Stearic Acid and Stearates

The most widely used surface modification is treatment with stearic acid. This is believed to result in a stearate salt coating on most fillers and metal stearates are also used. Stearic acid will react with basic minerals to give a surface that is covered with strongly bonded long organic ions (this is discussed in more detail in Chapter 4). Stearic acid-modified silicates are commercially available but in these cases the stearic acid is almost 

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A fatly aeid in which Ihe carbon atoms of the alkyl chain are connected by single bonds. The most important of these are butyric (Cjl. lauric (Cel. palmitic lCii.1. and stearic tC ist. Stearic acid leads all other falty acids in industrial use. primarily as a dispersing agent and accelerator activator in rubber products and soaps, See also Stearic Acid and Stearates. 

The major properties of nine of the principal edible vegetable oils are summarized in Tbble 2. For descriptions of the constituent acids, see also Arachidic Acid Capric Acid Caproic Acid Lauric Acid Linoleic Acid Linolenic Acid Myristic Acid Oleic Acid Palmitic Acid and Stearic Acid and Stearates. 

The 12-nitroxide stearic acid and the 8-nitroxide methyl palmitate were donated by J. D. Morrisett (John Baylor College of Medicine, Houston, Tex.). All other nitroxide stearic acid and stearate probes were purchased from Syva (California). All probe molecules were subsequently purified by preparative thin layer chromatography (TLC) until a single spot was obtained under all development conditions. TLC was carried out in a dry nitrogen atmosphere to avoid possible oxidation or hydrolysis during purification. Ultrapure silica gel, free from any plasticizers, was used to avoid possible further contamination. 

The application of stearic acid and stearates to magnesium hydroxide surface can be achieved by the following methods ... 

In nonaqueous systems the disadvantages of extender hydrophilicity can be overcome by surface treatment (stearic acid and stearates for carbonates, silanes for silicates). Such treatment is not necessary for aqueous systems and may even be damaging. 

PVC (medium to high molecular weight) plasticizers (most fi-equently phthalates) fillers (most fi equently ealcium carbonate) lubricants (stearic acid and stearates are the most popular) thermal stabilizers (metal soaps dominate)... 

Stearic acid and stearates, as anionic surfactants, are widely used in emulsion preparation and study [3, 24, 25]. 

The specific bases formulation was determined based on the nature and purpose of certain preparations. Table 2 provides three cream bases containing stearic acid and stearates [40],... 

Polymerized dispersion is still another technique to increase stability of the nucleating agent dispersion." Stearic acid and stearate lanthanirm complex were polymerized into isotactic polypropylene via in situ polymerization." The content of P-phase in nucleated PP can reach as high as 88.7% with only 0.135 wt% of nucleating agent."... 

It has to be admitted that the situation regarding fatty acid salts is not well established. Indeed there is much ambiguity in the literature with the terms stearic acid and stearates often being used interchangeably. As discussed earlier, some form of salt is the effective coating material after a fatty acid has reacted with the surface of fillers, but a part salt has to be involved if the acid is to be thought of as reacted onto the filler surface. A full salt will only he weakly attached. 

Polymers may crystallize in different structures, for example, isotactic PP is known to crystallize in a, jS, y and smectic structures (7). Nucleating agents may favor specific types of crystallites. For isotactic PP, stearic acid and stearate lanthanum complexes are jS-nucleating agents. Similarly, cadmiumbicyclo[2.2.1]hept-5-ene-23-dicarboxyl-ate is a j3-nucleating agent (8). 

Stearic acid and stearates may also be used as release agents, but NOT with a litharge cure system as scorching occurs and a short induction time during curing. Zinc stearates should be avoided in heat-resistant compounds as zinc chloride forms and lead to dehydro-halogenation of the polymer upon aging, or exposure to weather. 

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. 

This chapter reports the results of studies on the physical, dynamic mechanical, and rheological behavior of zinc oxide neutralized m-EPDM, particularly in the presence of stearic acid and zinc stearate, with special reference to the effects of precipitated silica filler. 

Zinc salt of maleated EPDM rubber in the presence of stearic acid and zinc stearate behaves as a thermoplastic elastomer, which can be reinforced by the incorporation of precipitated silica filler. It is believed that besides the dispersive type of forces operative in the interaction between the backbone chains and the filler particles, the ionic domains in the polymer interact strongly with the polar sites on the filler surface through formation of hydrogen bonded structures. 

An analytical solution for molecules with alkaline functionality is acid/base titration. In this technique, the polymer is dissolved, but not precipitated prior to analysis. In this way, the additive, even if polymer-bound, is still in solution and titratable. This principle has also been applied for the determination of 0.01 % stearic acid and sodium stearate in SBR solutions. The polymer was diluted with toluene/absolute ethanol mixed solvent and stearic acid was determined by titration with 0.1 M ethanolic NaOH solution to the m-cresol purple endpoint similarly, sodium stearate was titrated with 0.05 M ethanolic HC1 solution [83]. Also long-chain acid lubricants (e.g. stearic acid) in acrylic polyesters were quantitatively determined by titration of the extract. 

The most effective lubricants are the hydrophobic stearates, such as magnesium stearate, calcium stearate, and stearic acid. Magnesium stearate is the most widely used lubricant [117,118]. Lubricants proposed as being less hydrophobic such as hydrogenated vegetable oils, polyethylene glycols, and sodium stearyl fumarate are less effective in this application [118]. 

Zinc stearate is formed during the vulcanisation process with sulphur accelerated compounds, but the addition of zinc stearate alone as replacement for stearic acid and zinc oxide does not produce... 

The neutral fats used in the preparation of the hydrophobic core of the several liposphere-vaccine formulations described here included tricaprin and tristearin, stearic acid, and ethyl stearate. The phospholipids used to form the surrounding layer of lipospheres were egg phosphatidylcholine and dimyristoyl phosphatidylg-lycerol. Polymeric biodegradable lipospheres were prepared from low molecular weight polylactide (PLA) and polycaprolactone-diol (PCL). 

RA and transmission techniques [3], and applied it to the studies of LB films of cadmium stearate [3], azobenzene-containing long-chain fatty acids and their barium salts [4], dipalmitoylphosphatidylcholine (DPPC) [5], and polyion complexes [6]. Furthermore, we explored the relationship between the molecular orientation evaluated by this method and pyroelectricity in alternating (noncentrosymmetric) Y-type LB films consisting of a phenylpyrazine-containing long-chain fatty acid and deuterated stearic acid and of their barium salts [7]. 

A typical salt is sodium stearate. This is the salt of stearic acid and sodium hydroxide. The formula of stearic acid is CjjHjjCOOH and the formula of sodium stearate is Na+Cj HjjCOO". 

Lubricants are used in tablet preparation and include magnesium stearate, stearic acid and polyethylene glycol. They only comprise at most 1-2% of the tablet bulk so that their potential to interfere is slight, particularly since their chromophores are weak. The fatty acid lubricants can often be observed if analysis of a tablet extract is carried out by GC-FID. Tablet coatings are often based on modified sugar polymers such as hydroxypropylmethylcellulose. These coatings are used at about 3% of the tablet bulk, are water soluble and do not absorb UV light. 

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. 

Stearate Aluminum stearate AfiCuH O , yellowish-white powder, by reaction of aluminum hydroxide suspended in hot H20. shaken with stearic acid, and then drying the pioduct. used (1) as a thickenei for lubricating oils, (2) as a drier for paints and varnishes, (3) in waterproofing textiles, paper, leather, (4) as a gloss for paper,... 

Figure 12 shows the FTIR spectrum of a butyl sample. This sample contains BHT, ESBO, stearic acid, and calcium stearate. The contents of all these components can be determined from this single spectrum. In some cases, the assigned peak absorbance is relatively small, so a thick film,. 6 mm, is used. 

Lubricants act by interposing an intermediate layer between the tablet constituents and the die wall, to prevent adherence of the granules to the punch faces and dies. Thus, they ensure smooth ejection of the tablet from the die. In addition, many lubricants also enhance the flow properties of the granules. Stearic acid and its magnesium and calcium salts are widely used. The most effective lubricants, such as magnesium stearate, are very hydrophobic and can also prevent wetting of powders and hence retard dissolution (Figure 6.9). 

If a powder does not have all the required qualities, one can add lubricants to aid the sliding and positioning of the microgranules. Such lubricants can be liquid (water, mineral oil) or solid (tale, graphite, stearic acid, and various stearates). Binders are also added to increase the post-compression adhesion, as for example starch is added for pelletizing active carbon. An increase in the adhesive forces title to chemical bonds resulting from contact between the granules can also be... 

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