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Additives.

Additives have long been the unsung heroes of the plastics industry, consistently dedicated workhorses that receive little of the glory. Now, with specifications getting tougher and pockets getting tighter, additives are often the only resource when an acclaimed polymer must look good, whether in processing equipment or in a design functioning under demanding conditions. In their many enhancing forms, additives must take up much of the slack between an end-product's requirements and a plastic resin's performance limits.

Big business

Combining the U.S., Canada, Western Europe, and Japan, the chemical additives business reached $9.2 billion in 1991, according to Carolyn Reilly, project manager, Phillip Townsend Associates, Inc., a leading business consulting firm. Western Europe consumed the greatest volume of plastic additives in 1991, using 41% of the total 9 billion lbs, followed by the U.S. and Canada with 32% and Japan with 27%. Western Europe also accounted for nearly half of the world consumption of processing aids. Reilly says that polyvinyl chloride (PVC) is by far the largest user of additives, accounting for 60% of the total pounds and 50% of the total dollars in the U.S. in 1991. If plasticizers are excluded, the leading class of additives in the U.S. are the property extenders, accounting for 57% of the dollars and 51% of the volume of additives that year.

Tougher markets

Plastics now must provide their range of durable properties and high appearance standards in demanding environments for longer time periods. Arthur Dellheim, president of Adell Plastics, Inc., a custom compounder, says that with the market for plastic resins shifting to more engineered end-uses, additives are critical tools for satisfying customer needs, whether as improved processing aids, pigments, fillers, reinforcing agents, stabilizers, or compatibilizers.

Polypropylene, for instance, is on the threshold of increasing engineering applications. But not without the help of modern additives. Consider, for example, a polypropylene resin intended for new, highly functional, aesthetic, and economical plastic outdoor furniture. Dellheim reminds us that without the hindered amine light stabilizers (HALS), the plastic furniture would degrade before long, and never get the chance to demonstrate its appearance and durability.

In medical applications, barium sulfate as a filler has opened many uses for plastic parts that must be opaque to X-rays. Depending on the resin, loadings of 15% to 25% (and in some cases up to 60%) of the X-ray-detectable additive are incorporated into the plastic. As body implants or in other surgical applications, such parts then can be observed in-situ to ensure precision positioning and functionality.

Sink marks and other surface irregularities can be the bane of a custom compounder's existence; that is, if he doesn't enlist chemical blowing agents to help eliminate them. Dellheim adds that inorganic fillers and high-purity fatty acids (both saturated and unsaturated) make possible the widespread use of polyethylene film for garment bags, grocery sacks, and agricultural film.

Since compounding is typically a post-reactor function, the custom compounder will frequently ensure end-product success by his expertise in integrating a variety of additives, often with positive synergistic effects. Dellheim says, for example, that recent developments include additives to control the rheology of polypropylene and the production of effective compatibilizing agents.

Plastics in agriculture

Many probably do not realize the extent to which our food chain is dependent upon plastic additives. Victor J. Mimeault, vice president, technical, Ampacet Corp., believes that although double-digit growth is projected at least through the next three to five years, end-users may often be unaware of the contributions of additives to product success. "One area where additives play a significant role," Mimeault says, "is in films for agriculture where multifunctional packages that enhance crop yields are incorporated. Uses include greenhouse, silage, and mulch films for hot, arid climates of Europe, the Mideast, North Africa, and North and South America."

Where the cultivation of roses is a viable commercial business, largely because of the plastic film used to make greenhouses, an antifog additive (to prevent water droplets from forming on the inside of the film), an infrared absorber (to keep the soil warm during cool nights), and an ultraviolet (UV) stabilizer package (to protect the film) make the system work. The choice of the UV package is critical, since some pesticides may interact with HALS. Ampacet's 10303 UV PEMB was developed for such applications.

Corn cultivation in arid regions is another demonstration of the critical role of additives. Mulch film used for corn must be adequately stabilized to last between germination and harvesting. Here, Ampacet's 10407 and/or 10561 HALS products are used at levels of 2000 to 3000 ppm.

"Tunnel" film (micro greenhouse) for watermelons incorporates both antifog and IR barrier additives, such as Ampacet's product 100218 IR Barrier MB. The IR barrier keeps the soil warm enough to prevent crop failure when night temperatures drop below freezing.

For most general-purpose film applications, such as trash, carry-out, and merchandise bags, antioxidants in the final product, at levels of 250 to 1000 ppm, typically benefit the converter and usually have no role in the end-product performance. However, as Mimeault says, cast or blown film for geotextile applications such as pond and landfill liners, and fabrics to stabilize pavement, must be guaranteed to last 10 to 20 years. Small-particle-size carbon black, added for long-term performance, may interact with the antioxidants if they are not carefully selected. Also, since the film must be edge-sealed, which is usually done with hot-melt adhesives, the choice of antioxidant is critical in order to avoid extraction by the adhesive. A weak spot in the seal could cause premature failure of the liner. Ampacet's products 190191 and 19717 contain a small-particle-size carbon black and different antioxidant packages for reliability in geotextile applications.

A series of slip and antiblock additives, and their combinations, and process aids containing fluoropolymers (typified by Ampacet products 10562, 10720, and 10919 with different levels and types of fluoropolymers) have an affinity for the metal of the extruder. The resulting coating reduces the "slip-stick" mechanism of polymer flow through the die, offering basic advantages to the film producer.

Aids to dispersion

BASF Performance Chemicals' Luwax product line, comprising both polyethylene and copolymer waxes, may be added to many resin systems, including polystyrene, PVC, and polyamide. The waxes improve color dispersion and color intensification with difficult-to-disperse pigments, even with pigment contents of 50% or more, and impart lubrication, gloss, and protection to products in more than 30 industries. For difficult-to-disperse pigments, especially carbon black, the high polarity of Luwax EVA 1 granule and Luwax EVA 2 powder enables them to wet pigments more effectively and thus promote the breakdown of agglomerates.

A new booklet on color masterbatches and concentrates for plastics, entitled Luwax Polyethylene and Montan Waxes, is available from BASF Performance Chemicals. The publication covers wax choices, dispersion processes, levels of addition for wax types in masterbatches, and production methods. Included are batch and continuous single-stage and continuous two-stage processes, utilizing batch kneaders, twin-screw extruders, planetary mixers, high-speed stirrers, and other equipment.

"Gatekeepers"

For John Theberge, president, Materials Development Corp. (and a consultant to Bay Resins, Inc.), additives are the "gatekeepers" that determine the amount of added value that can accrue to a particular plastic family. It would be difficult to imagine the development of PVC resin without the proper heat stabilization packages, or the extent to which polybutylene terephthalate (PBT) and polyphenylene sulfide (PPS) resins would have developed without the aid of fillers and reinforcements.

Processors and designers requiring increased thermal stability, melt flow enhancements, improved surface appearance, increased wettability, better compatibility of alloys and blends, and favorable environmental effects look more and more to additives to help meet their specifications.

Areas that beg for attention, Theberge says, are developments of new organic antistatic additives that would eliminate dust collection or potential explosion hazards in certain environments; improved nonhalogenated flame-retardant additives with nonvolatility, greater thermal stability, better arc tracking resistance, improved comparative tracking index, and lower smoke generation, and which would not be dependent on moisture for activation; thermal stabilizers for processing of higher temperature engineering resins; organic blowing agents for high-temperature processing and greater evolution of gas per unit weight; and chemical coupling agents that would withstand thermoplastic processing temperatures in the 600 |degrees~ F to 750 |degrees~ F range.

An additional area of opportunity is in additives that can react chemically with specific thermoplastic resins, to allow reactive processing of flame retardants, internal lubricants, colorants, and chemically coupled fillers. The additional chemical reactivity could mitigate some of the problems encountered with volatility (gassing), incompatibility (formation of two-phase structures), separation of colorants, and poor mechanical properties.

Many additives are primarily used, except where enhancement of tensile strength and modulus is desired, to satisfy functional surface phenomena requirements, whether mechanical, tribological, electrical, or environmental. Theberge believes that the development of additives with the preferred geometry, chemistry, and rheology to allow for concentrated activity at the surface of the molded part, either during the molding process or by migration to the surface after molding, should be an area of research activity.

Expanded turf

Originally developed over 25 years ago as an optical brightener for polyester fibers, Eastman Chemical Co.'s Eastobrite OB-1 has recently begun to be used in varied processes with ABS, EVA, nylon, PET, PP, and polystyrene, and the company has petitioned the U.S. Food and Drug Administration for food contact approval for the additive. Existing applications, in white and natural colors, include kitchen countertop appliances, golf ball covers, and tennis-shoe soles. Eastman Chemical says the additive, used to reduce yellowing, improve whiteness, and enhance the brightness of a product, shows no observable weight loss below 375 |degrees~ C, thus permitting its use in high-melting-point plastics.

Additive interactions

Plastics in automobiles are expected to last ten years, often under extreme heat and sunlight conditions; as a result, suppliers must cope with the interaction between pigments used for critical color matches and UV stabilizer systems. Ferro's Bedford Chemical Division says that its UV-Chek AM-340, most commonly used as a synergist in polyolefins with HALS, boosts the performance of the stabilizer package. Weathering specifications that cannot be met by HALS alone are being successfully satisfied after the addition of the UV-Chek AM-340 synergist to stabilize both the polymer and the pigments.

If improperly stabilized, black and then painted thermoplastic olefins and polypropylene bumpers can, if too high a loading is used, lose properties through possible migration of HALS to the surface. The UV-Chek AM-340, as partial HALS replacement, enhances the performance without interfering with the paint.

Pond liners and other geomembranes are subjected to constant moisture and must be protected against micro-organisms present in the ground where they are installed. Ferro Micro-Chek antimicrobial's nonleachability prevents the antimicrobial ingredient from leaving the polymer system as a result of constant contact with water, thus both protecting the polymer and preventing the active antimicrobial ingredient from being released into the environment.

Without CFCS

With ozone-depleting chemicals under siege, notably in the wake of the 1987 Montreal Protocol for progressive elimination of chlorofluorocarbons (CFCs), mold release agents using the materials as propellants face increasing environmental pressure. Under the U.S. Clean Air Act, as a spur to industry to shift away from their use, CFCs are being taxed at $2.65/lb in 1993, up 58% from last year. Taxes on 1,1,1, trichloromethane rose 22%. Even though propellants for mold release agents are currently exempted under the Clean Air Act, this special treatment is not expected to continue indefinitely.

One alternative, the Actilease System from George Mann & Co., eliminates the need for solvents and carriers through use of compressed air and a series of specially designed nozzles that create a fine aerosol cloud of 100% active mold release compound in an enclosed chamber. Available in a number of silicone- and wax-based formulations, the compounds are designed to release nitrile, chlorinated polyethylene, natural neoprene, urethane, and silicone elastomers from mandrels and molds. The company says that in field tests, using both rigid and flexible hose mandrels, more than 90% of the Actilease release agent was effectively deposited, with virtually all the overspray being recirculated. In comparison, the company says, conventional spray application of release agents typically achieves utilizations of 10% to 30%, with the remainder being lost through overspray to the atmosphere or ventilation system filters.

In addition to improved control of deposition levels of release lubricant, the company says, reductions in utilization costs are substantial. One user, Kryptonics, Inc., a co-developer of the system and a major manufacturer of cast urethane wheels for in-line roller skates, reports that prior to using the new technology the company consumed 40 gallons per week of CFC-propelled release agents. Since the switch to the compressed air system, mold release consumption has dropped to less than 5 gallons per month, with monthly expenditures for release agents reduced by 75%, and virtual elimination of surface-finish rejects related to mold release.

Making magic

"A fraction of a percent of additives in polypropylene can work magic," says Robert H. Heinold, technical director, A. Schulman, Inc. "Under a car hood, in UL appliances, or in outdoor applications, all requiring long-term heat-aging properties, the unstabilized polymer would be essentially useless. The additives ensure ten-year-plus durability; without the inhibitors the same material would rapidly degrade under Florida and Arizona conditions."

Heinold adds that coupling agents help provide glass-reinforced polypropylene with creep resistance, allowing stressed parts to function for years under severe conditions, rather than failing within hours; antistatic additives prevent buildups of electrostatic charges, preventing papers in plastic files from sticking to the folders; flame retardants and smoke suppressants can change a material that normally burns like a candle to one that self-extinguishes after being set on fire; and optical clarifiers reduce haze and thereby make a material suitable for packaging films. The broad array of colors available with pigment additives; special additives that achieve a metallic look and glow-in-the-dark effects; blush-control additives that eliminate stress whitening of high-impact-resistant polypropylene, allowing use of the material where white spots cannot be tolerated; and additives that improve the mar resistance of softer grades of polypropylene, permitting replacement of more expensive, scratch-resistant polymers, all add to the wide range of versatility available to processors and designers.

Material substitution

Additives not only play major roles in the enhancement of specific resins, they also can be the avenue for efficient material substitution, such as the replacement of glass/mineral nylon with chemically coupled polypropylene. Thermofil, Inc.'s Jeff Neupauer, vice president, sales and marketing, contends that chemically coupled, glass-reinforced polypropylene provides the "highest tensile strength per unit cost of any engineering thermoplastic." In automotive applications, including a radiator support bracket and an under-the-dash cover for a fuse block, glass fiber/mineral-filled nylon was replaced by a chemically coupled polypropylene. The fiber/mineral addition to chemically coupled polypropylene allowed customers to use existing tools, since the compound mirrored the nylon's shrink rates.

Neupauer adds that ease of processing was improved, allowing for reduced heat profiles and cycle time reductions, and, in addition to part weight reduction, cost per cubic inch was reduced 20% to 40%. In another application, an appliance timer cam, a glass-filled, chemically coupled polypropylene, in combination with a flame-retardant additive, replaced a glass-filled PBT material.

Partnering for efficiency

Continuing efforts to downsize company workforces present a unique opportunity for the innovative additive supplier to partner with customers in developing solutions to meet special needs, says Uniroyal Chemical Co., Inc. The partnership trend is common whether an additive is used as an antioxidant, chemical blowing agent, or lubricant or to meet other processing or functional requirements. Alternative physical forms such as free flow, low or nondusting products, liquids, blends, and masterbatches represent some typical methods of meeting today's manufacturing requirements.

Uniroyal Chemical also cites the plastics processor's need for improved or different properties derived, for example, from lower-volatility additives in polyurethane foam; activated blowing agents for lower temperature paint ovens; and antioxidants for broadening requirements in wire and cable.

Another developing trend relates to additives packaging. Safety, environmental acceptability, and loading/feeding flexibility are now gaining more importance, together with cost and performance. Suppliers and customers increasingly work together to develop innovative packaging to reduce costs, waste, and operator exposure to chemicals, and to make additive incorporation more efficient. Direct liquid feeding from tote bin to extruder, for example, reduces operator exposure to chemicals or dust. Uniroyal Chemical packages additives in 1000- to 2000-lb bags made of a woven polypropylene fabric with a polyethylene liner. Only the liner is discarded, and the empty sacks minimize shipping cost and space when returned to the plant. The company's Naugard 76 is supplied in a 25-lb consumable polystyrene bag, which is compatible with the customer's polystyrene, thus allowing it to be added directly to the reaction, and eliminating packaging waste entirely.

Without lead

High performance and comparatively low-cost lead-based heat stabilizer compounds, the material of choice for many years, attract increasing environmental concerns. Wire coaters and PVC compounders are now able to supply primary insulation and jacketing stabilized with non-lead additives.

Witco Corp.'s Polymer Additives Group has developed a series of Mark barium zinc powder heat stabilizers for compounds that meet UL standards and provide the necessary performance. Witco says that the barium zinc products have much lower specific gravities than lead-based stabilizers, which narrows the cost-competitive gap on a pound/volume basis.

The new Mark 6736 stabilizer possesses enhanced electrical properties and joins Mark 6731, the first product developed in the series. Another powder type, Mark 6735, offers improved color control under heat processing and long-term temperature conditions, notably for jacketing applications. A third product, TS-153, is a lower lubricating version of the Mark 6736 stabilizer and provides processing characteristics more closely resembling lead types. The difference in lubricity allows faster development of physical properties during extrusion, with the potential for higher output rates. Witco has also developed Mark 4716, a general-purpose barium zinc liquid stabilizer, which offers an alternative to powders. It is best suited for vinyl jacketing where premium electrical properties are not critical.

New heat stabilizer systems are also helping manufacturers of continuous vinyl flooring to meet changing printability requirements for their topcoats. The UV-cured, water-based inks that are becoming more popular for decorating topcoats can be more sensitive to substrate formulations than are solvent-based inks; they require stabilizer systems that will not detract from their printability. Two general-purpose barium zinc stabilizer boosters from Witco, TS-171 and TS-172, do not interfere with the printability of flooring topcoats and also help achieve higher levels of clarity.

Other heat stabilizers from Witco, with environmentally friendly implications, are Mark 4794, a barium zinc liquid that contains no volatile solvents; and a calcium/potassium/zinc liquid that offers another alternative to cadmium-based heat stabilizers.

The automotive industry's tightening standards for its vinyl interiors, such as door panels and headliners, sparked a search for materials that would withstand polyurethane staining and heat degradation and would avoid problems such as windshield fogging and plate-out. Witco's two-component powdered system, Mark 6045, gave three times the protection of traditional stabilizer products but also exceeded the standards. It has been followed by barium zinc liquid stabilizer refinements, Mark 4754 and Mark 4748, especially suited for moderate temperature heat stability and windshield fogging control, respectively. Witco says that another recent development, Mark 6729, a barium zinc powder, functions with a complete absence of plate-out, which is unusual for a solid product.
COPYRIGHT 1993 Society of Plastics Engineers, Inc.
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Title Annotation:chemical additives enhance performance and quality of plastic products
Author:Wigotsky, Victor
Publication:Plastics Engineering
Article Type:Cover Story
Date:Aug 1, 1993
Words:3225
Previous Article:When the going gets hot.
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