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Advancements in AEM polymers for improved processing and improved properties.

AEM polymers were introduced to the elastomers market almost 40 years ago. They are copolymers of ethylene and methyl acrylate that contain a cure site monomer which allows for curing with a diamine. The original AEM polymers were converted to compounds that met a certain set of properties/ processing conditions. Parts made from these compounds are used in a variety of automotive applications, and the use of original AEM polymers has grown steadily.

There are some general perceptions in the rubber literature about AEM compounds (refs. 1-3). These include:

* ASTM rating as EE polymer (type, class)

* Used for hoses--turbocharger and transmission oil cooler (TOC) applications

--Extrude well

--Concerns with scorch

* Seals and gaskets for automatic transmissions and for engines

--Mold fouling concerns

--Difficult to process low hardness compounds

* Issues with DOTG accelerator

This article will review developments in the AEM polymer family over the past five years and highlight the improved properties that are available with AEM compounds.

Influence of market trends on AEM compounds

There have been many changes in the automotive marketplace over the years that favored the growth of AEM polymers. Other changes in the market place limited or have the potential to limit the use of AEM polymers. Some of the changes include:

* Higher engine temperatures

* Longer warranty times/higher mileage warranties

* Changes in automotive fluids

--More aggressive engine oils

--More aggressive automatic transmission fluids

--More PCV and exhaust gas recirculation in turbocharger systems

--Redesigns of the PCV system that have led to higher concentrations of fuel/acid condensate

* Government changes in allowable emission levels from cars

* Trends from compression/transfer molding to injection molding

* Stricter regulations about what raw materials that can be used with AEM compounds

The higher temperatures and longer warranty times have led to AEM compounds replacing some chlorinated elastomer compounds which could not meet the higher temperature requirements needed now for some TOC hoses. In some cases, the temperature requirements have gotten too high for AEM compounds and they have been replaced by FKM compounds (high temperature turbocharger hoses).

The stricter emission levels, like LEV II, have led to AEM gaskets replacing some silicone gaskets.

The acid condensate that is in recycled gas has led to replacement of some chlorinated elastomers by AEM compounds on the turbocharger cold side.

There will continue to be changes in the automotive marketplace that will affect the use of AEM polymers.

ASTM D 2000 ratings--heat and oil resistance

The ASTM D 2000 is a system that rates rubber products for automotive applications. The first two letters in the line callout are for heat resistance (type) and oil resistance (class). The typical literature rating for AEM polymers is EE (ref. 4).

Heat resistance

Heat resistance of a rubber compound is a function of time, temperature and the criteria used for pass/fail. The ASTM criteria for type (heat rating) is based on 70 hours at a temperature where the criteria is 50% loss in elongation, 30% loss in tensile strength and a 15 point change in hardness.

AEM compounds easily meet these criteria at 175[degrees]C, which is a Type E rating. Some AEM compounds can be formulated to meet these criteria at 200[degrees]C, which is a Type F rating. The AEM compounds would not be recommended for use at 200[degrees]C because they will not last much longer than 70 hours.

Automotive specifications have moved away from the ASTM ratings. They typically use criteria of 50% loss in elongation, 50% loss in tensile strength and a 15 point change in hardness, but vary the time and temperature requirements. Consequently, AEM compounds have been tested extensively in different heat aging conditions. Figure 1 shows the heat aging performance of a "good" AEM compound as a function of time and temperature.

Fluid resistance

ASTM rates elastomers by how much the compounds made from them swell after aging for 70 hours in IRM 903. In actuality, AEM compounds are never used with IRM 903. The two main types of fluids for AEM compounds are engine oils and automatic transmission fluids (ATFs). The swell in the engine oils and ATFs for AEM compounds is much lower compared to the swell in IRM 903. There are two main families of AEM polymers and they have different values for swell in IRM 903.

* AEM G family of polymers

--Meet EE (80% swell) and EF (60% swell in IRM 903)

--Swell in engine oils/ATFs ranges from 10 to 30%

* AEM GLS family of polymers

--Meet EG (40% swell) and EH (30% swell in IRM 903)

--Some compounds can meet EJ (20% swell in IRM 903); involves some trade-offs

--Swell in engine oils/ATFs ranges from 5 to 15%

AEM GXF development

One of the largest applications for AEM polymers is turbocharger hoses. In the early 2000s, the turbocharger volume was growing strongly, especially in Europe, and there was a need for better performance. AEM GXF was introduced in about 2003 for this application (ref. 5). Compounds made from the AEM GXF have a combination of good processability for making hoses, along with good physicals for hoses. In particular, the AEM GXF compounds have relatively long scorch times, and the surfaces of the hoses are relatively smooth. The AEM GXF compounds also have good dynamic properties as measured in the DeMattia flex test.

The successful development of the AEM GXF polymer was based on a team effort with help from the research and development group, the manufacturing group and the marketing group. This team effort set the stage for the next generation of AEM polymers.

Improvements for injection molding

Injection molding of elastomer compounds has been growing for many years, and it appears to be the preferred molding process for many new applications. It provides high quality parts that can be molded quickly for a relatively low cost of manufacture.

Injection molding of compounds based on the original AEM polymers was not always easy, and the molding community wanted a better AEM compound for injection molding. There were concerns with mold fouling, the frequency of cleaning the molds, parts being torn as they were taken out of the mold, etc.

This was not an easy problem to work on because there is not a standard laboratory test that predicts molding problems. Lab studies were done on a small molding machine for a limited number of cycles. The lab studies were important, but they could not duplicate an 8 or 12 hour production trial with large molding machines.

Several different approaches were used to work on this program. The ideas that were eventually incorporated into an upgraded AEM polymer were:

* Higher polymer viscosity--the original AEM polymers are relatively low viscosity polymers compared to other elastomers. A typical Mooney viscosity, ML (1+4) @ 100[degrees]C, for the standard AEM polymers is about 15 to 20. The upgraded polymer viscosity is almost 30. A "typical" compound viscosity with the upgraded polymer is about 50% higher versus the original AEM polymer.

* Lower scorch values--cure system was modified to make the polymer less scorchy, but still meet the end use requirements.

* Improved polymer architecture led to less compound being deposited on the mold

Compounds made from the upgraded polymer were tested in the laboratory compression molding machine and they ran significantly better than a control compound based on one of the original AEM polymers, AEM G. The laboratory molding machine made 40 o-rings from preforms, and then the o-rings were automatically removed. The number of o-rings that had to be removed manually was the major indicator of how well the compounds ran. Figure 2 shows the number of o-rings that stuck to the mold after each cycle. After almost 30 cycles, many more of the o-rings made from the AEM G control compound had to be removed by hand compared to the number of o-rings made from the compound using the upgraded polymer (AEM IP). There was also significantly less build-up on the mold surface with the compound based on the higher viscosity polymer.

The laboratory molding tests used compounds that were designed to be difficult to mold, i.e., low hardness, low viscosity, etc. This allowed the trials to be run with a relatively few number of cycles.

The key test for the upgraded polymer was a trial run by a molding customer using the formulation that they had developed for their injection molding process. They replaced the AEM G in their formulation with the AEM IP polymer. The compound based on the AEM IP ran much better than the AEM G control. The run was longer, there was less mold fouling and the cycle time was faster. After the trial, the molding customer wanted to immediately place an order for the upgraded polymer.

Improved properties for AEM IP--low hardness compounds, alternative accelerators

The AEM IP polymer was developed for improved processing. An added benefit was that it had better physical properties after curing, i.e., lower compression set, higher elongation, higher tensile strength, etc. These benefits were used to address two other issues with AEM compounds, namely processing of low hardness compounds and replacement of DOTG with alternative accelerators.

Low hardness compounds

It is difficult to make low hardness compounds (about 50 durometer A) from the original AEM polymers that have a combination of good physical properties and good processability. The low hardness compounds made from AEM G can have compound Mooneys that are under 20 (ML [1+4] @ 100[degrees]C), which makes them difficult to process.

The higher viscosity of the AEM IP polymer made it an ideal candidate to evaluate in low hardness compounds. Compounds of 50 durometer A based on the AEM IP have Mooney viscosities that range from 25 to 40 (depending on the plasticizer level). They are much easier to process compared to the AEM G compounds.

A trend in the automotive industry is that cam covers for car engines are switching/have switched from metal to plastic. Typically, the gaskets used with plastic cam covers need to be lower in hardness compared to the gaskets used with metal covers. Lower hardness compounds based on AEM IP are typically used for these applications.

DOTG replacement

For many years, DOTG was used as the primary accelerator for AEM compounds because it provided fast cure speeds and low compression set. There have been regulatory concerns with DOTG, especially in Europe, and it is being or has been eliminated from most AEM compounds.

Many different accelerators have been evaluated as replacements for DOTG, but none has the same combination of fast cure speed and low compression set. This is where the improved physical properties of the AEM IP have been helpful.

An example is when a compound based on AEM G and DOTG has to be reformulated to eliminate DOTG, while not sacrificing any compression set properties. An alternative accelerator can be used with the AEM G to provide similar cure speed, but in some cases, the compound may not meet the compression set requirements. The combination of the alternative accelerator and the AEM IP can have the same cure speed and the same compression set as the AEM G/DOTG control (ref. 8).

Improved AEM polymer for turbocharger hoses

The tremendous growth in the number of turbocharged engines has been driven by the need for higher fuel efficiency and lower emissions. The performance of the turbochargers continues to improve, which results in higher operating pressures and higher temperatures for the hot side hoses. Consequently, there has been a market demand for compounds with better properties than the AEM GXF compounds.

The lessons learned from the improved molding polymer were applied to the improved hose polymer. The improvements include:

* Higher polymer viscosity: The Mooney viscosity of the new hose polymer, AEM HT, is almost double that of the AEM GXF. A "typical" hose compound viscosity using AEM HT is about 50% higher than a compound using AEM GXF. The higher viscosity compounds have higher green strength in the uncured hose and they have less of a tendency to flat spot when pan cured in an autoclave. The higher green strength also helps with processing of lower hardness hose compounds (55 to 60 durometer A).

* Lower scorch values: Compounds made with the improved hose polymer are slightly less scorchy compared to AEM GXF compounds, even though they are about 50% higher in viscosity. This was accomplished by improving the cure architecture.

* Improved polymer architecture led to better dynamic properties in combination with lower compression set values. This is an unusual combination; one can normally improve one of these two properties, but not both.

Producers of hoses want compounds that are easy to process, have long scorch times, smooth surfaces and high green strength. Compounds made from the AEM HT polymer have these advantages over the AEM GXF compounds. The higher green strength is also beneficial for lower hardness hose compounds.

The dynamic properties of AEM GXF and AEM G compounds (and most other elastomer compounds) can be improved by going to a lower state of cure and/or a lower hardness (lower modulus). However, there are trade-offs with these approaches. One trade-off is that the compression set will increase (lower state of cure) and another trade-off is that the "push on" forces will be higher. ("Push on" refers to the amount of force needed to push the hose on to the fitting. Hoses with a lower hardness require more effort to get them on to the fitting.) The AEM GXF/G compounds can be optimized for either compression set or dynamic properties or "push on" forces, but not for all three.

The AEM HT compounds have the same concern with the trade-offs mentioned above, but they provide much more opportunity to have a significantly better balance of properties.

* If the hardness and compression set are held constant: Compounds made from AEM HT have about 10x better dynamic properties compared to AEM GXF compounds, at the same hardness and compression set. The dynamic properties were measured on a DeMattia flex tester.

* If hardness and dynamic properties are held constant: Compounds made from AEM HT can have compression set values that are about 5 points lower than an AEM GXF compound, at the same hardness and same DeMattia flex properties (compression set measured at 70 hours/150).

* If compression set and dynamic properties are held constant: Compounds made from AEM HT can have hardness values that are about 10 points higher than an AEM GXF compound. The higher hardness (modulus) helps to optimize the "push on" forces.

The property improvements in AEM HT compounds make it much easier to design a hose compound that has good processability with a good combination of dynamic properties, compression set and hardness.

Improved oil resistance with good low temperature properties

Like most oil resistant elastomers, AEM polymers can be modified to have better oil resistance, but at the expense of low temperature properties. For AEM polymers, the oil resistance is improved by going to higher levels of methyl acrylate (MA) and lower levels of ethylene in the polymer. MA has a higher glass transition temperature (Tg) than ethylene, and when the MA level is increased, there is an increase in the polymer Tg.

Low volatility plasticizers

Addition of a plasticizer to an AEM compound has many benefits, including:

* Better low temperature properties

* Better oil resistance

* Lower viscosity (can be positive or negative)

* Lower cost compound (can add additional carbon black to maintain a constant hardness)

There are some problems with using higher levels of plasticizers, especially in applications needing good heat resistance. Some of the problems include:

* Plasticizer may not survive heat aging in air due to volatility

--Post cure in air for 4 hours at 175[degrees]C (this requirement eliminates most low cost plasticizers)

--Heat age in air for one week at 175[degrees]C (this requirement eliminates many of the plasticizers that have relatively good heat resistance)

* Higher compression set (may not be able to meet end use requirements)

* Processing issues with low hardness compounds because of low compound viscosity

Most plasticizers that are compatible with AEM polymers do not survive the heat aging in air for one week at 175[degrees]C. Over the past five years, two types of low volatility plasticizers have become more widely available, and these plasticizers will survive in AEM compounds for one week at 175[degrees]C. They are:

* Low volatility polyether/ester plasticizer (ref. 9)

* Tri(n-octyl-n-decyl) trimellitate

These plasticizers have been evaluated in AEM compounds and the compounds maintain good low temperature after heat aging at 175[degrees]C.

Low swell AEM polymer for molding applications

AEM IP compounds have better molding properties than compounds made from standard AEM polymers. For some applications, the end use requirement calls for lower swell in certain fluids. The end use requirement also calls for good heat resistance and good low temperature properties.

Compounds made from AEM GLS polymers can meet the lower swell requirements, but they also can be difficult to mold since relatively high levels of plasticizer are needed to meet the low temperature requirements. An upgraded version of AEM GLS was developed with the same basic principles as AEM IP, i.e., higher viscosity, less scorch and less mold fouling, but with higher MA levels. This upgraded polymer will be referred to as AEM LS (low swell). The compounds made from the AEM LS polymer, along with a low volatility plasticizer, have a good balance of properties, including:

* A 70 durometer A compound with 15 phr of plasticizer has a volume increase in IRM 903 less than 30% (type H by ASTM rankings). The volume increase in SF 105 is under 10%.

* The compound Tg by DSC is -35[degrees]C. The Tg will still be low after aging for a week in air at 175[degrees]C.

* Compression set (70 hours/150[degrees]C) will be under 25%.

The AEM LS compounds made with the low volatility plasticizer are significantly easier to injection mold compared to compounds made from AEM GLS. The improvements in injection molding are similar to those seen with the AEM IP compounds. The AEM LS polymers can also be used to make low hardness compounds with low swell and with workable viscosities.

Low swell AEM for hoses

There is also a market demand for AEM hoses that have lower swell compared to those based on compounds made from AEM G, GXF or HT. A polymer, AEM HT-OR (oil resistant), has been developed that has many of the same features as the AEM HT polymer, except that it has higher methyl acrylate levels and this provides lower swell values. The features of the AEM HT-OR include the higher MA levels along with a higher polymer viscosity, lower scorch values and better dynamic properties. The addition of a low volatility plasticizer helps compounds based on AEM HT-OR to meet the low temperature requirements before and after heat aging.

Compounds made using AEM HT-OR have processing characteristics that are similar to AEM HT compounds which include high green strength, long scorch times and smooth surfaces. The cured AEM HT-OR compounds have the combination of a good balance of compression set, hardness and dynamic properties seen with the AEM HT compounds.

Fluid resistance--more than polarity

Fluid resistance is a very important property of elastomeric compounds and often it is the key factor in determining which polymer to use in a compound. A general comment is that a more polar polymer is better in fluid resistance.

Other factors besides polarity can affect the performance of elastomers in automotive fluids. These include the resistance to some of the minor impurities and/or additives that are in the fluid or that build up in the fluid. Some examples include:

* As some engine oils age, they become more acidic. The aged engine oils can be very aggressive to elastomeric compounds when tested at temperatures used for today's engines. Some elastomer compounds age well in the original engine oil (when it has little or no acid), but do not perform well in the aged oil.

* There is a build-up in impurities in the air in turbocharger systems as more exhaust gas is recirculated and more PCV vapors are recirculated. A major concern is the build-up of acid condensates that can aggressively attack some elastomers. The organic acid condensates are generally more aggressive than the mineral acid condensates. They can be very aggressive at the higher temperatures like those seen on the hot side of a turbocharger system.

* The stabilizer package added to engine oil or to automatic transmission fluid is only added at low levels, but it can have a large effect on some elastomers.

The traditional way to improve the fluid resistance for an AEM polymer is to increase the methyl acrylate level (and decrease the ethylene level). The compounds using the AEMs with higher levels of MA have lower swell in engine oils and ATFs. However, in certain applications, the AEM polymers with lower levels of MA actually have better fluid resistance than the higher MA polymers.

A study was done to look at the effect of the ester concentration for fluid aging using AEM and HT-ACM polymers. The three types of polymers studied were:

* Polymers from the AEM G family with relatively low levels of ester (MA)

* Polymers from the AEM GLS family with relatively high levels of ester (MA)

* HT-ACM polymers with 100% ester. These polymers are based on ethyl acrylate (EA) and butyl acrylate (BA). They also have a cure site monomer that allows for a diamine cure system that is similar to the AEM cure system.

Aged engine oils

An OEM had problems in the field with engine gaskets that were not performing well in aged engine oils. The engine was a direct injection gasoline engine. This OEM developed a laboratory test that was based on a "worst case" engine oil that had a low pH. This "worst case" oil was used to evaluate compounds from several different AEM and HT-ACM polymers where the testing was done at 150[degrees]C for different times.

Three representative formulations used in the study are shown in table 1, along with their initial physical properties. These three compounds are based on polymers with relatively low levels of esters (AEM IP), relatively high levels of ester (AEM GLS) and 100% esters (HT-ACM). All three compounds were 60 to 65 durometer A hardness.

The compounds were aged for various times at 150[degrees]C in the "worst case" engine oil using an autoclave. The fluid aging results are shown in table 2.

The compound with the lowest ester level (AEM IP) had the best fluid aging properties in the "worst case" engine oil. It had only a 3 point increase in hardness, and it had less than 50% change in elongation. The volume swell was a positive number, while the more polar polymers had negative swell values.

Variations of this study were done with a variety of AEM and HT-ACM compounds, and the same trends were seen. The compounds that used the polymers with relatively low ester content aged better in the "worst case" oil compared to the compounds using a polymer with higher ester content. The HT-ACM compounds with all esters in the polymer aged poorly.

As part of the study, the aging times were varied from 70 hours out to 504 hours. As expected, the fluid aging results dropped off as the test time was increased. The compounds based on the polymer with the relatively low levels of esters performed better at each time interval.

Acid condensates in turbocharger systems

The turbocharger systems are getting more complex because more exhaust gas is recirculated back to the engine. The exhaust gas has combustion products which can react with water to form acid condensates. Also, more of the gases in the engine chamber are recirculated back to the engine via the PCV systems, and in some cases, this vapor goes through the turbocharger system. The gases coming from the PCV system also contribute to the formation of acid condensates.

The materials used in the turbocharger system need to hold up to the acid condensates that build up in the system. This is especially important for the materials used in the hot side of the system.

A series of studies was done with different elastomer compounds in acid condensates, and the results are discussed (ref. 10). Compounds from the AEM G and AEM GLS family were included, along with HT-ACM compounds.

The most aggressive of the tests used an organic acid condensate (based on formic acid) in the liquid phase at 90, 120 and 150[degrees]C (highest temperature tested). The testing was done in an autoclave because of the high pressure.

The formulations for three of the compounds are shown in table 3.

These three compounds were aged in an organic acid condensate for one week at three different temperatures. The graph in figure 3 shows the volume increase at the different temperatures. As the temperature increases, the volume increase values for the two AEM compounds are similar and the values are relatively low. The HT-ACM compound has a moderate volume increase value at 90 and 120[degrees]C, but then a dramatic rise in volume increase at 150[degrees]C.

Aging in AdBlue

AdBlue is the registered trademark, held by the German Association of the Automobile Industry (VDA), for an aqueous urea solution (32.5% by weight in demineralized water), and is used in a selective catalytic reduction process (SCR) to reduce NOx emissions of diesel engines. The trademark AdBlue will not be used in the U.S., where it will be referred to with a generic name of diesel emissions fluid.

Seals and gaskets used for AdBlue need to hold up to the AdBlue, and they are usually required to have some oil resistance and some resistance to diesel fuel. The oil resistance eliminates the non-polar polymers like EPDM.

A series of AEM compounds was studied for resistance to engine oils and AdBlue. Two representative compounds are shown in table 4. One of the formulations was based on a relatively low ester polymer (AEM IP), while the other formulation was based on a relatively high ester polymer (AEM GLS). Both compounds were about 70 durometer A.

The AdBlue fluid aging results after aging for one week at 120[degrees]C are shown in table 5. The table also has the volume increase values after aging in engine oil (Lubrizol OS) for 504 hours at 160[degrees]C. The AEM IP compound aged well in both fluids. It is interesting to note that the volume increase was the same in both fluids, 16%. The AEM GLS compound aged well in the engine oil; only 6% swell. However, it aged poorly in the AdBlue. There was a large change in hardness, tensile and elongation, and the volume increase was almost 90%.

Compressive stress relaxation (CSR) studies

CSR is a test that helps to predict the performance of a gasket in an end use application. It is used to measure the retained sealing force after long exposure times to fluids at elevated temperatures. A series of compounds was made with AEM and HT-ACM polymers, and CSR tests were run on them in various automotive fluids. The samples were compressed 25% in automotive standard fixtures, and then they were aged for 2,000 hours at 150[degrees]C. Three of the compound formulations are shown in table 6.

The CSR results for aging in an automotive transmission fluid, Dexron VI, at 150[degrees]C are shown in the graph in figure 4. The AEM IP compound with the relatively low ester level has the highest retained sealing force. The CSR results with mineral based engine oils and synthetic based engine oils also showed that the AEM IP compound had the highest retained sealing forces.

Laboratory methods

The ASTM and ISO methods used for this work are shown in table 7.

Conclusions

AEM polymers can be made into compounds with ASTM ratings of EE to EH, and anywhere from 30 to 80% swell in IRM 903. The compounds easily meet the ASTM heat aging criteria for 70 hours at 175[degrees]C.

Most OEM heat aging requirements include a change in hardness, a change in tensile strength and a change in elongation. Typically, AEM compounds can last for three weeks at 175[degrees]C versus OEM specs, which is significantly longer than the ASTM requirements of 70 hours.

There have been some significant upgrades to the AEM family of polymers. Some of the key features of the upgrades include:

* Higher polymer viscosity, almost 2x that of the original grades

* Modification of the cure system to make compounds less scorchy

* Modification of polymer architecture to minimize mold fouling for molding applications

* Modification of polymer architecture to increase the dynamic performance of hose compounds

The polymer upgrades have been made to the AEM G family of polymers (standard MA) and to the AEM GLS family (higher MA--lower oil swell). The polymer upgrades help to meet the compression set targets when switching away from DOTG to alternative accelerators.

The combination of a low volatility plasticizer with the upgraded AEM LS and AEM HT-OR (high MA levels) provides compounds that have good fluid resistance and good low temperature properties, even after heat aging.

Recent studies with automotive fluids have shown that, in some cases, compounds based on AEM polymers with relatively low ester content perform better than compounds based on an AEM polymer with relatively high ester content. The AEM compounds age better than the HT-ACM compounds (all ester) in some fluids, especially those with low pH values and at high temperature.

This article is based on a paper presented at the 184th Technical Meeting of the Rubber Division, ACS, October 2013.

References

(1.) http://www.dupont.com/Vamac. Background information on AEM polymers.

(2.) Handbook of Specialty Elastomers, edited by Robert Klingender, 2007, published by CRC press, chapter on AEM.

(3.) Kirk-Othmer Encyclopedia of Chemical Technology, chapter on "Ethylene Acrylic Elastomers," Wu and McBride, 2003, published by John Wiley and Sons.

(4.) Vanderbilt Rubber Handbook, 14th edition, edited by M.F. Sheridan, 2010, published by R.T. Vanderbilt Company, Inc.

(5.) "New Vamac polymer with improved high temperature flex resistance," E. McBride, Y.T. Wu, D.D. King and K. Kammerer, Rubber Division, ACS, Meeting, October 2003.

(6.) "Vamac Ultra--new high viscosity AEM polymers with extended application possibilities, " K. Kammerer, IRC 2009.

(7.) "Vamac Ultra--new AEM polymers and developments meeting demands of modern engine technology, " K. Kammerer, IRC, 2012.

(8.) "Formulation suggestions for replacing DOTG in AEM compounds," E. McBride, K. Kammerer and L. Lefebvre, Rubber Division, ACS, Meeting, October 2010, paper 32.

(9.) "New high and low temperature esters for acrylic elastomers," S. O'Rourke, Rubber Division, ACS, Meeting, October 2009, paper 62.

(10.) "Testing of AEM and FKM compounds in acid condensates for turbocharger systems," E. McBride, K. Kammerer and L. Lefebvre, Rubber Division, ACS, Meeting, October 2011, paper 7.

Edward McBride and Theresa Dobel, DuPont Performance Polymers

Table 1--formulations used for fluid aging
studies in "worst case" engine oil

                                AEM IP   AEM GLS   HT-ACM

AEM IP                            100        --        --
AEM GLS                            --       100        --
HT-ACM                             --        --       100
Hindered amine AO                   2         2         2
Alkyl phosphate release             1         1       0.5
Octadecyl amine                   0.5       0.5       0.5
Stearic acid                        2         2         1
N550 black                         --        --        55
N772 black                         45        45        --
N990 black                         30        30        --
Polyether/ester plasticizer,       15        15        --
  low volatility
Polyether/ester plasticizer        --        --         5
HMDC curative                     1.3       1.3       0.6
DBU accelerator--70% active         3         3        --
DBU compound, 70% active                                2

Original physicals
  after 4 hour post cure
  at 175[degrees]C
Hardness, durometer A              64        64        60
M100, MPa                         4.1       4.1        --
Tensile, MPa                     17.4      14.7       9.5
Elongation, %                     310       262       215

Table 2--fluid aging results in "worst case"
engine oil--1 week at 150[degrees]C

Aged in autoclave,           AEM IP   AEM GLS   HT-ACM
  1 week at 150[degrees]
  C in worst case oil
Hardness durometer
 A (1 sec.)                     67        84       90
M100, MPa                      5.7      14.3       --
Tensile, MPa                  14.2      14.4     18.7
Elongation, %                  193       102       57
Delta hardness                   3        19       30
Delta M100 (%)                  41       248       --
Delta tensile strength (%)     -18        -2       97
Delta elongation (%)           -38       -61      -74
Volume increase (%)              3        -6      -12

Table 3--formulations used in organic acid
condensate study

                    Relatively    Relatively
                     low ester    high ester        All
                       content      content       ester
                      AEM G 66      AEM GLS      HT-ACM
                    durometer A   60 dur. A    50 dur. A

AEM G                      100           --          --
AEM GLS                     --          100          --
HT ACM                      --           --         100
Hindered amine AO            2            2           2
Octadecyl amine            0.5          0.5           1
Alkyl phosphate              1            1         1.5
Stearic acid               1.5          1.5           1
Carbon black,
  N 550                     60           40          55
Polyether/ester
  plasticizer               10           10          --
HMDC                      1.25          1.5         0.6
DBU compound,
  70% active                 1            2           1
DPG                        2.5           --          --
Total PHR                179.75       158.5       162.1

Table 4--formulations and original
physicals used for AdBlue study

                              AEM IP   AEM GLS

AEM IP                        100.5        --
AEM GLS                          --     100.5
Hindered amine AO                 2         2
Stearic acid                    1.5       1.5
Alkyl phosphate release           1         1
Octadecyl amine                 0.5       0.5
N550 black                       60        60
Polyether/ester plasticizer      10        10
HMDC curative                   1.2       1.5
DBU compound, 70% active          2         2

Original physicals
after 4 hour post
cure at 175[degrees]C

Hardness, durometer A            71        74
M100, MPa                       5.7       6.8
Tensile, MPa                   17.7      16.9
Elongation, %                   307       236

Table 5--fluid aging results in AdBlue

Aged in autoclave,                     AEM IP   AEM GLS
  1 week at 120[degrees]C in AdBlue
Hardness, durometer A (1 second)          75        54
Tensile, MPa                            21.2       3.5
Elongation, %                            221        26
Delta hardness                             3       -20
Delta tensile strength (%)                20       -79
Delta elongation (%)                     -28       -89
Volume increase (%)                       16        89
Aged in oil--Lubrizol OS
  206304 for 504 hours
  at 160[degrees]C
Volume increase (%)                       16         6

Table 6--compound formulations used for
CSR study

                     Relatively   Relatively    All
                     low ester    high ester   ester

AEM IP                  100           --        --
AEM LS                   --          100        --
HT-ACM                   --           --        100
N550                     45           45        65
Octadecyl amine         0.5          0.5        0.5
Alkyl phosphate          1            1          1
Low volatility
  plasticizer            2            2          2
Hindered amine AO        2            2          2
Stearic acid             1            1         0.5
HMDC curative           1.25         1.25       0.6
DBU compound,            2            2          1
  70% active
Total phr              154.75       154.75     172.6
Post cure 4 hours
  at 175[degrees]C
Hardness,
  durometer A            67           67        63

Table 7--laboratory methods

Rheology                 ASTM      ISO

Mooney viscosity        D 1646   289-1
Mooney scorch           D1646    289-2
MDR                     D 5289    6502

Physicals

Hardness                D 2240   7619-1
Tensile, elongation,
  modulus               D 412       37
Volume increase         D 471     1817
Air aging               D 573      188
Tg by DSC               D 3418   22768
Compression set         D 395    815-1

Figure 1--heat aging performance of AEM
compounds

Heat resistance for a "good" AEM compound--time vs. temp.

Time in hours

Temp. [degrees]C   Hours

200                72
185                168
175                504
150                4,032

Three criteria for heat resistance:
Less than 50% loss in tensile
Less than 50% loss in elongation
Less than 15 point change in hardness

Note: Table made from line graph.
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Author:McBride, Edward; Dobel, Theresa
Publication:Rubber World
Date:Apr 1, 2014
Words:5853
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