Effect of metal stearates

Hoang, E.M., Liauw, C.M., AUen, N.S., Fontan, E., and Lafuente, P, Effect of Metal Stearate Antacid on the Melt StahiUzation Performance of Phenolic/Phosphite Antioxidants in Metallocene LLDPE. Part 1 Melt Processing Stahility /. Vinyl Addit. Technol., 10, 3, 137 (2004)... 

EFFECT OF METALLIC STEARATES ON THERMAL OXIDATION OF ABS PLASTICS [333]... 

Effect of Metal Stearates. The oxygen uptake curves of isotactic and atactic polypropylene in the presence of transition metal stearates in trichlorobenzene are shown in Figures 1 and 2, respectively. The order of decreasing catalytic effect of the metal stearates at the early stage of the oxidation of the polymers is for isotactic PP, Cu > Mn > Fe > Cr > Co > Ni > Ti > control > A1 > > Zn > > V and for atactic PP, Cu > Mn> Fe > Cr > Ah Ni Co control Ti >> Zn >> V. The order of the catalytic effect of the metals is quite different from that in bulk reported previously (16). In particular, V-stearate inhibits the thermal oxidation, and Co-stearate is not as effective as in bulk. In the presence of effective metal stearates such as Cu and Fe, the oxygen uptake levels off after a certain time. However, the amount of oxygen absorbed in the isotactic polypropylene is higher than that in the atactic polypropylene. 

For IPP Co + > Mn + > Cr + > Fe + > Cu +. Oxygen uptake of IPP in the presence of Co takes place at lower temperatures than in the presence of Co. The catalytic effect of metal stearates in IPP oxidation in solid state varies in the following order ... 

Hoang EM, Liauw CM, Allen NS, Fontan E, Lafuente P. Effect of metal stearate antacid on the melt stabilization performance of phenolic/ phosphite antioxidants in metallocene LLDPE. Part 1 melt processing stability. J Vinyl Addit Technol 2004 10(3) 137 3. 

Duvdevani(40) have been directed at modification of ionomer properties by employing polar additives to specifically interact or plasticize the ionic interactions. This plasticization process is necessary to achieve the processability of thermoplastic elastomers based on S-EPDM. Crystalline polar plasticizers such as zinc stearate can markedly affect ionic associations in S-EPDM. For example, low levels of metal stearate can enhance the melt flow of S-EPDM at elevated temperatures and yet improve the tensile properties of this ionomer at ambient temperatures. Above its crystalline melting point, ca. 120°C, zinc stearate is effective at solvating the ionic groups, thus lowering the melt viscosity of the ionomer. At ambient temperatures the crystalline additive acts as a reinforcing filler. 

This chapter describes the effects of various stearates on the rheological, mechanical, and chemical properties of metal sulfonate-containing EPDM s. 

Table I. Effects of Metal Counterion and Metal Stearates...

Figure 4. Effect of zinc stearate on the melt index of metal sulfonate CR-2504 (base polymer—CR-2504 sulfonate content—33 meq/100...

The plasticizing effects of a larger number of metal stearates on the zinc sulfonate ionomer were examined, and the results are given in Table III in terms of flow and mechanical properties. Lead stearate, zinc stearate, and ammonium stearate significantly improved melt flow along with the stearic acid control. The barium, magnesium, sodium, lithium, and calcium stearates showed little, if any, improvement in melt flow. Of the four melt flow improvers, both stearic acid and ammonium stearate exerted deleterious effects on tensile properties. Only the zinc and lead stearates substantially improved tensile properties. Thus, while zinc stearate is not unique, the number of fatty acid derivatives that improve both melt flow and mechanical properties is limited. 

TABLE 5.16 Effect of metal-base (zinc stearate and SXT 2000) and nonmetallic lubricant (ST 3100) in formulated packages on flexural strength and flexural modulus of a WPC (61-63% wood flour, 34% HDPE, polybond 3029 as a coupling agent)... 

The effect of conflicting of the maleated polyolefins with zinc stearate and other metal-containing stearates is commonly known in the industry. Therefore, a number of companies have developed nonmetal lubricants, such as Ferro Corporation RC-553, RC-571, RC-572, RC-576, SXT 3100 (see Table 5.16 Ferro s SXT 2000 is a blend of metal stearates with other nonmetal lubricants [3]), Struktol TPW-113 (Struktol s TPW 104 contains zinc stearate), Lonza Glucolube WP-2200 (a new proprietary amide lubricant that contains no metal stearates [12]). 

Metal stearates, including predominately calcium stearate as well as zinc stearate, are the most widely used lubricants. In PVC calendering and extrusion, the stearates provide heat stabilizing effects as well as act as an internal Inbri-cant. In polyolefins, stearates act as external lubricants as well as deactivators of catalyst residues. Ferro (Synpro, Petrac), Baerlocher (Hydense), and Crompton (Witco) are the major producers of metal stearates in North America. 

Cobalt Salts. Barker" studied the effects of cobalt stearate, cobalt naphthenate, and a proprietary boron-containing metal-organic complex on adhesion to brass. He concluded that, with properly optimized compounds, little or no benefit is obtained from the use of cobalt insofar as initial adhesion is concerned. All salts, however, improved steam-aged adhesion to some extent. Other studies tend to support these claims. 

It was proved that some compounds of transitional metals such copper stearate could retard the photo-degradation of HOPE [66] and PP [67]. Cooper stearate can acts both as UV light absorber and as radical scavenger, respectively. The stability effect of copper stearate on polyolefin was explained by two directions [67] ... 

PVC can be protected with a variety of stabilizer systems. The choice of stabilizer depends on the probable decomposition mechanisms involved. Primary and secondary stabilizers are generally used in combination. The primary stabilizers are mainly acid acceptors such as metallic soaps. Typical examples are, metallic soaps such as cadmium, barium, and zinc stearates which also act as lubricants. These chemicals simply react with HCl and are able to reduce further degradation. The mechanism of stabilization and properties of various metal soaps are reviewed (39,40). Calcium and zinc stabilizers are low in toxicity and they are often prepared in the form of a dispersion in epoxidized oil. Barium and cadmium stabilizers are mainly solid products those which are liquid contain phosphite groups. The compatibility of PVC stabilizers containing heavy metals (41) and synergetic effects of metal stabilizers (42) are reviewed. 

The potential for the formation of ionic crosslinks with Vamac terpolymers precludes the use of fillers that may contain soluble divalent metal ions. Metal stearates, metal stearate-coated fillers, clays, and precipitated silicas are not recommended for use in Vamac terpolymers. Precipitated fillers can contain impurities, which can lead to ionic bonding. Another potential source of soluble divalent metal ions is the pigment used to color mineral-filled compounds. Ionic bonds can significantly increase the viscosity of the uncured stock and increase the compression set of vulcanizates. The effect of metal ions and ionic bonds on stock and vulcanizate properties can vary considerably from batch to batch and is dependent on the impurity concentration in the lot of filler as well as the mixing/processing procedures. 

Neutralise acidity (e.g. deriving from acidic catalyst residues) effectively. Commonly salts of weak organic acids (metal stearates) or inorganic bases (hydrotalcite). Also called antiacids. 

Because the forces of attraction prevail when molecules are brought into sufficiently dose proximity under normal conditions, release is best effected if both the strength of the interaction and the degree of contact are minimized. Aliphatic hydrocarbons and fluorocarbons achieve the former effect, finely divided solids the latter. Materials such as microcrystalline wax [64742 42-3] and hydrophobic silica [7631-86-9] combine both effects. Some authors refer to this combined effect as the ball bearing mechanism. A perfluoroalkylated fullerene nanosphere would perhaps be the ultimate example of this combined effect (17). These very general mechanistic remarks can be supplemented by publications on the mechanism of specific classes of release agents such as metallic stearates (18), fatty acids and fluorinated compounds (19), and silicone-coated rdease papers (20,21). The mechanism of release of certain problem adherents, eg, polyurethanes, has also been addressed (22,23). 

Sears and Schulman (51) measured surface pressures and potentials vs. molecular area (20 to 110 sq. A. per molecule) for the alkali metal stearates over 0.5N solutions of LiOH, NaOH, and KOH. Like Adam and Miller, they detected a specific cation effect on the 7r-A and AV-A isotherms of the ionized monolayer at high pH the ir-A curves were expanded in the order of the crystalline sizes of the alkali metal cations K > Na > Li. The sequence is the reverse observed for the long-chain... 

Costabilizers. In most cases the alkyltin stabilizers are 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 alkyltin mercaptides. Mercaptans are quite effective costabilizers for some of the alkyltin mercaptides, particulady those based on mercaptoethyl ester technology (23). Combinations of mercaptan and alkyltin mercaptide are currently the most efficient stabilizers for PVC extrusion 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-roll mill performance of some methyltin stabilizers in a PVC pipe formulation as a function of the tin content and the mercaptide groups at 200°C. The test formulation contains 100 parts of PVC (Fikentscher K = 65), 1.2 parts of paraffin wax, 0.6 parts of calcium stearate, and 0.4 parts of methyltin-based stabilizers. 

The effect of the particular functional group on adsorption, however, is not always the same as seen on oxide surfaces. For example, carboxylic acids adsorb strongly on metal oxide surfaces, and the heat of adsorption of stearic acid is higher than that of the corresponding ester, methyl stearate (Hironaka et al., 1978). For adsorption on the nascent surface, however, propionic acid is a poor adsorbate, and the adsorption activity of propionic acid is lower than that of methyl propionate. Although propyl amine adsorbs easily on metal oxide surfaces, the adsorption activity of propyl amine is low on the fresh steel surfaces. Also, the heat of adsorption of organic sulfides on iron oxide is less than that of esters (Forbes et al., 1970b), but the results of adsorption activity on the nascent surface were the opposite. It is thus noteworthy that the chemical nature of the nascent surface of steel is often opposite to that of oxide-covered metal surfaces, with respect to adsorption. 

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