I. Basic Profile

Sodium Tripolyphosphate (STPP), chemical formula Na₅P₃O₁₀, molecular weight 367.86, CAS No. 7758-29-4. It is an amorphous, water-soluble linear polyphosphate, commonly known as "pentasodium" due to its five sodium atoms. Appearance: white powder or granules, readily soluble in water, with a 1% aqueous solution pH of approximately 9.7 (weakly alkaline).

The anhydrous form exists in two crystalline phases: high-temperature (Type I) and low-temperature (Type II). Both have identical chemical properties but differ in thermal stability, solubility, and hygroscopicity. Type I dissolves rapidly but is highly hygroscopic and prone to caking; Type II absorbs moisture more slowly and resists caking.

II. Key Functional Properties

1. Metal Ion Chelation
STPP exhibits excellent chelating ability toward hardness-inducing metal ions such as calcium, magnesium, and iron, effectively softening hard water. Every 100 g of STPP can chelate approximately 19.5 g of calcium ions, preventing them from forming insoluble salts with surfactants.

2. Dispersion and Emulsification
It swells and solubilizes proteins, emulsifies fats and oils, and disperses solid particulates, effectively removing various types of soil.

3. pH Buffering
It provides strong alkaline buffering capacity, maintaining wash solutions at approximately pH 9.4, which facilitates the removal of acidic soils.

4. Anti-Caking Effect
Upon absorbing moisture, it forms a hexahydrate with a dry, free-flowing characteristic, preventing powdered detergents from caking due to humidity.

III. Major Applications

1. Detergent Industry (Primary Use)
STPP is an essential and superior builder in synthetic detergents, typically comprising 10%–50% of detergent formulations. It is used in laundry powders, dishwashing detergents, and other cleaning products to enhance detergency.

2. Food Industry
As a food additive (E451), it functions as a moisture retainer, quality improver, pH regulator, and metal chelator. Key applications include:

• Meat products (ham, sausages): water retention, tenderization, reduced cooking loss

• Seafood: moisture retention, prevention of freeze denaturation

• Canned goods: softening bean skins, maintaining product integrity

• Dairy products and beverages: stabilizer, emulsifier

According to China GB2760 standards: maximum usage of 5.0 g/kg in meat and dairy products; 1.0 g/kg in canned goods and beverages.

3. Industrial Water Treatment
Used as a water softener and scale inhibitor, effectively removing mineral precipitates and preventing scaling in pipes and equipment.

4. Other Industrial Applications
Leather pretanning agent, dyeing auxiliary, drilling mud dispersant, papermaking anti-soil agent, paint dispersant, etc.

IV. Industry Development Trends

STPP is the most widely consumed industrial phosphate in China. In 2021, the national production capacity reached approximately 750,000 tons, with an output of about 380,000 tons. Notable trends include:

• Environmental Policy Impact: Phosphorus-containing detergents contribute to water eutrophication. With the introduction of phosphorus-restriction policies, STPP usage in detergents has gradually declined, partially replaced by layered sodium silicate, zeolites, and other alternatives.

• Growing Food-Grade Demand: The export share of food-grade STPP increased from 16.3% in 2015 to 42.1% in 2021, with major export destinations including Brazil, Thailand, and Mexico.