1. What is Polyacrylamide?
Polyacrylamide (PAM) is a linear, water-soluble synthetic polymer with the chemical formula (C₃H₅NO)ₙ, produced by free-radical polymerization of acrylamide monomers. It appears as a white powder or granules, readily dissolves in water, and forms a transparent, viscous liquid.
Due to its excellent flocculation, thickening, drag reduction, and adhesion properties, PAM is widely used in water treatment, oil extraction, papermaking, mining, textiles, and other fields. It is often called the “versatile industrial aid” or “universal product.”
Basic Information:
- CAS Number: 9003-05-8
- Molecular Formula: C₃H₅NO
- Molecular Weight: Ranges from several million to over 20 million
- Melting Point: >300°C
- Appearance: White powder or granules; also available in colloidal or emulsion forms
- Storage Requirements: Moisture-proof, light-proof, heat-proof; avoid long-term storage
Safety Note: Polyacrylamide and its hydrolysates are non-toxic. PAM meeting relevant standards can be used in drinking water treatment and the food industry. However, the monomer acrylamide is neurotoxic, so residual monomer content in finished products is strictly limited (typically ≤0.05%-0.2%).
2. Chemical Structure & Basic Properties
2.1 Molecular Structure
The PAM molecular chain contains numerous reactive amide groups (-CONH₂). These amide groups are key to PAM’s functionality—they can interact with and adsorb various substances, forming hydrogen bonds.
2.2 Key Physicochemical Properties
| Property | Characteristics |
|---|---|
| Solubility | Readily soluble in cold water; insoluble in ethanol, acetone, and most organic solvents |
| Dissolution Rate | Slow; high molecular weight PAM requires 30-60 minutes to dissolve |
| Temperature Sensitivity | Dissolution temperature should not exceed 50°C to avoid degradation; decomposition temperature >120°C |
| Hygroscopicity | Solid PAM readily absorbs moisture; rate depends on ionic characteristics |
| Compatibility | Incompatible with strong oxidizers and metal ions such as aluminum, copper, and iron |
2.3 Special Behavior
When the concentration of high molecular weight PAM exceeds 10%, it forms a gel-like structure. This property has special applications in laboratory gel electrophoresis and oilfield water shutoff and profile control.
3. Water Treatment Principles: How Does PAM “Purify” Water?
Polyacrylamide is primarily used as a flocculant in wastewater treatment. Its mechanisms of action can be divided into three types, which often work synergistically:
3.1 Adsorption Bridging (Core Mechanism)
This is PAM’s most important flocculation mechanism. The long PAM molecular chain acts like a “rope,” with amide groups that can simultaneously adsorb multiple suspended particles. When one chain adsorbs different particles, it forms a “bridge” connecting them into larger flocs. As more particles are “bridged,” flocs grow and eventually settle by gravity, achieving solid-liquid separation.
3.2 Charge Neutralization
Ionic derivatives of PAM (e.g., cationic PAM) carry positive charges that can neutralize the negative charges on suspended particles in wastewater, eliminating electrostatic repulsion and promoting particle aggregation.
3.3 Sweep Flocculation
When dosed appropriately, the settling flocs act like a “net,” entraining and sweeping down non-aggregated fine particles, further improving treatment efficiency.
4. Four Main Types: Classification by Ionic Character
Polyacrylamide is divided into four main categories based on the charge characteristics of its molecular chain:
4.1 Anionic Polyacrylamide (APAM)
- Appearance: White granules or powder
- Molecular Weight Range: 3-25 million
- Degree of Hydrolysis: 10-35%
- Optimal pH Range: 7-14 (neutral or alkaline)
- Market Position: Holds the largest global market share (~46.87%), continuing to dominate due to growing demand in water treatment
Characteristics: Negatively charged molecular chain; good flocculation effect on positively charged suspended particles.
Main Applications:
- Coal washing wastewater treatment
- Steel plant, electroplating, and metallurgical wastewater
- Drinking water purification
- Enhanced Oil Recovery (EOR)
4.2 Cationic Polyacrylamide (CPAM)
- Appearance: White granules
- Molecular Weight: 0.5-12 million
- Ionicity: 5-80%
- Optimal pH Range: 1-14 (broad range)
- Dissolution Time: ≤60 minutes
Characteristics: Positively charged molecular chain; strong neutralization and flocculation capability for negatively charged organic pollutants and colloids. It is the preferred chemical for sludge dewatering.
Main Applications:
- Municipal and industrial sludge dewatering
- Paper retention and drainage aids
- Organic-rich wastewater treatment
4.3 Nonionic Polyacrylamide (NPAM)
- Appearance: White granules or powder
- Molecular Weight: 0.2-15 million
- Degree of Hydrolysis: 0-5%
- Optimal pH Range: Neutral or acidic
Characteristics: Uncharged molecular chain; suitable for treating acidic or complex charge wastewater systems.
Main Applications:
- Acidic wastewater treatment
- Drinking water purification in combination with inorganic flocculants
- Textile sizing agents, sand fixation, soil moisturizers
4.4 Amphoteric Polyacrylamide (ACPAM)
- Appearance: White granules
- Molecular Weight: 5-17 million
- Cationic Degree: 5-60%; Anionic Degree: 0-10%
- Optimal pH Range: 1-14 (broadest range)
Characteristics: Molecular chain contains both cationic and anionic groups; can be used across an extremely wide pH range. Important Note: Amphoteric PAM is NOT a simple mixture of anionic and cationic types—mixing those separately would cause precipitation.
Main Applications:
- Complex wastewater with fluctuating pH
- Oilfield profile control and water shutoff agents
- Metal recovery from acidic mineral solutions
5. Quick Reference Table for the Four Types
| Type | Optimal pH Range | Main Applications | Typical Use Cases |
|---|---|---|---|
| Anionic | 7-14 | Inorganic suspended solids, high turbidity water | Coal washing wastewater, steel plant wastewater, EOR |
| Cationic | 1-14 | Organic sludge, negatively charged colloids | Sludge dewatering, municipal sewage, papermaking |
| Nonionic | Acidic/Neutral | Acidic systems, complex charge systems | Acid mine drainage, textile sizing |
| Amphoteric | 1-14 | Extreme or variable pH, special industrial wastewater | Oilfield profile control, complex chemical wastewater |
6. Physical Forms and Selection Guide
Polyacrylamide is mainly available in three commercial forms: solid powder, emulsion (liquid), and gel.
6.1 Comparison of Forms
| Characteristic | Solid Powder | Emulsion | Gel |
|---|---|---|---|
| Active Content | Highest (88%-92%+) | Medium (20%-50%) | Lowest (<10%) |
| Dissolution Speed | Slow (30-60 minutes) | Fast (minutes) | Very slow, easily clumps |
| Dissolution Equipment | Requires dry powder feeder | Dosing pump only | Not recommended for direct use |
| Transport Cost | Low | High | Very high |
| Main Applications | Large-scale water treatment, sludge dewatering | Automated lines, oilfields, small facilities | Laboratory (electrophoresis gels) |
| Storage Notes | Strictly moisture-proof | Avoid freezing (for oil-based emulsions) | Easily degrades, short shelf life |
6.2 Form Selection Recommendations
- Monthly consumption > 1 ton (powder equivalent): Powder is the first choice. Although equipment investment is higher, the significant chemical cost advantage reduces total annual costs by more than 30%.
- Monthly consumption < 200 kg: Consider emulsions. Eliminating equipment investment and labor maintenance may be more economical despite higher chemical costs.
- Laboratory use: Use specialized gel-type PAM.
7. Main Application Areas
7.1 Water Treatment (Largest Application Area)
In the global polyacrylamide market, water treatment is the largest end-use application, accounting for approximately 36%. Driven by increasing water scarcity and tightening environmental regulations, demand for PAM in municipal and industrial water treatment continues to grow. PAM plays a key role as a flocculant, coagulant aid, and sludge dewatering agent in achieving solid-liquid separation and reducing sludge moisture content.
7.2 Oil Extraction
Anionic PAM is widely used in Enhanced Oil Recovery (EOR). When dissolved in injection water, PAM increases water viscosity and improves fluid movement in reservoirs, thereby enhancing oil displacement efficiency and recovery rates. This application is a significant driver of PAM market growth in regions such as the Middle East and North America.
7.3 Other Industrial Fields
- Mining: Coal slurry water treatment, tailings concentration
- Papermaking: Retention aids, dry strength agents, drainage aids
- Textiles: Sizing agents, finishing agents
- Agriculture: Soil conditioners, moisturizers
8. Market Overview
The global polyacrylamide market size was 4.37billionUSD∗∗in2025andisprojectedtoreach∗∗4.37billionUSD∗∗in2025andisprojectedtoreach∗∗7.56 billion USD by 2034, growing at a CAGR of 6.30%.
Regional Landscape:
- The Asia-Pacific region holds the largest global market share at 45%
- Countries such as China and India are major consumers due to rapid industrialization and expansion of water treatment infrastructure
- The United States promotes PAM use due to shale oil development and strict water treatment regulations
Major Manufacturers: SNF, Kemira, Solenis, Henan Hangrui Environmental Protection Technology Co., Ltd., among others.
9. Usage Precautions
9.1 Dissolution Key Points
- Temperature Control: Dissolution temperature should not exceed 50°C to avoid molecular degradation
- Thorough Mixing: Ensure complete dissolution to prevent “fish-eye” undissolved particles
- Concentration Control: Typically prepare a dilute solution (0.1%-0.3%) before dosing
9.2 Storage Requirements
- Store in a cool, well-ventilated, dry area
- Protect from moisture, light, and heat
- Use opened bags of solid PAM as soon as possible
- Protect emulsions from freezing to avoid breaking the emulsion
9.3 Incompatibilities
- Incompatible with strong oxidizers
- Incompatible with metal ions such as aluminum, copper, and iron
- Do not mix cationic and anionic types (will cause precipitation)
10. Conclusion
Polyacrylamide is a powerful water-soluble polymer material. Selecting the right PAM product requires comprehensive consideration of:
- Wastewater/Sludge Characteristics: pH, suspended solids charge, organic content
- Treatment Equipment Type: Belt filter presses, centrifuges, settling tanks have different chemical requirements
- Consumption Scale: Determines selection between powder or emulsion forms
- Cost Budget: Balancing chemical, equipment, and labor costs
It is recommended to conduct jar tests to determine the most suitable PAM type, molecular weight, and dosage for optimal treatment performance and economic efficiency.
