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PVC heat stabilizers: getting the lead out.

As a wire and cable stabilizer, lead has become the latest target in the heavy-metal replacement war.

With heavy-metal-based additives falling further into disfavor, the search for more innocuous alternatives has recently extended from cadmium to lead. Owing to its cost-effectiveness and superior electrical properties, lead still dominates as the preferred stabilizer for most PVC wire and cable compounds. Yet several additives suppliers and at least one major compounder are betting that anticipated regulatory changes and lead's tarnished public image will force processors to consider alternatives.

"Processors are actively looking for lead substitutes. The handwriting, they feel, is on the wall," says Victor Struber, marketing director of Witco's Argus Div. This attitude change has reached enough of a crescendo to bring Argus once again into the wire and cable stabilizer field. Over the past year, a few suppliers have started to market lead-free stabilizers or proprietary compounds for jacketing applications. These firms continue to press ahead with long-term testing for more critical insulation applications while a growing circle of other suppliers proceed with their own R&D. Even some of those in the lead trade have broken ranks and started to look for substitutes just in case. "We're looking into it to protect our market share," says James Keenan, business manager for stabilizers at both Synthetic Products and its Anzon Lead Products Div. The alternatives, however, may still fall short of drop-in status. Notes Keenan, "Everybody is looking at lead replacement, but very few are buying."


By all accounts, lead is a tough act to follow. From a processing standpoint, the alternatives require increased lubrication. And they appear to carry a price premium right now, albeit only a small one. Of the nonlead possibilities, Akzo marketing manager Mitch Silkotch notes that "the only advantage right now is that they're not as toxic as lead."

Despite lead's advantages, the future may shape up differently. According to Argus and compounder Synergistics Industries, developmental complexes could eventually improve upon lead stabilizers electrical properties. Argus's lab is evaluating a formulation that appears to have electrical properties twice as good as its lead forerunners, according to director of technical services Don Brilliant. Synergistics technical director Jay Kotak has similar news about a developmental stabilizer for its wire and cable compounds. "This material looks even better than lead," he says. In the meantime, several suppliers say they have alternatives right now that already function in the same ballpark as lead in terms of physical and electrical properties. All these suppliers say they're on the verge of meeting UL standards with only some long-term testing remaining.

A handful of lead alternatives have already hit the market. This diverse crop includes formulations based on barium-zinc and calcium-zinc, although no company would cite specific ingredients.

Argus just this month introduced a barium-zinc stabilizer called Mark 6731, which comes as an off-white powder. When used at 4.0-5.0 phr in conjunction with epoxidized soybean oil at 3.0-5.0 phr, this new stabilizer serves as a replacement for lead- or cadmium-based products. According to Brilliant, the product works for both primary insulation and jacketing applications in the 60 C to 105 C temperature range. Compared to lead, Mark 6731 offers similar heat stability and only slightly lower insulation resistance, Brilliant adds. Physical properties of wire stabilized with Mark 6731 remain unchanged in properly formulated compounds. The price ranges from comparable to only slightly higher.
Ingredients, phr A B C D
PVC 100.0 100.0 100.0 100.0
DIDP-E 50.0 47.0 47.0 45.0
Drapex 6.8 -- 3.0 3.0 5.0
Atomite 20.0 20.0 20.0 20.0
Clay #33 10.0 10.0 10.0 10.0
Stearic Acid 0.2 -- -- --
Dythal 7.0 -- -- --
Mark 6731 -- 5.0 4.0 4.0
Specific gravity 1.3744 1.3472 1.3457 1.3460
$/lb 0.3360 0.3415 0.3325 0.3332
Lb-vol cost, $ 0.4492 0.4601 0.4474 0.4484
Vol. resistivity,
 ohm-cm initial 2.9E13 1.2E13 -- --
Aged 7 days in
@ 50 C 4.5E12 2.4E12 -- --
Source: Argus Div. of Witco. a Dibasic lead phthalate.

Akzo's efforts at heavy-metal replacement currently focus on a barium-zinc-phosphite liquid called Interstab LT-4797. Recommended for use at 3.5-5.5 phr for extrusion applications, the liquid works best with the addition of a metallic stearate lubricant. Silkotch reports that the liquid "marginally makes 105 C," mostly in jacketing applications. A barium-zinc powder called BZ4847 is even more promising from cost and processing standpoints, but not yet available. It's now undergoing field tests.

Baerlocher USA, the two-year old domestic arm of a German additives supplier, offers a liquid barium-zinc stabilizer system in addition to its conventional lead stabilizers. Called Baerostab UBZ709, it is recommended for use at 2.0-4.0 phr with 0.1-0.2 phr of stearic acid.

As a large-scale supplier of PVC compounds to the wire and cable market, Synergistics has formulated its own nonlead stabilizer for both jacketing and primary insulation. The company is currently offering non-lead jacketing compounds available while continuing testing to satisfy UL requirements for insulation, according to v.p. Jack Etlinger (see PT, Jan. '92, p. 13). Synergistics would identify its technology only as a proprietary combination of barium, zinc, aluminum, and magnesium.

Harcros Organics Div., another European additives company that recently became active in the U.S., just began to sell both calcium-zinc and barium-zinc stabilizers in addition to its lead product, says v.p. Frank Dorn. Ciba-Geigy also reports working on lead replacement.


Not all the lead replacements rely on barium as an ingredient. Baerlocher, for instance, makes a powdered "one-pack" additive that pairs a calcium-zinc stabilizer with a lubricant package. Dosage ranges between 3 and 6 phr, depending on whether the product goes into jacketing or primary insulation compound. According to technical manager Thomas Kaseler, current calcium-zinc stabilizers compare favorably with lead in insulation and jacketing compounds but do not meet electrical requirements in 105 C insulation applications. Meanwhile, a developmental Baerlocher one-pack for even the most critical applications relies on a calcium-aluminum complex for the heat stabilizer. The company plans to run tests needed to obtain UL approval.

And Ferro Corp. is in the process of commercializing a stabilizer that is also free of barium, calcium and lead, says sales director Sally Lenhart. Cardinal Stabilizers passes up barium in favor of a calcium-zinc complex sold as CC511. Company president Tim Ross says his customers already use the product in applications not requiring UL approval. Cardinal too, he adds, is striving to finish long-term testing.

More New Products

New lead: Halstab Div. has introduced Halstab 40, a highly lubricated barium-lead complex for general-purpose use.

One-packs: Elf Atochem has designed two solid "one-packs" that pair a high-efficiency organotin heat stabilizer with a blowing agent: Thermocel 1002 for profile and sheet and Thermocel 2365 for foam-core pipe. Both exclude pigments and fillers. PI 1006 is an injection-molding one-pack without a blowing agent.

For injection molding: Atochem has introduced a new liquid organotin stabilizer called Thermolite PI 1008 for custom injection molding applications where improved melt flow, color hold and outdoor weathering are desired.

No plate-out: Witco's Argus Div. has come out with a powdered barium-zinc that reportedly prevents plate-out altogether. Sold as Mark 6729, it serves as either a primary heat stabilizer for flexible applications like calendering or as an anti-plateout additive for liquid systems.

New tins: Akzo has come out with two new tin stabilizers. Stanclere T-4817 works in rigid, weatherable PVC applications with colors ranging from white to medium pastel shades. Stanclere T-4851 is designed for flooring and wall-covering topcoats.
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Copyright 1992, Gale Group. All rights reserved. Gale Group is a Thomson Corporation Company.

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Title Annotation:Additives '92: Formulations in Flux; includes related article; lead preferred stabilizer for most polyvinyl chloride wire and cable compounds
Author:Ogando, Joseph
Publication:Plastics Technology
Article Type:Cover Story
Date:Jul 1, 1992
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