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). The same ash-free logic applies to non-soap thickeners such as bentonite clay grease, while high-load duty more often turns to a complex soap such as barium complex grease.
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). For lower-cost industrial duty, producers often run polyurea alongside a conventional sodium soap grease line, or the more common lithium grease manufacturing process, choosing chemistry by application rather than defaulting to one thickener.
| Component group | Typical role | Typical share |
|---|---|---|
| Base oil(s) | Carrier fluid (mineral / synthetic / bio) | ~75–90% |
| Thickener / soap system | Builds structure & consistency (NLGI grade) | ~8–15% |
| EP / anti-wear additive package | Load-carrying & wear protection | ~2–6% |
| Antioxidant, corrosion inhibitor, tackifier | Service life, rust protection, adhesion | balance |
Indicative high-level composition only. The exact components, treat rates, performance additives and approved suppliers are shared under NDA as part of a Lubechem formulation engagement.
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 indicative grease plant setup cost breakdown for a line-by-line estimate. 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.
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