Lead stabilizers

Commercial Stabilizers. There are six lead salts and soaps that typically are used in the commercial PVC stabilizers. The lead stearate soaps are often combined with the lead salts to provide lubrication and added stabilizer activity. The key to the high activity of these stabilizers is the very high lead content. Table 5 describes six commonly used lead stabilizers. 

By far the most common lead salt used for PVC stabilization is tribasic lead sulfate. It can be found either alone or combined with another lead salt in almost every lead-stabilized PVC formulation. Many of the combinations are actually coprecipitated hybrid products, ie, basic lead sulfophthalates. Dibasic lead stearate and lead stearate are generally used as costabilizers combined with other primary lead salts, particularly in rigid PVC formulations where they contribute lubrication properties dibasic lead stearate provides internal lubrication and lead stearate is a good external lubricant. Basic lead carbonate is slowly being replaced by tribasic lead sulfate in most appHcations due the relatively low heat stabiHty of the carbonate salt which releases CO2 at about 180°C during PVC processing. 

Flexible Applications. The mainstay of the lead stabilizers in the United States is in flexible wine and cable coating appHcations. The nonconductive nature of lead stabilizers is unsurpassed by other classes of stabilizers. Rather high levels of stabilizers are necessary for these uses because... 

Rigid Applications. The use of the lead stabilizers is very limited in the United States but, they are stiU used in several rigid PVC appHcations in Europe and Asia. The highest use of lead stabilizers in rigid PVC is for pipe and conduit appHcations. Tribasic lead sulfate is the primary heat stabilizer with lead stearates included to provide lubrication. The lead products are typically fully formulated, usually including lubricants and pigments for pipe extmsion appHcations. These lead one-packs, when used at about 1.8—2.5 phr, provide all of the stabilizer and lubrication needed to process the polymer. A lead one-pack contains tribasic lead sulfate, dibasic lead stearate calcium stearate, polyethylene wax, paraffin wax, ester wax, and pigments. 

Stabilizers. Lead stabilizers, particularly tribasic lead sulfate, is commonly used in plasticized wire and cable compounds because of its good nonconducting electrical properties (122). 

The stabilizer or stabilization system used depends on the heat and shear likely to be experienced by the polymer during processing, the end use application requirements, such as clarity or color, and the health concerns. A major health issue has been identified with the lead salts and soaps, because of their relative solubility and their corresponding potential to leach into water. For this reason, lead stabilizers currently find use only when other stabilizer systems do not provide the necessary stabilization or end use properties. Wire and cable sheathing is the only remaining application where the use of the lead stabilizer systems is widespread. Since most humans do not chew on wires (though mice, rats, and squirrels do) and lead-based stabilizers provide superior electrical properties, lead salts persist in this application. 

Boliden s Kaldo process of, 14 742-743 Isasmelt process of, 14 743-745 Kivcet process of, 14 739-740 Outokumpu process of, 14 745 QSL process of, 14 740-742 Lead stabilizers, for PVC polymers, 25 671 Lead storage battery, 14 783. See also Lead-acid batteries Lead-calcium alloy batteries... 

Poudrerie Royale de Wetteren SA, BelgP 654268(1965) CA 64, 11022(1966) (Flexible expls are prepd from Nitroglycerin and/or Nitroglycol with plasticized NC and red lead stabilizer. More flexibility can be had by adding diburylphthalate)... 

One possible function of lead stabilizer is the removal of ionic impurities which form during thermal decomposition. To study this possibility, we aged both stabilized and unstabilized compositions in a 175°C. circulating air oven up to the point of severe darkening (Table V). 

Johnson and co-workers (62) have come to the conclusion that interaction of lead with Pt crystallites results in the formation of an inactive phase in which the Pt atoms are ionized and soluble in HC1. These data were derived from engine tests, in which the catalysts were exposed to fuels with 0.03-0.1 g Pb/gal. The amount of crystalline Pt in these catalysts was smaller than in catalysts run on lead-free fuels. The authors indicate that noncrystalline forms of Pt are present on A1203 supports under certain conditions, and that lead stabilizes such forms. The question whether the noncrystalline, ionic Pt is a surface or a bulk phase remains unanswered. Bulk mixed Pt-Pb oxides have been described (98, 99), but, again, the dispersed forms of noble metals supported on A1203, which lead (and other elements) may stabilize, are known to be associated with the surface only. Palladium can be expected to form such noncrystalline dispersed phases to a still greater extent since it is more easily oxidized than Pt. 

Another global trend in this general direction is the drive toward PVC wire and cable reformulation to remove lead stabilizers. Among the replacements are stabilizers based on zinc or calcium.161 In addition to lead, concern about certain phthalate plasticizers is increasingly being encountered, such as California s proposition 65, which may continue the pressure on certain PVC-based materials. 

Kaseler, T.G., Non-lead stabilizer systems for PVC wire and cable extrusion (An Update), J. Vinyl. Addit. Tech., 1993, 15(4), 196-201. 

Mizuno, K.M., Hirukawa, H., Kawasaki, O., Noguchi, H., and Suzuki, O., Development of Non-Lead Stabilized PVC Compounds for Insulated Wires and Cables, Furukawa Review, 1999, 18, 111-118. 

Internal stabilization is a novel method of enhancing the thermal stability of vinyl polymers. Braun, who proposes this term, reports that metal salts of unsaturated carbonic acids are suitable comonomers acting as internal stabilizers. For example, a copolymer of vinyl chloride with only 0.3 mole % of lead undecylenate has a significantly longer and better thermal stability than externally lead-stabilized PVC. 

STRUCTURE OF LEAD STABILIZERS. I. BASIC LEAD CARBOXYLATES... 

One major use of PVC is for pipes in plumbing systems. Here, even though the inexpensive lead stabilizers would be preferred from an economic standpoint, the possibility that the toxic lead could be leached from the pipes into the drinking water necessitates the use of more expensive tin and antimony compounds as thermal stabilizers. Because about one-half of the annual U.S. production of PVC is formed into piping, the PVC formulation used for pipes represents a huge market for companies that manufacture additives, and the competition is very intense. A recently developed low-cost thermal stabilizer for PVC is a mixture of antimony and calcium salts. This mixture has replaced stabilizers containing tin compounds that have become increasingly costly in recent years. 

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