for an unfilled E-51/cycloaliphatic amine network, but absorbed water can lower glass transition temperature and reduce tensile strength. Pre-drying substrates at 40 °C for 2 h is required when ambient humidity exceeds 60 %, and bulk resin should not be processed directly from cold storage without dew-point monitoring because condensation on the drum surface can introduce free water into the mix.

When E-51 with an epoxide equivalent weight of 189 g/eq is mixed with a cycloaliphatic amine having an amine hydrogen equivalent weight of 60 g/eq, stoichiometric demand is 31.7 phr. The same amine demanded by E-44 at 225 g/eq is 26.7 phr. Vacuum mixing at -0.09 MPa for 10 min removes air, but batch volume above 1.5 L shortens gel time because exotherm retention accelerates the amine-epoxide addition. Differential scanning calorimetry under ISO 11357-5 typically records reaction onset near 40 °C, peak exotherm between 95 °C and 120 °C at 10 K/min, and residual enthalpy below 5 J/g only after post-cure at 80 °C for 2 h. Ratios below 90 % of stoichiometry produce under-crosslinked regions with solvent sensitivity, while ratios above 105 % can leave free amine available for moisture uptake and surface bloom.

When cold-weather dispensing raises E-51 viscosity beyond 25,000 mPa·s

At resin temperature below 15 °C, E-51 viscosity can approach 30,000 mPa·s. Meter-mix equipment fitted with 24-element static mixers and dynamic pressure control at 120 bar may show ratio drift and cavitation when resin and curing agent viscosities differ by more than 10:1. Preheating E-51 to 35–40 °C reduces viscosity to approximately 2000–4000 mPa·s without initiating significant homopolymerization. Dwell time at 60 °C should not exceed 2 h unless nitrogen blanketing is applied because tertiary amine residues from epichlorohydrin processing can accelerate oligomerization. Static mixers shorter than 24 elements can produce striations visible under 50× optical microscopy, and gear pump ratio drift exceeding 3 % is corrected by installing jacketed feed lines rather than by increasing pump speed alone.

In structural anchoring applications, E-44-based adhesives are formulated with quartz or basalt aggregate at filler loadings between 40 wt% and 65 wt%. Pull-out performance is evaluated under ASTM E488 or ETAG 001, with sustained-load creep tests conducted at 50 °C according to ETAG 001 Part 5. Cured E-51/E-44 amine systems can exhibit tensile strength above 50 MPa when tested per ASTM D638 Type IV, but bond strength falls rapidly when substrate moisture exceeds 6 % by weight or when bond-line thickness exceeds 5 mm. E-44 is preferred over E-51 in high-sag vertical anchoring because its higher room-temperature viscosity reduces flow before gel, but installation below 5 °C requires preheated cartridges and field verification of cure because alkali-silica reactions in saturated concrete can consume amine curing agent at the interface.

Coatings formulation thresholds and VOC compliance

E-51 is used in high-solids protective primers because its viscosity at 25 °C permits formulation at 80 wt% solids while maintaining airless sprayability. Solvent demand can be reduced to meet volatile organic compound limits under GB/T 23986 or ISO 11890-2. Addition of benzyl alcohol at 5–8 wt% reduces viscosity by 30–40 %, but delays through-cure at substrate temperatures below 10 °C and can produce films with König hardness below 60 s after 7 days when tested per ISO 1522. High-solids E-51 primer applied at wet film thickness 200 µm can be checked for sag resistance by ISO 16862, and pot life is typically shorter in plural-component airless spray with 65:1 ratio pumps because shear heating raises the material temperature inside the fluid section.

For simple ambient casting, E-51 is mixed with curing agent for 3 min until streak-free before pouring into ambient-temperature molds.

In electrical encapsulation, E-51 systems filled with 60 wt% fused silica exhibit dielectric strength above 15 kV/mm under IEC 60243-1 and comparative tracking index above 600 V when tested per IEC 60112. Thermal shock from -40 °C to 125 °C according to IEC 60068-2-14 can initiate filler-to-resin debonding if the coefficient of linear thermal expansion exceeds 35 ppm/K. Dissipation factor measured at 1 kHz by IEC 60250 remains below 0.02 at 25 °C for a properly post-cured silica-filled E-51 system. E-44-based casting compounds are processed at 60 °C to reduce viscosity, but amine curing agents containing free phenol or nonyl phenol accelerators can introduce regulatory restrictions under REACH.

Cure shrinkage falls below 0.15% only when silica filler exceeds 70 wt%

Linear cure shrinkage of an unfilled E-51/diethylenetriamine system measured by ASTM D2566 commonly falls between 0.8 % and 1.2 %. Replacement with 70 wt% silica flour on a 25 mm × 25 mm × 250 mm bar reduces shrinkage to 0.10–0.15 %. Crosslink density derived from DMTA storage modulus above the glass transition by ASTM D5023 shows a rubbery plateau near 20–40 MPa for aliphatic amine-cured E-51; values below 10 MPa after post-cure indicate incomplete conversion or amine carbonation. Glass transition temperature measured by ISO 11357-2 at 20 K/min can range from 60 °C for room-temperature cycloaliphatic systems to above 120 °C after 2 h at 150 °C. Post-cure is not optional for electrical or structural parts because residual unreacted oxirane can plasticize the network and lower creep resistance under load.

What limits E-44 use in vacuum-assisted resin transfer molding?

E-44 requires heating above 60 °C to reach viscosity below 1000 mPa·s, which shortens pot life and increases the risk of premature gelation in feed lines. E-51 at 45 °C with viscosity below 1500 mPa·s remains injectable under 0.08 MPa vacuum pressure gradient through 400 g/m² biaxial glass fabric with permeability on the order of 1 × 10^-10 m². Fill time is governed by Darcy’s law and is inversely proportional to preform permeability and pressure gradient. Published data for E-44 in vacuum-assisted resin transfer molding is limited because high melt viscosity and exotherm in sections above 10 mm increase the likelihood of thermal runaway. When E-44 is used in casting or molding, jacketed vessels and heated static mixers with 32 elements are required to maintain laminar flow without sacrificing cure uniformity.

Solid E-44 grade is converted to flake or powder below 100 µm and used in epoxy-polyester hybrid powder coatings. Compounding on a twin-screw extruder with a length-to-diameter ratio of 44:1 at barrel temperatures between 80 °C and 100 °C disperses pigment and curing agents into the resin matrix. Gel time measured by ISO 8130-6 at 180 °C commonly falls between 90 s and 180 s, and storage stability of the extruded powder is assessed by blocking resistance testing at 40 °C for 24 h. Softening point variation of more than 2 °C between E-44 batches can alter melt viscosity in the extruder, so feed screw speed and barrel zones are re-qualified after each lot release.