November / December 2015 NLGI Spokesman

NLGI

SPOKESMAN

Serving the Grease Industry Since 1933 – VOL. 79, NO. 5, NOV/DEC 2015

In this issue . . .

6 Extreme-Pressure, Antiwear and FrictionReducing Performances of Molybdenum Dithiophosphate and DMTD Derivatives in Greases 16 The Running-in Effect of CV Joint Grease 24 Biorefinery-Derived Long Chain Dibasic Complexing Agents for Lithium Thickened Lubricating Grease 30 The Adhesiveness of Grease

The revised NLGI Lubricating Grease Guide is now available for purchase.

Please visit https://www.nlgi.org/ products-page/lubricating-greaseguide/

Branching Makes It Better with

MOLYVAN 3000 ®

Friction Reducer

MOLYVAN® 3000 Friction Reducer is an exceptional oil soluble MoDTC friction modifier containing 10% molybdenum with anti-wear and antioxidant properties.

hemic ilt C a rb

LLC

UL

, ls

Van de

Its unique molecular branching provides superior fluid compatibility/stability at low temperature and enhanced robustness for improved retention of friction reduction in aged oil.

®

46

1

IS

O

90

0 1:2

008 100

30 Winfield Street, PO Box 5150, Norwalk, CT 06856-5150 (203) 853-1400 • F: (203) 853-1452 petro@vanderbiltchemicals.com • www.vanderbiltchemicals.com

02

Registered and pending trademarks appearing in these materials are those of R.T. Vanderbilt Holding Company, Inc. or its respective wholly owned subsidiaries. For complete listings, please visit this location for trademarks, www.rtvanderbiltholding.com.

PRESIDENT:

VICE-PRESIDENT:

Bruce M. Urban FMC-Lithium Division 2801 Yorkmont Rd., Ste. 300 Charlotte, NC 28208

David Como Dow Corning Corp.

P.O. Box 0994 Midland, MI 48686

SECRETARY:

TREASURER:

Kim Smallwood Citgo Petroleum Corp.

1293 Eldridge Pkwy.

Houston, TX 77077

Joe Kaperick Afton Chemical Corporation 500 Spring St. Richmond, VA 23218-2158

PAST-PRES./ADVISORY:

EXECUTIVE DIRECTOR:

Chuck Coe Grease Technology Solutions LLC 7010 Bruin Ct. Manassas, VA 20111

Kimberly Hartley NLGI Inter­national Headquarters 249 SW Noel, Suite 249 Lee’s Summit, MO 64063

DIRECTORS Barbara Bellanti Battenfeld Grease & Oil Corp. of NY P.O. Box 728 • 1174 Erie Ave. N. Tonawanda, NY 14120-0728 Richard Burkhalter Covenant Engineering Services 140 Corporate Place Branson, MO 65616 Faith Corbo King Industries, Inc. Science Road Norwalk, CT 06852 Gary Dudley Exxon Mobil Corporation 3225 Gallows Road Room 7C1906 Fairfax, VA 22037 Gian L. Fagan Chevron Lubricants 100 Chevron Way Room 71-7338 Richmond, CA 94802-0627 Jim Hunt Tiarco Chemical 1300 Tiarco Drive Dalton, GA 30720 Tyler Jark Lubricating Specialties Co. 8015 Paramount Blvd.

Pico Rivera, CA 90660 Dr. Anoop Kumar Royal Manufacturing Co., LP 516 S, 25th West Ave. Tulsa, Oklahoma 74127 Wayne Mackwood Chemtura 199 Benson Rd. Middlebury, CT 06749

Dennis Parks Texas Refinery Corp.

One Refinery Place Ft. Worth, TX 76101 Tom Schroeder Axel Americas, LLC P.O. Box 12337 Kansas City, MO 64116 Raj Shah Koehler Instrument Co. 85 Corporate Dr. Holtsville, NY 11716-1796 Dr. Huafeng “Bill” Shen Bel-Ray Co. P.O. Box 526 Farmingdale, NJ 07727 Terry Smith Lubrication Engineers, Inc. P.O. Box 16447 Wichita, KS 67216 Thomas W. Steib The Elco Corporation 1000 Belt Line Street Cleveland, OH 44109 Lisa Tocci Lubes ’n’ Greases 6105 Arlington Blvd., Suite G Falls Church, VA 22044 William (Bill) Ward The Lubrizol ­Corpo­ration 29400 ­Lakeland Blvd.

Mail Drop 051E Wickliffe, OH 44092 Ruiming “Ray” Zhang R.T. Vanderbilt Company, Inc. 30 Winfield St. Norwalk, CT 06855

TECHNICAL COMMITTEE CO-CHAIRS:

CHAIR, SESSION PLANNING:

J oe Kaperick Afton Chemical Corporation 500 Spring St. Richmond, VA 23218-2158

Joe Kaperick Afton Chemical Corporation 500 Spring St. Richmond, VA 23218-2158

David Turner 22110 Stone Cross Court Katy, TX 77450

SERVICE INDUSTRY ASSISTANCE COMMITTEE CHAIR: J im Hunt Tiarco Chemical 1300 Tiarco Drive Dalton, GA 30720

EDITORIAL REVIEW COMMITTEE Joe Kaperick Afton Chemical Corporation 500 Spring St. Richmond, VA 23218-2158

SPOKESMAN

Serving the Grease Industry Since 1933 – VOL. 79, NO. 5, NOV/DEC 2015

5 6

ALERT & Call for Papers Extreme-Pressure, Antiwear and Friction-Reducing Performances of Molybdenum Dithiophosphate and DMTD Derivatives in Greases

Aili Ma1, Minli Gu1, Junbing Yao1 and Ruiming “Ray” Zhang2 1 Vanderbilt (Beijing) Trading, Ltd., Beijing, PR China 2 Vanderbilt Chemicals, LLC, Norwalk, CT 06856, USA

16 The Running-in Effect of CV Joint Grease

Ko Tanimura,

Kyodo Yushi Co., LTD., 2-2-30 TSUJIDO , KANDAI, FUJISAWA-SHI, KANAGAWA 251-8588, Japan

24 Biorefinery-Derived Long Chain Dibasic

Complexing Agents for Lithium Thickened Lubricating Grease Paul A. Bertin,† and Paul A. Bessette‡ †Elevance Renewable Sciences, Woodridge, IL 60517 USA ‡Triboscience and Engineering, Inc., Fall River, MA 02740 USA

30 The Adhesiveness of Grease

Dwaine (Greg) Morris Shell Lubricants 526 S. Johnson Drive Odessa, MO 64076

CHAIR:

NLGI

OFFICERS

Daniel M. Vargo Functional Products Inc. Macedonia, Ohio, U.S.A.

36 Advertiser’s Index ON THE COVER

The revised NLGI Lubricating Grease Guide is now available for purchase.

Visit https://www.nlgi.org/ products-page/lubricatinggrease-guide/

Published bi-monthly by NLGI. (ISSN 0027-6782) KIMBERLY HARTLEY, Editor NLGI International Headquarters 249 SW Noel, Suite 249, Lee’s Summit, MO 64063 USA Phone (816) 524-2500, FAX: (816) 524-2504 Web site: http://www.nlgi.org — E-mail: nlgi@nlgi.org One-year subscriptions: U.S.A. $65.00; Canada $80.00; International $109.00; Airmail $147.00. Claims for missing issues must be made within six months for foreign subscribers and three months for domestic. Periodicals postage paid at Kansas City, MO. The NLGI Spokesman is indexed by INIST for the PASCAL database, plus by Engineering Index and Chemical Abstracts Service. Microfilm copies are available through University Microfilms, Ann Arbor, MI. The NLGI assumes no responsibility for the statements and opinions advanced by contributors to its publications. Views expressed in the editorials are those of the editors and do not n­ ecessarily represent the official position of NLGI. Copyright 2015, NLGI. Postmaster: Send address corrections to the above address.

INTRODUCING

GREASE

IN THE UNCOMPROMISING WORLD OF INDUSTRIAL, WHERE METAL MEETS METAL - HIGH LOADS, CORROSION AND CONTAMINATION RARELY RELENT. THAT’S WHERE AFTON’S GREASE MICROBOTZ™ SMOOTH THE WAY. PROTECTING EQUIPMENT, PREVENTING WEAR, AND PROLONGING THE LIFE OF INDISPENSABLE MACHINERY WHERE CONDITIONS ARE AT THEIR HARSHEST. AFTON’S BROAD RANGE OF MULTIFUNCTIONAL GREASE ADDITIVE PACKAGES AND COMPONENTS KEEP GREASE FORMULATION SIMPLE; MAKING COMPLEX, MULTI-INVENTORY MANUFACTURING A THING OF THE PAST, AND GRANTING MAXIMUM FLEXIBILITY FOR PRODUCERS OF SPECIALIZED GREASES. THE GREASE MICROBOTZ™ WORK HARD SO YOU DON’T HAVE TO. CUSHIONING THE GRIND OF HEAVY LOADS. KEEPING WEAR, CORROSION AND CONTAMINATION AT BAY. BEARING DOWN ON BEARING DAMAGE, AND GIVING BOTH GREASE MANUFACTURERS AND CONSUMERS PEACE OF MIND. UNRIVALLED ALLIES. ALWAYS PROTECTING. ALWAYS FIGHTING. ALWAYS THERE.

www.aftonmicrobotz.com

© 2015. Afton Chemical Corporation is a wholly owned subsidiary of NewMarket Corporation (NYSE:NEU).

AFTON®, HiTEC®, MicrobotzTM and Passion for Solutions® are trademarks owned by Afton Chemical Corporation. Passion for Solutions® is a registered trademark in the United States.

ALERT ALERT

We hope this holiday season brings you peace, happiness and a healthy, prosperous 2016!

Best wishes, From all of us at NLGI

This is the LAST print issue of the NLGI Spokesman. Please ensure we have your email address on file for the January/ February 2016 all digital issue.

Call for Papers – NLGI 83rd Annual Meeting A call is hereby issued for technical papers for presentation at the NLGI 83rd Annual Meeting, which will be held at The Omni Homestead, Hot Springs, VA, USA from June 11th - 14th 2016. You do not need to be an NLGI member in order to present a technical paper at our Annual Meeting.

The NLGI 83rd Annual Meeting theme is: ‘Revolutions in Grease - Changing Technology for Changing Times’ Therefore, we would be looking for papers that Challenge the existing way of thinking with: • New thickeners • New additives • New or improved test methods • New applications • New or improved manufacturing techniques • All to fit into an ever-changing regulatory environment Papers covering any other phase of grease chemistry, grease formulation or grease manufacturing technology are also welcomed.

Technical papers approved for presentation at the Annual Meeting may be published in the NLGI Spokesman, after evaluation by the NLGI Editorial Review Committee.

COMMERCIAL PAPERS: NLGI will also accept up to 4 papers of a commercial nature. One presentation of a commercial paper will be held at the beginning of each of our 4 Technical Sessions during the NLGI Annual Meeting and will not conflict with any other presentations or events. Commercial papers will be accepted on a first come, first served basis. (A fee of $750 will be charged for all commercial papers accepted for presentation.)

You may download the Author Information and Author Instructions/Deadlines forms for your technical presentation, as well as the Commercial Presentation Application form, on our website: https://www.nlgi.org/call-for-papers If you are interested in submitting a technical or commercial paper for presentation, please send your name, contact information and abstract to: Marilyn Brohm - Marilyn@nlgi.org NLGI INTERNATIONAL OFFICE 249 SW Noel St. • Suite 249 • Lee’s Summit, MO 64063 USA. Phone 816-524-2500 • FAX 816-524-2504

Extreme-Pressure, Antiwear and Friction-Reducing Performances of Molybdenum Dithiophosphate and DMTD Derivatives in Greases Aili Ma1, Minli Gu1, Junbing Yao1 and Ruiming “Ray” Zhang2 1 2

Vanderbilt (Beijing) Trading, Ltd., Beijing, PR China Vanderbilt Chemicals, LLC, Norwalk, CT 06856, USA

Abstract: The four-ball test was employed to evaluate the extreme-pressure (EP), antiwear (AW) and friction-reducing (FR) performances of molybdenum dialkyl dithiophosphate, and 2,5-dimercapto-1,3,4-thiadiazole (DMTD) derivatives, i.e., DMTD dimer, and its complex with polyalkylene glycol (PAG), in greases.

DMTD dimer and its complex with PAG exhibit excellent EP properties, which can achieve high weld load in lithium complex greases, polyurea greases and calcium sulfonate complex greases.

In lithium complex grease, molybdenum dialkyl dithiophosphate possesses outstanding AW and FR performances, which results in low wear scar and low friction coefficient. In calcium sulfonate complex grease, molybdenum dialkyl dithiophosphate provides good EP properties with high last non-seizure and weld loads, and excellent FR performances. But in polyurea grease, molybdenum dialkyl dithiophosphate does not exhibit obvious EP, AW and FR capacities. In lithium complex grease, with the combinations of molybdenum dialkyl dithiophosphate and boron ester or DMTD dimer complex with PAG, excellent EP, AW and FR performances can be achieved simultaneously. In polyurea grease, just the combination of molybdenum dialkyl dithiophosphate and DMTD dimer complex with PAG can get good EP, AW and FR results.

In calcium sulfonate grease, the combination of molybdenum dialkyl dithiophosphate and DMTD dimer could achieve high weld load, low wear scar and low friction coefficient.

1. Introduction

Use of anti-friction, antiwear and extreme pressure additives in lubricating oils and greases is a common practice. These antiwear and extreme pressure additives play an important role in forming surface protective films either by adsorption or reaction. Such surface films can prevent direct metal to metal contact, thus provide metal surface protection against wear and weld between metal surfaces in relative motion under high load conditions. 2,5-dimercapto-1,3,4–thiadiazole (DMTD) derivatives are generally used in lubricants as metal passivating agents. Such additives also have antioxidant and antiwear properties, and are used in a wide range of lubricant applications. For example, as an additive for engine oil, gasoline engine oil oxidation stability can be significantly improved. In antiwear hydraulic oils, it can provide good anti-corrosive effect on copper and assist in improving hydrolytic stability [1]. Due to the high sulfur content of DMTD, their derivatives have potential as an extreme pressure additive. Previous studies showed DMTD dimer and DMTD dimer polyether complex, a new type high performance extreme pressure additive for greases, have excellent extreme pressure properties. The structure of DMTD provides its multifunctional properties which allows it to perform as an extreme pressure agent, metal deactivator, metal passivator/antioxidant. As such, this type of additive can overcome the limitations in reduced oxidation resistance and corrosion of copper that are inherent problems with other traditional EP additives [2-8]. DMTD dimer has following chemical structure:

Keywords: grease, extreme pressure, glycol, polyglycol, 2,5-dimercapto-1,3,4-thiadiazole, DMTD dimer, molybdenum dithiophosphate, antiwear agents, friction -6reducing agent, testing VOLUME 79, NUMBER 5

This additive in its physical form is a solid/powder and has been shown to exhibit excellent extreme pressure performance in four-ball EP test [2, 9]. In four-ball EP test, most base greases will have four-ball weld point between 126 kgf and 160 kgf. When 2.0% DMTD dimer is added to these base greases, four-ball weld point can be increased to between 250 and 400 kgf. When DMTD dimer treat rate is increased to 3.0%, four-ball weld point can reach between 620 kgf. and 800 kgf or above [9].

Extreme pressure performance of DMTD dimer comes from its bidentate adsorption on the metal surface [9]. Figure 1 is a diagram of this bidentate adsorption, i.e. the two ring structure of DMTD oriented parallel to the metal surface to form a bidentate complex structure, and if only one ring is desorbed from the surface, the molecule is still attached to the surface by the other ring.

Figure 1. DMTD dimer adsorption on metal surface

Four-ball weld point results of DMTD dimer in different base greases are listed in Table 1 [2].

As can be seen from Table 1, DMTD dimer exhibits good extreme pressure properties.

Table 1. Extreme pressure performance of different greases with 3.0% DMTD dimer

-7NLGI SPOKESMAN, NOVEMBER/DECEMBER 2015

DMTD dimer can be dissolved in a polyalkylene glycol (PAG) solution to obtaining a biodegradable liquid product of DMTD/PAG complex. The product has excellent Timken extreme pressure properties and good Four-ball extreme pressure performance [8, 9].

Instead of bidentate adsorption of DMTD dimer, DMTD/PAG complex forms multidentate adsorption on the surface, the strongest adsorption possible [9]. DMTD/PAG complex adsorption on metal surface is shown in Figure 2.

Figure 2. adsorption of DMTD dimer / butoxy triethylene glycol complex on metal surface Excellent EP performance supports the theory of such strong surface adsorption. Table 2 lists DMTD/PAG complex EP performance in various base greases [8, 9]. As can be seen from Table 2, this additive at low treat rate of 2% can provide a Timken OK load of up to 80 pounds and four-ball weld point up to 400 kgf in some base greases. To achieve this level of extreme pressure performance, normally heavy metals-containing EP additive is needed at 5% treat rate.

Table 2. Extreme pressure properties of DMTD/PAG complex in different base greases -8VOLUME 79, NUMBER 5

Molybdenum dialkyl dithiophosphate (MoDDP) is generally considered as a friction-reducing and antiwear additive, but it also can act as extreme pressure additive. Its chemical structure is as follows:

Extreme pressure performance of molybdenum dithiophosphate is mainly reflected in its ability to significantly improve last nonseizure load by reducing the four-ball wear scar diameter and steady state friction coefficient of the oil treated with this additive. A four-ball friction and wear tester was used in the evaluation of friction, wear and extreme pressure properties of a 650 SN base oil treated with this additive. Standard ASTM D4172 four-ball wear test method conditions were used, except test load was reduced from 40 kgf to 30 kgf for the base oil only. All the other tests were run at 40 kgf load, 1200rpm, 60 minutes and 75°C. The base oil without additives could sieze at 40 kgf. The ASTM D2783 four-ball EP test method was used to measure extreme pressure properties. Standard test conditions of 1760 rpm, 10 seconds and room temperature were applied. The molybdenum dialkyl dithiophosphate additive evaluated is a typical product of MoDDP (molybdenum content of 8.1%, phosphorus content of 6.1%, sulfur content of 12.3%) [10]. Test results are shown in Table 3.

Table 3. Four-ball friction and wear tests on 650 SN base oil with MoDDP

-9NLGI SPOKESMAN, NOVEMBER/DECEMBER 2015

As can be seen from Table 3, LNSL value of oil treated with MoDDP will increase from 36 kgf to 95-100 kgf, showing good extreme pressure performance but the weld point is only improved marginally. For four-ball wear test, the wear scar diameter under load of 30 kgf for base oil is 0.802 mm, by adding 1.0% and 2.0% MoDDP , the wear scar diameter under 40 kgf load is reduced to only 0.478 mm and 0.376 mm, respectively. It can also be seen from Table 3, the coefficient of friction (C of F) for oil with MoDDP will be reduced by 20%, from 0.083 to 0.077.

In general, though extreme pressure additives in grease can greatly improve the weld point, this often leads to lower antiwear performance of the grease, resulting in an increase in four-ball wear scar. As we know, MoDDP additive not only can provide excellent anti-friction and antiwear properties, but also can significantly improve the last nonseizure load. While on the other hand, DMTD derivatives can improve the EP performance in either 4-ball weld point or Timken OK load or both. Although for any lubricant oil or grease, four-ball weld point, the last nonseizure load (LNSL), four-ball wear scar diameter and friction coefficient are often mutually restrained since all these additives are competing for the same metal surface area for adsorption. In this paper, a combination of DMTD derivatives as EP additive and MoDDP as antiwear additive and friction reducer in various base greases were studied with several common grease performance evaluation test methods. It is expected that the combination of DMTD extreme pressure additive and molybdenum dialkyl dithiophosphate antiwear agent can provide the best balance of extreme pressure, antiwear and anti-friction properties in treated greases.

2. Experimental / Materials and Methods

obtained from real production batches courtesy of several grease manufacturers. DMTD dimer [10] used in this study has a sulfur content of 62.0-67.0% and a nitrogen content of 17.4-19.4%. DMTD dimer/ polyalkylene glycol complex [10] has a sulfur content of 20-28%, and a nitrogen content of 6.0 to 10.0%.

Molybdenum dialkyl dithiophosphate (MoDDP) has molybdenum, phosphorus and sulfur contents of approximately 8.1%, 6.1% and 12.3% respectively. All three additives are available commercially [10].

2.2 4-Ball Friction and Wear Test Standard ASTM D2266 four-ball friction and wear test method was used to evaluate additive performance in lubricating grease. Experimental conditions were: 40 kgf load, 1200 rpm speed, 60 minutes, 75°C. Real-time recording of coefficient of friction during the test is also available with the specific four-ball test machine used, in addition to measurement of wear scar diameters.

2.3 Four-Ball EP test Standard ASTM D2596 four-ball EP test method was used to evaluate additive EP performance in greases. Experimental conditions were: 1770 rpm speed, time duration 10 seconds. Both last nonseizure load (LNSL) and weld point were measured.

3. Results and Discussion 3.1 DMTD derivatives and molybdenum dialkyl dithiophosphate synergistic combination in lithium complex grease MoDDP, DMTD dimer and DMTD/PAG complex were added to the lithium complex base grease at the indicated treat levels. Four-ball wear and extreme pressure tests were performed on the treated grease, see results in Table 4.

2.1 Base Greases and Additives Base greases used in this study include a lithium complex grease, a polyurea grease and a calcium sulfonate complex grease. All three base greases were - 10 VOLUME 79, NUMBER 5

Table 4. Additive performance on friction, wear and extreme pressure properties in treated lithium complex base grease As can be seen from Table 4, MoDDP has excellent friction and wear performance in lithium complex grease.

After adding MoDDP, both the friction coefficient and four-ball wear scar diameter, have been substantially decreased, while the last nonseizure load has been increased greatly. After adding extreme pressure agents DMTD dimer and DMTD/PAG complex, extreme pressure performance of the lithium complex grease was greatly improved. Both LNSD and weld point have been increased significantly, especially the weld point. But the fourball wear scar diameter has been increased, indicating that these DMTD derivatives are good at improving EP performance but are poor in antiwear or wear resistance.

On the other hand, it is obvious from Table 4, that combinations of MoDDP and DMTD dimer or DMTD/ PAG complex, can significantly improve both extreme pressure, antiwear/friction performance simultaneously in lithium complex grease. Figure 3 and Figure 5 showed the different effects on friction reducing performance between individual additive and additive combinations. And Figure 4 and Figure 6 showed the different effects on antiwear performance between individual additive and additive combinations.

Figure 3.

Friction reducing performance of MoDDP and DMTD dimer in lithium complex grease

Figure 4. Antiwear performance of MoDDP and DMTD dimer in lithium complex grease

Figure 5.

Friction reducing performance of MoDDP and DMTD/PAG complex in lithium complex grease

- 12 VOLUME 79, NUMBER 5

Figure 6. Antiwear performance of MoDDP and DMTD/PAG complex in lithium complex grease 3.2 DMTD derivatives and molybdenum alkyl dithiophosphate synergistic combination in polyurea grease

MoDDP, DMTD dimer and DMTD/PAG complex were added to the polyurea base grease at the indicated treat levels. Four-ball wear and extreme pressure tests were performed on the treated grease, results shown in Table 5.

Table 5 Additive performance on friction, wear and extreme pressure properties in treated polyurea base grease - 13 NLGI SPOKESMAN, NOVEMBER/DECEMBER 2015

As can be seen from Table 5, polyurea grease treated with MoDDP does not show any improvement in extreme pressure performance. Its friction reducing and antiwear properties are also not obvious. But this does not mean that all organic molybdenum additives are not effective in polyurea greases. As a matter of fact, molybdenum dibutyl dithiocarbamate, i.e. a MoDTC [10] with molybdenum content of approximately 28% and sulfur content of about 24.5% is very effective in friction reducing and antiwear performance in the same polyurea used in this study. Adding 1.0% and 2.0% of MoDTC in the polyurea grease can effectively reduce friction coefficient from 0.089 to 0.071 and 0.058, respectively. It can also reduce 4-ball wear scar diameter from 0.423 mm to 0.359 mm and 0.349 mm, respectively.

At the same time, the weld point can be improved from 250 kgf to 315 kgf. Therefore, MoDTC might be more effective than MoDDP in polyurea greases (data for MoDTC treated grease is not shown in Table 5).

But unexpectedly, 2.0% DMTD/PAG complex can reduce friction coefficient from 0.089 to 0.077 in the treated grease, showing a strong friction reducing performance.

When combination of MoDDP and DMTD dimer or DMTD/PAG complex was used in this grease, the weld point of the treated grease can remain at high values (though LNSL is lower), and four-ball wear scar diameter is smaller than when only DMTD extreme pressure agent was used, although still higher than the value for the base grease. This indicates that MoDDP can be used to improve the antiwear performance when DMTD containing extreme pressure agents are used.

When combination of 2.0% MoDDP and 2.0% DMTD/ PAG complex was used, the overall performance of the polyurea grease is well balanced with a high weld point, a low wear scar diameter and a small coefficient of friction.

It can also be seen from Table 5, polyurea grease treated with DMTD extreme pressure agents DMTD dimer and DMTD/PAG complex, the weld point of the grease can be effectively increased, but there is no improvement in four-ball wear scar diameter, indicating that these additives are poor in antiwear performance.

MoDDP, DMTD dimer and DMTD/PAG complex were added to the calcium sulfonate complex base grease at the indicated treat levels. Four-ball wear and extreme pressure tests were performed on the treated grease, results shown in Table 6.

3.3 DMTD derivatives and molybdenum alkyl dithiophosphate synergistic combination in calcium sulfonate complex grease

Table 6. Additive performance on friction, wear and extreme pressure properties in treated calcium sulfonate complex base grease As it can be seen from Table 6, molybdenum dithiophosphate MoDDP can provide some extreme pressure performance in calcium sulfonate complex grease, and friction reducing effect is also relatively obvious, but there is almost no antiwear improvement. This is mainly due to the calcium sulfonate complex base grease having very good antiwear performance, making MoDDP less effective. Overall, calcium sulfonate complex grease treated with 2.0% MoDDP performed pretty well. The weld point was increased from 315 kgf to 400 kgf, and last nonseizure load was increased from 100 kgf to 152 kgf , friction coefficient was lowered from - 14 VOLUME 79, NUMBER 5

0.098 to 0.072, and wear scar diameter at 0.373 mm is still considered very good.

the treated grease exhibited excellent friction reducing, antiwear and extreme pressure properties.

It can also can be seen from Table 6, adding an extreme pressure agent such as DMTD dimer or DMTD/PAG complex to calcium sulfonate complex grease, can effectively improve the weld point of the grease, especially when DMTD dimer was added. When 2.0% DMTD dimer was added to the grease, the weld point can reach 620 kgf.

In fact, when 3.0% DMTD dimer was added to the grease, the weld point will reach 800 kgf (data not shown in Table 6). But, in both cases when DMTD dimer or DMTD/PAG complex was added to the grease, the grease will have an increased four-ball wear scar diameter, indicating that antiwear performance of the grease actually deteriorated.

When combination of MoDDP and DMTD/PAG complex was used, the overall performance of the grease did not show any major improvement, except a slight increase of the weld point to 500 kgf. On the other hand, when a combination of 2.0% MoDDP and 2.0% DMTD dimer was used, the treated grease gave a very high weld point (620 kgf) , small wear scar diameter (0.426 mm) and low coefficient of friction (0.078).

(4) When combination of molybdenum dialkyl dithiophosphate (MoDDP) and DMTD/PAG complex was used in the polyurea grease, the treated grease exhibited excellent friction reducing, antiwear and extreme pressure properties.

4. Conclusions

(1) DMTD extreme pressure agents, DMTD dimer and DMTD/PAG complex, exhibit excellent extreme pressure performance. Adding these EP agents to lithium complex grease, polyurea grease and calcium sulfonate complex grease can effectively improve the four-ball weld point of these greases.

(2) Molybdenum dialkyl dithiophosphate ( MoDDP) has excellent friction reducing and antiwear performance in lithium complex grease. This additive can greatly reduce wear scar diameter and friction coefficient in lithium complex grease. In calcium sulfonate complex grease, it has good extreme pressure properties (increasing the last nonseizure load and weld point in four-ball EP test), and excellent friction reducing properties.

In polyurea grease, it does not show obvious extreme pressure, antiwear and anti-friction properties.

(3) When combination of molybdenum dialkyl dithiophosphate (MoDDP) and DMTD dimer or DMTD/ PAG complex was used in the lithium complex grease,

(5) When molybdenum dialkyl dithiophosphate (MoDDP) was used in the calcium sulfonate complex grease, the treated grease achieved very high weld point, reduced wear scar diameter and lowered the coefficient of friction.

References

[1] Chen, Lihua; Zhang, Chunhui; Discussion on Function and Mechanism of Metal Deactivators.

Lubrication and Seal, 2003, (1): 73-76 (in Chinese).

[2] Hoffman, D. M., Feher, J. J., Lubricating Compositions Containing 5,5’-Dithiobis (1,3,4-Thiadiazole-2-Thiol), US Patent No. 4,517,103 (1985).

[3] Karol, T., Maleic Derivatives Of 2,5-Dimercapto1,3,4-Thiadiazoles and Lubricating Compositions Containing Same, US Patent No. 5,055,584 (1991).

[4] King, J.P., Hill, B. L., Thiadiazole Compounds and Lubricant Additives thereof．US Patent No. 5,102,568 (1992).

[5] Karol, T., Polyether Glycol Derivatives Of 2,5-Dimercapto-1,3,4-Thiadiazole, US Patent No. 5,138,065 (1992).

[6] Karol, T., Luo, R. J., Ether Derivatives Of 2,5-Dimercapto-1,3,4-Thiadiazoles, US Patent No. 5,194,621 (1993).

[7] Karol, T., Tepper, R. J., Bis-1,3,4-Thiadiazole Compounds and Lubricating Compositions Containing Same, US Patent No. 5,849,925 (1998).

[8] Karol, T., Tepper, R. J., Thiadiazole Additives and Lubricating Compositions Containing the Same, US Patent No. 6,365,557 (2002).

[9] Karol, T., Thiadiazole Technology: Motor Oil Antiwear and Grease Extreme Pressure Additives, Technical Paper of R. T. Vanderbilt Company.

[10] Product Brochure of Vanderbilt Chemicals, LLC, 2013.

- 15 NLGI SPOKESMAN, NOVEMBER/DECEMBER 2015

The Running-in Effect of CV Joint Grease Ko Tanimura Kyodo Yushi Co., LTD.

2-2-30 TSUJIDO KANDAI, FUJISAWA-SHI, KANAGAWA 251-8588, Japan

Introduction

Constant velocity joint (CV joint) is a generic term for a joint that transmits rotary movement at the constant speed irrespective of flexion angle. The main application of CV joints includes automotive drive and propeller shafts, where they are usually used in combination of a sliding-type joint such as tripod joints and double offset joints with a fixed-type joint such as ball fixed joints (BJ).

Figure 11) shows the typical CV joint assembly.

CV joints are generally lubricated with a speciallydesigned lubricating grease. The performance requirements for the CV joint grease have become increasingly severe owing to the market demands for high-performance vehicles of small size and light weight. For instance, the sliding-type joint is required to have reduced vibration. Hatakeyama2) and Yoshihara3) focused on improving vibration performance and developed a low-friction grease with vibration reducing effect by employing some additives in combination. As for the fixed-type joint, a long “flaking life” is of great importance. The typical flaking observed in the fixed-type joint includes subsurface-initiated flaking and surfaceinitiated flaking. For the latter, effective running-in process is thought to be critical for flaking life extension.

Taniguchi et al. provided a specific example of surfaceinitiated flaking resulting from insufficient running-in process and reported about a lubricating grease with enhanced flaking resistance developed by employing appropriate additives to improve wear property4).

Most fixed-type joint greases are made from molybdenum disulfide (MoS2) 5). MoS2 is a representative solid lubricant well known for its good friction property

and high load capacity. Nevertheless, very little information about the effect of MoS2 on CV joint flaking life can be found in literature.

This paper discusses the role of MoS2 in grease lubrication of fixed-type CV joint based on the results of the bench tests using a real CV joint and SRV friction wear tests to evaluate wear property.

Ball fixed joint - Lubrication condition and flaking resistance

Figure 2 shows the typical structure of BJ 5), which consists of an outer and an inner race, six balls, a cage, a boot and the lubricating grease filled inside the joint.

Balls are placed between an outer and an inner race and kept by a cage from axial dropping. A boot is used to hold the grease and to keep out dust and water.

Balls in rolling-sliding motion between the races travel back and forth in a short stroke. According to Garnham’s calculation of contact pressure for regular passenger cars based on the Hertz theory, the maximum Hertz pressure between the ball and the outer and the inner race are 2.7 GPa and 3.5 GPs, respectively6).

The fixed –type CV joint is in boundary lubrication with thin oil films because the rough track surface is exposed to high contact pressures at low speeds, and will supposedly be in mixed lubrication as runningin progresses and roughness projections are worn 7).

Therefore, BJ needs to be highly resistant to flaking, wear and heat. It should be noted that one of the major requirements for the lubricating grease filled in BJ is flaking resistance. Figure 3 shows an example of flaking on CV joint track surface.

- 16 VOLUME 79, NUMBER 5

Lubricating Action by Molybdenum Disulfide

condition employed 12,13,14).

MoS2, the representative solid lubricant with a layer-lattice structure can effectively lubricate the fixedtype CV joints in boundary and mixed lubrication thanks to its good friction and wear preventive properties under high-load and/or boundary lubrication conditions.

Bartz concluded that MoS2 prevents wear by cushion element action on friction surface or compound films produced by a chemical reaction with friction surface 8).

Contrary to his conclusions, it is also reported that the addition of MoS2 accelerated wear. Bartz suggested that such wear was brought on by antagonism between MoS2 and other EP additives9).

MoS2 in lubricating oil is considered to have a different effect depending on surface roughness. Cusano et al. reported that MoS2 on rough surface in pure sliding can effectively reduce friction by entering the contact area, but that on smooth surface cannot reach the contact area and so has no wear-reducing effect 10). According to their report, the surface roughness that MoS2 achieves the maximum friction/ wear reducing-effect varies with the size of particles11). It seems that, depending on the relation between the particle size and surface roughness which determines the accessibility of MoS2 to contact area, MoS2 sometimes reduces wear and sometimes not.

Some studies about the effect of MoS2 in lubricating oil and grease on flaking life produced different results in response to the lubrication

MoS2’s role in CV joint grease Evaluation on running-in effect using real CV joint

Bench tests were carried out to evaluate the running-in effect of CV joint greases. Grease A with MoS2 and grease B without MoS2 as shown in Table 1 were used to see if running-in process is affected by the presence or absence of MoS2. Grease A is a field-proven CV joint grease formulated with urea, MoS2, organic molybdenum and other additives in combination. Table 2 summarizes the test condition. The track between balls and races of tested CV joints were observed for surface roughness.

Figure 4 shows the surface roughness measurements of the inner race track after testing. Surface roughness was smaller with grease A than with grease B, confirming that roughness projections were worn by the effect of MoS2 and one of the MoS2’s roles in CV joint grease is to stimulate running-in process.

Wear property measurements

Wear that occurs during the initial period of CV joint operation is beneficial and referred to as runningin where roughness projections are worn. The early completion of running-in period associated with the rapid formation of smooth surface is desirable from the viewpoint of less stress to metal. On the other hand, in the subsequent steady state, wear accompanied by stress to metal has to be prevented as much as possible in order to maintain stable surface condition to prolong CV joint flaking life.

Lubrication tests in a ball-on-

plate configuration was carried out using Optimol’s SRV test machine to evaluate wear property with consideration for change in surface roughness during CV joint operation. Two types of test plates with different roughness were used.

One had a roughness of Ra0.2 μm (root-mean-square) to simulate lubrication condition during the initial period and the other was Ra 0.1μm found commonly in the steady state with worn roughness projections. Table 3 summarizes the test condition. Tested plates were observed for surface appearance and the roughness of the central part of wear track was measured using a laser microscope. In addition to greases A and B shown above, greases C, D and E with different combinations of additives as listed in Table 1 were tested to study how each additive affects the test results.

Figure 5 shows photographs of the tested Ra0.2 μm plates in which roughness of wear track in Ra is indicated. The ball on test plate reciprocated in sliding motion perpendicular to grinding marks.

As for grease A, the surface roughness decreased after testing as roughness projections were worn.

Grease B without MoS2 and grease C without organic molybdenum had no major change in surface roughness, which means that no wear occurred.

These results suggest that MoS2 and organic molybdenum can positively affect running-in process.

Following this, the same tests were performed with Ra0.1 μm plates (Figure 6). Greases A, B and C had no major change in surface roughness after testing. Unlike Ra0.2 μm plates, wear did not progress

- 17 NLGI SPOKESMAN, NOVEMBER/DECEMBER 2015

even when lubricated with grease A containing MoS2 and organic molybdenum.

To sum up these results of all test plates with different roughness, MoS2 and organic molybdenum can promote wear on roughness projections at high local contact pressure, but have no appreciable effect on a smooth sliding surface. MoS2 and organic molybdenum are likely to prolong the flaking life by promoting wear on the roughness projections of unworn surface during the initial period as shown in the CV joint bench tests. At the same time, they can effectively support the formation of robust reaction films in the steady state where surface roughness decreases and wear progresses no further.

MoS2 particle size and content in grease formulation

Considering that MoS2 functions to smooth the lubricated surface by promoting wear on rough projections, SRV tests were performed under the same test condition as the previous SRV tests as shown in Table 3 to study how the smoothing behavior is affected by the difference in MoS2 particle size and content in grease formulation. Tested greases had the same additive composition as grease A but with different MoS2 particle diameters of 1.9 μm and 12.5 μm in median size and different MoS2 content. The particle size distribution was measured by electrical resistivity method. Two types of test plates were used: one had a surface roughness of Ra 0.2 μm and the other was Ra 0.45μm.

Fig. 7 shows the change in wear track roughness before and after testing by grease type. Lower roughness means further progression of wear on roughness projections.

Both MoS2s with different particle diameters at low content promoted wear. MoS2 of a larger particle diameter did not promote wear when the content increased confirming that wear on roughness projections is related to MoS2 content. Two test plates of different roughness had the largest wear volume at different MoS2 content indicating that the most suitable MoS2 content for each surface roughness can optimize running-in effect.

Discussion

The results of the tests discussed in 4.1 and 4.2 proved that MoS2 stimulates running-in process by promoting wear on projections to achieve a stable surface condition.

Although it seems contradictory to the well-known wear

preventive property of MoS2, it often promotes wear when used in combination with EP additives as mentioned above9).

It is evident from no wear progression with grease B (with additives other than MoS2) that other additives in the formulation exhibited wear preventive property.

As for grease A, MoS2 probably overwhelmed the wear preventive property of other additives and promoted wear on projections due to antagonism with other additives as indicated by Bartz.

In the SRV tests discussed in 5, the wear behavior of 12.5 μm MoS2 varied more with changes in content compared to 1.9 μm MoS2. Again, the wear behavior at low content seemed to be attributed to antagonism with other additives. It should be considered that wear did not progress further when MoS2 content increased because the wear preventive property inherent in MoS2’s nature dominated the action of other additives. Given the fact that MoS2 is known to exhibit wear preventive property through the cushion action of solid particles8), larger MoS2 particles could have filled the surface pits to form apparent smooth surface and avoided wear on projections.

For the purpose of flaking life extension, selecting the appropriate MoS2 particle size and content depending on lubrication condition and track surface roughness can ensure sufficient wear on projections with a minimum contact pressure.

Conclusion

In this study, MoS2 and organic molybdenum were found to have a beneficial effect on running-in process through the bench and SRV tests to evaluate wear property of CV joint greases. Improved running-in process to mitigate stress concentration on projections is of benefit in flaking life extension. MoS2 has long been used in a CV joint grease and there has so far been no candidate additive to replace MoS2. In today’s circumstances where automotive parts are becoming smaller and lighter giving themselves severe condition than ever before and flaking life extension has been one of the most important issues, MoS2 is expected to remain the primary additive to ensure reliable CV joint operation.

References

1. Ikeda, T., NTN Technical review, 70, 8 (2002)

- 18 VOLUME 79, NUMBER 5

2. Hatakeyama, K., NLGI spokesman, 56, 232 (1992) 3. Yoshihara, M., NLGI spokesman, 76, 5, 14 (2012) 4. Taniguchi, A., Kondo, S., and Dong, D., NLGI spokesman, 68, 11, 12 (2005) 5. Fish, G., Euro Grease, May/June, 26 (1997) 6. Garnham, J.E., SAE Technical paper, 960572, (1996) 7. Sayles, R. S., Proceedings of the Institution of Mechanical Engineers, Part J, 209.149 (1995) 8. Bartz, W. J., ASLE Transactions., 15, 207 (1972) 9. Bartz, W. J., NLGI spokesman, 53, 9, 408 (1989) 10. Cusano, C., and Sliney, H. E., ASLE Transactions., 25, 2, 190 (1982) 11. Cusano, C., Goglia, P. R., and Sliney, H. E., ASLE Transactions., 27, 3, 227 (1983) 12. Kuhnell, B.T., and Stecki, J.S., Tribology Transactions, 31, 3, 324 (1988) 13. Soda, N., and Yamashita, M., Junkatsu , 21, 2, 116 (1976) 14. Nagamura, K., Terauchi, Y., Nagasaki, Y.,, and Ninomiya, S., The Japan Society of Mechanical Engineers(C), 58, 548, 223 (1992)

- 20 VOLUME 79, NUMBER 5

- 21 NLGI SPOKESMAN, NOVEMBER/DECEMBER 2015

- 22 VOLUME 79, NUMBER 5

Missed the 2015 NLGI Annual Meeting?

You missed a great meeting! We hope you can join us next year as we go to the historic Homestead Resort, which will be celebrating its’ 250th Anniversary!

The Homestead Resort Hot Springs, Virginia, USA June 11 - 14, 2016 http://www.omnihotels.com/hotels/homestead-virginia

Statement of Ownership, Management, and Circulation Publication Title: NLGI Spokesman

Publication No. 9331-900

Filing Date: 10/30/2015

Issue Frequency: Bi-Monthly

The 2014 NLGI Grease Production Survey is here!

No. of Issues Published Annually: 6 Annual Subscription Price: $65.00 Domestic, $109.00 International Complete Mailing Address: NLGI

249 SW Noel Street, Suite 249, Lee's Summit, MO 64063 Editor (Name and Complete Mailing Address)

Kimberly Hartley 249 SW Noel Street, Suite 249, Lee's Summit, MO 64063

Publication Name: NLGI Spokesman Issue Date for Circulation Data Below: September/October 2015 Extent and Nature of Circulation Total No. Copies (Net Press Run) Total Paid and/or Requested Circulation Total Free Distribution by Mail Total Distribution Copies Not Distributed (leftovers) Percent Paid and/or Requested Circulation

Average No. Copies Each Issue During Preceding 12 Months

Actual No. Copies of Single Issue Published Nearest to Filing Date

1200

1200

14

14

930 944

256 98.52%

Signature and Title of Editor, Publisher, Business Manager or Owner

930 944

256 98.52% Date

10-30-2015

The NLGI Grease Production Survey is now available for purchase. Members may download the Survey free of charge by visiting the Members Area of the NLGI Website, for non-member companies the cost is $150. The Survey covers the calendar years 2014, 2013, 2012, and 2011. For ordering information, please visit the NLGI website, https://www. nlgi.org/NLGI_store/

Biorefinery-Derived Long Chain Dibasic Complexing Agents for Lithium Thickened Lubricating Grease Paul A. Bertin,† and Paul A. Bessette‡ †Elevance Renewable Sciences, Woodridge, IL 60517 USA ‡Triboscience and Engineering, Inc., Fall River, MA 02740 USA

Abstract

Elevance Renewable Sciences, through recent commercialization of Nobel Prize-winning catalytic olefin metathesis of natural oils, can access novel long chain dibasic chemical building blocks from a joint world-scale biorefinery with Wilmar International Limited. In this paper, the authors report the feasibility of using specific long chain dibasic derivatives as complexing agent alternatives to azelaic acid in synthetic lithium complex grease.

Introduction

In 2013, Elevance Renewable Sciences (ERS) announced the startup and shipment of commercial products from a joint world-scale biorefinery with Wilmar International Limited located in Gresik, Indonesia. The biorefinery was constructed based on proprietary Nobel Prize-winning olefin metathesis technology capable of converting renewable natural oils (e.g. palm, soybean, canola, mustard, algal, etc.) into high-value specialty difunctional molecules, olefins, and oleochemicals with a capacity of 180 kMT. As shown in Figure 1, select ERS biorefinery products with potential lubricant applications include PAO precursor 1-decene and dimethyl octadecanedioate (DM-C18), a long chain α,ω-functionalized linear diester. The objective of this work was to examine the feasibility of using biorefinery-derived DM-C18 as a complexing agent in lithium thickened grease. Neat polyalphaolefin (PAO) was selected as a highly nonpolar base oil matrix to determine if inherent physicochemical differences, such as reduced water solubility, between DM-C18 and industry standard azelaic acid (C9) resulted in manifest differentiated base grease performance.

Figure 1. (Left) Elevance joint biorefinery. (Right) Select ERS biorefinery products and potential downstream bio-derived lubricant applications.

- 24 VOLUME 79, NUMBER 5

Background

Lithium complex greases represent nearly 40% of the North American market and a minor yet emerging proportion of global grease production.1 High operating temperatures accompanying modern transportation and industrial machinery often demand multipurpose lithium complex greases to function due to higher dropping points than simple soap alternatives. Complex grease properties depend on the nature of the base oil, thickener, and additive components with thickener chemistry and process predominantly dictating high temperature performance. Excluding borate ester technology,2 thickener systems typically comprise lithium carboxylate salts of 12-HSA and organic dibasic acids or esters. The salts are commonly formed in situ via neutralization or saponification of the corresponding acids or esters with lithium hydroxide during thickener kettle processing. Since lithium is an alkali metal that yields monovalent cations, it is generally accepted that “complexing” is not contingent on metaldirected assembly of 12-HSA and dibasic molecules into higher order networks but rather on strong adsorptive interactions between their corresponding salts during co-crystallization in base oil. Thus, it is well-known that the physicochemical properties of diacid complexing agents impact finished grease performance characteristics and manufacturing process parameters (e.g. one-step vs. two-step thickener formation).3,4 Table 1 lists relevant properties such as melting points and water solubilities for a range of α,ωdiacids with increasing chain lengths from adipic (C6) to octadecanedioic (C18) acid.5 As expected, water solubility drops precipitously as chain length increases while melting points plateau between azelaic and sebacic (C10) acids with additional influences from even-odd carbon number effects. For grease, it follows then that shorter chain complexing agents such as adipic acid would be more challenging to process and disperse in nonpolar base oils than longer chain counterparts due to decreased solubility of the corresponding lithium salts and greater susceptibility toward macroscopic phase separation. Thus, mid-chain azelaic acid and to a lesser extent sebacic acid are prevalent in grease owing to more

favorable performance properties and manufacturing process parameters despite generally less attractive economics than adipic acid. It is significant to note that longer chain complexing agents dodecanedioic acid (C12) and DM-C18 have been reported to yield acceptable lithium complex greases in mineral oil but widespread adoption of these technologies have most likely been hindered by even less favorable economics relative to mid-chain alternatives. 6,7 For years, the only commercial route to DM-C18 or the corresponding C18 diacid has been through a costly fatty acid fermentation biotechnology process. Metathesis now provides a competitive industrial-scale alternative and this preliminary study was initiated to identify if ERS biorefinery-derived DM-C18 has the potential to expand the slate of economically viable complexing agents available to lithium grease manufacturers.

Experimental

Synfluid® PAO 6 cSt was obtained from Chevron Phillips. Azelaic acid, 12-HSA, and lithium hydroxide monohydrate (LiOH·H2O) were obtained from commercial sources. Gas chromatography was used to confirm DM-C18 in sample compositions. Saponification number (SN) values were determined by ASTM D1387.

Three different samples of DM-C18 complexing agents of variable purity were synthesized from palm oil by proprietary olefin metathesis biorefinery processes and hydrogenation: DM-C18-A (SN = 252), DM-C18-B (SN

- 25 NLGI SPOKESMAN, NOVEMBER/DECEMBER 2015

= 256), and DM-C18-C (SN = 259). The samples were solids with melting points ranging from 56–60°C. Fourier transform infrared (FT-IR) spectroscopy of each sample confirmed methyl ester functional groups at 1739 cm-1.

Four laboratory scale lithium complex base greases were prepared for comparison. An azelaic acid complex grease (1) served as a reference control for experimental greases (2-4) with the three DM-C18 complexing agents (A-C). For each batch, an open kettle two-step reaction scheme was used with total thickener content fixed at 20% w/w. Ratios of 12-HSA to complexing agent were fixed at 2.7:1 (% w/w).

Table 2 shows formulation components for each. Grease preparation generally proceeded stepwise as follows: 1) Total batch size (base oil + thickener) approximately 2500 g.

2) A portion of PAO 6 and all 12-HSA were added to the vessel and heated to 80°C (176°F) till a homogeneous melt formed.

3) LiOH·H2O (1 equiv to 12-HSA) was mixed with deionized water (100 mL) and gently heated.

4) The aqueous base was then added to the oil solution under constant mechanical stirring and heated to about 100°C (212°F) for 1 h to complete neutralization (Step 1).

5) The complexing agent was then added to the vessel followed by additional LiOH·H2O necessary to neutralize or saponify this dibasic acid or ester (Step 2).

6) The reaction was gradually heated to 200°C (392°F) to complete lithium soap thickener formation and facilitate dehydration (and evaporation of methanol for DM-C18 samples).

7) Vessel contents were cooled by addition of the remaining PAO 6.

8) Upon cooling, base grease was finished by homogenization at 6000 psi.

Chemical and physical properties of each base grease are shown in Table 3.

- 26 VOLUME 79, NUMBER 5

Figure 2. Images of lithium complex base greases.

- 27 NLGI SPOKESMAN, NOVEMBER/DECEMBER 2015

Results and Discussion

Figure 2 shows a representative picture of each grease prepared in this study. Notably, the smooth textures of greases 2-4 with DM-C18 complex agents were impressive given the highly nonpolar nature of PAO 6. Azelaic acid control grease 1 was slightly grainier in comparison despite high pressure homogenization.

These observations suggest the reduced polarity of longer chain C18 complexing agents enabled greater thickener dispersability in PAO which may lead to improved formulation compatibility, manufacturing process parameters (i.e. lower temperatures), and performance properties.

All greases were compared by high temperature performance, unworked and worked penetration, oil separation, and thermo-oxidative stability using ASTM methods (Table 3). FT-IR data for all samples confirmed the formation of lithium carboxylate salt thickeners with characteristic carbonyl stretching frequencies around 1580 cm-1. A dropping point >260°C (500°F) for baseline control grease 1 with azelaic acid confirmed viability of the selected two-step open kettle process for preparing lithium complex greases. Experimental greases 2-4 had dropping points well above simple lithium 12-hydroxy stearate grease with sample 3 performing the best at a value >260°C (500°F) indicating a thermally robust thickener network. Furthermore, oil separation values at elevated temperatures were negligible for all samples.

Greases 1 and 2 displayed similar oxidation onset times

by PDSC (ASTM D4583 @ 150°C and 500 psi) with values trending higher for 3 and 4, respectively, indicating improved oxidative stability over the baseline.

Consistencies for each grease were determined by worked penetration after 60 strokes (P60) by ASTM D217. Control grease 1 had the highest yield (i.e. the lowest P60) with a penetration value of 259 dmm just between NLGI Grade 2 (265–295 dmm) and Grade 3 (220–250 dmm). Greases 3 and 4 were NLGI Grade 2 with a higher yield for 3. Although grease 2 was not confined to NLGI Grade 2, its mechanical stability was impressive and noteworthy with a slightly firmer consistency from 60 strokes to 10,000 strokes (P10k-P60).

Further work is warranted to validate this result from DM-C18-A. Water resistance properties were compared between base greases 1 and 3 with similar consistencies. The water washout test (ASTM D1264) was used to evaluate the ability of each lubricating grease to adhere to operating bearings while a stream of hot water (79°C) impinges the housing. Grease 3 with long chain complexing agent DM-C18-B displayed a nearly two-fold improved water washout value over azelaic control grease 1. A similarly improved water spray off (ASTM D4049) result was also observed for 3 compared to 1. The relatively poor values for both samples in these tests were most likely due to low base oil viscosity. Nevertheless, these data indicate that the reduced polarity of longer chain complexing agents (i.e. DM-C18) may enable the development of lithium greases with improved water resistance.

Conclusions and Outlook

The results presented herein demonstrate that ERS biorefinery-derived long chain dibasic esters are attractive complexing agent alternatives to azelaic acid for the preparation of lithium complex grease. Notably, in neat PAO at constant soap concentrations and ratios to 12-hydroxystearic acid (12-HSA), base greases with DM-C18 exhibited comparable dropping points with improved water resistance properties and oxidative stability over an azelate control. Furthermore, the long chain complexing agents yielded more uniform and smoother greases than azelaic acid despite high pressure homogenization suggesting improved thickener dispersability which may enable less intensive process parameters (i.e. time and temperature) during grease manufacturing. Future work will be directed toward optimization of thickener component ratios and grease manufacturing processes to improve yields and allow more extensive testing on fully formulated grease.

Acknowledgements

The authors would like to thank Courtnay Shaner and Daniel Mubima of Elevance Renewable Sciences for assistance in purification and characterization of DM-C18 samples.

- 28 VOLUME 79, NUMBER 5

References

1) NLGI 2012 Annual Production Survey.

2) Lorimor, J. J. “An Investigation into the Use of Boron Esters to Improve the High-Temperature Capability of Lithium 12-Hydroxystearate Soap Thickened Grease,” NLGI Spokesman 2010, 74(4), 27-37.

3) Morgan, D.; Kay, J. S.; Coe, C. R. “Critical Variables in Lithium Complex Grease Manufacturing,” 80th NLGI Annual General Meeting 2013, Tucson, AZ. 4) Tuszynski, W.; Bessette, P. A. “An Evaluation of Sebacic and Azelaic Acid as Thickeners in Lithium Complex Grease,” NLGI Spokesman 2008, 72(4), 30-38.

5) Johnson, R. W.; Pollock, C. M.; Cantrell, R. R. “Dicarboxylic Acids,” Kirk-Othmer Encyclopedia of Chemical Technology 2010, 1-18.

6) Clark, R. D.; Newman, R. H.; Pike, W. C. “Lubricating grease for rock drill bits and bits so lubricated,” Eur. Patent Appl. EP191608 A2, 1986.

7) Mertz, W. J.; Whitson, C. “Investigating the Influence of New Complexing Agents in a Lithium Complex Grease Formulation,” NLGI Spokesman 2002, 66(9), 18-25.

- 29 NLGI SPOKESMAN, NOVEMBER/DECEMBER 2015

Well-formulated lubricating oils and greases are crucial to the function of modern vehicles and industrial equipment. Unlike oils, greases are semi-solids. Therefore, at a given temperature, greases have a greater ability to stay in place and can provide a much greater film thickness than a lubricating oil. One of the advantages of a grease over lubricating oil is its ability to adhere to a metal part or bearing. This property is called adhesivity. A method has been proposed to determine adhesivity based on the probe tack test (ASTM D2979). This paper focuses on a technique where a metal plate is pulled away from a greased metal plate. The force required to separate the plates is calculated from the known mass as measured by an inexpensive spring scale. The results correlated with other well-known tests such as Cone Penetration (ASTM D217), Water Spray-off (ASTM D4049) and Water Washout (ASTM D1264).

Introduction

Functional Products Inc. Macedonia, Ohio, U.S.A.

Grease is widely used in lubrication applications including roller bearings and low speed gear systems. A lubricating grease comprises three components: base fluid, thickener, and performance additives. A grease is composed of liquid and solid phases. The liquid phase is the base fluid and the solid phase is formed by a network structure of soap molecules or a dispersion of solid particles such as inorganic clays or other thickeners. The solid phase thickener can consist of soap molecules with or without added polymer. The base oil in the grease is immobilized by the soap molecule network structure, resulting in a semi-solid to solid structure. The base oil solubilizes performance additives, including polymers.

Daniel M. Vargo

The Adhesiveness of Grease

Abstract

The function of the thickener is to provide the gel-like network structure. Generally, the soap thickener is a metallic salt of a long-chain, mono basic, fatty acid, e.g. lithium 12-hydroxystearate. The soap thickener will form interlocked fibers in grease.

Incorporating polymers into the grease can further enhance the properties of the grease such as consistency, shear stability, water resistance, adhesion, tackiness, and soap yield. Polymers such as polyethylene, polypropylene, polyisobutylene, halogenated polyethylene, and polymethacrylate are reported to improve the properties of greases.1,, Olefin copolymers (OCPs), Styrene-ethylene-butylene (SEBS) and OCP-anhydride (OCP-A) were studied. Pull-off force was compared to cone penetration, water spray-off, and water wash-out performance in greases containing polymeric additives. In a lithium complex grease an additional component or components are added such as azelaic acid, a dibasic acid. This forms a stiffer, more rigid 3-dimensional structure over that formed using a monobasic acid.

The structure of the polymer has a significant impact on grease properties including thickening efficiency and shear stability. The structure of the polymer determines the overall shape of the molecule. The development of advanced polymerization methods and catalysts allows polymers with a variety of structures to be synthesized. Figure 1 shows various polymer structures that may be obtained. Linear polymers are those with repeat units connected in a single long chain. Branched polymers or comb polymers comprise of structures with a long backbone and multiple side chains. In star polymers or dendrimers, repeat units are arranged radially. The polymers studied in this paper have linear or branched structures.

- 30 VOLUME 79, NUMBER 5

Tackifiers are typically polymeric additives that impart tack or stringiness to a lubricant. Tack is considered a composite property; the ability of a material to function as a tackifier is determined by its cohesive and adhesive forces, viscosity and other factors such as the molecular weight and concentration of the polymeric additives used in the formulation of such additives. Tackifiers have high cohesive and adhesive forces. High cohesive forces allow the tackifier to remain together as a single mass while high adhesive forces cause the tackifier to remain on the surfaces to be lubricated.

Tack is a composite property and therefore must be measured indirectly. Multiple tests are necessary to fully understand how well a polymeric additive such as a tackifier will perform as a grease additive. The water spray-off and water washout tests quantify only a portion of grease performance, the cohesiveness. The addition of the pull-off test allows an understanding of another important property of a grease tackifier, the adhesiveness.

A similar method to determine pull-off force in a lubricant using inexpensive equipment was previously developed.7

Current Test Methods to Measure Tack

Test methods for measuring tack are generally applied to the adhesives market which includes pressure sensitive adhesive tapes and adhesive coatings. Several organizations provide test standards to the adhesives market including the American Society of Testing and Materials (ASTM), the Pressure Sensitive Tape Council (PSTC), the European Association of the Self-Adhesive Labelling Industry (FINAT), the British Standards Institution (BSI) and the Tag and Label Manufactures Institute (TLMI). Test methods currently used for the pressure sensitive tape market include probe tack (ASTM D2979), loop tack (BS EN 1719, TLMI LIB 1/2) and rolling ball tack (ASTM D3121, BS EN 1721), as well as tests for double-sided tapes (BS 7116).8,9

These methods are useful when the adhesive can be coated onto a solid support or a tape and can then be placed in contact with a second surface. The force required to separate the surfaces is then measured and used as an indication of adhesiveness or tackiness. These tests are useful for comparing adhesives to one another but are not suitable for use in the grease industry; these tests measure pressure sensitive tack rather than adhesiveness as it relates to adherence of a grease to a metal part. Cohesion is also an important property that is generally not assessed using test methods designed for use in the adhesives industry. Cohesion provides the string-forming ability of a tackifier solution or a grease due to the interaction of the individual polymer molecules.

A grease should be able to adhere to a surface. This property is determined by factors including internal cohesiveness, surface adhesion, and tackiness or formation of thin string -like grease filaments. By varying the composition of the constituents, the properties of greases can be adjusted. For example, tackifiers containing high molecular weight polymers are added to grease to increase the tackiness or string formation. Most experimental methods to characterize lubricating greases with respect to their cohesive and adhesive properties are empirical in nature.

The cohesiveness of greases has been qualitatively measured by cone penetration10 and oil separation measurements11 while more recently rheological measurements provide further insight.12 Cone penetration measures the consistency or cohesiveness of grease by dropping a cone of known mass into a grease filled trough and recording the penetration depth of the cone. A low depth of penetration indicates stiff grease.

The adherence of grease to the substrate is characterized by water spray-off or water washout measurements.12

- 31 NLGI SPOKESMAN, NOVEMBER/DECEMBER 2015

In the water spray-off test, a greased metallic surface is subjected to direct water spray at elevated temperature and the adherence is determined based on the mass of grease lost over a certain time period.13, 14 Another method used for quantifying adherence is by subjecting greased cylinders to centrifugal forces. Depending on the mass of grease lost, the adhesion strength is ranked.15 In most cases, failure occurs within the grease, which is technically cohesive failure.

Approach- retraction experiments are also used to characterize adherence, cohesion, and tackiness of greases. A greased substrate is moved towards a ball attached to a flexible cantilever. On establishing contact, the greased substrate is moved further until a certain contact load is achieved. On reaching the target contact load, the greased surface is retracted from the ball until complete physical separation occurs.16 The basic technique is analogous to pull-off force experiments done using an atomic force microscope.17 After the approach-retraction cycle, the deflection force is plotted as a function of distance.

This paper presents an empirical method using inexpensive lab equipment to gauge the adhesivity of greases. It can be used as in in-house method to compare one grease to another. The results are correlated with cone penetration, water spray-off and water washout performance.

Adhesion and Cohesion

Cohesion is determined by the attractive forces between the molecules of a substance that tends to hold the substance together. Adhesion is determined by the

attractive forces between dissimilar molecules and causes one material to stay in place on another.

Adding a tackifier, such as an ultra-high molecular weight PIB, at approximately 0.05% wt to a lubricant package will tend to increase the cohesiveness and adhesiveness of the lubricant. The cohesive forces within a tackifier result in the string forming ability that is a key component of tackiness. Cohesion also drives the elastic nature of these materials. Greater cohesiveness is required to keep the lubricant from being squeezed out from between surfaces.18 Adhesion is also increased when using a tackifier. Higher adhesiveness is required to make a lubricant stick to surfaces.

Materials

The structures of the polymers used in this study are shown below in Figure 2. The base grease was a Lithium Complex Grade #2 grease with 10% soap content.

No additional additives were present. Polymers were incorporated into the base grease by mixing in a Hobart mixer at 90°C. The polymer additives used in this study were in powder, liquid or pellet form. Powdered polymers were added and mixed for 3 hours to ensure complete solubilization of the polymer. Liquid additives, OCP-A and OCP-P were mixed for 1 hour at 90°C. Polymer OCP-B is in pellet form and required longer mixing time and a higher temperature to complete solubilization. For reference, the base grease was heated and stirred using the same process as the samples containing the powdered polymers.

Data for the greases prepared incorporating the polymer additives is summarized in Table 1.

- 32 VOLUME 79, NUMBER 5

Experimental Methods

A 36.0 x 76.0 mm piece of sheet steel was attached to a wooden block. A 3mm deep grease containment area having the same dimensions was constructed on another piece of sheet steel. The volume of grease in the containment area for each test run was constant at 8.2 cm3. A screw-eye was attached to the center of the wooden block. Figure 3 on the following page shows the set-up of the test apparatus.

The test grease was added and leveled to the top of the containment area and the wooden block with a metal plate equal in area to the grease containment area was hung from the hand-held spring scale and pulled down and the block was pressed into full contact with the grease. The scale was calibrated such that a pull of 450 grams would be placed on the wooden block when the block and grease were in full contact. When the wooden

block was released a steady upward pull of 450 grams was applied to the block, normal to the surface of the grease until the block began to release. The time for the block to be completely released from the grease was recorded. This operation was repeated 5 times for each grease sample and averaged.

Results and Discussion

The data in Figure 4 shows that pull-off force is inversely related to cone penetration. As the grease becomes softer with certain additives it requires less force to remove the mass from the grease. Without any additives the base grease exhibits poor water spray-off performance. For certain additives, SEBS, OCP-A, OCP-B, and OCP-P improved water spray-off values correlate with a greater force required to remove the mass from the grease. This demonstrates that the grease has more adhesivity to the metal plate. The water washout test measures the ability of a grease to be removed from a bearing and is known to not typically correlate well with the water spray-off test. However, for additives OCP-A, OCP-B and OCP-P water washout performance correlates well with water sprayoff performance. It can be understood from the chemical structures shown in Figure 2 that polar acid anhydride allows for greater attraction or adhesivity to the metal surface.

Mechanism

In order to improve the water resistance of grease, the polymer must form a network structure. This network can be formed via physical crosslinking through a crystalline phase (e.g. semi-crystalline OCP), less soluble hard phases (e.g. SEBS), by hydrogen bonding (e.g. anhydride grafted OCP) or by long chain entanglement.

In a simple lithium soap the fiber network structure formed by the soap thickener is reversible. In the mixing process, the network formed by soap thickener is partially dissociated under heating. After cooling, the soap thickener resumes its fiber structure in the presence of the added polymer network. These networks - 33 NLGI SPOKESMAN, NOVEMBER/DECEMBER 2015

Figure 4: Grease test results for samples listed in Table 1. Relative to the base grease, A, all of the polymer additives improve the water spray-off performance. However, pull-off force is generally compromised.

interpenetrate as shown in Figure 5. In a complex lithium grease Lorimor has shown that little grease softening (dissociation) occurs therefore an interpenetrating network must form partly by another mechanism.19 Adhesion to a metal surface is driven by the electron rich oxygen of the acid anhydride group hydrogen bonding to the hydroxyl groups generally present on an iron surface, as shown below in Figure 6. As a result, the OCP-A and OCP-B polymers will be part

of the interpenetrating network of soap and polymer fibers and be attached to the metal surface through hydrogen bonding. The OCP-P polymer is a proprietary composition that exhibits significantly improved water washout and water spray-off performance. The mechanism attributed to its performance is a combination of multiple interpenetrating networks formed by semicrystalline phase and long chain entanglement linking sites, as well as hydrogen bonding to the metal surface.

- 34 VOLUME 79, NUMBER 5

Conclusion

Relative to the base grease, all of the polymer additives improve the water spray-off performance. However, pull-off force is generally compromised. Both the pulloff force and water washout performance of a grease are dependent on the cohesiveness of the material.

Cohesiveness is partly responsible for the property of a grease known as tack.

minimal equipment. Potential polymer additives can be qualitatively evaluated and judgments can be made about their performance. Based on the results of this study, a potential polymer additive should have a high pull-off force and excellent water spray-off performance.

Combined with other tests, such as mechanical stability and oil separation, a grease additive can be developed and evaluated more readily.

The pull-off and water spray-off tests used in this study are relatively quick and simple to perform and require - 35 NLGI SPOKESMAN, NOVEMBER/DECEMBER 2015

References 1.

2.

3.

4.

5.

6.

7.

8.

9.

10.

11.

12.

13.

14.

15.

16.

17.

18.

19.

“A comprehensive Review of lubricant chemistry, technology, technology, selection, and design” Rizvi, S.Q.A. ed., ASTM International, 2009, 443-496 Silverstein, S. and Rundnick, L. R., “Lubricant Additives Chemistry and Application”, Leslie R. Rudnick, ed., CRC, NY, 2009, 258-606 Larson, B. K. and Mroczek, W., “Benefits of Polymer Additives in Grease”, NLGI Annual Meeting, 2009. Paper #0918.

Scharf, C. R., and George, H. F., “The enhancement of grease structure through the use of Functionalized Polymer Systems,” NLGI Spokesman, 1996, 59 (11), 4 – 16.

Levin, V., “Tackifiers for High Temperature Lubricants,” NLGI Spokesman, 2004, 68 (4), 25 – 32.

Feldman, D. and Barbalata, A. “Synthetic polymers: technology, properties, application”, Springer, 1996.

Vargo, D. M., Ribera Serra, O., and Lipowski, B. M., “Quantitative Evaluation of Tackiness in Polymer-oil Solutions using Modified Probe Tack Method”, Lube: The European Lubricants Industry Magazine, 2014, 119, 23-30.

Lugt, P. M., Grease Lubrication in Rolling Bearings, Chichester : John Wiley & Sons, Ltd, 2013. 978-1-118-35391-2.

Roberts, R A. “Review of Methods for the Measurement of Tack”, Failure Criteria and their application to Visco-elastic/Visco-plastic materials. 5, 1997.

ASTMD217-97 Standard Test Methods for Cone Penetration of Lubricating Grease ASTM D1742-06 Standard Test Method for Oil Separation from Lubricating Grease during Storage Johnson M. Understanding Grease Construction and Function. Tribology and Lubrication Technology. STLE publication; June 2008 .

ASTM D4049-06 Standard Test Method for Determining the Resistance of Lubricating Grease to Water Spray.

ASTM D1264 Standard Test Method for Determining the Water Washout Characteristics of Lubricating Greases.

Berezhinskii VI, Klubkova NF, Terebilo VS, Chesnok LF. “Determination of adhesion properties of wire-rope greases”, Chemistry and Technology of Fuels and Oils 1977;13:525–8.

Achanta, M., Jungk, M. and Drees, D., “Characterization of cohesion, adhesion, and tackiness of lubricating greases using approach–retraction experiments”, Tribology International, 44 (2011): 1127-1133S. Capella B., Dietler G. Force-distance curves using atomic force microscopy.

Surface Science Reports 1999;34:1–104. www.tpub.com Integrated Publishing. Last modified: 2013. http://www. tpub.com/engine3/en32-38.htm.

Lorimer, J. J., “An Investigation inot the use of Boron Esters to Improve the High-temperature Capability of Lithium 12-hydroxystearate Soap Thickened Grease”, NLGI Annual Meeting, 2009. Paper #0912 - 36 VOLUME 79, NUMBER 5

Covenant Engineering Services, Inc. Quality Engineering Services Backed with Integrity Specialists: Grease Manufacturing and Lube Oil Blending

Conceptual, Process, and Detail Design 140 P.O. Corporate Place Box 761 Branson, MO Chesterton, IN 65616 46304 Phone: 417-336-9810 219-728-1054 Phone: 219-929-5781

www.covenantengr.com

Advertiser’s Index Afton Chemical, pg 4 Covenant Engineering, pg 36 Lubes N Greases, pg 38 Lubrizol Corporation, Back Cover Patterson Industries Canada, A Division of All-Weld, Co. Ltd, pg 39 Petro-Lubricant Testing Laboratories, Inc., pg 39 Vanderbilt Chemicals, LLC, Inside Front Cover

NLGI SPOKESMAN

GOING DIGITAL! THIS IS THE LAST PAPER ISSUE OF THE SPOKESMAN, TO CONTINUE RECEIVING THIS PUBLICATION WE MUST HAVE AN ACCURATE EMAIL ON FILE. NOTIFICATIONS HAVE BEEN SENT. IF YOU HAVE NOT RESPONDED, PLEASE SEND YOUR EMAIL ADDRESS TO NLGI@NLGI.ORG.

If you would like to see the magazine digitally, click below:

https://issuu.com/kim0824/docs/novdec2015 Oh, our apologies, you can’t click!

One of the many advantages of having a digital version of the NLGI Spokesman.

Good News.

Thought provoking and thorough reporting is at your fingertips.

LUBES’N’GREASES MAGAZINE Covering the global issues, trends and news that affect your success

LUBES’N’GREASES EUROPE-MIDDLE EAST-AFRICA MAGAZINE Offering a focused look at EMEA, Russia and India

LUBE REPORT A weekly round-up of trending industry news and base oil price reports Reaches 139 countries and is translatable into 80 languages

LUBE REPORT ASIA A free weekly e-newsletter for and about the lubricant industry in Asia. Featuring breaking news and base oil price reports in English and Simplified Chinese

GET YOUR SUBSCRIPTIONS TODAY www.LubesnGreases.com

PATTERSON INDUSTRIES

CANADA

"The Process Equipment People"

A D i v i s i o n o f A L L - W E L D C O M P A N Y L I M I T E D • Engineers Since 1920 49 PASSMORE AVE • SCARBOROUGH (TORONTO), ONTARIO M1V 4T1 • TEL: (416) 694-3381 • FAX: (416) 691 2768 E-MAIL: process@pattersonindustries.com WEB: www.pattersonindustries.com

• Designers & Manufacturers of

Grease Kettles • Autoclave and Atmospheric types (pressurized and non-pressurized) • Capacities from 1 gallon to 6000 gallon GlobAl leAder in quAlity And teChniCAl innovAtion Your source for Pressure Vessels, Heat Exchangers, Process Equipment, Autoclaves, Filter Housings from stainless steel, carbon steel, nickel alloys, non-ferrous alloys to ASME Codes, European PED, Canadian CSA B51, ISO 9001 certified.

www.pattersonindustries.com — 1-888-368-8884

Helping the World Run a Little More Efficiently In today’s complex marketplace, you need a technology partner that understands the demands of ever-changing applications, environmental concerns, LEAN manufacturing and worldwide standards and protocols.

Lubrizol is at the forefront of industry advancements offering our customers superior functionality, product consistency, R&D and testing. We are improving grease performance and processes worldwide.

To learn more visit www.lubrizol.com.

© 2014 The Lubrizol Corporation.

All rights reserved. 14-0132