Barium-cadmium soaps

II elements invariably are not used singly, but in Subgroup A-B couples. Aside from lead compounds, the elements currently used in most applications are barium, cadmium, calcium, zinc, and tin—e.g., the calcium-zinc soap systems for nontoxic (food contact) applications, the general purpose barium-cadmium soap stabilizers, and the organotin stabilizers. The objective of this paper is to consider the rheological consequences of... 

Typically, soHd stabilizers utilize natural saturated fatty acid ligands with chain lengths of Cg—C g. Ziac stearate [557-05-1/, ziac neodecanoate [27253-29-8] calcium stearate [1592-23-0] barium stearate [6865-35-6] and cadmium laurate [2605-44-9] are some examples. To complete the package, the soHd products also contain other soHd additives such as polyols, antioxidants, and lubricants. Liquid stabilizers can make use of metal soaps of oleic acid, tall oil acids, 2-ethyl-hexanoic acid, octylphenol, and nonylphenol. Barium bis(nonylphenate) [41157-58-8] ziac 2-ethyIhexanoate [136-53-8], cadmium 2-ethyIhexanoate [2420-98-6], and overbased barium tallate [68855-79-8] are normally used ia the Hquid formulations along with solubilizers such as plasticizers, phosphites, and/or epoxidized oils. The majority of the Hquid barium—cadmium formulations rely on barium nonylphenate as the source of that metal. There are even some mixed metal stabilizers suppHed as pastes. The U.S. FDA approved calcium—zinc stabilizers are good examples because they contain a mixture of calcium stearate and ziac stearate suspended ia epoxidized soya oil. Table 4 shows examples of typical mixed metal stabilizers. 

The basic metal salts and soaps tend to be less cosdy than the alkyl tin stabilizers for example, in the United States, the market price in 1993 for calcium stearate was about 1.30— 1.60, zinc stearate was 1.70— 2.00, and barium stearate was 2.40— 2.80/kg. Not all of the coadditives are necessary in every PVC compound. Typically, commercial mixed metal stabilizers contain most of the necessary coadditives and usually an epoxy compound and a phosphite are the only additional products that may be added by the processor. The requited costabilizers, however, significantly add to the stabilization costs. Typical phosphites, used in most flexible PVC formulations, are sold for 4.00— 7.50/kg. Typical antioxidants are bisphenol A, selling at 2.00/kg Nnonylphenol at 1.25/kg and BHT at 3.50/kg, respectively. Pricing for ESO is about 2.00— 2.50/kg. Polyols, such as pentaerythritol, used with the barium—cadmium systems, sells at 2.00, whereas the derivative dipentaerythritol costs over three times as much. The P-diketones and specialized dihydropyridines, which are powerful costabilizers for calcium—zinc and barium—zinc systems, are very cosdy. These additives are 10.00 and 20.00/kg, respectively, contributing significantly to the overall stabilizer costs. Hydrotalcites are sold for about 5.00— 7.00/kg. 

The metallic soaps of barium, cadmium, lead, and calcium are commonly used as stabilizers. They are HCl acceptors, but their reaction products often cause cloudiness in clear formulations. Alkyl and aryl phosphates are often used with them to inhibit precipitation of insoluble chlorides. Tin complexes have also been used successfully. 

Stabilizers are almost invariably added to PVC to improve its heat and light stability. The species found effective in stabilizing PVC are those that are able to absorb or neutralize HCl, react with free radicals, react with double bonds, or neutralize other species that might accelerate degradation. Lead compounds, such as basic lead carbonate and tribasic lead sulfate, and metal soaps of barium, cadmium, lead, zinc, and calcium are used as stabilizers. Obviously, they can react with HCl. Epoxy plasticizers aid in stabilizing the resin. Another group of stabilizers are the organotin compounds, which find application because of their resistance to sulfur and because they can yield crystal-clear compounds. 

As a function of temperature, and up to 350 °C in some cases, magnesium and cadmium soaps exhibit only one or two eylindrical structures, whereas calcium soaps present both different successive struetures with disk and cylinders. These two classes of structure are found also in strontium and barium soaps, with, in addition, a body-centered cubic structure. These cubic phases have interesting features in that the polar groups are present on rods of finite length which belong to two, interwoven, infinite three-dimensional networks and the hydrocarbon chains constitute a eontinuous, paraffinic matrix (Figure 45). 

Unmodified polyesters Alcohol-modified polyester Add-modified polyester Chlorinated paraffins Basic lead silicates Barium salts Cadmium salts Cadmium soaps Zinc soaps Di-n-allqrltin mercaptide Di-n-aUcyltin dilaurates Dibutyltin dimaleate Epoxy resins Hydroxybenzo phenones Benzotriazoles Lead stearate... 

Typical thermal stabilizers for PVC are organic metal salts and soaps, phosphite, esters, and epoxy compounds. Examples are barium/zinc carboxylates [46], barium/cadmium carboxy-lates [47], calcium/zinc stearate [48], lead stearate [49],organotinmercaptides[50],organotin sulfides, organotin carboxylates[51], among others. Costabilizers such as 1,3-diketones, dihydropyridines, epoxy plasticizers, P-ketocarboxylic acid esters, phenolic antioxidants, a-phenylindols, and phosphates are used to improve the stabilizer s elfectiveness. 

Metal soaps of barium, cadmium, lead, zinc, and calcium obviously can react with HCl. The addition of a zinc soap (or zinc oxide) to poly(vinyl chloride) gives a material that can be heated at 175°C for 10 or 15 min with scarcely any discoloration, as opposed to a control with no zinc that turns yellow or brown as a result of the conjugated unsaturations and oxidized structures. However, once the zinc is converted in large measure to zinc chloride, there is a very rapid and copious evolution of HCl and the remaining material is blue-black and brittle. The zinc soap, which was a stabilizer, is converted to zinc chloride, a rapid and efficient degradation catalyst. 

Ultimately, as the stabilization reactions continue, the metallic salts or soaps are depleted and the by-product metal chlorides result. These metal chlorides are potential Lewis acid catalysts and can greatiy accelerate the undesired dehydrochlorination of PVC. Both zinc chloride and cadmium chloride are particularly strong Lewis acids compared to the weakly acidic organotin chlorides and lead chlorides. This significant complication is effectively dealt with in commercial practice by the co-addition of alkaline-earth soaps or salts, such as calcium stearate or barium stearate, ie, by the use of mixed metal stabilizers. 

Whilst lead compounds have been, and still are, the most important class of stabiliser for PVC the metallic soaps or salts have steadily increased in their importance and they are now widely used. At one time a wide range of metal stearates, ricinoleates, palmitates and octoates were offered as possible stabilisers and the efficiency of many of them has been examined. Today only the compounds of cadmium, barium, calcium and zinc are prominent as PVC stabilisers. 

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