Enhancing metallocene TPE's performance for extruded applications.

The use of ethylene/[alpha]-olefin elastomers started as an impact modifier of polypropylene in hard TPO compounds. The addition of between 20-35 weight percent elastomer increases the room temperature and low temperature (-30[degrees]C) notched izod impact strength of homopolymer polypropylene by a factor of almost 10.

Attributes that are inherent in the elastomers are contributing to their qualification in automotive, industrial and consumer extruded profile applications. Such attributes include, but are not limited to:

* Halogen free;

* saturated hydrocarbon backbone--excellent UV resistance;

* clarity;

* high resilience in the absence of plasticizer;

* low temperature flexibility; and

* less than 0.9 g/cc density--offers weight reduction opportunities vs. flexible PVC.

The density range of typical extrusion grade elastomers is between 0.868-0.902 g/cc. The density is inversely proportional to the co-monomer content (octene or butene) and directly proportional to hardness. The melting temperature increases with density (hardness). While the melting temperatures range from 60-105[degrees]C (as measured by differential scanning calorimetry [DSC]), extrusion temperatures can be up to 80[degrees]C higher and depend on the shape and wall thickness of the profile, as well as the screw design employed. The upper service temperature performance of the polymer in a given application is dictated by density or co-monomer level and generally ranges from 60-100[degrees]C.

Soft applications which need greater than 80[degrees]C service temperature often require that the elastomer undergo some kind of modification. Enhancing the upper service temperature performance of the elastomers, without going to the extent of fully crosslinking, can be achieved in two ways:

* Irradiation (electron beam or gamma radiation) crosslinking, or

* via reactively compounding with polypropylene (using peroxide and optionally coagent).

Electron beam processing equipment generates ionizing radiation that interacts with the polymer and yields a free radical, which forms crosslinks in ethylene elastomers. The degree of crosslinking (measured by gel content) depends on the dosage applied (between 5-30 mega rads is typical for plastics) to the polymer, and the resultant improvements are in dimensional stability at higher service temperatures and compression set properties. Reactively modifying the elastomers and PP with low levels of peroxide/coagent during compounding improves the upper service temperature performance with little impact on the recyclability aspects, as the resultant compound is free from gel (measured in boiling xylene).

The technologies being developed and which are showing success in automotive sheet extrusion processes are based on blends of ethylene-octene and polypropylene that are reactively modified using small amounts of peroxide and coagent, during compounding, to impart the necessary performance requirements of thermoformed instrument panel skins (ref. 1). Such compounds show between 50-70[degrees]C improvement in upper service temperature performance, as measured by thermal mechanical analysis (TMA), and enhanced melt strength over the elastomers when used alone. Unlike TPOs, which are primarily polypropylene, these peroxide modified blends are primarily elastomer (70 to 80 weight percent is typical) which results in the elastomer being the continuous phase.

Having the elastomer in the continuous phase has two important advantages. First, the compound has a low gloss and can be compounded to have a rubbery or leathery feel. Clarity is achievable by matching the ethylene-octene and polypropylene refractive indices. Second, the modification of the elastomer with peroxide allows a great deal of flexibility in tailoring the melt and solid-state characteristics to meet the physical property and processing requirements of various applications.

The polypropylene imparts dimensional stability to the compound at elevated temperatures, though only present as a dispersed phase at 20 to 30 weight percent of the compound. Additionally, it contributes to the compound's gain in modulus through the onset of crystallization during cooling which helps with shape retention upon cooling. Both features are contributing to these compositions' implementation into extruded sheet applications, and extend their applicability to extruded profiles.

This article will cover the general characteristics of Engage polyolefin elastomers (EG) and the breadth of technologies available to enhance certain physical and processing properties of the elastomers for extruded profile applications. Technologies shown include: Designed polymer architecture in the reactor to achieve enhanced extrusion processing; post extrusion elastomer modification with electron beam crosslinking to enhance upper service temperature performance; and blends with polypropylene and crosslinking agents like peroxide and coagent to meet the processing and performance requirements for extruded profile applications.

Experimental

Ingredient description

A description of the ethylene elastomers presented is shown in table 1. The other raw materials (see table 4) are described as follows:

* A 0.6 melt flow rate (2.16 Kg @ 230[degrees]C) homopolymer polypropylene;

* a 12 MFR homopolymer polypropylene;

* a 2 MFR random copolymer polypropylene;

* 20% active di(2-tert-butylperoxyisopropyl benzene) peroxide on polypropylene carrier;

* 2,5-dimethyl-2,5-di-(t-butylperoxy) hexane;

* 1,1,1 trimethylolpropane trimethacrylate; and

* hydrotreated heavy paraffinic process oil, 0.87 g/cc, 14.9-105 cSt viscosity at 40[degrees]C, non-fogging oil at up to 15 weight percent.

Sample preparation

Compounds of varying hardness were produced via twin screw compounding

for research and development purposes, and are not commercially available. The zones of the extruders were set so as to achieve a polymer melt temperature between 190-200[degrees]C so that 99.9% of the peroxide was consumed and to insure that the polypropylene (PP) was completely melted. For non-peroxide based compounds, the zone temperatures were set between 165-185[degrees]C to ensure that the polypropylene was completely melted and mixed with the elastomers. Developmental com-pounds did not contain stabilizers beyond what was originally present in the polymers used for compounding. Application development should include the addition of a stabilizer package designed for the end use environment, as reaction of peroxides with the stabilizers may affect elevated temperature performance.

Sample testing

Standard mechanical properties

Hardness (durometer A) was measured according to ASTM D-2240. The tensile properties were determined according to ASTM D-412. Tear properties were determined according to ASTM D-624. Compression set properties were determined according to ASTM D-395. Abrasion properties were run according to DIN 53 516, and density according to ASTM D-792.

Melt flow rates (MFR)

Melt flow rate values were determined using standard test method ASTM D-1238 (Procedure A). The measurement conditions were 190[degrees]C using a 2.16 kg load, unless otherwise denoted, for ethylene elastomers, and 230[degrees]C using a 2.16 kg load for polypropylene. Melt index is measured on pellets in all cases.

Differential scanning calorimeter (DSC)

A DSC instrument was used in an unmodulated mode to define the relative percent crystallinity and to monitor the [T.sub.c] and [T.sub.m] characteristics of each polymer or compound. The heat-cool-heat method using nitrogen purge was mn on a sample of 9-10 mg. The cooling and heating rates were 10[degrees]C/min. The cooling and second heats were recorded.

TMA procedure

A thermomechanical analyzer instrument was used which was equipped with a 0.89 mm contact diameter probe. A force of one Newton was applied and the testing was initiated at 23[degrees]C. A ramp rate of 5[degrees]C/min. was used until the final temperature was reached. The results give an indication of the relative thermal stability of each polymer or compound.

Melt strength

Samples were compared using a capillary die rheometer heated to 190[degrees]C fitted with a Gottfert Rheotens attachment. Melt tension and draw speed to break were measured on filaments exiting the capillary die. Melt strength was measured on pellets.

Rheology

A rubber processing analyzer (RPA) having a rotorless biconical die design that contains two cone shaped 41.25 mm diameter dies having a die gap of 0.487 mm was used. Samples were tested at 15% strain and a frequency of 1.6 Hz.

Shear thinning index

The ratio of the RPA complex viscosity measurement at 0.02 Hz divided by the complex viscosity measurement at 15.06 Hz was determined. The higher the value the greater the shear thinning characteristics of the material.

Ozone resistance

ASTM D 1149-99 and test specimens per ASTM D 518-99, Method A were use& The specimens were exposed 120 hrs. @ 50 pphm ozone @ 40[degrees]C and 30% elongation. Observations were made at 7x magnification.

Extrusion

A single screw (3/4") extruder having a L/D of 15/1, to compare processing characteristics, was used. A tube die (inner diameter [ID] = 11.1 mm, wall thickness 1.6 mm) was employed and the extrudate was air-cooled on a conveyor. Throughput, head pressure and torque readings were taken at various screw speeds once the head pressure and torque stabilized.

Results and discussion

Selecting the appropriate elastomer depends on the physical requirements of the end-use profile and the processing characteristics. Extrusion grades of ethylene elastomers vary by density and [alpha]-olefin type and are typically less than three melt index (MI). The hardness and other associated properties correlate to the density and MI, while extrusion processing is strongly influenced by the elastomer's molecular weight characteristics (molecular weight, molecular weight distribution and branching). The physical properties of these extrusion grades are shown in table 2.

The data shown in table 2 depict the range of physical properties available from the elastomers if used alone. In addition to the commercially available ethylene-octene elastomers, two new polymers are shown (ENR 8556 and ENX 7270) as they represent some of technologies which will be available this year. The ENR 8556 is being introduced as a differentiated reactor grade ethylene-octene copolymer that exhibits excellent clarity and flexibility for low modulus applications. Its broader molecular weight distribution and high long chain branch level allow it to be extruded at lower temperatures and it shows reduced surface melt fracture compared to the equivalent density 8100 (0.5 mm wall thickness). An example of the effects of broader mwd and branching is seen in the substantially lower extruder head (die) pressures compared to some of the other extrusion grade elastomers, shown in figure 1.

[FIGURE 1 OMITTED]

The ethylene-butene offers twice the abrasion resistance, 1.5 times the tensile strength and 1.3 times the tear strength, but 30% higher compression set and 9[degrees]C higher DSC glass transition temperature over the nearly equivalent crystallinity ethylene-octene elastomer (8100). These distinctions in the physical properties between ethylene-octene and ethylene-butene at 75-77 durometer A hardness should be considered when selecting the elastomer for an extruded profile application.

Electron beam crosslinking

Some soft thermoplastic elastomer applications may dictate upper service temperature performance properties above that offered by the neat elastomer. One way to enhance the upper service temperature performance of the elastomer is via post-extrusion electron beam crosslinking. The amount of crosslinking depends on the radiation dosage that is applied to the polymer, and the cost is directly proportional to dosage. The physical properties at various dosage levels are shown in table 3.

The upper service temperature performance (as measured by thermal mechanical analysis [TMA]) is dictated by the density (table 1) of the unmodified elastomers as shown in figure 2, and is substantially improved with electron beam crosslinking of the elastomers as shown in figure 3.

[FIGURES 2-3 OMITTED]

As shown in figure 3, the upper service temperature can be substantially improved with only 10 mrads dosage level over the elastomer with no e-beam crosslinking. Based on previous laboratory studies, the penetration resistance is essentially the same as a silane crosslinked (87% gel) ethylene-octene (0.87 g/cc, 1 MI) elastomer. The optimum balance of physical properties, service temperature and cost are application specific, but generally 5-10 mrads dosage serves as a good starting point if electron beam crosslinking equipment is available.

Compounding

An alternative for achieving improved service temperature is by reactively modifying the elastomers and polypropylene (PP) with low levels of peroxide or peroxide and co-agent during extrusion compounding (simple blending does not offer this enhanced temperature performance). Laboratory studies have shown that either co-rotating twin screw extruders or kneaders can be used and that the resultant com-pounds have immeasurable gel content when dissolved in boiling xylene, making them ideal for extruded applications. Hardness values similar to the extrusion grade elastomers are attained when the softer ethylene/(octene of butene) elastomers are used at between 70-80% by weight on a polymer basis. Examples of the reactively modified compounds are compared to unmodified (no peroxide or coagent) compounds in table 4. The physical properties of the compounds appear in table 5.

Studies reveal polypropylenes with MFRs ranging from fractional (sheet extrusion) to 35 effectively satisfy typical property and processing requirements in extrusion, and that homopolymer or copolymers of ethylene-propylene can be used in the compound. Since the PP is in the discrete phase, choice of PP grade is less critical, although higher MFR grades have been confirmed to provide smoother surfaces in extruded profiles. The incorporation of polypropylene increases the DSC melting temperature of the elastomeric compound to between 155-165[degrees]C, as noted in table 5, which means the processing temperatures should be higher than this to insure complete melting of the compound. However, without reactive modification with peroxide/coagent, the upper service temperature performance is less than that of an equivalent density ethylene/octene elastomer (EG 8003), as shown in figure 4.

[FIGURE 4 OMITTED]

When applications require longer term upper service temperature performance or heat aging properties, it is necessary to understand that higher levels of peroxide used during compounding may consume a fair amount of the stabilizer(s) supplied in the neat elastomers and polypropylenes, thus making it necessary to add a stabilizer before subjecting the compound to elevated temperatures for extended periods of time. For example, studies have revealed that Compound E loses essentially all of its original elongation properties within seven days of oven aging at 150[degrees]C when no stabilizer is added, whereas it maintains all of its original elongation properties over a 14 day period with the addition of 0.1 phr Irganox B921FF or 0.3 phr Irganox B225. Compound B, on the other hand, because of its lower level of peroxide, maintains its original properties over 14 days of oven aging at 150[degrees]C (without stabilizer). Applications requiring heat aging performance should have these properties confirmed prior to putting the material into service, and generally it is good practice to employ a stabilizer package during extrusion processing.

Further inspection of the physical properties shown in table 5 reveals that the hardness can be tailored by using higher density (hardness) ethylene/-(octene or butene) elastomers, which notably improves the abrasion resistance properties. Another means of improving the abrasion properties is by incorporating ultra-high molecular weight siloxane polymer (ref. 2). Studies have shown that the addition of 2% by weight (or 1% of the siloxane polymer) of the siloxane polymer improves the abrasion resistance of Compound B by at least 30%, and Compound E by at least 50%, which has proven to improve rope abrasion of tarps produced from ethylene/octene elastomers. As is the case with other elastomer families, fillers and process oils are often used to balance the properties with cost, however caution should be applied because some fillers and oils reduce peroxide activity and may need to be added downstream of the peroxide addition during compounding.

The decision on choice and levels of peroxide and coagent largely depends on the desired end use performance, processing and application economics. Improved processing generally follows with higher shear thinning materials (the compounds containing higher levels of peroxide) at the expense of 190[degrees]C melt and 23[degrees]C tear strength properties and often depends on die design and wall thickness of the profile being extruded.

Extrusion processing

The extruder output characteristics are equally important to the physical properties, and help establish the relative cost of the extruded article. The optimal output is determined by the screw speed that produces the desired aesthetics and shape without post-die collapse. Shape control for round profiles such as tubing or hose is easily achieved with post-die calibration equipment in which the profile is air- or water-cooled before being optionally irradiated and cut to size.

The shape retention of more complex profiles requires that the polymer of compound possess sufficient melt strength after it exits the die to resist collapse of sagging. Since the profile is under low stress as it exits the die, it is desirable that the polymer has relatively high low shear viscosity, which correlates to melt strength, to retain the shape. The low shear viscosity comparison between Compounds D-F and equivalent density EG 8003, as measured using an RPA, is shown in figure 5.

[FIGURE 5 OMITTED]

Based on the data shown in figure 5, peroxide modified Compound E clearly exhibits higher lower shear viscosity or improved melt strength, and improved shear thinning, as evidenced by the lower high shear viscosity, than either the simple (unmodified) Compound D (same composition as Compound E without the peroxide) of the equivalent density EG 8003. These data corroborate the melt strength results shown in tables 2 and 5. At a shear rate of 0.02 [sec.sup.-1], Compound E exhibits an order of magnitude higher complex viscosity than the unmodified Compound D, and about eight times higher viscosity than the EG 8003. This noted property advantage is visibly seen when extruding 11.1 mm ID tubing onto a conveyor belt, in that Compound D and the EG 8003 show tube collapse of sagging, whereas Compounds E and F maintain a regular round shape. This becomes an important feature for profiles that are being produced without post-die calibration equipment. The same trend holds true with Compounds A-C.

The addition of process oil, or process oil and filler, lowers the overall viscosity, as one would expect, and the shear thinning characteristics are maintained, which translates to improved processibility. The resultant shear thinning characteristics are due to the combination of the elastomer's response to the peroxide, which is thought to be due to the development of increased polymer entanglements, and the polypropylene's response, which is considered to be polymer chain scissioning. The addition of coagent tends to retard the chain scissioning of the polypropylene, and along with reduced levels of peroxide, yields a lower shear thinning index, as shown in the comparison of Compounds B vs. E in table 5.

Another factor affecting the shape retention of semi-crystalline elastomers and flexible TPOs is the rate at which they solidify, which is influenced by the rate of crystallization that occurs during cooling (post-die). When the polymer or blend is cooled below its melting point, crystallization occurs because the crystal phase has a lower free energy than the melt phase. As monitored by DSC and shown in figures 6 and 7, the peroxide/coagent modification during compounding increases the DSC peak crystallization temperature (Tc) by as much as 20[degrees]C which gives demonstrable improvements to polymer solidification time compared to the unmodified compounds, and enhances shape retention during extrusion.

[FIGURES 6-7 OMITTED]

The rheological properties of the molten polymer of compound influence many aspects of processing including screw pumping efficiency and die pressure (hence output rate). The output is limited by the maximum pressure which achieves the desired surface aesthetics at a given screw speed. The pressure is directly proportional to the viscosity (shear and extensional) and the surface aesthetics depends on the external friction of the polymer on the metal surface (screw and die) and the amount of die swell upon exiting the die. The head or die pressures (11.1 mm ID tube) of the compounds (table 5) versus screw speed is shown in figure 8.

[FIGURE 8 OMITTED]

Reducing the external friction of the polymer (compound) on the metal surface can be achieved by incorporating process aids such as fluorpolymer or siloxane polymers. Literature reports that the fluoropolymer additives migrate to the internal wall of the extruder and induce slippage between themselves and the main polymer (a polyethylene) (ref. 3).

In laboratory (tube die) extrusion studies (at constant screw speed of 50 rpm) it has been found that the addition of Viton FreeFlow Z100 at 0.038% by weight (1% by weight of a masterbatch of Compound E containing 3.83% Z100) to Compound E reduces the pressure by 16% and the torque by 20%, in addition to improving the surface aesthetics of the profile. Addition of 2% by weight siloxane polymer in a LDPE masterbatch to compound E reduces the the pressure by 10% and the torque by 30%.

Summary

For applications that require clarity and flexibility (softness), the EG 8556 is a good choice because its broader mwd and branching allow it to be processed at lower temperatures (giving improved shape retention) and it achieves lower head (die) pressure than the other extrusion grade ethylene-octene elastomers. If upper service temperature performance is required along with clarity, then either e-beam crosslink the EG 8556 post the or match the refractive index of the elastomer to that of the PP and reactively modify during compounding.

The compounding of the ethylene elastomers with PP or reactively modifyiug the elastomer(s) with PP using peroxide (or peroxide and coagent) allow for lower die pressures during extrusion than the straight ethylene/1-octene elastomers (the exception being EG 8556). Further reductions in pressure are seen with the addition of process oils (and optionally fillers) and process aids. As is the case with other types of elastomers, balancing the physical properties with the processing characteristics is achievable with the proper selection of raw materials. The cost is dictated by the processing characteristics (speed at which acceptable profiles can be produced) and the raw materials selected (including compounding).

Conclusions

The upper service temperature performance of ethylene elastomers is enhanced via two different ways: 1) electron beam crosslinking, or 2) by reactively modifying during com-pounding with polypropylene, using peroxide and coagent.

Electron beam or gamma radiation crosslinking enhances the dimensional stability at upper service temperatures and improves the compression set resistance properties of ethylene elastomers. Typical dose levels are between 5-30 megarads, however doses between 5-10 megarads appear to be sufficient to achieve enhanced upper service temperature performance and reduced compression set properties, and ultimately depend on the desired physical properties of the application.

Peroxide-modification during compounding of ethylene elastomers and polypropylene (optionally extended with fillers and/or process oils) renders benefits in extrusion processing such as improved shape retention, reduced head (die) pressures, enhanced shear thinning and improved dimensional stability at elevated temperatures compared to ethylene elastomers (octene or butene) used alone or blended with polypropylene, without impacting recyclability aspects.

Abrasion properties are substantially improved by using higher density ethylene elastomers during compounding with polypropylene and peroxide (peroxide and coagent), or alternatively by incorporating two weight percent of siloxane polymer which also improves the processing characteristics by lowering the torque and die pressure during extrusion.

Table 1--product description for ethylene elastomers

                                           ENR

EG                             8842    8180    8100    8556
Density, g/cc                 0.857   0.863   0.870   0.870
Hardness, durom. A               50      66      75      73
Melt Index                      1.0     0.5     1.0     2.0
  (2.16 Kg @ 190[degrees]C)

                                       ENR             ENX

EG                             8003    8480    8540    7270 *
Density, g/cc                 0.885   0.900   0.910   0.880
Hardness, durom. A               86      94      96      77
Melt Index                      1.0     1.0     1.0     0.8
  (2.16 Kg @ 190[degrees]C)

* Ethylene-butene with all other comparative resins being
ethylene-octene

Table 2--physical properties of extrusion grade ethylene
elostomers

Property                             8100     ENR      8003
  (compression molded)                        8556

Co-monomer                         Octene   Octene   Octene
Hardness, durometer A                  75       73       86
Density, g/cc                        0.87     0.87    0.885
Melt Index, dg/min.                   1.0      2.0      1.0
DSC % crystallinity                    18       19       24
DSC melting peak, [degrees]C           60       57       78
DSC glass transition, [degrees]C      -55      -54      -49
  (inflection point)
Tensile at yield, MPa                 1.9      1.8      2.2
Elongation at yield, %                 38       25       18
Tensile at break, MPa                 8.5      6.0     20.0
Elongation at break, %                870    1,000      730
Compression set, 25%,                  29       31       24
  22 hrs. at 23[degrees]C
Tear strength, Die C,                  37       35       57
  N/mm
DIN abrasion, [mm.sup.3] loss          75      115       20
Melt strength
  Force to break, cN                  4.5      2.5      4.5
  Velocity to break, mm/s             135      150      150
Shear thinning index at               4.7      6.9      5.4
  190[degrees]C

Property                             8480     8540     ENX
  (compression molded)                                 7270

Co-monomer                         Octene   Octene   Butene
Hardness, durometer A                  94       96       77
Density, g/cc                        0.90     0.91     0.88
Melt Index, dg/min.                   1.0      1.0      0.8
DSC % crystallinity                    37       42       19
DSC melting peak, [degrees]C          100      103       61
DSC glass transition, [degrees]C      -41      -39      -46
  (inflection point)
Tensile at yield, MPa                 5.4      6.9      2.0
Elongation at yield, %                 21       18       28
Tensile at break, MPa                22.4     23.0     12.8
Elongation at break, %                660      700      715
Compression set, 25%,                  24       22       40
  22 hrs. at 23[degrees]C
Tear strength, Die C,                  83      100       48
  N/mm
DIN abrasion, [mm.sup.3] loss          15       12       39
Melt strength
  Force to break, cN                    4        4        4
  Velocity to break, mm/s             150      150      150
Shear thinning index at               7.3      8.5      4.5
  190[degrees]C

Table 3--properties versus electron beam radiation dosage

Property *                               8100            8556
  (injection molded)

Hardness, durometer A                      71              68
  5 mrads                       68.5 (6% gel)   67 (0.5% gel)
  10 mrads                         66.8 (77%)        67 (75%)
  15 mrads                         67.7 (86%)        66 (82%)
  30 mrads                        63.3% (87%)        64 (88%)
Tensile at break, MPa                     5.8             5.5
  5 mrads                                 6.3             6.9
  10 mrads                                6.4             7.1
  15 mrads                                4.7             6.5
  30 mrads                                4.5             4.5
Elongation at break, %                    517             576
  5 mrads                                 563             713
  10 mrads                                517             650
  15 mrads                                380             592
  30 mrads                                311             333
Compression set, 25%,                      29              31
  22 hrs. at 23[degrees]C
  5 mrads                                22.3            25.4
  10 mrads                               24.8            24.7
  15 mrads                               24.3            27.8
  30 mrads                               22.0            23.8
Tear strength, Die C,                    39.5              40
  N/mm
  5 mrads                                39.8              40
  10 mrads                               35.8              38
  15 mrads                               34.9              36
  30 mrads                               27.6              30
DIN abrasion, [mm.sup.3] loss              75             115
  5 mrads                                  75             103
  10 mrads                                117             104
  15 mrads                                128             136
  30 mrads                                303             305

Property *                             8003
  (injection molded)

Hardness, durometer A                    85
  5 mrads                       84 (0% gel)
  10 mrads                         83 (80%)
  15 mrads                         84 (86%)
  30 mrads                         82 (94%)
Tensile at break, MPa                   9.0
  5 mrads                              10.6
  10 mrads                             10.1
  15 mrads                             10.7
  30 mrads                              9.0
Elongation at break, %                  427
  5 mrads                               451
  10 mrads                              432
  15 mrads                              429
  30 mrads                              341
Compression set, 25%,                    34
  22 hrs. at 23[degrees]C
  5 mrads                              22.8
  10 mrads                             24.0
  15 mrads                             22.0
  30 mrads                             23.5
Tear strength, Die C,                    62
  N/mm
  5 mrads                                62
  10 mrads                               58
  15 mrads                               56
  30 mrads                               46
DIN abrasion, [mm.sup.3] loss            20
  5 mrads                                18
  10 mrads                               30
  15 mrads                               38
  30 mrads                              128

* E-beaming of test slabs was done courtesy of Mercury Plastics

Table 4--compounds of ethylene elastomers and
polypropylene

Material            A      B      C     D

EG 8100                                45
EG 8842                                30
EG 8180            70    69.85
EG 8003
EG ENX 7270
0.9 MFR            30    29.85
  homopolymer PP
12 MFR                                 25
  homopolymer PP
2 MFR random
  copolymer PP
Compound B                       85
Compound E
Paralux 6001                     15
  process oil
Vulcup 20-P
Luperox 101              0.15
  peroxide
SR-350 coagent           0.15
Total              100    100    100   100

Material             E      F      G       H

EG 8100            44.72
EG 8842            29.81
EG 8180
EG 8003                          74.55
EG ENX 7270                              74.55
0.9 MFR
  homopolymer PP
12 MFR             22.97
  homopolymer PP
2 MFR random                     24.85   24.85
  copolymer PP
Compound B
Compound E                 85
Paralux 6001               15
  process oil
Vulcup 20-P         2.5
Luperox 101                       0.6     0.6
  peroxide
SR-350 coagent
Total               100    100    100     100

Table 5--physical properties of compounds

Property                                           A      B      C
  (compression molded)

Hardness, durometer A                              83     87     85
Density, g/cc                                    0.88   0.88   0.88
Melt Index, 10kg, dg/min.                           5      4     12
DSC melting peak, [degrees]C                      162    161    157
DSC crystallization peak, [degrees]C              106    116    110
DSC glass transition, [degrees]C
  (inflection point)                              -56    -57    -64
Tensile at yield, MPa                             3.2    2.7    1.7
Elongation at yield, %                             19     17     21
Tensile at break, MPa                             8.0     11      8
Elongation at break, %                            710    500    435
Compression set, 25%, 22 hrs. at 23[degrees]C      46     36     33
Tear strength, Die C, N/mm                         53     64     40
DIN abrasion, [mm.sup.3] loss                     185    169    269
Melt strength
Break force, cN                                     9     30     16
Velocity to break, mm/sec                         125     45     65
Shear thinning index @ 190[degrees]C               12     54     46
Ozone resistance
  48 hrs.                                       Nc **     Nc     Nm
  96 hrs.                                          Nc     Nc     Nm
  120 hrs.                                         Nc     Nc     Nm

Property                                          D      E      F
  (compression molded)

Hardness, durometer A                             77     86     79
Density, g/cc                                   0.88   0.88   0.88
Melt Index, 10kg, dg/min.                         14     14     38
DSC melting peak, [degrees]C                     165    158    155
DSC crystallization peak, [degrees]C              96    119    115
DSC glass transition, [degrees]C
  (inflection point)                             -56    -63    -61
Tensile at yield, MPa                            1.6    2.5   1.34
Elongation at yield, %                          18.4     18     22
Tensile at break, MPa                              5     10      6
Elongation at break, %                           415    420    363
Compression set, 25%, 22 hrs. at 23[degrees]C     29     35     27
Tear strength, Die C, N/mm                        49     49     31
DIN abrasion, [mm.sup.3] loss                    168    143    221
Melt strength
Break force, cN                                  3.5     17   Nm *
Velocity to break, mm/sec                        125     40     Nm
Shear thinning index @ 190[degrees]C               7    114     71
Ozone resistance
  48 hrs.                                         Nc     Nc     Nm
  96 hrs.                                         Nc     Nc     Nm
  120 hrs.                                        Nc     Nc     Nm

Property                                          G      H
  (compression molded)

Hardness, durometer A                             93     90
Density, g/cc                                   0.89   0.89
Melt Index, 10kg, dg/min.                          1      3
DSC melting peak, [degrees]C                     151    153
DSC crystallization peak, [degrees]C             114    100
DSC glass transition, [degrees]C
  (inflection point)                             -44    -44
Tensile at yield, MPa                            3.7    3.5
Elongation at yield, %                            16     19
Tensile at break, MPa                             18     11
Elongation at break, %                           605    600
Compression set, 25%, 22 hrs. at 23[degrees]C     39     51
Tear strength, Die C, N/mm                        80     77
DIN abrasion, [mm.sup.3] loss                     39     77
Melt strength
Break force, cN                                   35     20
Velocity to break, mm/sec                         35     40
Shear thinning index @ 190[degrees]C             196    143
Ozone resistance
  48 hrs.                                         Nm     Nm
  96 hrs.                                         Nm     Nm
  120 hrs.                                        Nm     Nm

** no cracks

* not measured

References

(1.) K.L. Walton, J.D. Pomije and E.S. Gisler, "Development of ethylene/alpha-olefin copolymer elastomer compounds with improved thermoforming capability," SPE Automotive TPO Global Conference 2001, October 2001.

(2.) Patent Number 5,902,854 issued to Dow Chemical (1999).

(3.) K.B. Migler, C. Lavellee, M.P. Dillon, S.S. Woods and CL. Gettinger; "Visualizing the elimination of sharkskin through fluoropolymer additives: Coat and polymer-polymer slip-page," J. Rheol. 4.5, 565-581 (2001).

Laura B. Weaver, Henry G. Heck and Dan Moldovan, DuPont Dow Elastomers