High molecular weight EPDM via metallocene catalyst and gas phase process.

N-MG represents the combination of two of the latest technologies in EPDM manufacture, gas phase polymerization and metallocene catalysis. This combination of the two technologies extends the product capabilities to manufacture high molecular weight polymers without any process constraints or cost penalties that are associated with solution processes. High molecular weight EPDM is produced as oil extended grades in the conventional solution process. These high roof ecular weight grades find a niche in EPDM applications. The granular form of N-MG. exert at high molecular weights, provides short mixing times with good filler dispersion.

This article highlights some of the advantages of high molecular weight N-MG compounds vs. oil extended and regular grades of EPDM.

The granular form of these products also lends capabilities for continuous processing in a twin screw extruder, thus making them ideal products for the production of TPVs.

Large-scale commercial production of EPDM via Metallocene catalyst technology was started by DuPont Dew in 1997. This is based on Insite (catalyst and process technology From Dew Chemical). Insite is a combination of Dew's constrained geometry catalyst (CGC) system and proprietary solution process. About the same time. Union Carbide introduced its gas phase EPDM utilizing vanadium based Ziegler-Natta catalyst technology. The gas phase EPDM process technology for the manufacture of EPDM came to DuPont Dew through the acquisition of Union Carbide by Dow. The gas phase EPDM process was greatly improved by the application of a metallocene catalyst system. Commercial production of metallocene based gas phase EPDM started in early 2002.

The advantage of EPDM produced via metallocene catalyst and the advantages of granular gas phase EPDM are well documented (refs. 1 and 21. Some of the advantages of EPDM produced via metallocene catalyst technology are:

* High catalyst efficiency resulting in low catalyst residues and potential for low cost:

* consistency of product composition:

* low odor;

* low gel; and

* the granular gas phase EPDM provides exceptionally fast mixing with good filler dispersion.

EPDM produced via metallocene catalyst and the gas phase process provides the combined advantages of the catalyst and the granular form of the product. The properties and advantages of EPDM via gas phase process and metallocene catalyst were presented by Grant, et al (ref. 3).

High molecular weight EPDM (HMW-EPDM)

One of the limitations of solution process EPDM is the economic and technical viability of producing high molecular weight polymers. For conventional solution process production of EPDM above 90 Mooney (ML1+4@ 125[degrees]C). the solution viscosities in the process are too high, and throughput is considerably reduced. When a high molecular weight EPDM (HMW-EPDM) is produced, isolation becomes difficult without the addition of a process oil, thereby producing oil extended EPDM (OE-EPDM). Without oil extension, HMW-EPDM becomes impossible to process in conventional rubber equipment due to its high viscosity. In general, 70 to 100 Mooney products need to be finished as "friable bales" or pellets. Above 100 Mooney, conventional EPDM products need to be oil extended to provide practical processing polymers.

HMW-OE-EPDM products provide some desirable properties lot the rubber compounder. Many of these are general to all high molecular weight elastomers. The desirable properties of HMW-EPDM are:

* High physical properties:

* low compression set:

* high crosslink efficiency:

* high hot green strength;

* good shape retention of extrudates;

* high extensibility of compounds: and

* ability to accept high levels of process oils to provide low hardness compounds.

Some of the drawbacks of HMW-OE-EPDM are:

* Lack of choice of oil to the end user: and

* overall cost of the product.

Despite the disadvantages, they find a niche in low hardness compounds requiring good physical properties, extruded profiles that require good shape retention and low compression set, extruded sponge with good cell structure, in the production of thermoplastic vulcanizates (TPV) and for the modification of thermoplastic polyolefins (TPO).

High molecular weight gas phase EPDM

The product capabilities of gas phase EPDM are considerably broader than either the Insite solution process or the conventional vanadium based solution process. The manufacturing limitations of solution process to produce non-oil extended EPDM are overcome by the gas phase process. Figure 1 compares the EPDM product capabilities for gas phase and solution processes (ref. 5). Since polymerization takes place in a fluidized bed gas phase reactor, the achievement of high molecular weight is not constrained by any solution viscosity limitations.

[FIGURE 1 OMITTED]

Experimental products in excess of 200 Mooney have been produced with excellent mixing and processing characteristics. Figure 2 shows the black incorporation times (BIT) for products up to 200 Mooney (ML [1+4] at 125[degrees]C). The BIT for a 200 Mooney product is very comparable to that achieved with a 60 Mooney pelletized product.

The morphology of gas phase EPDM is shown in figure 3. This is important for its mixing behavior. N-650 carbon black is used, at a nominal level of 30 phr, as the partitioning agent in MG grades. The idealized representation of the MG particles is a polymer core with the carbon black shell acting as the partitioning agent. The average particle size ranges between 1.0 to 1.5 mm in diameter. The small granular panicles make it easier and taster to mix and incorporate fillers compared to a traditional bale or pellets, which must go through an initial breakdown stage in a mixer. The high surface area of the particles also makes it easier to rapidly absorb oil.

High molecular weight MG grades

To enable the industry to benefit from the advantages of gas phase metallocene catalyzed HMW-EPDM. three new high molecular weight grades have been introduced, and a fourth is being developed for later market introduction. The compositional characteristics of these new products are summarized in table 1.

High molecular weight MG grades in formulated recipes

High molecular weight MG grades were evaluated in compounds with different levels of extension. The levels of extension were varied by varying the filler and oil loadings. The filler to oil ratio was changed to maintain similar hardness levels for all compounds. All recipes were compensated for the carbon black in the MG grades and oil in the OE-EPDM grades to reflect the same filler and oil in the final recipes. Table 2 shows the test recipes used for the four extension levels used in the evaluation.

The discussions in this article will be limited to NDR 47130 as the example. However, the results and trends observed are similar for NDR 46140. The results for NDR 46140 and NDR 47100 along with the commercial competitive grades are available upon request.

NDR 47130 vs. regular clear grades of EPDM

These comparisons were carried out with commercial grades of EPDM designated A, B and C. Their compositions are summarized in table 3 (compositions as reported in producer literature).

The tensile strength graph (figure 4) shows that NDR 47130 can be loaded to a higher extension level and still retain the same strength. Despite the very high molecular weight (Mooney viscosity), NDR 47130 mixes considerably faster than the lower viscosity clear grades as shown by black incorporation times (BIT) (figure 5). The extension levels appear to have little effect on mixing times. While these mixing studies were carried out in a laboratory mixer using an upside down mix procedure, the mixing advantage has also been demonstrated in full size production equipment. Figure 6 shows the compression set (22 h. at 70[degrees]C, "cooled in clamps" method) for different extension levels. Compared with the clear EPDM grades, NDR 47130 maintains low compression set, even at extreme extensions.

[FIGURES 3-4 OMITTED]

NDR 47130 vs. oil extended grades of EPDM

NDR 47130 was compared with three commercial grades of OE-EPDM designated D, E and F. The compositions of these grades are summarized in table 4 (compositions as reported by producer literature).

Figure 7 shows mixing to be more rapid for NDR 47130, despite having to absorb 75 to 100 phr more "free oil" in the mix compared to the OE-EPDM grades. The oil absorption is very rapid due to the high surface area of the particles. The compound viscosity (figure 8) suggests that the NDR 47130 has a slightly lower molecular weight than the OE-EPDM grades in this comparison. Despite the lower molecular weight of NDR 47130, its tensile strength (figure 9) was similar to the OE-EPDM compounds, and it exhibited less strength loss at higher extension levels. This may be due to better filler incorporation and dispersion. Internal studies have shown that MG grades show better black dispersion than conventional baled EPDM. Like tensile strength, compression set was also better maintained at high extension levels in NDR 47130.

[FIGURES 7-9 OMITTED]

MG grades in TPV

Typically, HMW-EPDM grades are used in the production of high performance TPVs (high tensile strength and low compression set). In most cases, an OE-EPDM is used to provide the strength properties and also to facilitate the incorporation of large amounts of oil. TPVs are produced using continuous twin screw extruders or are mixed in an internal mixer. Continuous mixing provides the most economical route for TPV production. Baled rubber needs to be reduced in size to teed a continuous mixer. The granular high molecular weight MG lends itself to continuous mixing without the costly stage of size reduction. The advantages of MG grades for TPV were well documented by Williams, et al (ref. 6) in their paper presented at the 2003 TPE Conference in Brussels.

Summary and conclusions

A new family of high molecular weight granular EPDM grades has been introduced. These products have shorter mixing times with good filler dispersion when compared with regular or oil extended grades of conventional baled EPDM. They can be highly extended with fillers and plasticizers to provide low cost compounds with good physical properties and low compression set. The high molecular weight MG grades have the potential to be an alternative to oil extended grades of EPDM at reduced overall compound cost. The granular form may provide a route to continuous compounding in a twin screw extruder, as in the production of TPVs. These products are suitable lot the manufacture of dense and sponge extruded profiles, hose, vibration isolation parts and other molded goods. They can also be blended with conventional grades of EPDM to enhance physical or processing properties.

Figure 2--black incorporation time of 60 Mooney
N-IP vs. granular gas phase EPDM of varying
Mooney viscosities

Mixing time vs. viscosity

N-IP          60 MU

N-MG           86
              120
              150
              200

Note: Table made from bar graph.

Table 1--composition of HMW MG Grades

Product      Wt. %     % ENB     Mooney viscosity *
            ethylene           (ML 1+4@125[degrees]C

NDR47130       67       4.9              130
NDR46140       58       4.9              140
NDR47100       73       4.7              100
NDX551 **      54      High             High

NDR 47130:
Very high viscosity, semi-crystalline EPDM; optimized for maintaining
physicals in highly extended compounds and low compression
set. Suitable for replacing oil extended polymers and replacing
regular EPDM with highly extended compounds. Designed for
extruded profiles, hose and TPV.

NDR 46140:
Very high viscosity, amorphous EPDM: optimized for--maintaining
physicals in highly extended compounds and low compression
set, even at low temperatures. Suitable for replacing oil extended
amorphous polymers and replacing regular clear grades with highly
extended compounds. Designed for extruded profiles, hose, seals,
vibration isolation parts and TPV.

NDR 47100:
Fast curing semi-crystalline EPDM: optimized for high green
strength compounds; suitable for high hardness compounds, high
modulus and high tensile strength. Designed for industrial hose and
a blend component for improved green strength.

NDX 551XX (future product):
Ultra fast curing amorphous EPDM; optimized lot fast cure rates
and low compression set over a range of temperature. Suitable for
good cell structure formation and replacing oil extended amorphous
fast cure EPDM grades. Designed for continuously cured
sponge extrusions and blend component to increase cure state and
rate.

* Calculated Mooney value based on an internal model that compensates
for the carbon black

Table 2--test recipes with varying extensions

Filler and oil     280          330           400        475
EPDM               100          100           100        100
N-550 black        180          200           240        285
Paraffinic oil     100          130           160        190
Stearic acid        1
Zinc oxide          5
Sulfur             1.5
MBTS (80%)         3.1
TMTD (80%)         1.0
ZDBC (80%)         1.6
ZDMC (80%)         0.5
Total phr         393.7        443.7         513.7      588.7

Table 3--compositions of regular clear grades of
EPDM

Polymer          Mooney    Wt. % ethylene  Wt. % ENB

A                  70            70            5
B                  60            68.5          4.5
C                  59            73            5

Table 4--composition of OE--EPDM grades

Polymer          Mooney    Wt. % ethylene  Wt. % ENB   Oil/phr

D                  52            64           4.5         75
E                  48            64           8.7        100
F                  46            66           5           75

References

(1.) D.R. Parikh, B.W. Smith, M.S. Edmondson, M.J. Castille, D.J. Mangold and J.M. Winter. "Composition and structure-property relationships of single site constrained geometry EPDM elastomers," paper no. 81, ACS Rubber Division, May 1997.

(2.) A.U. Paeglis and A. Sen, "Granular gas-phase EPDM single-pass mix," paper no. 11, ACS Rubber Division, October 1995.

(3.) E.T. Italiaander. "Granular gas-phase EPDM--continuous mixing becomes a reality," paper no. 79, ACS Rubber Division, May 1997.

(4.) C.S. Grant, R.G. Vara and S.H.K. Tang, "Properties and performance of EPDM produced via gas-phase process using constrained geometry catalyst technology," paper no. 19, ACS Rubber Division, Oct. 8-12 2002.

(5.) S. Martin, D. Denton, L. Cady and D. Ramage, "Development of metallocene catalyst technology for the manufacture of EPDM rubber via the gas phase process, " ACS Rubber Division, Oct. 8-12, 2002.

(6.) G. Williams, R. Johnston and T. Clayfield, "Nordel MG the game changer for TPV, " TPE 2003, Brussels, Oct. 2003.