Peroxide cured HNBR/methacrylate blends with improved low temperature performance.

Hydrogenated nitrile butadiene rubber (HNBR)/zinc dimethacrylate (ZDMA) blends have been available for many years now, and the improved mechanical properties that are offered are well recognized within certain areas of the rubber industry, such as belting, roller covering and the oil industry. It is also understood that HNBR terpolymers, which offer improved low temperature performance, also provide lower mechanical strength when compared to copolymer grades of HNBR. The incorporation of methacrylate reinforcement technology in HNBR terpolymers has the potential to offer a material with excellent mechanical, thermal and chemical resistance properties. This material has potential for application not only in the automotive industry, but also in the oil industry and other areas where elastomers fail due to the arduous nature of their service environment.

This article studies the phenomenon of significantly enhanced mechanical strength that occurs when HNBR elastomers are correctly blended with methacrylate additives, and how this technology can be applied to HNBR elastomers with improved low temperature performance. It will review the basic reinforcement mechanism that occurs within the HNBR/ ZDMA blend, typical laboratory test data and how this technology can be translated into practical applications for these HNBR based materials.

Evolution of HNBR elastomers

In 1984, HNBR was first commercialized by Zeon. According to the Institute of International Synthetic Rubber Producers (IISRP), HNBR has been the fastest growing specialty elastomer over the last decade (ref. 1). HNBR offers significant performance advantages over nitrile butadiene rubber (NBR) in terms of heat resistance, mechanical strength and resistance to aggressive fluids. As such, HNBR has become the material of choice in many demanding elastomeric applications such as power transmission belts, seals and hose in automotive, industrial and other arduous service environments.

HNBR is produced via the catalytic hydrogenation of NBR. This proprietary manufacturing process selectively hydrogenates the C=C bonds present in the butadiene repeat unit. Figure 1 shows a schematic diagram of the hydrogenation process.

[FIGURE 1 OMITTED]

Each hydrogenated butadiene unit results in the formation of saturated ethylene/methylene units (ref. 2). So a fully saturated HNBR comprises acrylonitrile, ethylene and a small quantity of residual butadiene, dependant on the degree of hydrogenation. It is the presence of these ethylene units that generates the high mechanical, heat and chemical resistance properties seen with HNBR (ref. 2). The ethylene units enable the polymer structure to exhibit strain-induced crystallization, which creates the significantly enhanced mechanical properties over NBR. However, this ability to crystallize causes the material to stiffen considerably at low temperatures, although it does not become brittle until very low temperatures.

It is postulated by Treloar that the rotation of the polyethylene chains in certain random linkages becomes more difficult than with butadiene units that have double bonds in the same random linkages (ref. 2). Figure 2 shows a schematic diagram of the chain orientation. The spheres are just for reference purposes. The remaining double bond in the lower chain effectively prevents close alignment with the other chains. The acrylonitrile (ACN) group containing a pendant CN also inhibits close chain packing; however, due to its polar nature, it shows signs of hydrogen bonding and also can inhibit low temperature flexibility. Therefore, the lower the ACN content and more highly saturated the polymer becomes, the less flexible the chains become, due to closer chain packing. The use of terpolymer technology, which will be explained later in the section on low temperature HNBR, prevents this close packing of the long ethylene chains, and therefore inhibits the low temperature stiffening process. The resultant polymer also shows lower mechanical properties due to this same effect inhibiting strain-induced crystallization.

[FIGURE 2 OMITTED]

Figure 3 shows the effect of varying acrylonitrile content and saturation level in HNBR, with the original low temperature grades as point references (Z-3110 and Z-4110 were the original low temperature HNBR terpolymer grades produced, containing 25% and 18% ACN, respectively). In fact, this demonstrates that, at high levels of saturation, the ethylene content has a greater influence on low temperature flexibility than acrylonitrile (ACN) content. So, in highly saturated HNBR copolymers, reducing the ACN content can actually impair the low temperature performance, which runs against conventional thinking for NBR elastomers. Figure 3 shows quite clearly that at around 36-37% ACN, the curve is at its flattest, and therefore shows the best balance of oil resistance and low temperature properties. To simplify the explanation, for grades containing 36% and above ACN, it is the ACN content that is the predominant influence on low temperature flexibility, and below 36% it is the number of residual double bonds that is the primary influence. This is one of the key reasons why 36% was selected for the majority of the HNBR grades produced. It is also the reason why copolymer HNBR materials are not available with ACN levels below this region, as they would exhibit decidedly plastic behavior and be undesirable to the elastomer industry. While HNBR copolymers do exhibit significant stiffening at moderate low temperatures, they do not become brittle until much lower temperatures. For example, a simple recipe based on a 36% ACN fully saturated material can have a TR10 value of -21[degrees]C, yet have a brittle point below -40[degrees]C (ref. 3).

[FIGURE 3 OMITTED]

In this respect, the functional performance of the final article must be fully understood, and these special characteristics of copolymer HNBRs must be accounted for. Quite early in the life of HNBR, it was recognized that this was an issue that must be addressed, and a range of terpolymer grades of HNBR was developed that incorporated a third monomer specifically designed to improve low temperature properties.

Low temperature HNBR

One of the most significant steps in the evolution of HNBR was the introduction of terpolymer grades. The introduction of terpolymers of HNBR allowed the low temperature performance of HNBR to be improved significantly (ref. 4). Terpolymer HNBRs greatly improve low temperature flexibility because of the disruption of the crystallization process that takes place due to the ethylene units. The introduction of a third monomer containing a bulky pendant group interferes with the close ethylene chain packing and improves the low temperature flexibility of the elastomer. However, as mentioned above, the desirable mechanical properties are inhibited at the same time. There has been much research effort placed in improving the low temperature performance of HNBR, while minimizing the impact on other functional properties. Recently introduced grades with improved molecular weight control and new polymerization technology have shown a significantly improved property balance, and as such have further widened the potential areas for application of HNBR (refs. 5 and 9). Figure 4 shows the improved balance of low temperature resistance versus oil swell in IRM 903 when the NCHNBR polymers are compared to copolymer and the original low temperature terpolymers.

[FIGURE 4 OMITTED]

HNBR/methacrylate blends

Traditionally, carbon black has been the primary means of reinforcement of elastomer compounds. Over the years, many widely varying types of reinforcement techniques have been developed to offer some benefit or other to the mechanical properties of a vulcanizate. However, in recent times, none have offered such huge increases in mechanical strength as the use of zinc dimethacrylate based systems. The use of ZDMA had been investigated prior to its application in HNBR, and gains in mechanical strength were moderate.

However, when Zeon developed a unique and proprietary process and applied this technology to HNBR, tensile strength and elongation at break values in excess of 40 MPa and 250% were achieved with compounds of approximately 90 (A) hardness (refs. 6 and 7).

A carbon black reinforced material would not produce such desirable mechanical properties, and in order to get close to these values, its processing and dynamic behavior would have to be greatly sacrificed due to the type and loading of filler. Another advantage of ZDMA reinforced materials is that they can be colored, so that product differentiation is more readily achieved. This unique new material was named ZSC.

The mechanism by which this material is reinforced has been well documented in the past (ref. 8), but will be summarized below.

Zinc oxide and methacrylic acid are added to HNBR via a proprietary process and react in situ to form polymeric ZDMA crosslinks. It is the extremely high level of dispersion attainable with this process that yields the excellent mechanical properties. Figure 5 shows a TEM photograph of a section of ZSC (ref. 8). The picture shows clearly how the poly-ZDMA forms a continuous micro-network throughout the HNBR matrix, a state which is unattainable by adding commercially available, pre-reacted ZDMA to the polymer.

[FIGURE 5 OMITTED]

The ZSC, when vulcanized with an organic peroxide, forms both C-C crosslinks (as would be expected of a peroxide cured elastomer) and poly-ZDMA links that graft onto the main polymer chain.

These poly-ZDMA crosslinks reinforce the elastomer in a very similar way to that which occurs in XNBR. Figure 6 shows the dual crosslink network that is formed in ZSC materials.

[FIGURE 6 OMITTED]

It is the presence of these poly-ZDMA grafted crosslinks that imparts the reinforcement, but the length of the chain allows the material to retain high levels of elongation at break. An analogy can be made from the difference between organic peroxide generated C-C crosslinks and polysulfidic crosslinks formed from elemental sulfur and their relative influence on mechanical and dynamic behavior of a vulcanizate.

The nature of HNBR lends itself perfectly to blending with these materials, and shows by far the greatest property enhancement of all elastomers evaluated with this technology. When compared to a typical carbon black filled compound of equivalent hardness, ZSC based materials tend to exhibit much higher tensile strength, tear strength and elongation at break,, which are also retained to a higher level at elevated temperatures. Lower hysteresis and compound viscosity are also seen (ref. 7).

This reinforcement technology can be applied to any type of HNBR and a wide range of these materials is available to satisfy a host of functional requirements. One of the more recent introductions to this range has been to combine the methacrylate reinforcement technology with that of low temperature terpolymer HNBRs to create yet another unique elastomer composite.

The principal application areas for ZSC materials are transmission belts, roller covering and oil industry products. While there are significant advantages in using ZDMA reinforcement in HNBR compounds, there are also some areas where caution should be exercised. One is that these materials tend to adhere to metal surfaces during vulcanization, and therefore an appropriate mold release system must be employed. Also, the resistance to concentrated acids and alkalis is impaired, and compression set is somewhat higher than conventional HNBR vulcanizates. However, there are many companies that have followed advice and are now molding a wide variety of components from ZSC reinforced HNBR without any problems.

Applications

Low temperature terpolymer HNBRs are predominantly used in automotive and industrial sealing applications, where extremes of heat resistance are required in conjunction with lubricant resistance. It is very much a niche area of HNBR application, but one that is growing quite rapidly. Its recent acceptance in automotive boot type sealing has opened up a whole new range of applications for this material. There is also increasing application of these types of HNBR elastomers in the oil industry, in regions where very low ambient temperatures are reached.

ZDMA reinforced HNBR is typically used where high strength and excellent dynamic properties are demanded, such as in transmission belting, roller covering in the steel and paper manufacturing industries and in "down-hole" applications (such as steerable drill head seals, blow out preventers and expandable packers where the extremes of mechanical toughness are required).

The combination of these highly desirable properties should enable users to further increase the levels of performance attainable with elastomeric materials. The target is to offer users the ability to develop true -40[degrees]C to +150[degrees]C functioning materials that offer excellent all round durability. The data and subsequent discussion in this paper are intended to demonstrate the properties that are attainable with these unique materials, and will hopefully stimulate technologists and elastomeric product manufacturers to continue to push the boundaries of performance.

Experimental

This basic laboratory work attempts to demonstrate the beneficial properties attainable by specifying methacrylate reinforced terpolymer HNBR.

Compound design

ZSC4195 and HNBR4300 materials were selected due to their unique balance of properties and extremely wide operating temperature range. Four typical recipes of both straight HNBR and ZSC/HNBR blends were used to demonstrate the mechanical properties across a range of hardness values. These recipes are not optimized for any particular property other than that they clearly show the performance gains achievable with ZSC/ HNBR blends. The recipes are shown in table 1, and full details of the raw materials used are shown in table 2.

Processing

The compounds were weighed, mixed and molded in the European Technical Service Laboratory (ETSL) in the UK, according to normal working practice. Full details of these methods can be provided if required.

Test methods

Table 3 shows the results and appropriate standard to which the vulcanizate properties were measured.

Discussion of results

For the sake of simplicity, all graphs have been plotted with hardness on the x-axis, as this is a commonly used method of categorizing elastomer compounds. The trend lines added to the graphs (figures 7-18) are either second order polynomial or exponential, and were calculated by the Excel software. They are intended for guidance only to assist in differentiating the materials.

[FIGURES 7-18 OMITTED]

Processing characteristics

One of the key processing benefits attainable with the ZSC4195 based compounds is due to the mechanical properties being generated by the zinc dimethacrylate crosslinks, rather than via high levels of carbon black reinforcement. Figure 7 shows very clearly how, with the carbon black filled HNBR4300, as hardness increases, so does compound Mooney viscosity. In fact, with the HNBR4300 for a 25 point hardness increase, the Mooney increases by over 120 points, to greater than 200 Mooney units. However, with ZSC4195, the Mooney only increases by eight points for an increase of 32 points hardness. This unique characteristic opens countless possibilities for processing improvements, where high hardness and mechanical properties are essential.

It must always be born in mind that zinc dimethacrylate reinforced compounds will exhibit metal adhesion during vulcanization, which can lead to mold sticking. However with the appropriate mold treatment, this issue can easily be resolved.

Mechanical properties

Figures 8-11 plot the hardness versus tensile stress and strain for both types of compounds. It can clearly be seen that the ZSC4195 based compounds offer significantly increased tensile strength, and at the same time, the elongation is dramatically improved. However, the modulus data for M50% and M100% show that in this range the two materials function in a similar way. With some adjustment, it would be feasible to produce a material with very similar stress-strain characteristics at low strains, but with higher ultimate tensile and elongation properties, which should translate into increased functional performance.

[FIGURES 8-11 OMITTED]

Figures 12 and 13 plot the hardness versus tear strength in both nicked crescent and unnicked angle type tests. This ties in with the above data in confirming the significantly improved properties attainable with the ZSC4195 material. It also shows an increasing benefit with the ZSC4195 material towards the higher end of the hardness scale, this being due to the increasing content of the ZSC4195 in the blend.

[FIGURES 12-13 OMITTED]

Figures 13 and 14 compare the un-nicked angle tear strength at 23[degrees]C and at 150[degrees]C. Tear resistance at elevated temperatures is one of the key areas where zinc dimethacrylate modified HNBR shows significantly improved performance. At lower blend ratios, which result in lower hardness, the advantage of the ZSC4195 is not so apparent, and a carbon black filled HNBR4300 material may offer some advantage. However, as the ratio of ZSC4195 is increased, the tear strength increases significantly, indicating quite clearly that, for maximal performance, the ratio of ZSC4195 to HNBR4300 should be high. This implies that the greatest benefits are with high hardness compounds.

[FIGURES 13-14 OMITTED]

Figure 15 shows the compression set performance of these materials. It can be seen that the ZSC4195 materials show slightly higher compression set than the carbon black filled HNBR4300 material. However, the difference is relatively small. It must also be noted that for hardness values above 80 durometer A, only 15% strain was used on the specimens, and only 10% strain when above 90 hardness. Short term compression set for ZSC compounds is usually higher than for a conventional compound, and this has been a factor preventing its application in some circumstances; however, this difference decreases as the test period increases. As figure 15 shows, a compression set of below 25% after 504 hours at 150[degrees]C is very good.

[FIGURE 15 OMITTED]

Figure 16 shows the resistance to abrasion of these materials according to the DIN method. As would be expected from other mechanical property data, the ZSC4195 based materials offer improved abrasion resistance, which undoubtedly would translate into enhanced longevity in an abrasion service environment. Most importantly, the HNBR4300 material shows an upward trend as hardness increases, whereas the ZSC4195 blend material decreases at the highest hardness.

[FIGURE 16 OMITTED]

Low temperature performance

Figures 17 and 18 plot the low temperature retraction properties of these materials. As would be expected, as the hardness of the compound increases, the low temperature properties appear to become poorer. This is primarily due to the less-elastic nature of a harder compound. In fact, the tensile modulus of the harder material was so high that it was almost impossible to strain the original specimens to begin the test.

The TR10 value is commonly accepted as the minimum temperature at which a seal will function, and the TR70 value is where the seal regains the majority of its elasticity.

Even at 90 hardness it can be seen that both HNBR4300 and ZSC4195 offer TR10 values of below -30[degrees]C. With the judicious use of an appropriate plasticizer, it is quite possible to bring these values down to -40[degrees]C; however, original mechanical properties may have to be compromised to a small degree.

The TR 70 values differ between the two material types. The ZSC4195 compounds have a slight advantage, and it is likely to be due to the higher relative polymer content of the ZSC4195 compounds. Only at the very extremes of high hardness does the HNBR4300 show improved TR70 figures. The HNBR4300 shows a more or less straight-line relationship, due to the gradual increase in carbon black content as hardness increases.

Summary

The results reported and discussed above quite clearly show how, with an HNBR/zinc dimethacrylate blend, it is possible to produce elastomer compounds capable of yielding very high tensile and tear strength values, coupled with high elongation. These advantages are particularly evident at high hardness levels. When the HNBR component is of the fully-saturated terpolymer variety, these properties can be achieved in conjunction with excellent low temperature and heat resistance. The work reported in this paper is by no means exhaustive, and further data are available on these materials should they be required.

Conclusions

The data reported in the article have demonstrated the extremely high performance and versatility of both terpolymer HNBR and its blends with zinc dimethacrylic acid. In particular, it shows the processing and functional advantages possible if these materials are correctly compounded and processed. It is the authors' opinion that these new materials offer the widest possible window of application due to the excellent temperature range, mechanical properties and chemical resistance offered.

These data should be used for reference in designing and developing high performance elastomeric products that requite high and low temperature performance, coupled with excellent mechanical properties.

References

(1.) Web page www.iisrp.com.

(2.) Kubo, Hashimoto and Watanabe, "Structure and properties

(3.) Zeon ETSL report number 1478Z.

(4.) Zetpol Sales Aid 25-April 1984.

(5.) Tarafumi Kawanaka, et al. "Novel high performance cold flexibility HNBR." IRC 2003.

(6.) Sachio Hayashi "Structure and mechanical properties of HNBR/zinc di-methacrytate," Zeon Corp. manuscript of an oral presentation.

(7.) Zrtpol Sales Aid 03-Zeoforte ZSC-Zeon Super Composite.

(8.) Nomura, Takano, Toyota and Saito. "Structural analysis of very high strenght HNBR/(zinc dimenthacrylate) composites." ACS Rubber Division. November 3-8, 1992.

(9.) Files and Jones, "Novel low temperature HNBR polymers," ACS Rubber Division, October 16-18, 2001.

Nick Sandland, Suguru Ito, Motofumi Oyama and Edmee Files, Zeon Chemicals

Table 1--recipes

Ingredients              1        2        3        4        5        6

Zetpol 4300            100      100      100      100       60       40
ZSC 4195CX                                                  40       60
Zinc oxide               5        5        5        5        5        5
Stearic acid             1        1        1        1        1        1
N550 carbon black       40       60       80      100
Naugard 445            1.5      1.5      1.5      1.5      1.5      1.5
Rhenogran ZMMBI          3        3        3        3        3        3
50                       8        8        8        8        8        8
Luperox F40          158.5    178.5    198.5    218.5    118.5    118.5

Ingredients              7        8

Zetpol 4300             20
ZSC 4195CX              80      100
Zinc oxide               5        5
Stearic acid             1        1
N550 carbon black
Naugard 445            1.5      1.5
Rhenogran ZMMBI          3        3
50                       8        8
Luperox F40          118.5    118.5

Table 2--description of materials

Additive name   Detail

Zetpol 4300     18% ACN, 60-100 ML 1+4 at 100[degrees]C, iodine
                value <15
ZSC 4195CX      16.6% ACN, 60-100 ML 1+4 at 100[degrees]C, iodine
                value 10 to 201
Zinc oxide      White seal, 99.8%, [N.sub.2] surface area 5 [m.sub.2]/g
Stearic acid    Octadecanoic acid beads
Corax N550      Iodine absorption number 43, CTAB 42
Naugard 445     4,4'-Bis (a,a-dimethylbenzyl) diphenylamine
Rhenogran       Zinc methly mercapto
ZMMBI 50        benzimidazole, 50% in EPDM/EVA binder
Luperox F40     1,3 1,4-Bis(tert-butyl peroxy isopropyl) ben-
                zene 40% active on CaC[O.sub.3] carrier

Table 3--results

Compound reference no.                           1       2        3

Monsanto MDR cure properties         ISO
  (12 minutes at 180[degrees]C)     3417
Min. torque, ML (inch lbs.)                   1.32    2.14     3.24
Max. torque, MH (inch lbs.)                   12.8    17.8     23.4
MH-ML (inch lbs.)                             11.5    15.7     20.2
Ts2 minutes                                   1.08    0.89     0.69
Tc50 minutes                                  2.19    2.14     2.06
Tc90 minutes                                  5.51    5.39     5.28
Mooney viscosity ML 1+4 at                    72.5    98.5    135.5
100[degrees]C
Physical properties                Method
Cured 10'@ 180[degrees]C, P/C 4
  hrs. @ 150[degrees]C
Hardness, Duro A (plied             ASTM        64      76       83
sheet)                              D2240
Tensile strength MPa               ISO 37:    21.3    21.8     20.1
                                   type 2
Elongation at break, %                         310     240      160
Modulus @ 50% ext., MPa                        1.7     3.2      5.8
Modulus @ 100% ext., MPa                       4.5     8.4     13.3
Compression set--large,            ISO 815
  15% strain
168 hrs. @ 150[degrees]C                       7.7     7.7      5.4
504 hrs. @ 150[degrees]C                      18.1    19.0      7.7
Crescent tear                      ISO 34       22      31       33
Angle tear                         ISO 34       36      41       39
Angle tear @ 150[degrees]C         ISO 34       13      12       12
DIN abrasion (loss, [mm.sup.3])      ISO       120     122      141
                                    4649
Low temperature                      ISO
  retraction                        2921
TR 10                                          -34     -33      -31
TR 30                                          -29     -26      -23
TR 50                                          -24     -20      -17
TR 70                                          -15     -12      -10
Air (Geer oven) 168 hours          ISO 188
  @ 150[degrees]C
Tensile strength, %                           18.8    19.3     18.5
Change in tensile strength, %                  -12     -12     -8.0
Elongation @ break, %                          360     270      190
Change in elongation, %                       16.1    12.5     18.8
Modulus @ 100%, MPa                            5.5     9.4     13.8
Change in modulus %                           22.2    11.9      3.8
Hardness (plied sheet)                          72      81       87
Change in hardness                               8       5        4

Compound reference no.                           4       5        6

Monsanto MDR cure properties         ISO
  (12 minutes at 180[degrees]C)     3417
Min. torque, ML (inch lbs.)                   5.62    0.54     0.63
Max. torque, MH (inch lbs.)                   30.4    11.8     23.5
MH-ML (inch lbs.)                             24.8    11.3     22.9
Ts2 minutes                                   0.52    0.70     0.55
Tc50 minutes                                  1.93    1.65     1.43
Tc90 minutes                                  5.06    4.99     4.70
Mooney viscosity ML 1+4 at                    >200    45.5     46.5
100[degrees]C
Physical properties                Method
Cured 10'@ 180[degrees]C, P/C 4
  hrs. @ 150[degrees]C
Hardness, Duro A (plied             ASTM        89      63       78
sheet)                              D2240
Tensile strength MPa               ISO 37:    19.9    25.1     31.2
                                   type 2
Elongation at break, %                         130     430      410
Modulus @ 50% ext., MPa                        9.4     1.5      3.7
Modulus @ 100% ext., MPa                      15.9     2.9      6.4
Compression set--large,            ISO 815
  15% strain
168 hrs. @ 150[degrees]C                       6.0    16.5     18.7
504 hrs. @ 150[degrees]C                       8.7    18.5     20.9
Crescent tear                      ISO 34       35      23       39
Angle tear                         ISO 34       37      39       56
Angle tear @ 150[degrees]C         ISO 34       12       7       12
DIN abrasion (loss, [mm.sup.3])      ISO       168      92      113
                                    4649
Low temperature                      ISO
  retraction                        2921
TR 10                                          -31     -35      -32
TR 30                                          -20     -32      -28
TR 50                                          -13     -28      -25
TR 70                                           -6     -20      -18
Air (Geer oven) 168 hours          ISO 188
  @ 150[degrees]C
Tensile strength, %                           18.0    28.6     26.5
Change in tensile strength, %                 -9.5    13.9    -15.1
Elongation @ break, %                          130     450      310
Change in elongation, %                        0.0     4.7    -24.4
Modulus @ 100%, MPa                           15.7     3.8      8.5
Change in modulus %                           -1.3    31.0     32.8
Hardness (plied sheet)                          91      67       81
Change in hardness                               2       4        3

Compound reference no.                            7        8

Monsanto MDR cure properties         ISO
  (12 minutes at 180[degrees]C)     3417
Min. torque, ML (inch lbs.)                    0.85     1.01
Max. torque, MH (inch lbs.)                    53.8    115.7
MH-ML (inch lbs.)                              52.9    114.8
Ts2 minutes                                    0.47     0.41
Tc50 minutes                                   1.09     0.81
Tc90 minutes                                   4.01     2.91
Mooney viscosity ML 1+4 at                     49.0     53.5
100[degrees]C
Physical properties                Method
Cured 10'@ 180[degrees]C, P/C 4
  hrs. @ 150[degrees]C
Hardness, Duro A (plied             ASTM         89       95
sheet)                              D2240
Tensile strength MPa               ISO 37:     31.2     26.5
                                   type 2
Elongation at break, %                          290      110
Modulus @ 50% ext., MPa                         8.4     19.3
Modulus @ 100% ext., MPa                       12.8     25.3
Compression set--large,            ISO 815
  15% strain
168 hrs. @ 150[degrees]C                       14.3     15.2
504 hrs. @ 150[degrees]C                       15.3     16.6
Crescent tear                      ISO 34        52       48
Angle tear                         ISO 34        59       56
Angle tear @ 150[degrees]C         ISO 34        22       20
DIN abrasion (loss, [mm.sup.3])      ISO        145       85
                                    4649              Bounced
Low temperature                      ISO
  retraction                        2921
TR 10                                           -31      -32
TR 30                                           -24      -18
TR 50                                           -18       -7
TR 70                                           -10       10
Air (Geer oven) 168 hours          ISO 188
  @ 150[degrees]C
Tensile strength, %                            19.5     23.5
Change in tensile strength, %                 -37.5    -11.3
Elongation @ break, %                           110       30
Change in elongation, %                       -62.1    -72.7
Modulus @ 100%, MPa                            18.1       --
Change in modulus %                            41.4       --
Hardness (plied sheet)                           88       95
Change in hardness                               -1        0