Poly(diallyldimethylammonium chloride) (PolyDADMAC) is widely used as an efficient flocculant and charge neutralizer in industries such as water treatment, papermaking, and petroleum extraction, thanks to its high cationic charge density and excellent stability. However, its performance is closely related to its molecular weight (MW). PolyDADMAC products of different molecular weights show significant differences in charge neutralization ability, flocculation efficiency, and application suitability. Therefore, proper selection according to specific working conditions is essential.

I. Influence of Molecular Weight on PolyDADMAC Performance

  1. Low Molecular Weight PolyDADMAC (< 100,000 Da)

    • Characteristics: Short polymer chains, good mobility, fast solubility, and relatively high charge density.

    • Advantages: Quickly combines with negatively charged colloidal particles, achieving efficient charge neutralization.

    • Limitations: Weak bridging effect, limited performance in forming large flocs or treating high-turbidity systems.

  2. Medium Molecular Weight PolyDADMAC (100,000–500,000 Da)

    • Characteristics: Balanced structure, maintaining high charge density with moderate chain length.

    • Advantages: Provides both charge neutralization and partial adsorption–bridging effects.

    • Applications: Effective in municipal wastewater, industrial effluent treatment, and papermaking retention/drainage aid.

  3. High Molecular Weight PolyDADMAC (> 500,000 Da)

    • Characteristics: Longer polymer chains, higher viscosity, and stronger bridging effects.

    • Advantages: Forms more stable and larger flocs, enhancing sedimentation and filtration efficiency.

    • Limitations: Slower solubility and higher viscosity, requiring optimized dosing and mixing conditions.

II. Application Scenarios of Different Molecular Weight PolyDADMAC

  1. Low Molecular Weight PolyDADMAC

    • Initial charge neutralization in drinking water purification;

    • Pre-treatment for ultrapure water in electronics, requiring fast reaction and low residue;

    • Blended with inorganic coagulants (e.g., PAC, aluminum sulfate) to enhance overall flocculation.

  2. Medium Molecular Weight PolyDADMAC

    • Municipal wastewater treatment, offering a balance between speed and floc strength;

    • Industrial effluents (e.g., textile, metallurgy, chemical wastewater) coagulation and sedimentation;

    • Papermaking industry as a retention and drainage aid, improving paper strength and productivity.

  3. High Molecular Weight PolyDADMAC

    • Treatment of high-turbidity wastewater and oily wastewater separation;

    • Sludge dewatering processes, improving sludge cake solid content;

    • Produced water treatment and floc strengthening in petroleum extraction.

III. Considerations for Customers in Selection

  • Water Quality Characteristics: For low-turbidity water with fine particles, low MW PolyDADMAC is preferable; for complex or high-suspended solids systems, medium-to-high MW products are recommended.

  • Treatment Objectives: If charge neutralization is the priority, choose low MW; if particle capture and large floc formation are required, opt for high MW.

  • Process Conditions: High MW products require longer dissolution time and better mixing; otherwise, treatment efficiency may be reduced.

IV. Conclusion

PolyDADMAC is not a “one-size-fits-all” flocculant; its molecular weight determines specific performance and application value.

  • Low MW → Strong charge neutralization, ideal for rapid purification and special processes.

  • Medium MW → Balanced performance, suitable for most wastewater and papermaking applications.

  • High MW → Excellent bridging effect, ideal for sludge dewatering and high-turbidity wastewater treatment.

In practical applications, customers should carefully match PolyDADMAC molecular weight with water characteristics, treatment goals, and process conditions to achieve the best performance and cost-effectiveness.