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Metallocenes: the next step.

Metallocene catalysts are extending the range of available LLDPE packaging film products and enhancing their properties, such as toughness and clarity. The strong mLLDPE film was produced at Mobil Chemical Co.'s gas phase reactor facility in Beaumont, Texas.

Having crossed the line between theory and practicality, into the real world of dynamic market competition, metallocene catalysts are pushing the plastics industry into the twenty-first century. Technologists can now anticipate achieving creativity in polymerization and product design that was never before possible.

The key to the metallocene catalysts is their potential for modeling and predicting a plastic's structural properties. At present, the emphasis is almost entirely on the polyolefins, to the extent that the traditional boundaries for these materials are being pushed outward. As a result, the margins of competition are changing; tomorrow, the engineering resins may feel their impact. Everything stems from the metallocenes' ability to control the production of the materials and their resultant properties.

Expenditures on metallocene catalyst research is now in the hundreds of millions of dollars per year, verifying that an expensive race to the marketplace is occurring. The cumulative global outlay, for the period of only the last few years, has been estimated to be in excess of $1 billion.

The great interest in metallocene catalysts was evident at May's SPE ANTEC in Boston, where sessions devoted to the subject attracted overflow crowds. The significance of the metallocenes was also characterized in simple terms by a presenter of a technical paper at the recent Metallocenes '95 International Conference in Brussels, sponsored by Schotland Business Research, Inc.: "I think of the new single-site catalyzed materials as providing cost-effective polymer attribute advantages that can be linked directly to end-user attributes," said Fred J. Steininger, director, Sales Development, Exact Plastomers, Exxon Chemical Co. "Traditional catalysts produce polymers with low, medium, and high molecular weights of various composition distributions. It is analogous to wanting to play soccer or tennis or ping-pong and getting one ball that has the features of all three, but which is not totally adequate for any of the games. You would certainly need to make a compromise. The metallocene single-site catalysts can produce materials that give us the one type, the correct type, that we need, with the right attributes for the game we want to play, with no compromises."

Molecular modeling

The impact of the new catalyst technology was expressed in another way by Tony Torres, senior research manager, Polyolefins Research, Dow Plastics, at the MetCon '95 International Conference in Houston, in May, sponsored by The Catalyst Group. The comments by Steininger and Torres reflect, respectively, Exxon's and Dow's sophisticated computerized capabilities relative to the greatly enhanced molecular structuring and control. "The significance of the new catalyst revolution goes beyond technology," said Torres. "The real impact of the single-site catalysts might well be a uniquely synergistic combination of complementary abilities, which include speed-to-market, optimum product design, and manufacturing prediction and control."

Torres suggested that by combining the molecular structure control that has been demonstrated by the metallocene catalysts and the capabilities of kinetic modeling of materials (and products), the new technology will be able to achieve in as little as six days what previously took three years to develop. "The day could come," he said, "when dynamic modeling will allow polymer engineers to fully design and characterize new polymers, and to be more accurate than quality control testing instruments could verify. This ability to predict structure as well as corresponding performance could result in tremendous efficiencies for both commodity and specialty products."

Today, with single-site catalyst technology, Torres continues, an initial design can be completed within minutes, while the optimization process may take a few hours to analyze a number of alternatives and provide additional information such as lowest cost, highest quality, and availability and timing. He adds that once the polymer structure is defined and the properties are reviewed and accepted, the product models cascade up to the process models. With the ability to kinetically predict reactor conditions, the product models can work in conjunction with the process models to set reactor/plant conditions to manufacture the new product quickly.

It is envisioned that the on-line process models will be more accurate than existing quality control tests, thus expediting the scale-up and manufacturing processes. Another by-product of the enhanced molecular architecture capability is that it permits the quick evaluation of a multitude of options, without the need for costly and time-consuming pilot-plant generation of test samples. The combined catalyst and kinetic modeling technologies allow for a "cafeteria" approach to polymer assembly and design, in which, given a set of performance criteria, a polymer chemist can pick and choose molecules to provide the needed product performance. Torres says that the Dow Plastics' molecular simulator, for example, permits the extracting of information from a number of models and predicting the resultant material from a set of molecular options, which ultimately are homogenized and optimized into a final working product.

A jump forward

Many say that the new capabilities represent a basic revolution in polymer science. Others see the metallocene-based technology as another major step in the evolutionary development of the plastics industry, in which a significant jump forward is taken every 20 or 25 years. Key advancements in olefin technology, for example, have been ICI's development of low-density polyethylene (LDPE) in the 1940s; the commercialization of linear low-density polyethylene (LLDPE) and polypropylene in the 1960s; and, currently, the emergence of the metallocene catalysts.

As Douglas M. Selman, Exxon's vice president of Polymers Technology, puts it, polyolefins technology is "proving to be vibrant and far from the end of its life cycle. The new metallocene catalysts are changing the 'rules of the game' for polyolefin manufacturing processes, the polymers produced, and their applications." Selman adds that the symbiotic relationship between advances in metallocene catalyst technology and polymer science creates the ability to meet the demands of plastics fabricators and end users for new polymer properties.

Lively competition

With their narrow molecular weight distribution and controlled comonomer incorporation, the metallocene-catalyzed polymers provide improved properties that should result in increased intermaterial competition between polyolefins and other resins. Application development and the higher-value-in-use that are attainable, compared to the olefins polymerized with the conventional Ziegler-Natta catalyst systems, are expected to stimulate growth.

"Metallocene polyolefins have the potential to increase both the rate of growth and the margins on that growth," said Kenneth E. Jacobson, principal, Charles River Associates, Inc., at the Brussels conference. "Based on currently available information, the metallocene polyolefins will substitute for a significant volume of Ziegler-Natta polyolefins, and will displace PVC and other commodity resins, and engineering resins in selected applications. The net effect will be a stimulus to demand above and beyond the growth anticipated otherwise. We believe an average increase of about 1% per year (above that provided by conventional polyolefins) is a reasonable expectation."

Customer satisfaction

The real basis for the expanding interest in the metallocenes is that, in the final analysis, they are so integral with "ancient" dreams in the plastics industry. Although the industry basically started in a garage or two with some rickety injection molding machines, success always involved meeting customer needs. Today, though there is an exponentially higher degree of sophistication, the same goal is expressed in terms of global competitiveness, total quality control, and speed-to-market. The formula is still the same: Customer satisfaction equals success, and the metallocene catalyst technology inherently works with that age-old formula, whether it involves material supplier, converter, or customer. As Ed Gambrell, vice president of Dow's Business Platform for Insite Technology, comments, "The new technology provides the opportunity to use material science to a greater degree than in the past to optimize material use in specific applications. The offshoot of metallocene catalysis will be a whole new field of material science capability that will result in new approaches and improved economics in many applications."

Higher productivity

Early work on the metallocene catalysts did not yield sufficient activity in polymerizing ethylene to warrant significant investment and commercialization. However, since 1989, the pace in polyolefin development with metallocene catalysts has been accelerating. Following the discovery by Professor Walter Kaminsky (now at the Institute for Technical Micromolecular Chemistry, University of Hamburg, Germany) of the extraordinary activating efficiency of methylaluminoxane (MAO) with simple biscyclopentadienyl metal compounds, Exxon Chemical Co. expanded the range of useful biscyclopentadienyl compounds for ethylene and propylene polymerization. Exxon was the first company to make metallocene catalysts commercially practical. This led to the development of the company's high-pressure Exxpol process utilizing biscyclopentadienyl zirconium, which was commercialized for ethylene polymerization in 1991 for the production of the company's metallocene-based Exact resins. These plastomers use butene or hexene as the comonomer or both of them together to make a terpolymer. Exxon's current metallocene-based capacity is 45 million lbs/yr; applications include packaging, wire and cable, health care, polymer modification, and specialty uses. Exxon says it has produced 40 commercial and developmental resins since the first plant began operating in 1991 in Baton Rouge, La., with each resin designed for a specific application.

After filing their patent in 1989, Dow Plastics developed the constrained geometry monocyclopentadienyl titanium catalyst. This led to the commercial introduction, in 1993, of ethylene-octene copolymers using Dow's Insite technology with the company's solution process. At that time, Dow converted 125 million lbs of existing Dowlex polyethylene capacity that was used for launching the company's metallocene-based materials. Dow is selling its constrained geometry catalyst-produced ethylene polymers as Affinity polyolefin plastomers and Engage polyolefin elastomers, claiming improved processability because of long-chain branching in the molecular structure. Targeted applications include packaging, automotive, medical devices, and wire and cable. This year, Dow announced an additional conversion of 125 million lbs to produce polymers using the metallocene technology. To date, Dow has commercialized 23 Affinity and Engage polymers.

Accelerated growth

Since the initial discovery of ferrocene in 1951, hundreds of complex metallocene molecules have been synthesized and characterized. Interest in the unique catalysts grew only gradually during the next 30 years, however, until Professor Kaminsky's discovery in the late 1970s that methylaluminoxane (MAO) functioned as a highly efficient and dynamic cocatalyst for primary catalysts in ethylene polymerization. The catalytic combination had the effect of unleashing a new powerhouse and awakening the possibilities of great market potential with broader development. Besides Exxon's and Dow's work in catalyst development, significant metallocene catalyst technology has been developed by Chisso, Exxon, and Hoechst for isotactic polypropylene (iPP); by Hoechst and Mitsui Petrochemical for cycloolefin copolymers; by Fina and Mitsui Toatsu for syndiotactic polypropylene (sPP); and by Dow and Idemitsu for syndiotactic polystyrene.

It is of interest to note that Mitsui Petrochemical has been selling Tafmer-brand plastomers for over 15 years, with targeted applications in packaging and polymer modification. The vanadium-catalyzed polymers have many of the same properties of the new metallocene-produced materials, but have been more expensive to make because of much lower catalyst efficiencies. The newer metallocene catalyst technology, however, has greatly accelerated plastomer production.

Exciting new polypropylenes, sPP, and iPP are in development and currently being sampled by customers. Fina, for example, has scaled up its technology to make market development quantities of sPP in its production plant. Exxon and Hoechst also are producing samples of iPP from pilot plants, and customers are evaluating new performance capabilities from these unique polymers. Dow and Idemitsu are sampling syndiotactic polystyrene to customers for specialty molding applications, and Mitsui Petrochemical and Hoechst are selling cycloolefin polymers into engineering thermoplastic applications, such as compact discs. BFGoodrich has also reported development work in this area.

Coming next

The next wave, which will lead us into the twenty-first century, will be the application of metallocene catalysts to commodity polyethylenes, offering improved strength, clarity, and processability. That is the prediction of Bruce Story, intellectual asset manager, Polyolefins & Elastomers R&D, Dow Plastics. Dow, Exxon, and Mobil have announced the scale-up of metallocene catalysts into commercial-scale polyethylene reactors. Mitsui, BP Chemicals, BASF, and Phillips are not far behind. Union Carbide has announced that its soon-to-be-finished Unipol II plant will be metallocene-ready.

The near future should reveal much regarding the capabilities of the metallocene catalysts. In only the last year, there has been much technical development and commercial progress. In 1994, Exxon and Hoechst announced a joint venture to commercialize metallocene-based catalysts for polypropylene; BP Chemicals announced it had developed improved higher productivity condensing gas phase technology; Shell and Himont began their new global joint venture, Montell, Inc., which brings together the resources for polyethylene processes and existing Spheripol polypropylene capacity; and Novacor acquired DuPont's polyethylene capacity and Sclairtech LLDPE technology and later announced it would commercialize a Sclair II version that was metallocene retrofittable.

In February of this year, Exxon announced its patent for supercondensed-mode technology in all gas phase polymerization processes. In April, the company announced the successful gas phase manufacture of mLLDPE (metallocene LLDPE) and a patent that covers polyotefin production with metallocene catalysts in supercondensed and condensed mode polymerization. Exxon already has produced more than 10 million lbs of mLLDPE in the years 1993 to 1995; the mLLDPE is produced in a 200,000 metric ton gas phase plant, which is readily expandable to 400,000 metric tons/yr.

In January, Dow and DuPont announced the intent to form a joint venture in global elastomers to utilize Dow's Insite technology and to build 200 million lbs/yr of EPDM capacity by late 1996; output will include ethylene octene and ethylene propylene elastomers.

Also in January, Mitsui and Ube Industries announced an agreement to produce mLLDPE, using a BP Chemicals gas phase process. The mLLDPE will be retrofitted into existing Ube capacity, and production will begin this year. Also, Idemitsu reconfirmed its intent to proceed with a 10,000 metric tons/yr syndiotactic polystyrene plant in 1996. Additionally, Dow and Idemitsu are jointly developing production, marketing, and commercialization; and Hoechst and Mitsui announced a joint venture to produce 3000 metric tons/yr of cycloolefin copolymers in Japan. Mitsui will service the Asia market, while Hoechst will cover Europe and North America.

Dow's third Insite technology train of 56,000 metric tons/yr is due on-stream at Tarragona, Spain, in early 1996. Others, including BP Chemicals, BASF, Phillips, Mobil, and Novacor, have already proven existing processes and are also capable of providing retrofit capacities.

More mLLDPE resins

Mobil Chemical Co. recently announced that at the company's gas phase reactor facility in Beaumont, Tex., it has successfully produced commercial-scale quantities of a clear, packaging-grade mLLDPE film resin, using patented metallocene catalyst technology. Mobil says that the commercial trials also demonstrated a capability of producing a broad range of LLDPE products previously unavailable from gas phase reactors, and that the new packaging film is as strong as the company's "Super Strength" hexene copolymer grade, with excellent clarity.

The metallocene catalyst technology was scaled up, with high catalyst productivity and with excellent correlation, from pilot plant to a conventional commercial gas phase reactor, with minimal hardware modifications. Compared to a conventional Ziegler-catalyzed hexene copolymer, the new film resins demonstrate narrower molecular weight distribution, lower comonomer content, higher melt elasticity, and a lower melting point. The company adds that despite the metallocene grade's narrower molecular weight distribution, the material's processability appeared to be equivalent to that of a standard Ziegler-catalyzed hexene copolymer, in terms of bubble stability and draw resonance.

Value-creating tool

According to Jonathan E. Trollen, director of product development, James River Corp., the large flexible packaging converter sees the metallocenes as highly effective tools for creating value, allowing versatility in designing films and extrusion-coated materials with high hot tack, low seal initiation temperatures, low static cling, and high seal strength, at high production speeds and product loads. Speaking at the Brussels conference, Trollen said that the materials demonstrate excellent resistance to puncture, tear, and abrasion; clean organoleptics; and relatively high gas permeation rates for oxygen and carbon dioxide, for use in controlled-atmosphere packaging of fresh produce and other foods. He predicted a steady growth of the metallocene catalyst resins in blown and cast films and extrusion-coated materials.

Penetrating new markets

In another area, the advantages of metallocene-produced polyethylene foam have potential in markets normally dominated by conventional neoprene, SBR, EPDM, and PVC/nitrile blends. In the past, conventional catalysts, which resulted in wide molecular weight distributions and nonuniform branch structures, made it difficult to match the physical properties of the traditional cellular rubber materials. The metallocene-catalyzed polyolefin resins, with their narrow molecular weight distributions, uniform comonomer compositions, and tailorability, have now made it possible for the polyethylene foams to penetrate the diverse cellular rubber markets.

Sentinel Products Corp., for example, says it has developed a proprietary crosslinking and foaming process that also enhances the processability of the olefinic materials. Sentinel has grown from about $15 million in sales to $30 million over the last year, largely because of "the overwhelming acceptance of metallocene foams," says chief operating officer Scott C. Smith. Projected sales for fiscal '96 are approximately $50 million, with continued growth to $100 million expected over the next three years. "It is anticipated that the bulk of this growth will come from the sale of metallocene-based materials," Smith says. "With the advent of the metallocene foams, there is tremendous opportunity for new and exciting applications across many market segments. The key to the success of these materials is that they combine the high level of physical properties offered by cellular rubber with the converting ease of polyethylene foams."

Similarly, A. Schulman Inc. sees an even brighter future for polypropylene and other thermoplastics as a result of the metallocene technology. The large compounder has been incorporating the single-site catalyst-based plastomers and elastomers as modifiers in its compounded polyolefin products, and, according to Robert H. Heinold, technical director, significant positive results have been documented. Among the improvements are higher clarity, high-impact grades that do not stress-whiten; combinations of impact strength and stiffness that could not be previously achieved; improved mar- and heat-resistance; stiffer sheet extrusion grades with excellent tear strength; and higher modulus blow-molding grades.

Already commercialized applications include a thermoformed speaker cone part and extruded and die-cut file folders with increased rigidity, which is facilitated by the ability to incorporate higher filler levels in the metallocene-based materials. Other applications under development include three automotive instrument panels, small appliance parts, packaging, and other thermoformed and blow-molded parts.

Cost coming down

The high cost of metallocene catalysts is coming down with the economies of scale, and the decreasing use of high levels of expensive cocatalyst. Extremely high polymerization productivities being achieved with the new catalyst systems also are allowing the manufacturing cost increment due to the catalyst to decrease. Dow's Story predicts, in fact, that the new commodity metallocene-based polyethylenes should become cost-competitive with today's high-performance LLDPEs, while providing superior toughness and optics.

Also, implementation of the developing computer models will allow a much higher production rate of in-specification end-product, compared with that achievable with conventional multisite catalysts. The utilization of processes for new product development, such as Dow's Speed-to-Market and Exxon's Product Innovation Process, makes the new technology available to customers much more quickly than before. The goal of using multifunctional teams, sometimes including a customer's representative, is to speed the conversion of the customer's product performance requirements into a successful new product.

Far-reaching effect

The effects on the plastics industry of the metallocene technology's much faster ability to hit special processing or application targets are expected to be far reaching. "For suppliers," says Kenneth B. Sinclair of SRI International, "it means that the commercial life of existing products could be very short, once they are in the line-of-sight of a metallocene-based competitor. For converters, it means that new resins or higher-performance drop-in replacements could be made available in a matter of weeks There is now a lot more speed available for those converters who have the will to win the race."

For those people charged with running the polymer production plants, Sinclair adds, metallocenes could present significant new challenges. "With the newfound capabilities to develop products so much faster, will the marketing team expect the plant to very significantly accelerate its production cycle? Or will they expect the plant to use the same production cycle but make three or four times as many grades? Both options are practically impossible with current process technologies and illustrate real pressures on the manufacturing infrastructure."

More product grades will require more frequent grade changes, Sinclair continues, leaving the options of either tolerating higher grade-change cost penalties, or of acquiring more production lines and/or more flexible production processes. "Producers who want to take advantage of metallocenes will need to sharpen their techniques to optimize production cycles among their various production lines, and will need to pay greater attention to plant grade-change flexibility. However, it is projected that the development and use of enhanced process control models will provide the needed flexibility so that the production processes can be matched to the accelerated molecular modeling requirements."

The opportunities are there, and widening. Commercialization of metallocene technology is on a fast track. In the final analysis, we can predict a highly creative, science-based competitive era as the plastics industry approaches the twenty-first century.
COPYRIGHT 1995 Society of Plastics Engineers, Inc.
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Title Annotation:use in plastics industry
Author:Wigotsky, Victor
Publication:Plastics Engineering
Date:Jul 1, 1995
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