General Description
White, hydrophobic powder with a slight, characteristic odor. Mp: 130°C. Density: 1.1 g cm-3. Insoluble in water, ethyl alcohol and diethyl ether. Soluble in acids. Non-toxic. In technical grades, the percentage of zinc may vary according to the intended use. Products with less than the theoretical amount of zinc are more acidic.
Reactivity Profile
ZINC STEARATE is non-flammable but combustible. Incompatible with oxidizing agents, dilute acids. Emits acrid smoke and fumes of ZnO when heated to decomposition (Hazardous Chemicals Desk Reference, p. 865 (1987)).
Description
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. 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.
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.
Chemical Properties
white powder with fatty acid odour
Chemical Properties
Zinc stearate occurs as a fine, white, bulky, hydrophobic powder,
free from grittiness and with a faint characteristic odor.
Application
It is widely used as a release agent for the production of many kinds of objects rubber, poly urethane, poly ester processing system, powder metallurgy. These applications exploit its "non-stick" properties . In cosmetics, zinc stearate is a lubricant and thickening to improve texture.
It is an "activator" for rubber vulcanization by sulfur and accelerators. 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 poly olefins.
Being lipophilic, it functions as a phase transfer catalyst for the saponification of fats.
Production Methods
An aqueous solution of zinc sulfate is added to sodium stearate
solution to precipitate zinc stearate. The zinc stearate is then washed
with water and dried. Zinc stearate may also be prepared from
stearic acid and zinc chloride.
Flammability and Explosibility
Notclassified
Pharmaceutical Applications
Zinc stearate is primarily used in pharmaceutical formulations as a
lubricant in tablet and capsule manufacture at concentrations up to
1.5% w/w. It has also been used as a thickening and opacifying
agent in cosmetic and pharmaceutical creams, and as a dusting
powder.
Safety
Zinc stearate is used in oral and topical pharmaceutical formulations,
and is generally regarded as a nontoxic and nonirritant
excipient. However, following inhalation, it has been associated
with fatal pneumonitis, particularly in infants. As a result, zinc
stearate has now been removed from baby dusting powders.
LD50 (rat, IP): 0.25 g/kg
storage
Zinc stearate is stable and should be stored in a well-closed
container in a cool, dry place.
Incompatibilities
Zinc stearate is decomposed by dilute acids. It is incompatible with
strong oxidizing agents.
Regulatory Status
GRAS listed. Included in the FDA Inactive Ingredients Database
(oral capsules and tablets). Included in nonparenteral medicines
licensed in the UK. Included in the Canadian List of Acceptable
Non-medicinal Ingredients.
