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Processing of AEM compounds: Scorch issues.

AEM polymers were introduced to the elastomers market about 40 years ago. Most AEM polymers are terpolymers made from ethylene, methyl acrylate and an acidic cure site monomer which allows for curing with a diamine. Some AEM polymers are dipolymers of ethylene and methyl acrylate, and these are cured with peroxides. Parts made from AEM compounds are used in a variety of automotive applications, and there has been a steady growth in the use of AEM polymers (ref. 1).

Some of the attractive properties of AEM compounds include:

* Heat and fluid resistance rating by ASTM D2000 as EE, EF, EG and EH

--175[degrees]C rating for aging in air

--Volume increase in IRM 903 from 25% to 80%

* Can meet low temperature requirements of -40[degrees]C

* Good compression set at 150[degrees]C

* Good CSR properties in engine oil and transmission fluid for 3,000 hours at 150[degrees]C

End uses for AEM compounds include:

* Turbocharger hoses

* Transmission oil cooler (TOC) hoses

* PCV (positive crankcase ventilation) tubes and EGR (exhaust gas recovery) hoses

* Seals and gaskets for automatic transmissions

* Seals and gaskets for engines

* Many other applications

Scorch issues

AEM polymers are converted into finished parts by a series of processing steps. The first step is to mix a compound, and this is usually done in an internal mixer followed by a roll mill. The second step is almost always either a molding or an extrusion step. To make good parts, the processing steps must avoid problems with scorch. AEM compounds are more scorchy than most elastomeric compounds, but they can be and are successfully processed around the world.

A high percentage of AEM parts are made from AEM terpolymer compounds cured with diamines. The diamine curative reacts with the cure site monomer in a two-step curing process (ref. 2). The first step of the cure involves formation of an amide. This is a relatively fast step, and this step is the source of the scorch concerns. The second step involves conversion of the amide to an imide. This reaction is slow and requires a long post-cure step to finish the cure.

Molded parts

For an AEM molded part that uses a diamine cure system, the first step of the cure occurs in the mold, and the second step occurs in the post-cure oven. After the molding process, the part has dimensional stability, but the compression set is high (70% to 90% after one week at 150[degrees]C), and the hardness and modulus values are relatively low. The post-cure step increases the hardness by about 5 points, and the compression set drops to about 20-30%.

Scorch issues can cause molding problems, including but not limited to:

* Underfilling the mold cavity

* Problems at knit lines

* Requires extra process aids to lower viscosity; can lead to poor physicals

Extruded parts

For an extruded hose or tube, the first step of the cure takes place in the autoclave. Depending on the time and temperature in the autoclave, part of the second step of the cure can also occur in the autoclave. The curing of hoses is typically finished in the post-cure ovens. The compression set after the autoclave step can range from 40-80%, while the post-cured compression set can range from 20-40%.

Scorch issues can cause extrusion problems, including but not limited to:

* High die pressure, especially in a crosshead extruder

* Much higher viscosity, especially in a cover layer, which can hurt adhesion to the tube layer

* Gel

Measurement of scorch: Mooney scorch test run at several temperatures

AEM compounds cured with diamines are designed to cure at temperatures of 170-190[degrees]C. Ideally, there should be no curing reaction at lower temperatures (scorch). Scorch reactions are a function of time and temperature, and they become an issue for AEM compounds at temperatures above 100[degrees]C.

One of the key tests for scorch in elastomeric compounds is the Mooney scorch test (ASTM D1646, ISO 289). For AEM compounds, this test is typically run at 12FC, while for many other elastomeric compounds, the scorch test is run at 135[degrees]C or 150[degrees]C (ref. 3). The fact that AEM compounds with a diamine cure system are tested for scorch at the lower temperatures indicates that they are more scorchy than most other elastomer compounds.

AEM compounds can also be cured with peroxides. The scorch test temperature for the peroxide cured AEM compounds is typically 135[degrees]C.

A series of scorch tests was run on a standard AEM G compound to look at the influence of temperature and time on scorch. The compound formulation is shown in table 1, along with the typical rheology information.

The Mooney scorch test for AEM compounds is typically run at 121[degrees]C using a small rotor. The test time is set for 45 minutes, or until there is a 15-point increase in viscosity. The actual test time is usually around 15 minutes, and it very rarely reaches 45 minutes.

The Mooney scorch test conditions were modified to look at scorch as a function of temperature. The test was run at 70, 80, 90,100,110 and 121 [degrees]C, and the test time was set to two hours, or until a 15-point increase. The results are shown in figure 1.

* At temperatures less than 90[degrees]C, there was very little change in the viscosity of the compound after two hours.

* At 100[degrees]C, it took almost two hours for the viscosity to double.

* As the temperature increased to 110[degrees] and 121 [degrees]C, there was a significant increase in viscosity; at 121[degrees]C, it only took about 13 minutes for the viscosity to double.

These results show how important it is to keep the processing temperatures low. For this AEM compound, the processing temperatures (mixing, molding and/or extrusion) should be kept under 100[degrees]C.

The series of Mooney scorch plots is a relatively easy test to run. If there is a scorch issue with an AEM compound, then running a series of Mooney scorches at different temperatures may help pinpoint the processing conditions to avoid.

Higher shear rates lead to higher temperature and potential problems

AEM compounds will heat up when they are exposed to high shear conditions. As the temperature increases, there is an initial decrease in viscosity, which can be helpful for processing. However, as the temperature further increases, there will be a point at which the viscosity starts to increase due to scorching of the compound. This can lead to major processing issues.

Extrusion study

A series of laboratory extrusion trials was run on a 63 mm (2.5 inch) Davis-Standard extruder with a 20 to 1 L/D (ref. 4). Two types of screws were used. The first was a general purpose rubber screw, which is a relatively low shear screw. The second was a vented screw, which has a high shear region in the venting area. Figure 2 shows pictures of these screws.

For one part of this study, the temperature profile was set up so that the die temperature was at 85[degrees]C, and then the rpm was varied from 4 to 26 rpm.

The compound formulation used for this work is shown in table 2.

The compound temperature was measured immediately after leaving the die. Samples were also collected so that rheological properties could be measured. Table 3 and figure 3 show the results for the extrudate properties from the trial with the general purpose screw. At low production rates, the extrudate temperature was similar to the die temperature, and the measured viscosity was similar to the initial viscosity. As the rpm and output were increased, there was a significant increase in the temperature of the compound and the viscosity of the compound. At the higher production rates, the compound viscosity almost doubled, indicating scorch problems. At the lower rates, there were no scorch issues.

The vented screw has a high shear region where the venting area is located. The temperature in the compound exiting the vented screw builds up faster than the temperature for the general purpose screw. The results from this study are shown in table 4 and figure 4.

At the same production rate, the vented screw had a much higher compound temperature and a bigger build in viscosity.

Both screw types work well at the low production rates. This implies that a production line may work well at one production rate, but have problems if the line capacity is increased. The higher line speed issues will show up sooner for a high shear screw.

Mixing of AEM compounds

There are several recommendations for minimizing scorch problems when mixing AEM compounds. These include:

* Avoid compound temperatures (not mixer temperatures) that are above 100[degrees]C.

--Use a dump temperature around 90-95[degrees]C because the measured mixer temperature is lower than the actual compound temperature.

* Use a relatively low rpm; the shear rate is proportional to the mixer rpm (ref. 5), so it is important to avoid the higher shear rates which can cause localized hot spots.

* Check rheology of mixed compounds at different mixing conditions; include Mooney scorch tests at different temperatures.

These recommendations will require the mixing process to run at lower rates than what is typical for other elastomers. The recommended conditions may eliminate the need for a two-pass mix, so in some cases, they will increase productivity.

Some AEM compounds, especially those high in viscosity, may require a two-pass mix. The temperature in the second pass should be kept under 100[degrees]C.

A well-mixed compound (one that is not scorched) will process much better in the extrusion or molding process.

Design of Experiments (DOE) for scorch of one compound

The three main components of an AEM compound are the polymer, the carbon black and the plasticizer. If these are held constant, there are many other factors that can affect the cure and scorch rate, including the cure package, the scorch retarder and the release package. These other factors also affect the cured physical properties, which can make it difficult to compare compounds.

A DOE model was built where the polymer, black and plasticizer were held constant, and then several of the other factors were varied. The DOE model uses the compound formulation to predict the scorch and cure rate, as well as cured physical properties. The compound formulations were varied to look at various cure rates for the compounds, while at the same time keeping the cured physicals (hardness, compression set, etc.) similar.

The DOE model was used for two major studies:

* Design faster curing compounds for injection molding, while keeping the physicals constant; the faster curing compounds were more scorchy than the control.

* Design extrusion compounds with longer scorch times, and similar physicals; these compounds had slower cure rates.

The control compound is shown in table 5, along with the five different raw materials that were varied as part of the DOE. The polymer, black and plasticizer were held constant for this study. The compounds were mixed on a small laboratory mixer with a dump temperature of 82[degrees]C, and then finished mixing on a mill. The mixing conditions were "mild" and probably did not contribute to any scorch issues.

The DOE design was a linear model with a center point consisting of 16 compounds. The five raw materials were varied, and the rheological and cured properties were measured. Most of the properties measured had a good fit, as shown by the high adjusted R squared values (0.90 or higher). Some of the properties are shown in table 6.

The predicted results for the hardness and tensile strength had low adjusted R squared values. A closer inspection of the results showed that there were only minor changes in the hardness and tensile strength of the 16 compounds. For the DOE, there were no changes in the polymer, black and plasticizer, which may explain the small change in hardness and tensile strength.

There were four different test conditions for compression set, and the adjusted R squared values ranged from 0.65 to 0.78. For most of the comparisons discussed later, the average of the four compression set tests was held constant.

Faster curing rate for injection molding

Companies that injection mold rubber compounds want a combination of fast cycle times and good quality parts. An increase in temperature will lead to a faster cure rate and shorter cycle times. However, if the mold gets too hot, there is a risk from the compound scorching or the compound having poor hot tear strength as it is removed from the mold.

The suggested curing time for an AEM compound is the t50 time from an MDR curve, where the MDR test temperature is the same as the molding temperature. At higher temperatures, the t50 time will be less, but the compound will be more scorchy and the hot tear strength will be worse. At t50, the part will be dimensionally stable and it will have high compression set. The post-cure step will reduce the compression set to its target value.

The DOE model was used to look at ways to reduce the t50 time, while keeping the mold temperature constant. The model showed that the three most important factors for t50 were:

* The accelerator level (Vulcofac ACT 55) was the most important variable; higher levels lead to faster cure (as expected).

* The curative level (Diak #1) was the second most important variable; higher levels lead to a slower cure, as measured by t50.

--As the curative level is increased, there is an increase in MH, which means that the t50 value is higher and the time to t50 can be longer.

--If the curative is the only variable increased in the formulation, then there is a decrease in compression set.

--The compounds in this study were compared at equivalent compression set and hardness, and the comparison compounds had MH values that were close together.

* The scorch retarder level (Armeen 18D) was the third most important variable; higher levels lead to a slower cure (as expected).

The model was used to look at how to speed up the cure rate, while holding compression set and hardness constant. The compression set target was the average value for the four different test conditions. Two different formulations are shown in table 7, along with the predicted properties. The two cases were:

* Control, midpoint of DOE model

* Faster cure staying within the ranges of the model

--Maximum level of accelerator (3.0 phr ACT 55)

--Minimum level of curative (1.0 phr Diak #1)

--Minimum level of scorch retarder (0.0 phr Armeen 18D)

These changes led to significantly lower predicted times for the t50 on the MDR curve. The control had a predicted t50 of 1.89 minutes, while the faster curing case had a t50 of 1.01 minutes. Both compounds had similar predicted cured physicals, including compression set and hardness. The t50 results imply that it is possible to cut the cycle time almost in half.

The concern with the faster curing compound is the scorch time. The predicted results for the Mooney scorch test at 121[degrees]C shows that the faster curing case has a t5 that is 55% of the control. If the faster curing compound is used, then the process needs to be designed so that the temperatures are low during the mixing process and the early stages of the molding process.

Long scorch time compound for extrusion

AEM compounds are converted to hoses in a process that uses two extrusion steps. The first extrusion step makes the inside tube, and this step usually proceeds without too many scorch issues. The tube is cooled down, and then the fiber is applied on the outside of the tube. The fiber coated tube is then fed to the second extruder, where the cover is applied. There are two main contributors to scorch when applying the cover layer:

* The crosshead die is a high shear region, and this can lead to localized hot spots.

* Good strike through adhesion is needed between the tube and cover; the tube is usually pre-heated before it goes into the crosshead die; the cover extruder is typically run at a higher temperature than the tube extruder to improve adhesion.

The DOE model was used to look at compounds that had longer scorch times, while at the same time matching the cured physicals of the control compound.

The model showed that the three most important factors affecting the Mooney scorch rate (t2, t3, t5, t10 and t15) were:

* The scorch retarder level (Anneen 18D) was the most important factor; higher levels lead to less scorch (as expected).

* The accelerator level (Vulcofac ACT 55) was the second most important variable; higher levels lead to more scorch (as expected).

* The stearic acid level was the third most important variable; increasing the stearic acid leads to less scorch; two possible explanations for why stearic acid is important for scorch are:

--It has the biggest effect on compound viscosity; as the stearic acid level increases, there is a significant drop in viscosity, which should help with minimizing scorch.

--The stearic acid may react with the diamine curative and act as a scorch retarder.

The DOE model was used to design a compound that had very good scorch safety, while also having similar cured properties as the control sample. The scorch retarder and the stearic acid levels were increased to the maximum levels used in the DOE, while the accelerator level was set at the minimum level. The curative level was adjusted so that the predicted compression set was the same as the control. Results are shown in table 8. Once again, the control was the midpoint of the DOE model.

These changes led to about a 50% increase in the t5, t10 and t15 scorch times from the Mooney scorch test. The cure time (t50 from the MDR test at 180[degrees]C) also increased by about 50%. The longer curing time should not be an issue because the hoses are typically cured in an autoclave for about 30 minutes and then are post-cured.

To further slow down the scorching process, the DOE model was used to look at conditions outside of the model ranges. The accuracy of the predictions will drop off as one gets further and further from the model ranges.

A potential compound with a long scorch time is shown in table 9. The compound is outside the limits for the scorch retarder (>1.0 phr), the accelerator (<1.0 phr) and for the curative (>1.5 phr). The predicted scorch times for the Mooney scorch at 121[degrees]C (t3, t5, t10 and t15) are about 1.8 times that of the control compound. The predicted curing time from the MDR (t50 at 180[degrees]C) is also about 1.8 times that of the control.

This proposed compound was mixed and then evaluated. The actual scorch times are slightly longer than predicted, as they are about 2 times that of the control. This is a nice improvement over the compound made within the ranges of the DOE.

The cured properties from the laboratory mixed compound with the improved scorch package are close to the predicted properties and close to the control. The compression set measurements for the follow-up study were done at four different conditions, but these conditions were slightly different from the DOE model. The control compound was also run as part of the follow-up experiment, and the average compression set value for the control is shown in table 9. The average compression set for the compound with the 2 times longer scorch times was slightly higher than for the control compound.

Conclusions

AEM compounds that are cured with diamines are more sensitive to scorch than most other elastomeric compounds. When the process temperatures are kept relatively low, the AEM compounds can be mixed, molded and/or extruded without scorch problems.

Running a series of Mooney scorch tests at different temperatures is a relatively simple technique to help pinpoint what processing temperatures need to be avoided.

High shear rates can cause localized hot spots that can lead to scorch issues, and should be avoided or minimized.

* Increasing the mixer rpm will lead to higher production rates in the mixing step, but this will also increase the shear rate; localized hot spots in the mixer can lead to scorch issues.

* General purpose screws are recommended for AEM compounds because they are relatively low shear compared to vented, mixing or barrier screws.

* Increasing production rates can lead to higher shear rates; a process that works well at one production rate may have scorch issues at higher production rates.

DOE (Design of Experiments) models can be used to study scorch issues where the cured compounds have similar properties. Keeping the polymer level, black level and plasticizer level constant, and then changing the cure package or retarder packages, can lead to:

* Cutting the molding cycle time in half while maintaining the cured physical properties; the concern is that the compounds may be too scorchy.

* Providing longer scorch times for an extrusion process without sacrificing cured properties.

The test methods used in the work are shown in table 10. This article is based on a paper presented at the 194th Technical Meeting of the Rubber Division, ACS, October 2018.

by Edward McBride, DuPont Transportation and Advanced Polymers

References

(1.) "Vamac Ethylene Acrylic Elastomers," http://www.dupont.com/Vamac, September 2017.

(2.) E. McBride, "Press cure and post cure options for AEM terpolymers," Rubber Division, ACS, Technical Meeting, October 2008, Paper Number 86.

(3.) Fundamentals of Rubber Technology, edited by R.J. Del Vecchio, published in 2003 by Technical Consulting Services in combination with the Rubber Division of the American Chemical Society.

(4.) E. McBride, B.A. Morris and C.S. Grant, "Computer model of extrusion process for AEM elastomers," Rubber Division, ACS, Technical Meeting, October 2007, Paper Number 149.

(5.) Private DuPont Document, M. Mori to E. McBride et al., March 2011.

Caption: Figure 1--Mooney scorch test at different temperatures

Caption: Figure 2--general purpose screw compared with a vented screw

Caption: Figure 3--Mooney viscosity and temperature of compound exiting die, GP screw

Caption: Figure 4--Mooney viscosity and temperature of compound exiting die, GP and vented screws
Table 1--AEM G compound formulation with typical rheology data

Compound formulation

Ingredient                 phr                         Description
AEM G                      100                                  --
Black, N550                 52                                  --
TP 759                      10                     Polyether ester
                                                       plasticizer
Stearic acid               1.5                       Release agent
Vanfre VAM                   1                    Alkyl phosphate,
                                                     release agent
Armeen 18D                 0.5    Octadecyl amine, scorch retarder
Naugard 445                  2                   Hindered amine AO
Diak #1                    1.5                       HMDC curative
Vulcofac ACT 55              2                     DBU accelerator
Total phr                170.5
Hardness, durometer A       66                     After post-cure

Rheology

Mooney viscosity                   MDR, 180[degrees]C, 15 minutes,
                                   0.5[degrees] arc
ML (1+4) at 100, MU           35   ML, dNm           0.33
                                   MH, dNm           11.8
M scorch, 121[degrees]C,
  small rotor
Minimum viscosity, MU         13   ts1, minutes      0.68
                                   ts2, minutes      0.94
t3, minutes                  6.5
t5, minutes                  8.2   t50, minutes       2.1
t10, minutes 11.4           14.9   t90, minutes       6.7
  t15, minutes

Table 2--AEM formulation used during
extrusion trial

Ingredient                             phr
AEM HVG                                100
Black, N550                             50
Stearic acid                           1.5
Alkyl phosphate release                  1
Octadecyl amine, scorch retarder       0.5
Hindered amine AO                        2
HMDC curative                          1.5
DOTG acclerator                          4
Total phr                            160.5
ML (1+4) at 100                         65
Hardness, durometer A (post-cure)       67

Table 3--extruder trial results using general
purpose screw

                 GP screw, lower shear
rpm   Kg/hour    Temperature exit            ML (1+4)
                  die, [degrees]C    at 100[degrees]C
4           9                  84                  62
14         31                  95                  72
23         54                 106                 103
26         60                 111                 103

Table 4--extruder trial results using general
purpose screw and vented screw

      GP screw, lower shear

rpm    Kg/         Temp, exit            ML (1+4)
      hour    die, [degrees]C    at 100[degrees]C

4        9                 84                  62
14      31                 95                  72
23      54                106                 103
26      60                111                 103

      Vented screw, higher shear

rpm    Kg/         Temp, exit            ML (1+4)
      hour    die, [degrees]C    at 100[degrees]C

4        7                 83                  63
14      23                 97                  71
23      37                111                 101
26      41                117                 124

Table 5--formulation and ranges used in Design
of Experiments (DOE)

Ingredient            phr      Low     High             Description
                  control    level    level
AEM IP                100       --       --                      --
Black, N550            50       --       --                      --
Tegmer 812              5       --       --    Low volatility ether
                                                  ester plasticizer
Naugard 445             2       --       --       Hindered amine AO
Stearic acid            1        0        2           Release agent
Vanfre VAM              1        0        2        Alkyl phosphate,
                                                      release agent
Armeen 18D            0.5        0        1        Octadecyl amine,
                                                    scorch retarder
Diak #1              1.25        1      1.5           HMDC curative
Vulcofac ACT 55         2        1        3         DBU accelerator
Total phr          162.75

Table 6--Design of Experiments (DOE)
results, adjusted R squared, minimum and
maximum values

                                 Adjusted R      Lowest     Highest
                                    squared    value in    value in

Rheology results                                    DOE         DOE
Mooney viscosity,
  ML (1+4) at 100[degrees]C            0.98          57          88
Mooney scorch 121[degrees]C,
  small, 0.5[degrees]
Minimum viscosity, MU                  0.96        20.9        34.3
t3, minutes                            0.91         3.2         9.0
t5, minutes                            0.91         3.6        11.8
t10, minutes                           0.90         4.5        16.3
MDR, 180[degrees]C/15 minutes
ML, N-m                                0.92        0.65        1.31
MH, N-m                                0.89        12.1        21.5
ts2, minutes                           0.94        0.47        0.98
t50, minutes                           0.94        0.95        2.97
t90, minutes                           0.92         3.1         9.6
Post cured for four
  hours at 175[degrees]C
Room temperature
  physicals
Hardness, durometer A                  0.65          64          70
M25, MPa                               0.90         1.2         1.5
M50                                    0.78         1.9         2.9
M100                                   0.86         4.1         8.2
Tensile, MPa                           0.39        18.5       21.21
% elongation                           0.90         217         380
ASTM compression
  set, plied large buttons
70 hours/150[degrees]C                 0.66          10          23
168 hours/175[degrees]C                0.65          22          38
ISO compression set,
  small molded buttons
70 hours/150[degrees]C                 0.78          17          30
168 hours/175[degrees]C                0.76          32          47

Table 7--DOE results, predictions for faster
cure, within model ranges

Properties predicted by            Control     Faster cure
model                             midpoint    within model
                                  of model          ranges

Vanfre VAM, 0 to 2 phr                 1.0             1.0
Stearic acid, 0 to 2 phr               1.0            0.25
Armeen 18D, 0 to 1.0 phr              0.50               0
Diak #1 level (1.0 to 1.5 phr)        1.25             1.0
ACT 55 level (1 to 3 phr)             2.00            3.00
Mooney viscosity, ML (1+4)
  at 100[degrees]C                      70              76
MDR, 180[degrees]C/15 minutes,
  0.5[degrees] arc
ML, N-m                               0.86            1.12
MH, N-m                               15.8            15.3
ts2, minutes                          0.69            0.51
t50, minutes                          1.89            1.01
t90, minutes                          6.29            3.65
Mooney scorch 121 "C,
  small, 45 minutes
Minimum viscosity, MU                 25.9            30.4
t3, minutes                            5.9             3.5
t5, minutes                            7.4            4.11
t10, minutes                          10.0             5 1
t15, minutes                          11.8            6.0l
Post-cured for four hours at
  175[degrees]C
Hardness, durometer A                 67.7            66.8
M100                                   5.3             5.1
Tensile strength, MPa                 19.7            19.2
% elongation                           305             321
Average of four
  compression sets                    26.0            26.0

Table 8--DOE results, predictions for longer
scorch time, within model ranges

Properties predicted by            Control    Longer scorch
model                             midpoint     times within
                                  of model     model ranges

Vanfre VAM, 0 to 2 phr                 1.0              0.9
Stearic acid, 0 to 2 phr               1.0             2.00
Armeen 18D, Oto 1.0 phr               0.50                1
Diak #1 level (1.0 to 1.5 phr)        1.25              1.5
ACT 55 level (1 to 3 phr)             2.00             1.00
Mooney viscosity, ML (1+4)
  at 100[degrees]C                      70               64
MDR, 180[degrees]C/15 minutes,
  0.5[degrees] arc
ML, N-m                               0.86             0.65
MH, N-m                               15.8             16.3
ts2, minutes                          0.69             0.92
t50, minutes                          1.89             2.75
t90, minutes                          6.29             8.83
Mooney scorch 121[degrees]C,
  small, 45 minutes
Minimum viscosity, MU                 25.9             21.9
t3, minutes                            5.9              8.4
t5, min                                7.4            10.9B
t10, m                                10.0
t15, m                                11.8            17.9H
Post cured for four hours at
 175[degrees]C
Hardness, durometer A                 67.7             68.4
M100                                   5.3              5.6
Tensile strength, MPa                 19.7             20.3
% elongation                           305              290
Average of four
  compression sets                    26.0             26.0

Table 9--DOE results, longer scorch time, outside of model ranges

Properties predicted       Control    Longer scorch    Actual results
by model                  midpoint    times outside        for longer
                          of model         of model      scorch times
                                             ranges    outside of the
                                                         model ranges

Vanfre VAM, 0 to 2 phr         1.0              1.0               1.0

Stearic acid, 0 to             1.0              2.0               2.0
2 phr

Armeen 18D, 0 to              0.50              1.5               1.5
1.0 phr

Diak #1 level                 1.25             1.68              1.68
(1.0 to 1.5 phr)

ACT 55 level                  2.00             0.50              0.50
(1 to 3 phr)

Mooney viscosity, ML            70               62                64
(1+4) at 100[degrees]C

MDR, 180[degrees]C/15
minutes, 0.5[degrees]
arc

ML, N-m                       0.86             0.57              0.63

MH, N-m                       15.8             16.7              14.3

ts2, minutes                  0.69             1.16              1.15

t50, minutes                  1.89             3.51               3.6

t90, minutes                   6.3             11.5              10.7

Mooney scorch
121[degrees]C, small,
45 minutes

Minimum viscosity, MU         25.9             20.1              21.6

t3, minutes                    5.9             10.0              11.0

t5, minutes                    7.4             13.1             14.50

t10, minutes                  10.0             18.1             20.21

t15, minutes                  11.8             21.7              24.2

Post-cured for four
hours at 175[degrees]C

Hardness, durometer A         67.7             69.8                70

M100                           5.3              5.7               5.0

Tensile strength, MPa         19.7             20.0              20.5

% elongation                   305              284               306

Average of four               26.0             27.5                 -
compression sets

See note:                     20.3                -              23.1

The four compression set test conditions were slightly different
than the DOE model. The value shown for the control is
the actual lab result, not a prediction, as the control was
run as part of the follow-up experiment.

Table 10--ASTM and ISO methods

Rheology                ASTM method    ISO method

Mooney viscosity             D 1646         289-1
Mooney scorch                D 1646         289-2
MDR                          D 5289          6502
Physicals
Hardness                     D 2240        7619-1
Tensile, elongation,
  modulus                     D 412            37
Compression set,
  method B                    D 395         815-1
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Author:McBride, Edward
Publication:Rubber World
Date:Mar 1, 2019
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