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Fluoropolymers: the new breeds.

Fluoropolymers: The New Breeds

Development trends for specialty grades are being steered by processing requirements, while overall resin quality--and price--are on the rise.

Greater control over morphology, crystallinity levels, molecular-weight distribution and resin quality, which will afford new leverage to tailor processing and performance properties, identifies the dominant thrust for fluoropolymers in the 1990s.

Major fluoropolymer producers say research efforts this decade will focus on new copolymers and alloys for melt-processable and elastomeric families. The development trend points to more specialized grades that take advantage of the resin's inherent combination of temperature and chemical resistance properties for targeted applications.

An overriding forecast by resin producers for the 1990s is a steady, moderate ratcheting upward of fluoropolymer prices. Most executives predict this resin group can expect annual price increases between 5-10% during the first half of this decade.

Reasons cited for the anticipated price hikes include "considerable cost pressures" on raw materials used to produce the resins, including the growing demand for more "ozone-friendly" CFCs. Another factor is a shift away from general-purpose grades and toward more diverse value-added, specialty compounds (especially conductive types), as advances in polymerization technology allow more flexibility in customizing resin properties.

Executives say higher prices also reflect pass-along costs from recent investments in capital equipment for new polymerization lines, which will result in higher resin quality and consistency.

BETTER QUALITY & PROCESSING

Among the most visible areas of improvement for fluoropolymers for the near-term will be a greater focus on resin quality that translates into more consistent processing, broader melt-temperature windows, reduced cycle times and more lot-to-lot consistency in both resins and finished products. Resin producers also are optimistic about prospects for marked improvements in mechanical properties of fluoropolymers, such as toughness, elongation and low-temperature impact strength.

While other properties, such as high-temperature performance, chemical resistance, and lubricity all may see small, incremental changes in the coming years, performance in these is generally viewed as already approaching the practical upper limits for these resins.

One proponent of this view of fluoropolymers' future is James MacLachlan, business planning manager of fluoro-products for Du Pont's Polymer unit. While fluropolymers have demonstrated their advantages in the areas of temperature and chemical resistance, he says, mechanical properties such as creep resistance, stiffness, and toughness are ripe for improvement in the 1990s. Advances in those areas could spur acceptance of fluoropolymers in markets where they were formerly considered too expensive, such as automotive.

NEW MELT-PROCESSABLES

Two new unfilled thermoplastic fluoropolymers, a perfluoroalkoxy (PFA) and a novel MFA type, will be commercially introduced to the U.S. in the first half of this year by Ausimont, according to Richard G. Fransen, product manager for melt processables. The resins, to be sold under the name Hyflon, are produced by Montefluos, an Ausimont affiliate based in Milan, Italy. Fransen expects the new resins to find specialty niches in components for harsh chemical/fuel environments. Both materials will come in extrusion and injection molding grades. Hyflon PFA also will be offered as a powder grade for rotomolding, and Hyflon MFA in a dispersion grade.

Hyflon PFA will be comparably priced to Du Pont's Teflon PFA line, and will offer similar chemical and temperature resistance (up to about 480 F), according to Fransen. Hyflon MFA (Ausimont declines to identify the acronym), believed to be an entirely new fluoropolymer, offers enhanced flow characteristics compared with PFA, with an in-service temperature range that falls between PFA and FEP. Pricing is not yet established for the MFA resin.

The two new resins have been undergoing evaluations by U.S. processors for several months. According to Fransen, Ausimont can tailor the molecular weight and crystallinity levels of the resins in order to match customer specifications for processing and end-use properties.

Improved processability and resistance to stress cracking are key claims made for two new grades of Neoflon EPA from Daikin Chemical of Japan. George Lin, technical manager, says Neoflon EPA SP-100 and SP-120 are copolymers of tetrafluoroethylene (TFE) and hexafluoropropylene, supplied in pellet form for extrusion and injection molding. Shinichiro Kai, technical v.p., says the two new grades are suitable for high-speed, repetitive-motion applications.

Neoflon EPA SP-100 has a low molecular weight and melt-flow rate of 20-30 g/10 min, which makes it suitable to making thin parts and wire coatings. Daikin says the resin has a service-temperature range from -328 F to +392 F, and offers crack resistance approaching PFA-type materials. The material, which is inherently non-flammable, has a specific gravity of 2.12-2.17, melting point of 509-527 F, Shore hardness of D55, and ultimate elongation of 330%.

Daikin also is introducing a SP-120 grade of Neoflon EPA, which has a higher molecular weight and melt-flow rate of 6.9 g/10 min, melting point of 509 F, and an elongation of 312%.

Longer-term developments in the melt-processable fluoropolymer field are on tap for the Fluoropolymer Div. of ICI Advanced Materials, according to Gregory S. O'Brien, technical development supervisor. One area is the new development of ICI's own line of fluorinated ethylene propylene (FEP), a type currently produced by Du Pont, which may be introduced next year.

HIGH-CLARITY AMORPHOUS GRADES

Du Pont continues development of its new Teflon AF line, two high-clarity, fully amorphous fluoropolymer grades, which were first previewed at the K'89 show in Germany (see PT, Jan. '90, p. 109). Teflon AF 1600 and 2400 are said to combine good chemical resistance with optical clarity of greater than 95%, refractive index between 1.29 and 1.31, and dielectric constant of 1.89-1.93.

Teflon AF 1600 has a glass-transition temperature of 320 F, ultimate elongation of 20.5%, tensile strength of 3915 psi, and specific gravity of 1.78. Typical molding temperatures range from 464 to 527 F. Teflon AF 2400 has a Tg of 464 F, ultimate elongation of 6.1%, tensile strength of 3567 psi, and specific gravity of 1.67. Typical molding temperatures are 644-680 F.

Both grades are supplied as a white powder. They're still in the test evaluation phase at processors, and test sample packages of 25 g are available for around $500.

Another new high-clarity, amorphous fluoropolymer, known as Cytop, is being test marketed in the U.S. by Asahi Glass of Japan. Cytop has an optical clarity of 95%, refractive index of 1.34, Tg of 226 F, ultimate elongation of 150%, and dielectric constant of 2.1-2.2; it reportedly is not degraded by uv light.

Shunichi Samejima, director of chemicals research and business development, says Cytop and Teflon AF are based on different proprietary monomer sources and formulations. He declined to give a price range for Cytop.

ADVANCES IN PVDF

The most recent material technology advance in Atochem North America's Kynar polyvinylidene fluoride (PVDF) line is its copolymer "flex" series, composed of PVDF monomer reacted with hexafluoropropylene (HFP), which alters the resin's molecular weight and crystallinity. David A. Seiler, marketing manager, says this development represents a trend for Atochem as well as other producers of melt-processable fluoropolymers, using copolymerization to formulate tougher, more flexible, lower-molecular-weight grades with modified levels of crystallinity.

The HFP in the Kynar copolymer serves as an impact modifier at a 20% level of modification; over 20% would result in an elastomer, according to Seiler. By varying the copolymer's molecular weight and crystallinity, it is possible to obtain advantages over homopolymer Kynar PVDF, such as up to tenfold improved impact strength at room temperature; useful impact and mechanical properties down to -60 F and possibly -80 F (compared with -40 F for homopolymer); elongation of 300-500% (vs. 50-250%); improved resistance to stress cracking; and enhanced alkaline chemical resistance.

Achieving improvements in the low-temperature physical properties in the Kynar copolymer would moderately compromise the heat-deflection characteristics, yielding service-temperature range up to 275 F for copolymer, vs. 300 F for homopolymer. However, Seiler points out these properties can be tailored and balanced to meet specific applications through polymerization technology. He also notes the copolymer has the necessary properties for rotomolding, such as a high melt-flow rate of 65-80 g/10 min.

According to Seiler, development work on PVDF in the 1990s will focus on improvements in mechanical properties in the low-temperature range. He believes prospects for cost-effective improvements on the high-temperature end have been virtually exhausted.

New ultra-high-purity grades of PVDF with improved processability are the prime R&D thrust for Solvay Polymers (formerly Soltex). Enhanced properties in Solef PVDF result from a proprietary, modified suspension polymerization method.

A new grade of Solef, currently identified as 21508-0003, is now being evaluated by processors for extrusion applications. The grade was initially designed for fiber-optic plenum cables. It offers improved elongation and flexibility compared with previous Solef materials, and has a flexural modulus of 55,000 psi.

Processability of this new grade is said to be improved, as Solvay has widened its processing window to 380-450 F. By reducing the lower end of the processing range, emission of corrosive hydrogen fluoride off-gasses is reduced significantly, minimizing harmful effects on production equipment and tooling, according to the company.

Solvay says the processability of the new PVDF grade will be similar to polyethylene, while retaining the properties of a fluoropolymer. The semi-crystalline material has a specific gravity of 1.78 and continuous-use temperature range of -20 to +257 F. For plenum-cable applications, the new grade is UL 910 rated at 257 F for thermal stability.

The commercial supply picture for PVDF was complicated in recent months by the merger of Atochem with the former Pennwalt Corp. and Federal Trade Commission concerns that this reduced competition in the material. The FTC recently approved the sale of Atochem's Kynar plant in Thorofare, N.J., to Ausimont USA (see PT, Oct. '90, p. 93). Prior to this acquisition, Ausimont did not have PVDF in its fluoropolymer portfolio. Atochem continues to produce and market Kynar PVDF from plants in Calvert City, Ky., and in France. (Atochem markets PVDF in Europe under the name Foraflon.) As a result, there will be a transition period during which both Ausimont and Atochem will market resin under the Kynar name. Ausimont says it eventually will change the name of its acquired PVDF line to Hylar.

The acquisition of a PVDF line, as well as the new Hyflon polymers noted above, reflect Ausimont's strategy to expand its thermoplastic fluoropolymer offerings. The company may also unveil new additions to its Halon ETFE line before year's end.

PROGRESS IN CONDUCTIVITY

ICI's O'Brien explains the growing trend in end-user requirements toward a more narrow, precise range of surface resistivity in fluoropolymer components makes it crucial for material suppliers to improve their resin quality and compounding operations. He says ICI has made major investments to upgrade its fluoropolymer compounding plant in Thorndale, Pa., installing statistical process control and testing equipment to better monitor such things as molecular weight, crystallinity, morphology and resin quality.

Antistatic and conductance properties combined with enhanced processability marks the development of Du Pont's new Teflon C PFA-type fluoropolymer line (see PT, Jan. '91, p. 13). Du Pont executives say this means that processors no longer have to choose between the processability of unfilled fluoropolymers and the antistatic performance of carbon-filled resins. Through a proprietary polymer formulation, choice of carbon filler and precise morphology control, Teflon C with a filler loading of up to 30% reportedly offers flow rates and processing characteristics similar to unfilled PFA. It's priced around $35/lb tl. Du Pont says Teflon C is the first in a series of new antistatic fluoropolymers with enhanced processing characteristics.

CADMIUM-FREE COLORS

Another key development area for ICI is a new line of cadmium-free color concentrates for its various fluoropolymer lines, expected to be commercialized later this year. These new cadmium-free colorants are being developed in response to tighter industry and environmental standards controlling toxic materials.

Len Harvey, ICI fluoropolymer specialties R&D group leader, says the major challenge is to find non-cadmium red, yellow and orange pigments that can withstand fluoropolymer processing temperatures and maintain their brightness in demanding end uses. Greater options in thermally stable cadmium replacements exist for partially fluorinated resins, which process below 650 F. Fully fluorinated resins, such as FEP or PFA, which process above 700 F, present fewer cadmium replacement options, he says.

|THERMOPLASTIC-LIKE' PTFE

Major developments in the mature realm of PTFE include the unique processing characteristics of new Hostaflon TFM from Hoechst Celanese Corp., which was previewed at K'89. (see PT June '90, p. 87; Jan. '90, p. 109), and has been test sampled by U.S. processors in recent months. Due to its proprietary formulation, preforms of Hostaflon TFM can be blow molded, and skived film can be thermoformed. Such thermoplastic-like processing capabilities are believed to represent breakthroughs for PTFE, traditionally processed by compression molding, ram extrusion, and sintering techniques analogous to powder metallurgy.

According to a technical article by W. Michel of Hoechst AG (published in Kunststoffe, Vol. 79, October 1989), melt rheology of Hostaflon TFM is modified for thermoplastic-like processing by "building in perfluoralkoxy side groups into the linear macromolecular chain of tetrafluoroethylene prepared by suspension polymerization. The modification of PTFE with a comonomer perfluoropropyl vinyl ether (PPVE) has been found useful." Machined or isostatically prepared Hostaflon TFM hollow preforms have been blown into bottles, beakers or cylinders in a heated mold using gas pressure.

The article goes on to say that low levels (0.1%) of PPVE result in a modified PTFE with special processing properties. Despite this modification, the PTFE retains virtually all its inherent physical, chemical, flame-resistance and thermal properties, including a continuous-use temperature range of -200 F to +500 F. The material also retains its full capability to be welded without additives.

The only adverse effect noted by Michel is "an appreciable increase in deformation under load." However, a Hoechst Celanese spokesman points out the deformation under load for Hostaflon TFM is still equal to a 25% glass-filled PTFE.

The company spokesman says Hostaflon TFM is "premium-priced" in comparison with standard PTFE. It's offered in two free-flow grades (TFM 1500 and 1600) and a 400-micron pelletized version (TFM 1700), as well as specialty compounds.

As it ramps up to fully commercialize the material in the U.S., the company recently made two strategic moves to support the effort. First, Hoechst AG will double production capacity for all Hostaflon PTFE this year to 17 million lb/yr at Gendorf, Germany. Second, Hoechst Celanese in December acquired Custom Compounding Inc., Aston, Pa., a leading PTFE compounder, which will henceforth operate as an independent subsidiary. The acquisition supports recent statements by Hoechst Celanese executives that the firm intends to become a more significant factor in the U.S. fluoropolymer market.

As noted above for melt-processable flouropolymer concentrates, selecting cadmium-free pigments for the Fluorocomp line of filled PTFE compounds is an important effort for ICI Advanced Materials. A new line of seven cadmium-free colors (green, yellow, brown, red, blue, orange and black), was announced late last year. They're designed to meet industry and environmental standards, and to address processor concerns regarding disposal of scrap. The new cadmium-free pigments also will be less expensive than their predecessors, says ICI's Len Harvey.

Other PTFE-related development programs at ICI include research on new fillers; improving elongation and toughness properties; achieving better control over particle size to enhance the free-flow aspects of the resin and reduce polymer/filler separation; and testing recycled grades of material.

NOVEL TP FLUOROELASTOMERS

True melt-processable thermoplastic elastomers are among the latest materials innovations in the fluoroelastomer field. Daikin recently initiated U.S. test marketing of two grades of Dai-el thermoplastic fluoroelastomers, consisting of a TP fluoropolymer hard segment that is bonded to a fluororubber soft segment. Available as translucent pellets, they're designed for extrusion, injection or compression molding. Though thermoplastic, they also can be cured through peroxide, polyol or radiation methods. The company also is developing dispersion grades for coatings.

Both grades are composed of a TFE-VDF-hexafluoropropylene (HFP) soft segment. The T-530 grade has hard-segment end groups made up of TFE-ethylene-HFP, while T-630 has VDF end groups. The Dai-el grades will be priced between $30 and $40/lb tl.

Dai-el T-530 has a melting point of 428 F, elongation of 650%, and compression set (24 hr @ 122 F) of 11%. T-630's melting point is 320 F, elongation 1000%, and compression set 80%. Both have a specific gravity of 1.89.

Meanwhile, 3M is continuing development of a fluorinated TPE alloy. Research on the proprietary, unnamed material was first unveiled by 3M last year (see PT, June '90, p. 87). It's composed of an unnamed 3M fluoroelastomer as the continuous phase and an unidentified nylon as the dispersed phase. 3M previously reported that the elastomer will have a continuous-use temperature range of -60 F to +365 F, 76 Shore A hardness, ultimate elongation of 260%, 1770 psi tensile strength, and a 35% compression set at 350 F. According to 3M, the elastomer can be processed as a thermoplastic, including the ability to recycle scrap. However, processors would have the option of radiation crosslinking finished components. Officials at 3M decline further comment on the material or on a target date for commercial introduction.

NEW THERMOSET ELASTOMERS

This year, two new specialty grades will expand Du Pont's Viton fluoroelastomer line, reflecting the company's two-year development effort to tailor its fluoropolymer lines through direct customer feedback, according to Mark Baunchalk, sales manager for Viton. In revising its fluoroelastomer technology during the last two years, Du Pont focused on improved rheological properties, along with faster cure rates, better mold release and reduced mold fouling or plate-out.

"We've been working with processors to fine-tune our resins," Baunchalk says. "We've attempted to demonstrate the benefits of some of our newer technologies, and we've targeted it from an overall savings standpoint for the processor. With our newer generations of Viton, molders should see their yields go up, with shorter cure cycles and reduced scrap rates." He adds that improvement in rheological properties will translate into fewer rejects from conditions such as flash.

The two new Viton grades are formulated for automotive applications. These extensions of the Viton GF line are peroxide-curable resins formulated to offer enhanced resistance to the changing mixtures of automotive fuels. Both have service temperatures within the normal Viton range of -40 to +400 F.

Viton GLT provides improved mechanical performance (compression set, tensile strength, flexibility and elongation) on the low end of the service-temperature scale, while Viton GFLT is designed for superior fluid resistance. The new grades are designed for extrusion, transfer molding, rubber injection molding, compression molding and calendering.

A trend for fluoroelastomers in the 1990s, according to Baunchalk, will be a more widespread commercial offering of precompounded or precatalyzed elastomers, with peroxide curing agents replacing other traditional curatives such as bisphenol types. It's belived that peroxide cure confers improved chemical resistance on fluoroelastomers, which is all the more necessary to resist the newer automotive fuels.

Executives at Ausimont concur on the trend to expand the number of peroxide-curable fluoroelastomer offerings. A new introduction for Ausimont in this arena is Tecnoflon PX-419, a material with a 70% fluorine content that is now in its final test development phase.

Angela Shand, product manager for Tecnoflon, says the new PX-419 grade represents a processing advance in rubber injection molding. She says PX419 has the correct molecular-weight distribution for this process, which often poses difficulties for peroxide-curable fluoropolymers. This reportedly allows processors to take advantage of injection molding's faster cycle times, compared with compression molding.

Properties for PX-419 after press cure and oven post-cure (24 hr @ 482 F) include a tensile strength of 2800 psi, elongation of 210%, and 72 Shore A.

PHOTO : More specialized fluoropolymer grades targeting a variety of applications that demand both chemical resistance and thermal stability will be seen in the 1990s.

PHOTO : Improvements in fluoropolymer quality will result in more consistent processing characteristics, allowing processors to boost productivity without damaging the resin's engineered properties.

PHOTO : Formulating cadmium-free color concentrates and PTFE compounds is a key effort of ICI Advanced Materials. Pictured is ICI's laboratory wire-coating line using Fluoromelt FEP color concentrate.

PHOTO : Processors are expected to benefit from higher-quality fluoropolymer resins, the result of new polymerization capacity and technology, which offers greater control over morphology and crystallinity levels.

PHOTO : A new advance in PTFE processing is Hostaflon TFM from Hoechst Celanese, which allows machined, hollow preforms to be blow molded, while retaining traditional physical, barrier and temperature properties.

PHOTO : Besides blow molding, the "thermoplastic-like" processing characteristics of Hoechst's Hostaflon TFM includes the thermoforming of skived PTFE sheets.
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Title Annotation:includes related article
Author:Gabriele, Michael C.
Publication:Plastics Technology
Date:Mar 1, 1991
Words:3410
Previous Article:Advanced composites.
Next Article:Metal powder injection: taming a tricky process.
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