Costabilizer

Many PVC stabilizer formulations also contain one or more organic costabilizers that can also absorb hydrogen chloride. Typical of these additives are epoxidized fatty acid esters and organophosphites ... 

Cost bilizers. In most cases the alkyl tin stabilizets ate particularly efficient heat stabilizers for PVC without the addition of costabilizers. Many of the traditional coadditives, such as antioxidants, epoxy compounds, and phosphites, used with the mixed metal stabilizer systems, afford only minimal benefits when used with the alkyl tin mercaptides. Mercaptans are quite effective costabilizets for some of the alkyl tin mercaptides, particularly those based on mercaptoethyl ester technology (23). Combinations of mercaptan and alkyl tin mercaptide ate currendy the most efficient stabilizers for PVC extmsion processes. The level of tin metal in the stabilizer composition can be reduced by up to 50% while maintaining equivalent performance. Figure 2 shows the two-roU mill performance of some methyl tin stabilizers in a PVC pipe formulation as a function of the tin content and the mercaptide groups at 200°C. 

The various lubricants formulated into PVC to improve the processing can also enhance the performance of the stabilizet. In pigmented apphcations, calcium soaps, eg, calcium stearate, ate commonly used as internal lubricants to promote PVC fusion and reduce melt viscosity. This additive is also a powerfiil costabilizer for the alkyl tin mercaptide stabilizers at use levels of 0.2 to 0.7 phr. Calcium stearate can significantly improve the eady color and increase the long-term stabiUty at low levels however, as the concentration increases, significant yellowing begins to occur. 

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. 

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. 

Many stabilizers require costabilizers. Several organic costabilizers are quite useful with barium—zinc and calcium—zinc stabilizers, eg, P-diketones, epoxies, organophosphites, hindered phenols, and polyols (122). 

Some typical dispersion polymerization recipes and the electron micrograph of the uniform polymeric particles with Recipe I are given in Table 5 and Fig. 10, respectively. As seen in Table 5, the alcohols or alcohol-water mixtures are usually utilized as the dispersion media for the dispersion polymerization of apolar monomers. In order to achieve the monodispersity in the final product, a costabilizer can be used together with a primary steric stabilizer, which is usually in the polymeric form as in... 

The same PVP series were also tried for the dispersion polymerization of styrene in the ethanol medium by using AIBN as the initiator and aerosol OT as the costabilizer [84]. PVP K-15 usually yielded polymeric particles with a certain size distribution and some coagu-lum. The uniform products were obtained with PVP K-30 and PVP K-90 in the presence of the costabilizer. The tendencies for the variation of the final particle size with the stabilizer concentration and with the molecular weight of the stabilizer were consistent with those obtained for the dispersion polymerization of methyl methacrylate [84],... 

In another study, uniform composite polymethyl-methacrylate/polystyrene (PMMA/PS) composite particles in the size range of 1-10 fim were prepared by the seeded emulsion polymerization of styrene [121]. The PMMA seed particles were initially prepared by the dispersion polymerization of MMA by using AIBN as the initiator. In this polymerization, poly(7V-vinyl pyrolli-done) and methyl tricaprylyl ammonium chloride were used as the stabilizer and the costabilizer, respectively, in the methanol medium. Seed particles were swollen with styrene monomer in a medium comprised of seed particles, styrene, water, poly(7V-vinyl pyrollidone), Polywet KX-3 and aeorosol MA emulsifiers, sodium bicarbonate, hydroquinone inhibitor, and azobis(2-methylbu-... 

Jacobsen H, Correa A, Costabile C, Cavallo L (2006) J Organomet Chem 691 4350-4358... 

We thank A. Zambelli, P. Longo, C. Pellecchia, G. Milano, G. Monaco, and C. Costabile of the University of Salerno, M. Toto and G. Minieri of the University of Naples, and L. Resconi, G. Morini, and G. Moscardi of Giulio Natta Research Center of Basell for useful discussions. This work has been supported by the Ministero della Ricerca Scientifica e Tecnologica of Italy within PRIN 2002 fundings, by Basell, and by the National Research Council of Italy. 

Organic corrosion inhibitors, 7 815-816 Organic costabilizers, for PVC polymers, 25 672... 

Table 2. Definitions of criteria used by children to distinguish between playful and real fighting (extended from Costabile et al., 1991)...

Costabile, A., Smith, P.K., Matheson, L., Aston, J., Hunter, T. Boulton, M. (1991). Cross-national comparison of how children distinguish serious and playful fighting. Developmental Psychology, 27, 881—887. 

Smith, P.K., Carvalho, A.M.A., Hunter, T., Costabile, A. (1992). Children s perceptions of playfighting, playchasing and real fighting a cross-national interview study. Social Development, I, 211—229. 

Costabilizers. The variety of known costabilizers for the mixed metal stabilizers is a very long listing. There are, however, a relatively small number of commercially used costabilizers. Some of these additives can also be added by the PVC compounder or processor in addition to the stabilizer package to further enhance the desired performance characteristics. The epoxy compounds and phenolic antioxidants are among the most commonly used... 

Hydrotalcite. Synthetic hydrotalcite minerals are gaining commercial acceptance for their ability to costabilize PVC in the presence of other primary stabilizers (see Table 2). The performance of the mixed metal stabilizers are particularly boosted when an equal part level, about 2—3 phr, of hydrotalcite is added to the PVC formulation. These minerals function by trapping HC1 within the layered lattice arrangement of atoms. The formula,... 

Calcium-zinc stabilizers are used in both plasticized PVC and rigid PVC for food contact where it is desired to minimize taste and odor characteristics. Applications include meat wrap, water bottles, and medical uses. Many stabilizers require costabilizers. 

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