Metallic stearate lubricants

As soon as the maleated coupling agents were introduced into the WPC, it was noticed that their effect often significantly depends on lubricants employed in the same system. The most striking was a conflicting effect between maleated polyolefins and metal stearate lubricants (Tables 5.15 and 5.16)... 

The determination of metal stearate lubricants by means of a hydrochloric acid/diethyl ether hydrolysis procedure has been described [2] and can be used if, for example, calcium or zinc stearate is known to be present. However, for... 

Lubricants. Lubricants are used to improve the melt flow, screw feeding, and mold release of nylons. Long-chain acids, esters, and amides are used together with metal salts, eg, metal stearates. Improved melt flow is mainly a function of molecular weight reduction during mol ding. Mold release is improved by waxes of limited compatibiHty with nylon, which migrate to and lubricate the mold surface. 

Fig. 10. A model of PVC lubrication mechanism showing (a) PVC adhesion to metal without lubricant (b) surface activity of calcium stearate (c) nonmetal releasing character of paraffin only and (d) synergy between calcium stearate and paraffin (62).

More than half the metal stearates produced in the United States are appHed as lubricants and heat stabili2ers (qv) in plastics, particularly in the processing of poly(vinyl chloride) (PVC) resins. 

Stearic acid and metal stearates such as calcium stearate are generally used as lubricants at a rate of about 1-3% on the total compound. Waxes such as camauba and ceresin or oils such as castor oil may also be used for this purpose. 

Metal stearates such as zinc, magnesium or aluminium stearates are commonly used as lubricants at about 1 % concentration. Other materials that have been used successfully include oxidised paraffin wax and sulphonated castor oil. 

Compacting of specific materials can be facilitated with certain kinds of additives. Binders are additives that confer strength to the agglomerates, and lubricants reduce friction during the operation. Some additives may function both ways. A few of the hundreds of binders that have been tried or proposed are listed in Table 12.12. Lubricants include the liquids water, glycerine, and lubricating oils and typical solids are waxes, stearic acid, metallic stearates, starch, and talc. 

Stearic acid is used (1) in the preparation of metallic stearates, such as aluminum stearate for thickening lubricating oils, for waterproofing materials, and for varnish driers, (2) in the manufacture of "stearin candles, and is added in small amounts to paraffin wax candles. As the... 

Three properties that contribute the most to migration are (1) incompatibility with the resin, (2) low melt point, and (3) low molecular weight. Examples of noncolorant additives that are prone to migrate are (1) lubricants/dispersants such as metal stearates and bis-stearamides, (2) mold release and slip agents, and (3) antistatic agents. All of these ingredients serve useful purposes in color formulations. If you exceed their solubility limit in the end-use resin, however, you risk blooming and its consequences. 

The production of briquettes may require little or no binders but when they are used, strength is conferred to the agglomerates and the addition of lubricants may reduce friction during the operation. Table 12.14 is a hst of some binders that have been used. The lubricants may be liquids such as water, glycerine, lubricating oils and solid waxes, metallic stearates, starch, and talc. 

Metal stearates, such as magnesium or calcium stearate that serve as lubricants in conventional tablets, are seldom used as intrinsic lubricants in connection with effervescent tablets due to their insolubility in water. Use of stearates results in an undissolved, foamy, soapy-tasting layer on the surface of the cloudy solution. In addition, normal lubricant concentrations of metal stearates make the tablets hydrophobic, which entails a slow dissolution of the effervescent tablet in the water. However, very low concentrations of metal stearates can be used to improve the rate of solution of effervescent tablets as the tablet will remain immersed in the water during dissolution and not float to the surface the way a tablet without metal stearate would. A floating tablet presents a smaller surface area to the water than a tablet immersed in the liquid. 

Lubricants To reduce the friction between the granules and the die wall during compression and ejection of the tableting process Water-insoluble metal stearates, stearic acid, talc Water-soluble boric acid, sodium chloride, benzoate and acetate, sodium or magnesium lauryl sulfate Carbowax 4000 or 6000... 

Boundary lubricants work by forming a thin solid film at the interface of the die and the tablet. Metallic stearates are the most widely used boundary lubricants, and their activity has been attributed to adherence of polar molecular portions on their surface to the surfaces of one particle species and of non-polar surface components to the other species surface. Such lubricants should have a low shear strength of their own and form interparticulate films that resist wear and reduce surface wear. A list of lubricants with typical ranges for their usage is given in Table 11.9. 

Lubricants may be added either as an additive or at the fabrication stage as a processing aid. In general lubricants prevent adhesion with metal parts. Lubricants may be solids, such as waxes, stearates, i.e. fatty acid esters, fatty acid amides, or liquids such as liquid paraffins. Lubricants may also improve the flow and thereby lower the temperature of the moulding operation. For example, a silicone additive polydimethyl siloxane may be used in LDPE and HOPE films to improve flow. Stearamides are also used. 

These agents are somewhat similar to lubricants in that they provide release, particularly from metals, i.e. moulds. The substances include metal stearates, i.e. zinc, calcium, magnesium stearates, stearic acid and silicone fluids (0.25-1%), e.g. poly (dimethyl) siloxane. 

Another consequence of the suggested chemical interaction between maleated polymers and zinc stearate is that the WPC material starts to decompose at lower temperatures (at about 300°C compared to 350°C) compared to that compounded without the metal-containing lubricant [25]. However, knowing that metal-containing compounds serve as catalysts of oxidation of plastics (see Chapter 15), the earlier plastic degradation could have occurred without any coupling agents, just due to the presence of zinc stearate. A simple test in that case would be to increase an amount of an antioxidant in the system, and the earlier decomposition temperature point would have predictably returned back to normal. Hence, the above experiment... 

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]). 

Petrac . [Syn. Prods.] Stearic acid, metallic stearates, amit or waxes hibii-cmt, activator, dispersant, dasticizer, mold release agent, emulsifier, slip agent, thickener, anticaking agent for plastics, syn. lubricants, bar soaps, cosmetics, rubbers, pdisbes, paims, inks, waieiptot ng. 

Synpron . [Syn. Prods.] Antimtmy mercaptide, dibutyltin dilaurate, or metallic stearates PVC heat stabilizer, lubricant, i ocess aid. 

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