Zinc stearate

Zinc stearate is a "zinc soap" that is widely used industrially. In this context, soap is used in its formal sense, a metal salt of a fatty acid: in this case stearic acid. It is a white solid that repels water. It is insoluble in polar solvents such as alcohol and ether but soluble in aromatic hydrocarbons (e.g., benzene) and chlorinated hydrocarbons when heated. It is the most powerful mold release agent among all metal soaps. It contains no electrolyte and has a hydrophobic effect. Its main application areas are the plastics and rubber industry, where it is used as a releasing agent and lubricant which can be easily incorporated.[2]

Zinc stearate
Names
IUPAC name
zinc octadecanoate
Other names
zinc distearate
Identifiers
3D model (JSmol)
ChemSpider
ECHA InfoCard 100.008.321
UNII
Properties
C36H70O4Zn
Molar mass 632.33 g·mol−1
Appearance soft, white powder
Odor slight, characteristic[1]
Density 1.095 g/cm3, solid
Melting point 120 to 130 °C (248 to 266 °F; 393 to 403 K)
Boiling point decomposes
insoluble
Solubility in alcohol insoluble
Solubility in ether insoluble
Solubility in benzene slightly soluble
Hazards
not listed
NFPA 704 (fire diamond)
Flammability code 2: Must be moderately heated or exposed to relatively high ambient temperature before ignition can occur. Flash point between 38 and 93 °C (100 and 200 °F). E.g. diesel fuelHealth code 1: Exposure would cause irritation but only minor residual injury. E.g. turpentineReactivity code 0: Normally stable, even under fire exposure conditions, and is not reactive with water. E.g. liquid nitrogenSpecial hazards (white): no code
2
1
0
Flash point 277 °C (531 °F; 550 K)
420 °C (788 °F; 693 K)
NIOSH (US health exposure limits):
PEL (Permissible)
 TWA 15 mg/m3 (total) TWA 5 mg/m3 (resp)[1]
REL (Recommended)
 TWA 10 mg/m3 (total) TWA 5 mg/m3 (resp)[1]
IDLH (Immediate danger)
 N.D.[1]
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

Zinc carboxylates, e.g. basic zinc acetate, adopt complex formulas, and are not simply dicarboxylates of zinc. Instead the formula for most zinc carboxylates is Zn4O(O2CR)6, consisting of a Zn4O6+ core with carboxylate ligands spanning the edges.

Applications

It is widely used as a release agent for the production of many kinds of objects: rubber, polyurethane, polyester processing system, powder metallurgy. These applications exploit its "non-stick" properties.[2] In cosmetics, zinc stearate is a lubricant and thickening agent used to improve texture.[3]

It is an "activator" for accelerated rubber sulfur vulcanization. As discovered in the early days of vulcanization, zinc has a beneficial effect on the reaction of the sulfur with the polyolefin. The stearate is a form of zinc that is highly soluble in the nonpolar medium of the polyolefins.

Being lipophilic, it functions as a phase transfer catalyst for the saponification of fats.[2]

Niche uses

It is a component of some paints, imparting gloss. As a chief ingredient in "fanning powder", it is used by magicians performing card manipulation to decrease the friction between playing cards.

References
  1. NIOSH Pocket Guide to Chemical Hazards. "#0676". National Institute for Occupational Safety and Health (NIOSH).
  2. David J. Anneken, Sabine Both, Ralf Christoph, Georg Fieg, Udo Steinberner, Alfred Westfechtel "Fatty Acids" in Ullmann's Encyclopedia of Industrial Chemistry 2006, Wiley-VCH, Weinheim. doi:10.1002/14356007.a10_245.pub2
  3. http://cosmeticsinfo.org/ingredient/zinc-stearate
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