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The pressure is on for top quality.


Compounding lives! It is more than ever at the heart of the plastics industry's efforts for innovation, quality, and optimum performance and cost.

The pressure continues. Compounding must provide the full range of properties and volumes, from small batch formulations with engineering resins to the dedicated singleproduct, massive volumes typical of many commodity materials. And compounding must do it all better than before.

Machinery manufacturers have scrambled to keep pace. Werner & Pfleiderer, for example, offers twenty twin-screw extruder sizes, ranging from the ZSK 30, with throughputs of 2 to 75 lbs/hr, to the ZSK 380, with a capacity of up to 100,000 lbs/hr. The latter can fill a 10- by 12- by 10-ft room with plastic pellets in about 20 minutes. It is a scale-up of the ZSK 300, a 65,000-lb/hr twin-screw, sixty of which are now in use worldwide. Asmut Kahns, W&P's director of plastics machinery, sees demand growing as more plants go global.


Compounding's traditional boundaries are stretching. W&P cites improved screw and vent design for "macro" devolatization directly in the extruder, thus achieving the polymer/solvent disengagement normally accomplished in the reactor. The potential for simplifying any solution process spans specialty olefins and engineering resins.

Compounding extruders now are often central parts of integrated manufacturing systems. Polypropylene from the reactor, for example, is chemically modified to a narrow specification in a 20,000 lb/hr W&P extruder to provide a constant-viscosity, low-swell, fast-molding resin. A closed-loop system controls the metering of peroxide and maintains consistent viscosity.

In the grafting of silane to linear polyethylene in a sequential process, active grafting sites in the polyethylene initially are achieved by adding peroxide to the melt. The material composition is monitored by on-line infrared spectroscopy, and the degree to which undesirable crosslinking in the polyethylene occurs is monitored by on-line rheometer. The extruder can process the high-viscosity materials, avoid contaminants, and closely control residence time and shear.

In another instance, color monitoring systems based on reflectance measurement work in tandem with continuous color compounding processes. The color meter evaluates plaques molded from material taken off a pellet side stream. If necessary, the feed to the extruder is adjusted to maintain a consistent product color.

Werner & Pfleiderer is continuing development of an axial or radial, hydraulically operated on-line throttle valve, which allows processing of a wider range of materials with one hardware setup. Inserted in the plasticating zone of the extruder, the valve links with the machine's on-line control system and permits adjustment of the material's flow restriction and thus its degree of plastication. The extrudate's properties are regulated without screw changes for different formulations.


Citing the growing application of reactive processing to provide specialty compounded materials, notably alloys and blends. Berstorff Corp. emphasizes that in recent years, knowledge and control of the process have had a more significant influence on product quality and consistency than have any fundamental changes in machine hardware. "Rather than the large dedicated high-volume twin-screw reactive machines of about fifteen years ago," says Dan Pearce, vice-president, compounding, "the machines of today are smaller and much more versatile, permitting rapid changeover for new formulations with the same in-place hardware. But the major advancements derive from greater understanding of process parameters and the ability to manipulate elements such as temperature, screw speeds, degree of mixing, vacuum levels, additive feed positions, and other factors, which, in the aggregate, determine the properties of the end product."

Berstorff offers twin-screw co-rotating intermeshing machines in seventeen sizes, ranging from 25 to 305 mm, with throughputs from 5 to 60,000 lbs/hr. The machines also feature a throttle valve for on-line adjustment of energy input to the polymer without change of screws.


Welding Engineers' counter-rotating non-intermeshing twin-screw compounder design controls shear rate for specific materials with special cylindrical, forward-flighted, or double-reverse-flighted kneading screw sections. Shear and dispersion mixing are regulated by varying the screw length and root diameter; the design is beneficial for blending, alloying, and reaction processing. The non-intermeshing screws, which avoid cumulative tolerance buildups, facilitate L/Ds ranging from 24:1 to 72:1 and long residence times with multiple processing stages, including reaction, devolatilization, and incorporation of additives.

Sales manager Mark A. Steller says some new offerings are special multi-flighted screw sections, and flight interruptions to further enhance mixing. Welding Engineers also is investigating operation of screws at differential speeds.


Farrel's continuous mixers have throughputs ranging from 25 to 75,000 lbs/hr. Rotor shapes, clearances, and L/Ds can be provided for given applications. Longer L/Ds afford more residence time for reactive processing capability. Adjustment of rotor speeds, with tailorability in each zone of the two-stage counter-rotating rotors, provides processing flexibility. Downstream addition, venting capability, and monitoring of temperature and power draw from the motor are provided. With closed-loop control, rotor feed and feed rate are set, and the position of the discharge orifice is checked and moved to preselected locations.


Thomas Sedlack, principal staff engineer, Buss America, Inc., says that the latest improvements in kneader technology relate to use of larger gear boxes to obtain higher speeds and torques. In five models, Buss offers L/Ds ranging from 7:1 to 17:1 and throughputs ranging from 100 to 10,000 lbs/hr. A 17:1 L/D in a kneader is equivalent to a 42:1 L/D in a co-rotating intermeshing twin-screw because the interaction of the flights and pins creates substantial distributive mixing in a comparatively short length.

Sedlack says the company is developing a potential for using the kneader as a single-stage compounder directly connected to a die, in contrast to a conventional discharge extruder. The effect could be reduced equipment cost and improvement in physical properties of the materials because of reduced residence time. At present, this technology will be limited to materials with good melt strength, such as reinforced polymers.


Joseph C. Golba, Jr., Manager of extrusion compounding technology at GE Plastics' plant in Mt. Vernon, Ind., says that although highly developed, compounding still is far from a mature technology. "We have advanced from simply feeding a resin powder to including specially designed mixing sections along the screws. Now we are involved in much more complex mixing processes, which we still do not fully understand, with specific chemistries and precise sequencing of additions along the machine. We also must know more about the kind of mixing that occurs during melting.

"We are combining amorphous and crystalline polymers and must understand how to design the extruder as a chemical reactor. Noryl GTX copolymer, for example, inherently an incompatible mixture of nylon and polyphenylene oxide, would be very difficult to produce in a reactor. A reactive compounding extruder is required. The same is true for materials such as supertough nylon, a combination of nylon and EPDM as impact modifier; or blending of amorphous polycarbonate and crystalline nylon, which also are normally incompatible. Reactive compounding can push the compatibilizing beyond the chemical action to include mixing and achieve the desired blend."

Golba says most of GE's plastics are still produced by basically standard compounding processes, which undergo continuous optimization of screw design to broaden the product range. However, growing emphasis on reactive technology, with the extrusion process designed to accommodate normally incompatible formulations, reflects the importance of blends and alloys. While the new extruders offer excellent productivity, Golba says that a learning process is needed to take fuller advantage of their capabilities. Some objectives are better control of temperature zones, efficient energy inputs to avoid polymer degradation, and production of glass-filled products with less fiber attrition or with longer fibers that approach continuous reinforcement.


The ranks of independent compounders, which exist largely in the U.S., are being depleted. There are only a few in Europe, mainly in England, and there are virtually none in Japan. Growth sometimes can create too great a debt burden, and some compounders just decided to fold. Without national and global sales and distribution channels, it is difficult to establish and service new customers.

Many corporations are concentrating on fewer sources for their material supply. For foreign corporations, the U.S. compounder can provide a domestic foothold; in the last five years, more than a dozen first-line U.S. compounders were absorbed by corporations.

Clifton Fleenor, technical director, Bay Resins, Inc., an independent compounder, says that "the progressive depletion means fewer facilities to deal with new compounds in their initial stages, when protection of the technology is most needed. Also, fewer small-volume sources are available to help keep prices down."

Bay Resins started with one nylon product line with simple additive systems for automotive interiors. Now, sophisticated additives include a variety of elastomers for impact modification, and alloys involve chemically modified polymer combinations that require more attention to stabilization and lubrication choices. Toll compounding is still important, but the emphasis has shifted to more proprietary products. About a year ago, Bay Resins doubled its capacity, expanded its nylon line into other markets, and added acetal, polybutylene terephthalate, polycarbonate, and their blends and alloys to its product portfolio.

Distribution channels have been broadened by not relying solely on sales representatives. Franklin Polymers now provides national distribution, and an internal marketing/sales manager focuses on a broader promotion effort. Customer are encouraged to view Bay Resins as an extension of their own business, with the ability to establish alliances outside the U.S. to further global objectives. Bay Resins sees continued growth through the 1990s.


While Bay Resins is determined to remain independent, another leading compounder, LNP, became a part of a major thermoplastics supplier, ICI Advanced Materials, in 1985. For John E. Theberge, director, Applications Engineering Center, the rationale is clear. He points to LNP's immediate access to ICI's application and process development centers, materials technology, and financial resources. ICI's strengths in interfacial and surface chemistries, and in tribology, and its funding of state-of-the-art compounding equipment, have been instrumental in establishing LNP's ability to market more sophisticated products.

Will LNP become less flexible as it inevitably includes more ICI materials in its proprietary compounds? Customers will still be accommodated with "formulations on demand," Theberge says. "But, without the merger, it would have been difficult for LNP to sustain its growth. New programs presuppose resources that ICI could provide."

LNP's recent addition of twin-screw extruders, kneaders, and thermoplastic pultruders has accelerated production of new composites, for example, a family of statically dissipative, flame-retardant materials, based on polycarbonate resin, with improved ductility for deep draw-down ratios. Stainless-steel-fiber-filled polycarbonates, with colorability that eliminates a secondary coating step, are possible because of the compounding machine's excellent dispersion, and adequate fiber lengths are maintained.

Good wetting of continuous fiber filaments, and maintenance of equivalent fiber and pellet lengths, are the keys to recent development of pultruded, long-fiber-reinforced thermoplastic composites, previously available only with thermosets. The low-shear compounding process can be viewed as an extension of more common high-shear compounding methods. In one case, a large utility company solved a severe corrosion problem in its underground cable-support stanchions by switching from malleable iron to nylon 6/6 long-fiber-reinforced thermoplastic. Substantial cost savings and weight reduction were bonuses.


Since the acquisition of Wilson-Fiberfil, another leading independent compounder, by Akzo in 1986, capital spending has been increased to improve all three North American facilities producing reinforced and specialty thermoplastics and formulating color and additive concentrates. Akzo Engineering Plastics' multimillion dollar capital programs include, says John Lomax, vice president and business director, bulk blending silos, fully automated extrusion lines and resin delivery systems, and computer-aided design and engineering capabilities. The goals are improved response time and product reliability, faster customer entry to market, and lower cost.

Akzo will attempt to evolve in three directions in the 1990s. It will continue the European initiative to acquire independent producers of specialty thermoplastics that will support current competitive strengths in materials for the electrical/electronics industry and for high strength/high impact application. Second, the company wants to establish a polymer/raw materials base in North America, to be built on the foundation of Akzo's strengths in Europe in nylons, polyesters, and thermoplastic polyester elastomers. Third, strategic alliances will be developed overseas with producers of specialty thermoplastics, with intentions of securing positions in U.S. markets, such as automotive transplants.

Akzo's efforts in its targeted markets, Lomax says, will emphasize metal replacement with thermoplastics, using toughening chemistry and long fiber reinforcements, and continuation of blending and alloying. Other compounded-product development programs will continue on internally lubricated formulations to reduce cost; conductive compounds to control static discharge; and flame-retardant materials with non-halogenated additive packages.


Dow plastics plans to improve the reliability and efficiency of its compounding operations both within the company and through its joint ventures. Dow's recently announced joint venture with M.A. Hanna Co. focuses on customer serviceability rather than R&D of new products. The two companies will invest a total of $30 million, which will include construction of an engineering thermoplastics compounding facility. With an initial capacity of 60 million lbs/yr, the plant is scheduled for start-up in mid-1991, primarily for automotive, office equipment, appliance, and medical products.

According to William Donberg, a business director for Dow Plastics, in addition to the company's global activities, more regional facilities are envisioned near the East and West Coasts, depending upon future demand. Dow's manufacturing strengths have typically lent themselves to large-volume production. With Hanna, the company now can respond to small-volume compounding requirements for engineering plastics with short lead times, fast and accurate color matches, and quick sampling capabilities. Donberg says every aspect of the Dow/Hanna facility, from order entry to distribution systems, will be geared toward responsiveness and reliability.


The recently announced alliance of Monsanto Chemical Co. and Vista Chemical Co. to develop styrenic- and polyvinyl chloride (PVC)-based alloys and polyblends relies strongly on advanced compounding technology. The plan is to penetrate the large market area between the commodity materials and the high performance engineering resins by developing new products that will combine Monsanto's styrenics and alloying know-how with Vista's expertise and manufacturing capabilities in PVC.

Vista produces about 850 million lbs/yr of PVC and has a compounding capacity of 350 million lbs/yr, with thirteen lines in four domestic locations. Vista's compounding lines comprise seven continuous mixers, two Banburys, a single-screw extruder, a twin-screw extruder, and two dry blend units for powder compounding. A Buss co-kneader line is being added for use in developing new alloys arising out of the alliance with Monsanto. The co-kneader will provide the temperature control needed for the heat-sensitive PVC components and the flexibility and mixing capability for incorporating additives and fillers. Vista will be the exclusive manufacturer of materials, which will be marketed independently by each company, evolving from the alliance.

The alliance already has produced a new flame-retardant alloy, to be marketed by Monsanto, for business machine housings and consumer electronics. Combining Vista's PVC with ingredients from Monsanto's high-heat acrylonitrilebutadiene-styrene (ABS) family, the material is said to provide inherent color stability without ultraviolet stabilizers and flame-retardant additives, eliminate plate-out and bloom, and offer cost savings over flame-retardant ABS. Heat resistance and processability are similar to those of ABS.


The Du Pont Co. is striving for a competitive advantage in engineering polymers by adding flexibility and responsiveness in compounded products. By 1992, says William H. Hopkins, compounding coordinator, the company plans to be able to respond to a customer request for a specific compound within a week.

Compounds are the fastest growing segment of Du Pont's engineering polymers market. In 1989, the worldwide growth rate for the base engineering polymers was 8%; for compounds, the growth rate was almost 20%. Hopkins asserts that this is a clear indication that the market is moving toward tailored resins for specific uses and away from the all-purpose "workhorse" resins.

Du Pont's goal is to have a global network in place to locally service customer requests with a faster turn-around time. Currently strong in North America, Japan, and Europe, the company is expanding extruding capabilities in the Asia-Pacific region and South America. Du Pont's strategy aims at servicing global customers in the countries where they manufacture products. "We plan not only to have the capability to produce samples of the compounds we develop for our customers, but also to have the capacity on hand to meet commercial requirements right away," Hopkins says.


Hoechst Celanese has promoted consistency in its compounded formulations by centralizing initial product development at its laboratory facility in Summit, N.J. Processing parameters are established and test quantities are produced for the given material at the company's Florence, Ky., small-volume development plant. The Florence facility is geared for quick turnaround to customer requests. A cohesive group keeps short communication lines to achieve product objectives.

In full-scale production, the processing parameters are executed identically at the company's compounding plants in Shelby, N.C., and Bishop, Tex. Standardization of equipment throughout the company's four compounding facilities is an essential part of the program for product uniformity.

Hoechst Celanese's compounding is now performed on single- and twin-screw extruders. John Cirello, materials manager, Engineering Plastics Div., says that to enhance flexibility of material formulating, Hoechst Celanese will progressively convert to twin-screw machines.


As environmental issues become more prominent, recycling and incineration programs place emphasis on special concentrates and put new demands on compounding. Mark Sova, marketing manager at Quantum Chemical Corp.'s USI Div., notes that tracer concentrates, heat stabilizers, and non-heavy metal pigments are currently under investigation.

Although research is in an early stage, tracer concentrates could help identify materials with similar melt properties and could assist in often difficult separation processes. Multiple melt histories with reprocessing will require improved heat stabilizers, including tailored antioxidants. HDPE bottles are prime candidates.

In addition, non-heavy metal pigments must make further inroads into color concentrates to facilitate disposal of waste ash produced by plastics incineration. Blowmolders already are converting, and bag film makers are expected to follow. Sova says the challenge with the synthetic organic pigments is to duplicate shades, provide desired opacity, and maintain costs.


Witco Corp.'s Argus Div. has extended the compounding of heat stabilizers for vinyl materials beyond processing to include enhanced resistance to staining when in contact with urethane. The new two-component, non-cadmium-type stabilizer system, found to give three times the protection of traditional stabilizers used in vinyl auto interiors, prevents staining for up to 21 days at 250[degrees]F. The current test standard is 14 days at 250[degrees]F. The company says that existing products generally have been unable to exceed performance levels of 7 days at 250[degrees]F. The heat stabilizer system is also reported to exhibit low windshield fogging and improved resistance to plate-out.

PHOTO : Werner & Pfleiderer's ZSK twin-screw extruder for engineering plastics features automatic, continuous, color control system.

PHOTO : Berstorff's ZE 130 A twin-screw extruder for high-torque, high-volume compounding includes water-ring pelletizer. Pellets in water slurry are easily handled.

PHOTO : Farrel's CP-45 compact processor mounts continuous mixer above hot-feed extruder on common frame. Extruder pumps mixer's discharge through die.

PHOTO : Buss America's MDK/E 140-mm kneader includes 150-mm discharge extruder, which generates pressure for pumping processed resin through die-face pelletizer.

PHOTO : Welding Engineer's 48:1 L/D, 30-mm reaction compounder, used for the controlled crosslinking of a polyester, includes a downstream vent for devolatization.

PHOTO : During strict quality control procedure, engineer checks temperature of strands of compounded Ultem polyetherimide resin, prior to pelletizing. GE Plastics.
COPYRIGHT 1990 Society of Plastics Engineers, Inc.
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Title Annotation:Compounding
Author:Wigotsky, Victor
Publication:Plastics Engineering
Date:Apr 1, 1990
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