Zinc Stearate, Zinc dioctadecanoate, Zinc Octadecanoate, Zinc Soap, 557-05-1

Zinc Stearate, Zinc dioctadecanoate, Zinc Octadecanoate, Zinc Soap, 557-05-1

ZINC STEARATE

1. PRODUCT DEFINITION AND CHEMICAL IDENTITY

Note: Some technical literature may list the molecular weight as ~623.33 g/mol due to variations in fatty acid composition (e.g., presence of palmitate). For pure zinc stearate, the accepted molecular weight is 632.34 g/mol.

2. PHYSICAL AND CHEMICAL PROPERTIES

• Physical form: White, impalpable powder; greasy or soapy to the touch.

• Melting point: 120–124 °C (lit.)

• Density: ~0.997 g/cm³ at 20 °C

• Solubility:

  • Practically insoluble in cold water, ethanol, and acetone.

  • Slightly soluble in hot ethanol and vegetable oils.

  • Soluble in aromatic and chlorinated hydrocarbons when heated; decomposes in strong mineral acids (forming stearic acid and corresponding zinc salts).

• Moisture content: Typically ≤1.0% (as specified by suppliers)

• Stability: Stable under normal conditions; hygroscopicity is very low; avoid strong acids and oxidizing agents.

• Compatibility: Compatible with many polymers, waxes, and oils. Acts as a Lewis acid, so may interact with certain alkaline additives.

3. FUNCTIONAL PROPERTIES

• Lubricant: Reduces friction and melt viscosity during polymer processing.

• Mold release agent: Prevents sticking to molds in rubber, plastics, and powder metallurgy.

• Stabilizer: Co-stabilizer for PVC and halogenated polymers (synergistic with calcium stearate and organotin compounds).

• Water repellent (hydrophobic agent): Imparts water resistance in construction materials, coatings, and textiles.

• Matting / Flatting agent: Controls gloss in paints and varnishes.

• Anti-caking / Free-flow agent: Prevents caking in powdered products and improves flow.

• Anti-foaming agent: Used in water-based paint and coating formulations.

• Pigment suspending agent: Aids dispersion of pigments and fillers.

• Polishing agent: Used in sandpaper and abrasives to improve surface finish.

4. ALTERNATIVE NAMES AND SYNONYMS

• Zinc stearate

• Zinc distearate

• Zinc octadecanoate

• Stearic acid, zinc salt

• Octadecanoic acid, zinc salt

• Zinc soap (common term in rubber and plastics industries)

• Tally powder (when used as a dusting agent for rubber)

5. SECTORAL APPLICATIONS, USAGE RATES, AND EXAMPLE FORMULATIONS

Example Formulations:

• PVC Pipe Compound (internal lubricant):

  • PVC resin: 100 kg

  • Stabilizer (Ca/Zn): 2.5 kg

  • Zinc stearate: 0.3 kg

  • Calcium stearate: 0.7 kg

  • Processing aids and fillers as required.

• Cementitious Waterproofing Mortar:

  • Portland cement: 100 kg

  • Silica sand: 150 kg

  • Zinc stearate: 2 kg (dry blended)

  • Re-dispersible polymer powder: 3 kg
    Mix thoroughly before water addition.

• Translucent Loose Powder (Cosmetic):

  • Talc: 70 g

  • Zinc stearate: 8 g

  • Silica microspheres: 10 g

  • Magnesium stearate: 2 g

  • Nylon‑12: 10 g
    Blend to uniform consistency for excellent slip and adhesion.

6. REGULATORY STATUS AND SAFETY

• CAS Number: 557-05-1 (harmonized)

• EINECS: 209-151-9

• Regulatory Approvals: Listed in many national inventories (TSCA, EU, etc.). It is not a food additive (unlike magnesium stearate). For cosmetic use, zinc stearate is a permitted colourant (when used as a colour, subject to purity requirements) but more commonly used as a cosmetic ingredient (INCI: Zinc Stearate) for its texturizing properties.

• Hazard Classification: Not classified as dangerous under GHS. Like many fine powders, airborne dust may form explosive mixtures with air; avoid dust accumulation.

• First Aid: Inhalation – move to fresh air. Eye/skin contact – flush with water. Ingestion – rinse mouth, seek medical advice if large quantity swallowed.

• Storage: Keep in tightly sealed containers in a cool, dry place (<30 °C), away from direct sunlight, heat, and incompatible materials (strong acids, oxidisers). Avoid generation of dust clouds.

7. FREQUENTLY ASKED QUESTIONS

Q1. What is zinc stearate commonly used for?
The largest volume use is in the plastics and rubber industries as a lubricant, mold release agent, and PVC heat stabilizer synergist. It is also widely used in paints and coatings for matting and in construction for water repellency.

Q2. Is zinc stearate soluble in water?
No, it is practically insoluble in cold and hot water. It can be dispersed in water with the help of surfactants to form an emulsion.

Q3. What is the difference between zinc stearate and magnesium stearate?
Both are metallic soaps. Magnesium stearate is primarily used in pharmaceutical tablets as a lubricant and is GRAS for food/pharma. Zinc stearate is preferred in non‑food applications, particularly in plastics and rubber, because zinc imparts better heat stability and does not cause toxicity issues in those industrial contexts.

Q4. Can zinc stearate be used in food contact applications?
Zinc stearate is generally not approved for direct food contact as a food additive. However, it may be used in certain food contact polymers subject to migration limits set by regional regulations (e.g., EU 10/2011, US FDA 21 CFR). Always check specific regulations for the intended use.

Q5. How should zinc stearate be incorporated into a polymer melt?
It can be pre‑blended with the polymer granules or added via a separate feeder during compounding. Because it melts between 120–124 °C, it dissolves into the melt and effectively reduces melt viscosity and metal adhesion.

Q6. Is zinc stearate hygroscopic?
No, it is practically non‑hygroscopic. This property helps in formulations where moisture sensitivity is a concern.

Q7. Can zinc stearate be used in transparent PVC?
Zinc stearate has limited solubility in PVC and tends to cause haze at higher levels; it is more suited for opaque applications. For transparent PVC, liquid organotin or other transparent stabilizer packages are used, often without zinc stearate or with very low amounts of zinc soaps.

Q8. What causes zinc stearate to have a “soapy” feel?
The long‑chain fatty acid moiety (stearate) lubricates the skin surface, producing a soapy, slippery sensation. This characteristic makes it useful in cosmetic powders and as a dry lubricant.