Lead stearate

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. 

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. 

Serious attempts to use LB films in commercial appHcations include the use of lead stearate as a diffraction grating for soft x-rays (64). Detailed discussion on appHcations of LB films are available (4,65). From the materials point of view, the abiHty to build noncentro symmetric films having a precise control on film thickness, suggests that one of the first appHcations of LB films may be in the area of second-order nonlinear optics. Whereas a waveguide based on LB films of fatty acid salts was reported in 1977, a waveguide based on polymeric LB films has not yet been commercialized. 

Whereas other metal salts, especially lead stearates and srdfates, or mixtures of Groups 2 and 12 carboxylates (Ba—Cd, Ba—Zn, Ca—Zn) ate also used to stabilize PVC, the tin mercaptides are some of the most efficient materials. This increased efficiency is largely owing to the mercaptans. The principal mechanism of stabilization of PVC, in which all types of stabilizers participate, is the adsorption of HCl, which is released by the PVC during degradation. This is important because the acid is a catalyst for the degradation, thus, without neutralization the process is autocatalytic. 

Normal and dibasic lead stearate have a stabilising effect but their main uses are as lubricants (see section 12.5.4). Lead silicate is sometimes used in leathercloth formulations but is today of little importance. Other lead compounds now of negligible importance are coprecipitated lead orthosilicates and lead salicylate. 

In Britain calcium stearate has been most commonly used with nontransparent products and stearic acid with transparent compounds. In the United States normal lead stearate, which melts during processing and lubricates like wax, is commonly employed. Dibasic lead stearate, which does not melt, lubricates like graphite and improves flow properties, is also used. 

These have been developed for special uses. For example, since petroleum-based materials harm natural rubber, a grease based on castor oil and lead stearate is available for use on the steel parts of rubber bushes, engine mountings, hydraulic equipment components, etc. (but not on copper or cadmium alloys). Some soft-film solvent-deposited materials have water-displacing properties and are designed for use on surfaces which cannot be dried properly, e.g. water-spaces of internal combustion engines and the cylinders or valve chests of steam engines. 

The proplnts described above are in the realm of prior art and depict those NC proplnts with low smoke potential that are used primarily as gun proplnts. Recent research and development work has been concentrated on creating both gun proplnts and rocket proplnts with reduced smoke output in order to foil countermeasures. Lavitt (Ref 76) found that the concurrent use of optimum proportions of lead stearate and sodium barbiturate in double-base proplnts resulted in a marked reduction in smoke output. This was attributed to the synergistic interaction of the two salts to produce more complete oxidation of the exhaust products. The importance of using the optimum ratio of the two catalysts is demonstrated by the higher smoke values shown in Table 4 for Propellants 105, 106 and 107, when compared to other... 

Heat stabiliser Organotin mercaptides/sulfides/carboxylates antimony mercaptides metal carboxylates lead stearate/phosphite/phthalate/sulfate S, Sb, Sn, Ba, Ca, Cd, Mg, Sr, Zn P, Pb, S... 

Cavalleri A, Minoia C. 1987. Lead level of whole blood and plasma in workers exposed to lead stearate. Scand J Work Environ Health 13 218-220. 

M28 propellant 60.0% nitrocellulose/23.8% nitroglycerin/ 9.9% triacetin/2.6% dimethyl phthalate/ 2.0% lead stearate/ 1.7% 2-nitrodiphenylamine... 

There was no accumulation of metals in either the anolyte or catholyte circuits when a spike of metals was fed with the M28 propellant to simulate particles from antiresonance rods. AEA attributes this success to the use of the catholyte-to-anolyte recycle and the anolyte purge operation. Lead, present in M28 propellant as lead stearate (approximately 0.5 weight percent), was oxidized to lead oxide (Pb02) and did not accumulate in solution. Lead oxide was found on the electrode surfaces and as a deposit in the bottom of the cell cavities (AEA, 2001d). A demonstration test successfully removed the lead oxide using an offline formic acid wash of the cell electrode cavities. This is the planned approach for removing accumulating lead oxide. No lead material balance was provided. 

The treatment of burster charges and M28 propellant in the SILVER II reactor must be tested, and the material preparation required to ensure reasonable treatment times with no energetic events must be evaluated. This testing must also determine what happens to the lead stearate in the propellant during SILVER II treatment. 

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