🌿 Ammonium Polyphosphate (APP): Core Phosphorus Source for Liquid Fertilizers and a Green Flame-Retardant Solution

Ammonium Polyphosphate (APP), CAS No. 68333-79-9, is a high-performance, low-nitrogen, high-phosphorus polymeric phosphate compound synthesized through the high-temperature condensation of phosphoric acid and ammonia. Its general formula is (NH₄PO₃)ₙ. Depending on the degree of polymerization, APP finds extensive use in both 🌾 agriculture (fertilizers) and 🧯 industry (flame retardants).

Physicochemical Properties

APP typically appears as a white powder or transparent viscous liquid. 💧 It is readily soluble in water and exhibits excellent thermal and chemical stability. The degree of polymerization (n) directly influences its solubility, slow-release characteristics, and usage. Liquid APP generally appears as a clear or slightly yellow solution with a specific gravity of 1.4–1.5 and a P₂O₅ content of 34%–54%, ensuring stable nutrient supply.

Production Process 🏭

APP is produced from phosphoric acid and ammonia through continuous polymerization. 🧪 Key factors affecting the degree of polymerization include temperature, reactant ratio, and residence time. 🌱 Modern processes emphasize eco-friendliness and by-product control, ensuring low chlorine and heavy metals while treating emissions like ammonia and acid mist.

📘 Detailed APP Production Process

🧪 Raw Materials

Material	Chemical Formula	Requirements
Phosphoric Acid	H₃PO₄	≥75% purity, low metal content, Cl⁻ < 0.1%
Liquid Ammonia Ammonium Hydroxide	NH₃ / NH₄OH	≥99.5% NH₃; 20–25% NH₄OH concentration

🧲 Low Fe, Ca, and Al are essential to avoid precipitation or side reactions.

⚗️ Reaction Principle

• Initial reaction forms monoammonium phosphate (NH₄H₂PO₄)

• High-temperature dehydration and condensation form polyphosphate chains

• Polymerization degree (n) is controlled by pH, temperature, and molar ratios
  

🛠️ Key Process Steps

1️⃣ Neutralization Stage

• Add phosphoric acid and ammonia/NH₄OH in controlled ratio (1.0–1.05)

• Exothermic reaction at 80–120°C forms intermediate ammonium phosphate

• Can use continuous or batch process
  

2️⃣ Polymerization Stage

• Heat to 180–300°C for condensation

• Higher temperature/time = greater polymerization

• Optional vacuum/low pressure helps remove water

• Degree of polymerization tailored to fertilizer or flame-retardant application
  

3️⃣ Cooling & Discharge

• 💧 Liquid APP: cooled and stored in tanks or IBCs

• 🌨️ Powder APP: spray-dried or pelletized

• QC: viscosity, P₂O₅ content, water-insolubles, pH
  

📘 APP Classification by Degree of Polymerization and Application

🧩 What is Degree of Polymerization (DP)? 

DP indicates how many phosphate units (PO₃) are linked in a chain. It determines the chain length, structure, and performance of APP.

📌 Relationship Between DP and Performance

Type	DP Range (n)	Structure	Form	Application Area	Key Features
APP-I	≈ 3–20	Short-chain	Liquid	Liquid fertilizers, clear NPK	High solubility, rapid P uptake
APP-M	≈ 20–100	Mid-chain & branched	Liquid/Powder	Drip fertigation, slow-release ferts	Balanced solubility & controlled release
APP-II	>100	Long-chain	Powder	Flame retardants, building aids	Excellent thermal stability, slow solubility

📊 Trends with Increasing DP:

Property	With Increasing DP
💧 Water Solubility	Decreases
🌱 Slow-Release Effect	Increases
🔥 Thermal Stability	Significantly increases
🧪 Viscosity (liquid)	Increases
⚗️ Compatibility	Slightly decreases

🔍 Type Descriptions and Examples

• APP-I (Low DP)

  • Application: liquid phosphate, foliar feed, water-soluble ferts

  • Features: Excellent solubility, primarily orthophosphate and short-chain polyphosphate; quickly absorbed

  • Typical scenarios: greenhouse fertigation, fruit & vegetable drip feed
    

• APP-M (Medium DP)

  • Application: advanced liquid ferts, drip ferts, granular slow-release core

  • Features: Moderate solubility with controlled-release effects

  • Compatibility: Stable, non-crystallizing, adaptable release rate
    

• APP-II (High DP)

  • Application: halogen-free flame retardants for plastics, coatings, construction

  • Features: Forms char layer at high temperature, intumescent performance

  • Examples: Combined with pentaerythritol, melamine in IFR systems
    

🌿 Quick Comparison: APP vs. Orthophosphates (MAP/DAP)

Attribute	MAP/DAP	APP
Phosphorus Type	Orthophosphate only	Polyphosphate + partial orthophosphate
Release Speed	Immediate	Controlled (slow release)
Crystallization	Possible precipitate	Highly stable, no crystallization
Use Case	Broadcast, water-soluble	Drip irrigation, foliar, specialty fertilizer

📦 Application Fields & Functional Roles

🌿A. Agricultural Applications (Core Market)

Ammonium polyphosphate serves as an efficient liquid phosphorus source, playing a vital role in modern agriculture due to its controlled release properties, compatibility, and low risk of crystallization. It is widely used in the following applications:

1️⃣ Base Raw Material for Liquid Fertilizers

• 💡 Role: Primary phosphorus source in NPK or NPK+TE formulations

• 💧 Dosage: Typically 20–40% (based on P₂O₅ content)

• ⚙️ Typical Concentration: 34–52% P₂O₅; Nitrogen content around 11%

• 🚿 Application: Via drip irrigation, spraying, or flushing systems; suitable for vegetables, fruits, and field crops

• ✅ Advantage: High stability, non-clogging, consistent phosphorus supply

2️⃣ Component for Drip/Spray Irrigation Fertilizers

• 💧 Use: Precision fertilization in greenhouses, sandy soils, or saline-alkaline regions

• 📏 Recommended dosage: 3–8 kg APP solution per mu per application (adjusted based on crop needs)

• 🧪 Compatibility: Mixable with potassium nitrate, potassium sulfate, EDTA-chelated micronutrients

• ✅ Advantage: No phosphate precipitation, improves system flowability

3️⃣ Intermediate for Controlled/Slow-Release Fertilizers

• ⚗️ Mechanism: Hydrolysis of polymeric structure gradually releases phosphorus

• 🧱 Form: APP powder (medium or high DP) blended with organic carriers or coating materials

• 📊 Suggested content: 10–20% of total formula, combined with polymer coatings or microbial enhancers

• 🌾 Crops: Grapes, citrus, corn, wheat, etc. requiring long-term phosphorus supply

4️⃣ Development of Multi-Nutrient Functional Fertilizers

• 🔬 Formulation: APP + EDTA-Zn + boron for drought-resistant Zn-phosphorus liquid fertilizer

• 📏 Application rate: 1–2 kg APP + 0.2–0.5 kg micronutrients per mu per use (drip-irrigated)

• 🌱 Function: Root stimulation, nutrient absorption, stress resistance

5️⃣ Base Solution for Seedling Cultivation or Hydroponic Systems

• 🌱 Purpose: Stable and balanced phosphorus source for seedlings and hydroponics

• 💧 Benefit: No crystallization, no clogging of nutrient circulation systems

• 📏 Dilution rate: 0.05–0.1% P₂O₅

🔥 B. Flame Retardant Applications (Industrial Use)

APP is also a major halogen-free phosphorus-based flame retardant widely used in plastics, rubber, wood, and coating industries.

1️⃣ Intumescent Flame Retardant Systems (IFR)

• 🔥 Function: APP decomposes at high temperature, releasing polyphosphoric acid to form a carbonized insulating layer, thus inhibiting combustion.

• 🧪 Typical Formulation:

  • APP (acid source) + melamine (blowing agent) + pentaerythritol (carbon source)

  • Common ratio: APP 60%, melamine 20%, pentaerythritol 20%

• 🧱 Suitable Substrates: polypropylene, polyethylene, epoxy resins, wood materials

• 📊 Dosage: typically 15–25 wt% of total resin

• ✅ Performance: LOI ≥28%, meets UL-94 V-0 fire safety rating
  

2️⃣ Fireproof Coatings for Waterborne Paints and Wood Protection

• 🎨 Function: Improves flame resistance of wood, cardboard, and decorative boards

• 🧴 Application: blended into acrylic latex or emulsion paints

• ⚖️ Dosage: 15–30% (dry weight basis)

• 🌱 Advantage: Non-halogen, low toxicity, REACH compliant

  
  

3️⃣ Additive for Flame-Retardant Textiles and Foam Plastics

• 🧵 Uses: PU foam, adhesives, textile finishing

• ✴️ Method: spray, dip, or blending

• 🔬 Effect: increases char yield and delay flame spread
  

🧪 C. Other Industrial Applications (Emerging Use Cases)

1️⃣ Boiler Water Treatment Agent

• 🔗 Function: APP chelates Ca²⁺ and Mg²⁺, serving as an anti-scale and softening agent

• 📏 Dosage: 10–50 ppm

• ✅ Advantage: stable, safe, non-degradable under normal use
  

2️⃣ Industrial Cleaner or Metal Chelator

• 💧 Function: Chelates metals and moderates pH; ideal for alkaline cleaning formulations

• 🏭 Industries: glass, electronics, metal components

• 📦 Dosage: 1–5% of cleaning formulation
  

3️⃣ Additive for High-Performance Building Materials

• 🧱 Use: incorporated in insulation foam, gypsum boards, calcium silicate panels

• 🔒 Feature: boosts flame retardancy and weather resistance
  

🔚 Summary: Value Highlights of APP

Application Field	Core Function	Key Advantages
🌾 Liquid Fertilizers	Controlled P Supply	Non-crystallizing, drip-irrigation friendly, highly compatible
🔥 Flame Retardants	Intumescent Action	Thermal stability, eco-safe, high carbon yield
🧪 Industrial Additives	Chelation, Anti-scale	Safe, eco-friendly, versatile

📦 Packaging & Storage

• 🧂 Powder APP: 25kg or 50kg plastic-lined woven bags
  

• 💧 Liquid APP: stored in IBC totes or transported in tankers
  

• 📦 Storage Conditions: keep dry, ventilated; avoid moisture, direct sunlight, and temperature extremes (especially for liquid types)
  

🌍 Market Overview & Trends

🌎 Global Market Landscape

✅ 1. Agriculture: Liquid Fertilizer Demand Drives APP Growth

With the advancement of fertigation and sustainable agriculture globally, APP is becoming a critical phosphorus source:

• 🇺🇸🇧🇷 North & South America: Liquid NPK fertilizers widely used

• 🇩🇪🇫🇷🇵🇱 Europe: Strict environmental standards favor low-impurity APP

• 🇨🇳 Asia: China is the largest producer and exporter; India & SE Asia are expanding fertigation systems rapidly

• 🇦🇺 Australia: High dependence on drip irrigation and precision nutrient systems in vineyards, orchards, and greenhouses

• 🌍 Middle East & Africa: Growing demand for stable, efficient phosphorus sources as drip systems expand
  

✅ 2. Flame Retardant Sector: Environmental Compliance Drives APP Uptake

• 🌱 Global regulations (REACH, RoHS, UL-94, SVHC) are phasing out halogen-based retardants

• 🔁 APP is now a leading halogen-free option for polyolefins, epoxy, wood coatings, insulation boards

• 💹 Global flame retardant market > USD 8 billion; APP CAGR projected at 6–8%
  

🇨🇳 China Market Overview

✅ 1. Concentrated Production and Technological Maturity

• 💡 Key provinces: Sichuan, Chongqing, Shandong, Hebei

• 🔄 Major plants have 30k–100k tpa capacity, some with integrated phosphoric acid

• ⚙️ Advanced process: thermal polymerization + ammonia removal + customized DP options
  

✅ 2. Export-Oriented Growth

• 📦 Main destinations: USA, Korea, Australia, India, Saudi Arabia, Brazil

• 🚢 Forms: IBC-packed liquid APP and powder APP for flame retardants

• ⚖️ Strengths: stable supply, cost-efficiency, maritime logistics advantage
  

⚠️ Market Challenges

Challenge	Description
💹 Raw Material Volatility	Price swings in phosphoric acid and ammonia affect production cost
♻️ Environmental & Impurity Control	Excess Fe, Al, Cl in high-DP APP affects safety and function
📐 Standard Discrepancies	Lack of unified global spec for agricultural vs industrial APP
📣 Market Education	Limited awareness among end-users, especially smallholder farmers

🔮 Future Outlook

✅ Agriculture

• 🔬 APP will continue emerging as the go-to liquid P source

• 🌿 Functionalization with trace elements, seaweed extract, biostimulants

• 🤖 Integration into digital fertigation & smart farming systems

• ✅ Push for "green label" certification under EU & global eco-regulations
  

✅ Industry

• 🔥 Broader halogen-free adoption in children’s products and green building materials

• ⚙️ Modular design of IFR systems to improve synergy

• 📜 Regulatory transparency drives material substitution, favoring APP

• 🧪 Innovation: High-DP APP + nanotech/microencapsulation for advanced performance
  

🧾 Conclusion: The Long-Term Value of APP

APP stands at the intersection of agricultural innovation and sustainable material development. As eco-conscious farming and industry evolve, APP will continue to unlock value in liquid fertilizers, halogen-free fire protection, and green industrial formulations.

Not just a phosphorus carrier—APP is a cornerstone of the next-generation green solution portfolio.

At Kelewell, we can provide: Liquid APP ratios: 8-24-0, 10-34-0, 11-37-0, 11-44-0, 8-28-0, etc. Solids ratios: 18-58-0, 17-59-0, 18-60-0 and 16-62-0, etc.

Contact: info@kelewell.de