Regulatory Compliant PTFE Powders for Grease Applications

COMPANY SENSITIVE & CONFIDENTIAL

Regulatory Compliant PTFE Powders for Grease Applications

NLGI 2021 Annual Meeting

Presented by: Shichiu Kwan

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Properties of PTFE Micropowders

Specific Gravity 2.20-2.30

Melting Point (˚C) 320-330

SolubilityInsoluble in all

solvents

Heat StabilityDecomposition starts

around 400˚C

Surface Area (m2/gram) 1-20

Surface Energy (mJ/m2) 18-22

Coefficient of Friction 0.04-0.10*

* Ebnesajjad S., Morgan R. 2012. Fluoropolymer Additives. 1st. Oxford, UK: Elsevier, Inc.

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PTFE Properties That Affect Performance

Type of PTFE

– Emulsion Polymerized

– Suspension Polymerized

– Recycled

Particle Size or Primary Particle Size (PPS)

Surface Area

Surface Properties

– Affected by irradiation dosage

Molecular Weight (MW)

– Controlled by irradiation dosage

Nature of PTFE

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Benefits of using PTFE Micropowders in Greases

Wide range of Operating Temperature

Chemically Inert/Resistant

Hydrophobic/Water Repellent

White or grey

Friction Modifier and Extreme pressure/Anti-wear Additive

More effective at high loads than liquid lubricant alone

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PTFE – where is it used

Thickener & Anti-Wear• PTFE is used as a thickener for PFPE oils, Silicone oils. Esters or other applications

where hydrocarbon based fluids will not work. • Food grade applications • Oxygen valve systems • Extreme temperature applications either high or low temperatures.

• Anywhere a standard / Conventional thickener will not hold up o Note: If used as a thickener it is the only thickener in the system.o Conventional thickeners , Bentone- Clay, Calcium , Aluminum complex,

Lithium, Lithium Complex Polyurea

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PTFE POLYMERIZATION

Particle Size

Mo

lec

ula

r W

eig

ht

Emulsion Grade/Paste PTFE

PS: 0.1-0.3 µm

MW: 1-5 million

Used to produce tape, fine tubing, wire coating

Suspension Grade/Granular PTFE

PS: 50-500 µm

MW: 5-50 million

Used to make parts or billets by sintering

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Nature of PTFE

Emulsion Grade

Small PPS

– ~0.2 µm

– 5-10 µm agglomerates

High BET Specific Surface Area (SSA)

– > 6 m2/g

SEM Picture of High MW

PTFE

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Nature of PTFE

Suspension Grade

Particle Size (MV)

– Originally 25-250 µm

– After micronization can be as small as 3-4 µm

Low Specific Surface Area (SSA)

– ≤ 3 m2/g

SEM Picture of High MW

PTFE

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Micronized PTFEMOLECULAR WEIGHT REDUCTION BY IRRADIATION

e*

e*e*

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Nature of Micronized PTFE

MW is controlled by irradiation/Higher dose gives lower MW

Irradiation improves friability or ease of de-agglomeration

MW affects PTFE performance in greases and lubricants

– Thickening efficiency directly proportional to MW

– Anti-wear performance inversely proportional to MW

Molecular Weight

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Formation of Small Molecules

Irradiation induced degradation of PTFE generates smaller radicals

Radicals react with oxygen and moisture to form carboxylic acid groups

A small fraction of these molecules are 8-carbons long

– Perfluorooctanoic Acid (PFOA)

– Concentration of PFOA is in the range of 0.1-10 parts per million (ppm)

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European Union Environmental Regulation (REACH)

REACH limits the concentration of PFOA

– 1 ppm (= 1000 ppb) until July 4, 2022

– 25 ppb after July 4, 2022

Other per- and polyfluorinated small molecules (PFAS)

– 1000 ppb total after July 4, 2022

Regulatory Compliance

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Process to Remove PFOA

Degraded PTFE heat treated to remove PFOA and other small molecules

Liquid Chromatography-Mass Spectrometry (LC-MS) is used to determine the concentration of PFOA

There is no globally accepted test method

Test method was developed using methanol extraction

Sensitivity of test is < 1 ppb

Products testing below 25 ppb are marked Regulatory Compliant (RC)

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Does PFOA Removal Process Affect PTFE Properties?

Properties that May be Affected

– Particle Morphology

– Surface Area

– Surface Polarity/Surface Energy

Could Result in Changes in Powder Behavior and Performance

– Thickening Capability

– Wear performance

– Dispersibility

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REM Pictures of Heat Treated Submicron PTFEs

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REM Pictures of Heat Treated Submicron PTFEs

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PTFE Thickening Efficiency

Thickening efficiency also depends on the base oil!

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PTFE Thickening Efficiency

Increases as Primary Particle Size decreases/Surface Area increases

Increases as Bulk Density decreases

– The lower the bulk density the more oil the PTFE will adsorb

– “Added by weight but volume fraction dictates rheology”

Increases with Molecular Weight

– Using an emulsion grade PTFE with same PPS and BD but much larger MW may lead to gummy consistency (at same loading in a given oil)

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Thickening Capability – Cone Penetration

The numbers are averages of all production lots made since January 2020

Emulsion Grade (Submicron) PTFEsSuspension Grade Virgin PTFE (5

Micron)

High MW

252 dmm

High MW-RC

253 dmm

High MW

340 dmm

High MW-RC

340 dmm

Medium MW

261 dmm

Medium MW-RC

260 dmmRecycle Grade PTFE (5 micron)

Low MW

271 dmm

Low MW-RC

271 dmm

Low MW

407 dmm

Low MW-RC

442 dmm

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4 Ball Wear Performance

High MW PTFE

Low MW PTFE

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4-Ball Wear Test Results(50% PTFE in PAO6)


Micron)

High MW

0.53 mm

High MW-RC

0.55 mm

High MW

0.65 mm

High MW-RC

0.57 mm

Medium MW

0.51 mm

Medium MW-RC

0.52 mmRecycle Grade PTFE (5 micron)

Low MW

0.50 mm

Low MW-RC

0.50 mm

Low MW

0.60 mm

Low MW-RC

0.59 mm

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Zeta Potential -using Zetasizer Nano zs

The numbers are averages of all production lots made since January 2020


Micron)

High MW

-39.4 mV

High MW-RC

-37.2 mV

High MW

-47.9 mV

High MW-RC

-39.4 mv

Medium MW

-39.6 mV

Medium MW-RC

-37.2 mVRecycle Grade PTFE (5 micron)

Low MW

-48.0 mV

Low MW-RC

-37.5 mV

Low MW

-61.9 mV

Low MW-RC

-29.7 mV

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Summary

Does PFOA Removal Process Affect PTFE Properties?

Properties that May be Affected

– Particle Morphology – Some change

– Surface Area - No

– Surface Polarity/Surface Energy – Yes, as indicated by Zeta Potential

Could Result in Changes in Powder Behavior and Performance

– Thickening Capability – Typically No

– Wear performance – Typically No

– Dispersibility – Typically No for PAO, Silicon, and PFPE oil. May change in Polar systems


Thank you for your attention!

Q&A

Contact: Shichiu Kwan

Email: [email protected]

Documents

Regulatory Compliant PTFE Powders for Grease Applications