Molecular weight is the single most important parameter in polyacrylamide performance. It determines floc size, settling speed, shear resistance, and viscosity. Yet most suppliers just say "high molecular weight" without giving you the actual number. Here is what molecular weight means in practice and how to choose the right range for your application.
Molecular Weight Ranges and Applications
| MW Range | Classification | Best Applications | Key Benefit |
|---|---|---|---|
| 1-5 million Da | Low MW | Dry strength, coagulation aid | Penetrates fiber network |
| 6-10 million Da | Medium-low MW | Filter press, dense floc applications | Dense, compact flocs |
| 10-15 million Da | Medium MW | Centrifuge, belt press, paper making | Balance of floc size and shear resistance |
| 15-20 million Da | High MW | Gravity settling, thickeners, drinking water | Large, fast-settling flocs |
| 20-25 million Da | Very high MW | Mining tailings, EOR, drilling | Maximum bridging, high viscosity |
| 25-28 million Da | Ultra-high MW | Fine tailings (gold, silver), paste thickeners | Fastest settling of finest particles |
What Molecular Weight Actually Means
Molecular weight (MW) measures the size of the polymer chain — how many monomer units are linked together. One million Daltons (1M Da) means roughly 14,000 acrylamide units in a chain. At 28M Da, that is nearly 400,000 units in a single molecule.
Longer chains extend further into solution. This is what creates the bridging effect — a single polymer molecule can simultaneously attach to multiple suspended particles and pull them together. The longer the chain, the more particles it can bridge, and the larger the resulting floc.
For projects like this, our our polyacrylamide products delivers consistent results with factory-direct pricing.
But longer chains also mean slower dissolution, higher viscosity in solution, and greater sensitivity to shear. There is always a tradeoff.
How MW Affects Performance
Floc Size
Higher MW = larger flocs. For gravity settling (thickeners, clarifiers, tailings ponds), you want large flocs that settle fast. Use 15-28M Da. For pressure filtration (filter press), smaller, denser flocs drain better. Use 6-12M Da.
Settling Speed
Floc settling speed follows Stokes' law — it scales with the square of floc diameter. Doubling floc size quadruples settling speed. Ultra-high MW PAM (25-28M Da) can reduce settling time from days to hours for fine mineral tailings.
Shear Resistance
High MW flocs are more fragile. In high-shear environments (centrifuges, pumps, pipe flow), long polymer chains break and flocs disintegrate. For centrifuge dewatering, medium MW (10-15M Da) gives better results than ultra-high MW because the flocs survive the G-force.
Dissolution Time
Higher MW = slower dissolution. Our 6M Da grades dissolve in 30-45 minutes. Our 28M Da grades need 60-90 minutes. If your process cannot wait, use emulsion format — it dissolves in under 5 minutes regardless of MW.
Viscosity
Higher MW = higher solution viscosity. For EOR (enhanced oil recovery), high viscosity is the goal — it improves sweep efficiency. For most water treatment applications, viscosity is just a handling consideration.
Our Molecular Weight Range
At our Zhengzhou factory, we produce PAM across the full molecular weight spectrum:
- APAM: 6-28 million Da (7 specifications)
- CPAM: 6-20 million Da (10 specifications)
- NPAM: 8-15 million Da
Every batch is tested for molecular weight with ±0.5M Da tolerance. We use viscometry and light scattering methods to verify MW — not just dissolution time, which is an indirect and unreliable indicator.
We can also produce custom MW grades for specific applications. If you need 22M Da APAM with 28% hydrolysis for a specific tailings application, we can formulate it.
Need PAM for your application?
Free sample + jar test report. WhatsApp: +86 150-0381-8598
How to Verify MW When Buying
Many suppliers claim high MW but cannot prove it. Here is how to verify:
- Ask for the COA — Certificate of Analysis should state the actual MW value, not just "high" or "ultra-high"
- Check dissolution time — 28M Da powder should take 60-90 minutes to fully dissolve. If it dissolves in 20 minutes, the MW is lower than claimed
- Measure solution viscosity — 0.1% solution of 20M Da PAM should have viscosity of 200-400 mPa·s at 25°C
- Run a settling test — Compare settling speed with a known reference. Higher MW should give faster settling
- Request third-party test report — Reputable suppliers can provide independent lab verification
Common Mistakes in MW Selection
- Always choosing the highest MW — Ultra-high MW is not always better. For centrifuge dewatering, it often performs worse than medium MW due to shear sensitivity.
- Ignoring charge density — MW and charge density work together. A 20M Da CPAM with wrong charge density will underperform a 12M Da CPAM with correct charge density.
- Not testing before bulk ordering — MW requirements vary by application and water chemistry. Always run jar tests with your actual water before committing to a grade.
- Trusting "high MW" claims without data — Always ask for the actual number and verify it.
Need Help Selecting the Right MW?
Send us your application details (water type, suspended solids, equipment type, target performance) and we will recommend the optimal MW and charge density combination. Free samples available for testing.
See also: Anionic vs Cationic PAM selection guide | Dosage calculation guide | Charge density explained
WhatsApp: +86 150-0381-8598 | Request a quote
Get a Quote
Our factory in Zhengzhou produces 100,000 tons/year of PAM across 18+ grades. MOQ 500kg, delivery 7-10 days standard. Contact us for pricing and free sample:
- WhatsApp: +86 150-0381-8598
- Email: info@chinapolyacrylamide.com