The only non-soap thickener in the modern premium grease range — polyurea grease is produced not by saponification but by in-situ reaction of an isocyanate (MDI) with an amine inside the base oil to form polymeric urea fibres. The result is an ash-free grease with drop point above 250°C, exceptional oxidation life, low noise, and natural compatibility with sealed electric motor bearings — the dominant chemistry for OEM sealed-for-life motor bearing applications. This guide covers the isocyanate-amine synthesis SOP, raw-material specifications, NLGI grade range, ASTM performance targets, and the moisture-excluded reactor capability required.
Polyurea grease is not a soap grease. The thickener is a polymeric urea formed by the addition reaction of an isocyanate (R-N=C=O) with an amine (R'-NH₂) to give a urea linkage (R-NH-CO-NH-R'). The reaction is fast, exothermic, and proceeds essentially to completion inside the base oil with no by-product other than the urea itself. There is no metal ion, no soap fibre, no metal salt — the grease is described as ash-free, an important characteristic for applications where metal ions could attack adjacent materials (electric motor winding insulation being the most cited example).
Two main variants are produced commercially. Diurea grease uses one diisocyanate (typically MDI — 4,4'-diphenylmethane diisocyanate) reacted with two monoamines (e.g., octylamine, oleylamine, or aromatic amines like cyclohexylamine) to form a thickener molecule with two urea linkages. Drop point is typically >250°C. Triurea grease uses a more complex amine mix (typically a monoamine + diamine combination) to build a three-urea-linkage structure, giving drop point >260°C and improved temperature performance for wheel-bearing and high-temperature electric motor applications.
The polyurea fibres precipitate from solution as the reaction proceeds — the bulk turns from clear to opaque cream as urea fibres form. These fibres are typically much finer and shorter than soap fibres, giving polyurea grease its characteristic smooth, low-noise feel and its excellent low-bleed properties. Polyurea has dramatically better oxidation stability than soap-thickened greases because there is no metal ion to catalyse base-oil oxidation — this is the technical reason for the long sealed-bearing service intervals (L10 life of 40,000 hours and beyond is routinely achievable).
| Component | Grade / Specification | Treat Rate (NLGI 2) | Function & Sourcing |
|---|---|---|---|
| Base oil — primary | Group I/II SN500, KV40 90–110 cSt; or PAO 6 for premium | 60–70% | Carrier fluid. Group II preferred for standard polyurea; PAO 6 for low-noise high-speed bearing grease. Must be pre-dried. |
| Base oil — secondary | Group I/II SN150, or ester (e.g., adipate) 5% | 15–25% | Diluent and polarity modifier. A small ester addition improves urea fibre dispersion. |
| Isocyanate (MDI) | 4,4'-MDI, technical grade, NCO content 33.5%, low isomer | 3–5% | The isocyanate for the urea reaction. MDI strongly preferred over TDI for safety. Sourced from Wanhua, Covestro, Huntsman. Stored in dry sealed containers, away from moisture. |
| Amine — monoamine | Octylamine, oleylamine, or cyclohexylamine | 3–5% | Capping amine for the urea linkages. The choice of monoamine drives the final fibre morphology and texture. Aromatic amines give higher-temperature triurea. |
| Amine — diamine (triurea only) | Ethylenediamine (EDA) or hexamethylenediamine | 0.5–1.5% | Bridging diamine for triurea structure — raises drop point further. Skip for diurea. |
| Antioxidant | Aryl-amine (PANA, ODPA) + hindered phenol blend | 0.8–1.5% | Critical for long-life sealed bearing applications. Higher dose than soap greases due to expectation of long service. |
| Rust inhibitor | Amine carboxylate (ash-free; NO calcium sulfonate) | 0.3–0.8% | Must be ash-free to preserve the ash-free claim. Calcium sulfonate would introduce ash. |
| EP / AW additive (optional) | ZDDP or amine phosphate (ash-free preferred) | 0–2% | For loaded polyurea applications. ZDDP introduces ash so true ash-free formulations use amine phosphate. |
| Tackifier (optional) | PIB 2400 cSt | 0.3–1.0% | For specific OEM specs requiring high adhesion. Most polyurea formulations skip tackifier. |
Polyurea synthesis is fast (under 30 minutes) and exothermic. The absolute requirement is moisture exclusion — isocyanate reacts with water to give an unwanted side product and CO₂ gas. Pre-drying base oil, nitrogen blanketing the reactor, and using fresh sealed isocyanate are non-negotiable. Total cycle time for a 200–500 kg batch is approximately 3–5 hours — much faster than soap-thickened greases.
| Property | ASTM Test Method | Typical Value | Electric Motor Spec |
|---|---|---|---|
| Worked penetration, 60 strokes | ASTM D217 | 265–295 (0.1 mm) | 265–295 |
| Penetration change, 100,000 strokes | ASTM D217 | +5 to +20 dmm | +30 max |
| Dropping point | ASTM D2265 | 250–270°C | 250°C min |
| Water washout @ 79°C | ASTM D1264 | 5–10% | 15% max |
| Four-ball wear scar | ASTM D4172, 40 kg, 75°C, 1h | 0.40–0.50 mm | 0.55 max |
| Four-ball EP weld point (no EP additive) | ASTM D2783 | 160–200 kgf | 160 kgf min (electric motor) |
| Oxidation stability, 100h @ 99°C | ASTM D942 | 1–3 psi pressure drop (best of any chemistry) | 5 psi max |
| Oxidation stability, 500h @ 99°C | ASTM D942 | 5–10 psi pressure drop | 15 psi max |
| Oil separation, 24h @ 100°C | ASTM D1742 / D6184 | 1–3% (very low) | 5% max |
| Bearing noise (BeQuiet) | SKF / DIN test | BQ4 / BQ5 grade (very low noise) | BQ3 min |
| Ash content | ASTM D482 | <0.1% (ash-free) | <0.5% |
| Failure Mode | Root Cause | Diagnostic Test | Fix |
|---|---|---|---|
| Foaming during amine addition | Moisture in base oil or isocyanate — water + NCO → urea + CO₂ | Karl Fischer on base oil; CO₂ off-gas | Verify base oil pre-dried at 110°C / vacuum to <0.05% water; check isocyanate moisture; nitrogen blanket reactor |
| Drop point below 250°C | Top temperature hold below 200°C; or amine/MDI stoichiometry wrong | D2265 drop point; FTIR for residual NCO | Raise top hold to 210°C, 15 min; verify NCO:amine equivalents 1:1 for diurea, 2:3 for triurea |
| Grease softens over storage | Residual unreacted NCO continuing to react slowly; or insufficient consolidation hold | FTIR for NCO; penetration shift over time | Extend consolidation hold at 150°C to 60 min; verify FTIR shows complete NCO consumption |
| Grease lumpy / coarse texture | Amine added too fast; localised exotherm caused inhomogeneous urea | Microscope; visual texture | Slow amine addition to 30 min minimum; oversize stirrer to dissipate exotherm; ensure base-oil pre-mix homogeneous |
| Drop point pass, but bleed high | Insufficient consolidation at top temperature; or base oil polarity mismatch | D6184 24h bleed; D2265 | Extend top hold; add 5% adipate ester to improve urea-oil compatibility |
| Discolouration (yellow/brown) | Aromatic isocyanate (TDI) or amine oxidation during synthesis | Visual; UV-VIS spectrum | Switch to MDI (lower colour generation); add antioxidant earlier in process; nitrogen blanket strictly maintained |
| Compatibility failure with lithium grease | Polyurea and lithium soap are inherently incompatible | D6185 compatibility test | Not a formulation fix — clean bearings completely before switching greases; document compatibility limit on TDS |
A polyurea grease plant requires specific capability that a standard soap-grease plant lacks: moisture exclusion (vacuum drying capability, nitrogen blanketing), sealed reactor head with positive-displacement amine feed, and isocyanate handling infrastructure with appropriate PPE and ventilation. Total capex is comparable to a CaSX plant. See our Plant Setup service for complete specification.
No — polyurea grease is NOT a soap grease. It is made by reacting an isocyanate (MDI or TDI) with an amine inside the base oil. The reaction is an addition reaction forming a urea linkage (R-NH-CO-NH-R'), not a saponification.
This is why polyurea grease contains no metal soap and is described as 'ash-free' — important for electric motor applications where metal ions can attack winding insulation. The manufacturing process is also fundamentally different: no metal hydroxide, no water of saponification, no high-temperature soap dissolution.
Tell us your target application, NLGI grade and reactor scale. We respond within one business day with an honest assessment and indicative timeline.