Zinc stearate

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.

The Uses of Zinc stearate

zinc stearate is used in cosmetic formulations to increase adhesive properties. It is also used as a coloring agent. This is a mixture of the zinc salts of stearic and palmitic acids.

The Uses of Zinc stearate

Used in Rubber, Plastic, Poyester, Abbrasive, Coating, Printing Inks and PVC Industry.

The Uses of Zinc stearate

In tablet manufacture; in cosmetic and pharmaceutical powders and ointments; as a flatting and sanding agent in lacquers; as a drying lubricant and dusting agent for rubber; as a plastic mold releasing agent; as a waterproofing agent for concrete, rock wool, paper, textiles.

What are the applications of Application

Zinc stearate is 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.

What are the applications of 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.

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)).

Flammability and Explosibility

Not classified

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 Profile

Poison by intratracheal route. Inhalation of zinc stearate has been reported as causing pulmonary fibrosis. A nuisance dust. Combustible when exposed to heat or flame. To fight fire, use water, foam, CO2, dry chemical. When heated to decomposition it emits toxic fumes of ZnO. See also ZINC COMPOUNDS.

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.