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Diurea / Triurea · NLGI 2–3 · Drop Point >250°C

Polyurea Grease Manufacturing
Diurea/Triurea Synthesis SOP, NLGI Range & Plant Equipment

Reviewed by Er. Manoj Kumar — Founder & Chief Formulator · 15+ years lubricant & grease R&D

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.

>250°C
ASTM D2265 Drop Point
NLGI 2–3
Consistency Range
8–12 wt%
Urea Thickener Loading
Ash-Free
No Metal Soap
Chemistry Overview

What Polyurea Grease
Actually Is

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.

Raw Materials

Raw Material Specifications
& Suggested Treat Rates

Component groupTypical roleTypical share
Base oil(s)Carrier fluid (mineral / synthetic / bio)~75–90%
Thickener / soap systemBuilds structure & consistency (NLGI grade)~8–15%
EP / anti-wear additive packageLoad-carrying & wear protection~2–6%
Antioxidant, corrosion inhibitor, tackifierService life, rust protection, adhesionbalance

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.

Manufacturing SOP

Isocyanate-Amine Synthesis —
5 Steps, Moisture-Excluded

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.

1
Pre-dry base oil and charge isocyanate (T = 60°C)
Pre-dry the base oil (Group I/II SN500 + SN150 blend, plus any ester additive) at 110°C under vacuum (28–29 inches Hg) for 30 minutes to drive moisture below 0.05%. Cool to 60°C under nitrogen blanket. Charge half the dry base oil and the full MDI charge (weighed accurately — isocyanate dose drives the soap content) into the jacketed reactor. Maintain anchor stirrer at 30–60 rpm. Keep the reactor head sealed and nitrogen-purged throughout.
2
Amine solution preparation and addition (T = 70–100°C)
In a separate sealed vessel, pre-dissolve the amine mixture (monoamine + diamine if triurea) in the remaining dry base oil at 60–70°C. Pump the amine solution slowly into the reactor over 20–30 minutes using a positive-displacement pump — rapid addition causes localised exotherm and inhomogeneous urea morphology. Bulk temperature rises 30–50°C above setpoint as the reaction is highly exothermic. Maintain agitation and have jacket cooling on standby. The bulk turns from clear amber to opaque cream as urea fibres precipitate.
3
Reaction completion and consolidation (T = 150–170°C, 30 min hold)
After amine addition, ramp temperature to 150–170°C using jacket heating and hold for 30 minutes. The polyurea precipitates fully and the urea fibres consolidate. Take a sample and verify isocyanate consumption with FTIR — the NCO peak at 2270 cm⁻¹ should be fully absent. Residual NCO indicates insufficient amine, which causes downstream stability problems.
4
Top-temperature hold and additive addition (T = 200–210°C, then cool to 90°C)
Ramp to 200–210°C and hold for 15 minutes to fully consolidate the urea fibre structure. This high-temperature hold develops final fibre morphology and drives any final reaction completion. Cool to 90°C using jacket cooling. At 90°C add the additive package: antioxidant, ash-free rust inhibitor, optional ash-free EP/AW. Stir 20 minutes to fully disperse without trapping air. Maintain nitrogen blanket throughout.
5
Milling and packaging under nitrogen (T = 60–70°C)
Cool to 60–70°C and discharge through a coarse screen. Pass through three-roll mill or homogeniser 2–3 passes (gap 50/25/25 µm). Polyurea benefits from aggressive milling because the urea fibres are short and need uniform dispersion. Test ASTM D217 worked penetration, D2265 drop point (>250°C), D1264 water washout (5–10%), D4172 wear. Package under nitrogen blanket for premium variants to preserve shelf life.
Performance Targets

Typical ASTM Properties —
NLGI 2 Diurea Electric Motor Grease

PropertyASTM Test MethodTypical ValueElectric Motor Spec
Worked penetration, 60 strokesASTM D217265–295 (0.1 mm)265–295
Penetration change, 100,000 strokesASTM D217+5 to +20 dmm+30 max
Dropping pointASTM D2265250–270°C250°C min
Water washout @ 79°CASTM D12645–10%15% max
Four-ball wear scarASTM D4172, 40 kg, 75°C, 1h0.40–0.50 mm0.55 max
Four-ball EP weld point (no EP additive)ASTM D2783160–200 kgf160 kgf min (electric motor)
Oxidation stability, 100h @ 99°CASTM D9421–3 psi pressure drop (best of any chemistry)5 psi max
Oxidation stability, 500h @ 99°CASTM D9425–10 psi pressure drop15 psi max
Oil separation, 24h @ 100°CASTM D1742 / D61841–3% (very low)5% max
Bearing noise (BeQuiet)SKF / DIN testBQ4 / BQ5 grade (very low noise)BQ3 min
Ash contentASTM D482<0.1% (ash-free)<0.5%
Application Matrix

When to Choose
Polyurea Grease

ELECTRIC MOTOR
Sealed Bearing, Long Life
NLGI 2/3 polyurea for sealed-for-life electric motor bearings. Ash-free, low noise, exceptional oxidation life. Standard OEM specification for premium electric motors, HVAC blowers, EV traction motors. L10 bearing life 40,000+ hours achievable.
OEM standard
HIGH-SPEED BEARING
Machine Tool & Spindle Bearings
NLGI 2 polyurea (PAO base) for high-speed machine tool spindles, textile spindles, precision bearings. Very low noise, very low bleed. PAO base gives excellent low-temperature pumpability for cold-start machine tools.
PAO premium
WHEEL BEARING (TRIUREA)
Automotive Hub Bearings, Hot Service
NLGI 2 triurea for high-temperature automotive wheel bearings — hub bearing bulk temperatures up to 160°C in heavy braking. Triurea variant gives drop point >260°C and long service life. Increasingly the standard for premium passenger car wheel-bearing grease.
Triurea variant
AUTOMOTIVE
CV Joint, Universal Joint
NLGI 1/2 polyurea + MoS₂ for constant velocity joints — high articulation angle, shock load, long service interval. The ash-free chemistry is compatible with the rubber boot materials.
CV joint
FOOD GRADE (NSF H1)
NSF H1 Polyurea on White Oil
NSF H1 polyurea grease using HX-1 listed isocyanate, amines and USP white oil base. Premium food-grade chemistry for high-temperature food processing — oven chains, baking equipment bearings, sterilisation tunnel bearings.
HX-1 compliant
NOT FOR
Wet Environments, Severe EP
Continuous water exposure (water washout limit), or severe shock-load steel-mill applications (limited EP without additive top-up) — for these, switch to CaSX or LiX. Polyurea is the premium chemistry within its envelope, not outside it.
Choose CaSX / LiX
Failure Modes

Common Failure Modes
& Production Fixes

Failure ModeRoot CauseDiagnostic TestFix
Foaming during amine additionMoisture in base oil or isocyanate — water + NCO → urea + CO₂Karl Fischer on base oil; CO₂ off-gasVerify base oil pre-dried at 110°C / vacuum to <0.05% water; check isocyanate moisture; nitrogen blanket reactor
Drop point below 250°CTop temperature hold below 200°C; or amine/MDI stoichiometry wrongD2265 drop point; FTIR for residual NCORaise top hold to 210°C, 15 min; verify NCO:amine equivalents 1:1 for diurea, 2:3 for triurea
Grease softens over storageResidual unreacted NCO continuing to react slowly; or insufficient consolidation holdFTIR for NCO; penetration shift over timeExtend consolidation hold at 150°C to 60 min; verify FTIR shows complete NCO consumption
Grease lumpy / coarse textureAmine added too fast; localised exotherm caused inhomogeneous ureaMicroscope; visual textureSlow amine addition to 30 min minimum; oversize stirrer to dissipate exotherm; ensure base-oil pre-mix homogeneous
Drop point pass, but bleed highInsufficient consolidation at top temperature; or base oil polarity mismatchD6184 24h bleed; D2265Extend top hold; add 5% adipate ester to improve urea-oil compatibility
Discolouration (yellow/brown)Aromatic isocyanate (TDI) or amine oxidation during synthesisVisual; UV-VIS spectrumSwitch to MDI (lower colour generation); add antioxidant earlier in process; nitrogen blanket strictly maintained
Compatibility failure with lithium greasePolyurea and lithium soap are inherently incompatibleD6185 compatibility testNot a formulation fix — clean bearings completely before switching greases; document compatibility limit on TDS
Plant Equipment

Pilot & Production
Plant Equipment for Polyurea

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.

Equipment List · 200–500 kg/batch polyurea plant
Polyurea Grease Plant — Indicative Equipment & Sizing
A jacketed reactor 400–700 L volume in 304 stainless steel, rated for 220°C operation and full vacuum (up to 29 inches Hg) for the pre-drying step. Sealed head with nitrogen blanketing capability, vacuum line with cold-trap for moisture capture, pressure/vacuum gauge. Anchor stirrer + frame agitator with variable-frequency drive, oversized to handle exotherm-driven viscosity changes. Heating by thermal oil (preferred) for the 210°C consolidation hold. Jacket sized for rapid heating-to-cooling switchover for exotherm management.
A sealed amine pre-mix vessel (50–100 L stainless, nitrogen blanket capable) with positive-displacement metering pump for controlled amine addition. Isocyanate handling: sealed drum heater, drum opener with dry-air purge, isocyanate-rated PPE for operators (chemical suit, full-face respirator with organic vapour cartridge), local exhaust ventilation at the reactor charge point. Three-roll mill or homogeniser 2–3 TPH (10–15 lakh, ~US$11,800–17,700). Lab: FTIR (critical for NCO peak monitoring — ₹12–20 lakh, ~US$14,000–23,600), high-temperature drop-point apparatus, four-ball wear rig, bearing noise tester (optional). Total capex band ₹1–3 crore (~US$118,000–354,000) for 300–700 kg/batch. The same moisture-controlled, stainless-reactor infrastructure also suits adjacent blending lines such as DEF / AdBlue manufacturing if you intend to diversify product mix.
Reactor
400–700 L stainless, vacuum + N₂ capable
Safety
Isocyanate PPE + ventilation mandatory
Critical lab
FTIR for NCO conversion verification
Capex band
₹1–3 cr pilot to production
Questions & Answers

Frequently Asked About
Polyurea Grease Manufacturing

Is polyurea grease made by saponification?

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.

What is the difference between diurea and triurea?
Diurea has two urea linkages per thickener molecule — formed from one diisocyanate and two monoamines. Triurea has three urea linkages — typically two diisocyanates and a bridging monoamine + diamine combination. Triurea gives higher drop point (>260°C vs >250°C for diurea) and is used in higher-temperature applications like wheel bearings, hot electric motors and oven applications. The trade-off is slightly more complex synthesis with the diamine addition.
Why must the base oil be pre-dried for polyurea synthesis?
Isocyanates react with water to form urea + CO₂ — an unwanted side reaction that consumes isocyanate, produces foaming from CO₂, and yields a different urea (typically a simple monomeric urea, not the chain polyurea desired). Pre-drying the base oil at 110°C under vacuum to <0.05% water and using nitrogen blanketing during reaction are non-negotiable for consistent polyurea synthesis. This is the single most important process control parameter for polyurea.
Is MDI or TDI safer to handle?
MDI (4,4'-diphenylmethane diisocyanate) is much safer than TDI (toluene diisocyanate) and is preferred for polyurea grease. MDI is a solid at room temperature, has lower vapour pressure, and lower acute toxicity. TDI is a volatile liquid and a known respiratory sensitiser requiring much more stringent handling. Polyurea grease producers worldwide, including in India, almost universally use MDI. Both still require chemical-suit PPE, full-face respirator with organic vapour cartridge, and local exhaust ventilation at the reactor charge point.
Is polyurea grease compatible with lithium grease?
No — polyurea and lithium soap greases are incompatible. When mixed, the combined grease softens dramatically and leaks from bearings. This is one of the most important compatibility cautions in grease selection. When switching equipment from lithium to polyurea (or vice versa), the bearing must be cleaned and purged before re-greasing. ASTM D6185 compatibility testing should be conducted for any mixed-grease scenario — we run this test as part of our testing service.
Why is polyurea preferred for electric motor bearings?
Three reasons: (1) ash-free — no metal soap ions that could attack winding insulation if grease bleeds into the motor air gap; (2) excellent oxidation stability and long service life — sealed bearing L10 life often 40,000+ hours; (3) very low noise (the urea fibre structure is quieter than soap fibres under bearing rolling-element passage). Polyurea is the dominant chemistry for sealed electric motor bearings worldwide.
How long does a polyurea grease batch take?
3–5 hours — significantly faster than soap-thickened grease batches. There is no saponification step, no dehydration step, and no slow controlled cool-down requirement. The reaction itself is fast (under 30 minutes) and the consolidation hold is 30 minutes at 150°C followed by 200°C for 15 minutes. The faster batch cycle improves plant productivity but the raw materials (especially MDI and the grease additive package) are more expensive — the per-batch material cost is roughly 2× an equivalent NLGI 2 calcium soap grease or lithium soap batch.
Can polyurea be made NSF H1 food-grade?
Yes — HX-1 listed MDI grades, HX-1 amines and USP white mineral oil base are available, allowing a fully NSF H1 compliant polyurea grease. Polyurea is the premium thickener choice for NSF H1 high-temperature food applications (oven chains, baking equipment, sterilisation tunnel bearings) where the higher drop point of polyurea offers performance gain over aluminium complex. See our NSF H1 grease page.
Related Pages

Polyurea Sits Inside
a Larger Grease Practice

Guide
Grease Formulation Explained
See how polyurea compares with soap and clay thickeners.
Soap Alternative
Lithium Complex Grease
Drop point >260°C, NLGI 1–3 — the soap-thickened alternative for industrial applications. Cheaper but contains metal soap.
Food Grade
NSF H1 Food-Grade Grease
Polyurea is a premium NSF H1 thickener for high-temperature food machinery — ash-free chemistry meets HX-1 whitelist.
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