Water-soluble; water-insoluble Ammonium polyphosphate CAS 68333-79-9

What is ammonium polyphosphate? What are its uses?

I. What is Ammonium polyphosphate?

Ammonium polyphosphate (APP) is a nitrogen-containing polyphosphate formed by the condensation polymerization of ammonium phosphate. It is also an important polyphosphate in flame retardant science and agricultural fertilizers. Its chemical formula is usually written as:

(NH4PO3)n (CAS No.: 68333-79-9, EINECS No.: 269-789-9)

It is a white powder or crystal at room temperature, odorless, and nearly neutral. Ammonium polyphosphate is classified into two categories according to its degree of polymerization: low degree of polymerization (Form I) products have good water solubility and are mainly used as fertilizers; high degree of polymerization (Form II) long-chain products are difficult to dissolve in water, have high crystallinity, good thermal stability, and begin to decompose at about 240℃, making them the standard object for flame retardant research.

From a molecular structure perspective, ammonium polyphosphate has a long backbone of alternating phosphorus-oxygen (POP) groups, with ammonium ions (NH4+) attached to the chain. This "phosphorus-nitrogen synergy" molecular design endows it with unique chemical functions: when heated, it decomposes into polyphosphate and ammonia, with polyphosphate promoting the formation of an expanded char layer on the surface—in scientific research, this "expansion to char" process is a classic system for studying flame retardant mechanisms and the pyrolysis behavior of materials; in agriculture, the dual nutrient elements of phosphorus and nitrogen make it the preferred form for high-concentration compound fertilizers.

Chemically, ammonium polyphosphate is nearly neutral, chemically stable, and sparingly soluble in water (Form II). It decomposes at high temperatures to produce ammonia and polyphosphoric acid. It is non-toxic, produces low smoke, and is halogen-free. It should be stored in a sealed, moisture-proof container.

Non-industrial grade ammonium polyphosphate refers to products intended for testing, research, and agricultural applications, primarily including reagent-grade, research-grade, and agricultural-grade specifications. Compared to industrial-grade products, these products place greater emphasis on the following indicators:

Content (purity)

Reagent-grade reagents require high content of main components, with phosphorus and nitrogen content precisely matching the labeled values. The content directly determines the accuracy of analytical results and experiments.

Phosphorus content and nitrogen content

Phosphorus content (as P2O5) and nitrogen content are core indicators of product composition, and precise control is required for both scientific research and agricultural applications.

Degree of aggregation

The degree of polymerization determines water solubility and decomposition behavior. Scientific experiments must specify the degree of polymerization level (Form I or Form II) of the selected product.

Heavy metal limits

Reagent-grade and agricultural-grade reagents have strict limits on heavy metal content to ensure experimental safety and soil environmental safety.

pH value

The product is nearly neutral; pH fluctuations affect the stability of experiments and fertilizer formulations.

II. What are the uses of Ammonium polyphosphate?

1. High-concentration nitrogen and phosphorus compound fertilizer (agricultural grade, core application)

Low-polymerization-degree water-soluble ammonium polyphosphate is an important component of high-concentration nitrogen-phosphorus compound fertilizers, liquid fertilizers, and water-soluble fertilizers. It provides efficient phosphorus and nitrogen nutrition to crops through the synergistic effect of phosphorus and nitrogen dual nutrients and is widely used in agricultural fertilization and drip irrigation fertilization systems.

2. Intumescent fire-retardant coating (fireproofing for steel structures)

Ammonium polyphosphate is the core raw material of intumescent fire-retardant coatings for steel structures. When a fire occurs, the coating expands to form a dense carbon layer, protecting the steel structure and building materials. It is widely used for fire protection in shopping malls, stadiums, factories, subways, and pipelines, and is the most important flame retardant for fire-retardant coatings.

3. Halogen-free intumescent flame retardant (core application)

Ammonium polyphosphate is the core component of the intumescent flame retardant (IFR) system. When combined with charring agent (pentaerythritol) and foaming agent (melamine), it achieves heat insulation and oxygen barrier flame retardancy through an expanded char layer. It is a halogen-free, low-smoke, and low-toxicity environmentally friendly flame retardant system, widely used in plastics, rubber, polyurethane and composite materials.

4. Flame retardancy and flame retardant modification

( 1 ) Ammonium polyphosphate is used for flame retardant modification of polypropylene, polyethylene, PVC, polyurethane foam and unsaturated polyester resin, helping the materials to reach flame retardant levels such as UL94, serving the home appliance, automobile, cable and insulation material industries.

( 2 ) Ammonium polyphosphate is used for flame retardant treatment of wood, plywood, fiberboard and paper, helping wood products and paper materials to meet building fire protection requirements. It is the mainstream agent for wood flame retardant treatment.

( 3 ) Ammonium polyphosphate is used for flame retardant finishing of flame retardant fabrics and coated textiles, helping curtains, carpets, curtains and protective clothing to meet flame retardant standards. It is a commonly used environmentally friendly flame retardant for textile flame retardancy.

( 4 ) Ammonium polyphosphate is used for flame retardant modification of polyurethane insulation boards, foams, adhesives, sealants, grouts and laminates, improving the fire resistance of building exterior wall insulation, furniture foam and other decorative building materials.

( 5 ) Ammonium polyphosphate is a classic reagent for studying the mechanism of intumescent flame retardancy, char layer formation, material pyrolysis behavior and phosphorus-nitrogen synergistic effect. It is used in flame retardant science, materials science and fire safety research, serving academic research and technology development.

5. Customized Synthesis and Modification Research

Ammonium polyphosphate can be used to synthesize modified ammonium polyphosphate, microencapsulated ammonium polyphosphate, and novel intumescent flame retardant systems, serving the research and development of flame retardant materials and new materials, and is a basic raw material in the research and development stage.

6. Other Applications

With the development of flame retardant science and efficient agriculture, the application scope of non-industrial grade ammonium polyphosphate continues to expand, including standard reagent supply, analytical testing services, and teaching reagent support.

It should be noted that non-industrial grade specifications do not mean "risk-free": inhalation of ammonium polyphosphate dust may irritate the respiratory tract, and protective masks should be worn and operations should be carried out in a ventilated area; reagent-grade products are for experimental use only and are strictly prohibited from consumption, while agricultural-grade products are for fertilization only and must be stored in a dry place away from high temperatures.

Summarize

Ammonium polyphosphate (APP, CAS No. 68333-79-9) is a white, powdery nitrogen-containing polyphosphate. Based on its degree of polymerization, it is classified into two types: water-soluble short-chain and insoluble long-chain. It is a core component of halogen-free flame retardants and an important ingredient in high-concentration nitrogen-phosphorus compound fertilizers. In daily life, we indirectly encounter it through agricultural fertilizers, testing and analysis services, scientific research and university laboratories, teaching experiments, home gardening, and industrial supply chains. In non-industrial applications, reagent-grade, research-grade, and agricultural-grade ammonium polyphosphate are widely used in high-concentration nitrogen-phosphorus compound fertilizers, flame retardant material testing, research on intumescent flame retardant mechanisms, teaching experiments, customized synthesis of modified ammonium polyphosphate, and water-soluble fertilizers for home gardening. It is a crucial polyphosphate bridging "phosphorus and nitrogen chemistry" with "agriculture, testing, and scientific research."