Mixed metal stabilizers liquids

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. 

Antioxidants. Phenolic antioxidants, added at about 0.1—0.5 phr, are usually chosen from among butylated hydroxytoluene [128-37-0] (BHT), and -nonylphenol [104-40-5] for liquid stabilizer formulations and bisphenol A [80-05-7] (2,2-bis-(p-hydroxyphenyl)propane) for the solid systems. Low melting thioesters, dilauryl thiodipropionate [123-28A] (DLTDP) or distearyl thiodipropionate [693-36-7] (DSTDP) are commonly added along with the phenolics to enhance their antioxidant performance. Usually a 3 1 ratio of thiodipropionate to phenolic antioxidant provides the desired protection. Most mixed metal stabilizer products contain the antioxidant ingredient. 

Economics, As with the alkyltin stabilizers, the market pricing of the mixed metal stabilizers tend to be directed by the particular application. The calcium—zinc and barium—cadmium packages are typically used at 2.0—4.0 parts per hundred of PVC resin (phr) in the formulation. These completely formulated products are sold for 2.50— 4.40/kg for the liquid products and 3.20— 6.50/kg for the solids and pastes. The higher efficiency products aimed at rigid applications tend toward the higher end of the cost range. 

TRENDS AND CHALLENGES IN LIQUID MIXED METAL STABILIZERS... 

The most common mixed metal stabilizers are octoates, naphthenates and benzoates of barium and zinc metals which are liquids. Barium, cadmium and zinc stabilizers contain solid salts of fatty acids including stearates and laureates. Barium and cadmium provide the most effective thermal stability followed by barium and zinc and then calcium and zinc. However, cadmium is currently considered undesirable from environmental and health standpoints and is being replaced in heat stabilizers, particularly those for polymers used with food. 

Mixed metal stabilizers. Mixed metal stabilizers are primarily used in flexible or semirigid PVC products. The most common are barium/zinc (Ba/Zn) metal salts. IVpical liquid barium, cadmium, and zinc stabilizer products consist of such salts as octoates, alkylphenolates, neo decanoates, naphthenates, and benzoates. Typical solid barium, cadmium, and zinc stabilizer products consist of the salts of such fatty acids as stearates or laurates. Generally, Ba/Cd products provide the best thermal stability, followed by Ba/Zn and finally Ca/Zn. However, Ba/Cd stabilizers have come under increased environmental and Occupational Safety and Health Administration (OSHA) pressure and are being replaced by cadmium-free products that are usually Ca/Zn and Ba/Zn. Several Ca/Zn stabilizers have been approved by the FDA for use in food-contact applications. 

The secondary heat stabilizers are usually organophosphites and epoxy compounds, but polyols and -diketones are also used. Alky/aryl organophosphites are often used with liquid mixed-metal stabilizers in the stabilization of PVC resin. Epoxy compounds function both as plasticizers and stabilizers in flexible and semirigid PVC. (3-Diketones are secondary heat stabilizers used in combination with Ca/Zn and Ba/Zn metallic heat stabilizers to improve initial color. Polyfunctional alcohols are secondary heat stabilizers used in combination with mixed-metal products. 

There are a number of minor uses of tin stabUizer in flexible PVC compounding. These, as with flooring components, typically date from times when the only suitably effective mixed metal stabilizers were based on cadmium. A common characteristic of these diverse uses is poorly controlled processing conditions. For example, the coating of wire lobster traps with plastisol can involve fusion in homemade ovens of variable and uncertain temperature. The same situation may occur in cottage industry manufacture of doll parts from plastisol. In such cases, the cost of the stabilizer may be irrelevant, and a tin maleate ester is a good choice. It is often not worthwhile for stabilizer suppliers to pursue such accounts with high-efficiency Ca/Zn liquids. 

Liquid stabilizers may also contain low levels of diphenyl phosphite (Weston DPP) specifically to reduce plateout through chelation of reaction products containing barium. The use of an active aryl phosphite such as diphenyl or triphenyl phosphite (Weston TPP and Doverphos 10) adds to early color and brightness, but is of little value in extended color retention as compared with aryl-alkyl phosphites that undergo the Arbuzov reaction. A liquid stabilizer composed of about half phosphite, as is common, will usually have no more than a few percent of triaryl phosphite, most often DPP, the balance either aU a phenyl isodecyl phosphite, or a blend with a hydrolysis-resistant grade. The development of more sophisticated use of phosphites has been a major factor in the replacement of cadmium in mixed metal stabilizers. 

When mixed esters of polyols are prepared using, in part, a dibasic acid, the product is an ester lubricant that is a low polymer. This leads to a high order of resistance to extraction, bloom, or deposition. Pentaerythritol adipate-stearate is used in clear rigid PVC compounds as an efficient multifunctional lubricant, despite its relatively high cost. The corresponding adipate-oleate, a liquid, is more generally used in plasticized compounds in conjunction with mixed metal stabilizers, particularly if the latter are relatively nonlubricating. 

Stabilization systems for plastisols are discussed under specifie applications in Section 4.4. Powder mixed metal stabilizers or powder boosters are often added with filler, and may be, as a result, preferred with compounds of substantial filler loading. Liquid mixed metal or organotin stabilizers are typically added with (or to) the plasticizer. As discussed in Chapter 4, there is no longer any compelling... 

Mixed Metal Salts (or Soaps). These consist of Ba/Cd salts (once the most widely used because of their effectiveness but now declining owing to regulatory pressure), Ba/Zn, and Ca/Zn salts. The efficacy of these mixed metal salts as thermal stabilizers follows that order. Mainly used in flexible or semirigid PVC, they are available in solid and liquid versions. Solids are typically salts of fatty acids such as stearates and laurates while liquid versions are octoate, phenolate, and neodecanoate salts. Mixed metal salts are almost always used in the presence of secondary stabilizers such as organophosphites, epoxies (eg, epoxidized soyabean oil), and j8-diketones. This is particularly the case for the less active Ba and Ca/Zn. The ratio of metal salt to secondary stabilizer is typically 4 1. Mixed metal salts or soaps are available from Akros, Baerlocher, Ferro, and Rohm Haas in North America. 

Wire and Cable A major area of powder mixed metal use is in replacement of lead stabilizers in wire insulation and jackets. Jackets having minimal wet electrical requirements have the longest history of use. These were at first Ba/Zn powders (or liquids) but with improving technology, are now mosfly Ca/Zn/ zeolite or Ca/Zn/hydrotalcite blends. Standard test recipes are as follows ... 

Plasticized PVC compounds using mixed metal powder stabilizers are frequently based on calcium or barium stearate or laurate. In the presence of plasticizer, such stabilizers typically act as multifunctional lubricants. Liquid stabilizers often use analogous salts of liquid acids, such as those of octoic, oleic, or taU oil acids. These are similarly multifunctional, as are combinations with organotin stabilizers. In many cases, mixed metal stabifizers provide sufficient lubrication such that no further lubricants are needed. This must be considered in replacement of nonlubricating lead stabilizer systems. 

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