Polydadmac (poly diallyldimethylammonium chloride) is a highly effective cationic polymer widely used in pulp and paper white water treatment systems. In modern papermaking, white water refers to the recycled process water that drains from the paper machine wire section. It contains fine fibers, fillers, dissolved organic matter, micro-particles, and various additives. Efficient treatment of white water is essential for improving water reuse, reducing raw material loss, stabilizing machine operation, and enhancing paper quality. Polydadmac plays a key role in improving retention, clarification, and system cleanliness in white water circuits.

1. Characteristics of white water in pulp and paper mills

White water is a complex suspension containing:

• Fine cellulose fibers
• Mineral fillers (calcium carbonate, clay, titanium dioxide)
• Dissolved and colloidal organic substances
• Starch, sizing agents, and retention chemicals
• Anionic trash (dissolved wood resins, hemicelluloses)
• Microbial growth products in recycled systems

Most of these components carry negative charges, making them stable in suspension and difficult to remove without chemical treatment. Without proper control, white water becomes increasingly contaminated, reducing papermaking efficiency.

2. Properties of Polydadmac in white water treatment

Polydadmac is a water-soluble quaternary ammonium polymer derived from diallyldimethylammonium chloride (DADMAC). It is widely used in papermaking systems due to its strong cationic nature.

Key properties include:

• Very high cationic charge density: Strong neutralization of anionic contaminants
• Excellent water solubility: Rapid dispersion in white water systems
• Fast adsorption kinetics: Immediate interaction with fine particles and dissolved substances
• Stable performance across pH 4–10
• Low to medium molecular weight (or customized grades): Suitable for charge neutralization and flocculation control

These properties make Polydadmac highly effective in controlling colloidal stability in white water loops.

3. Mechanism of white water treatment

Polydadmac improves white water treatment through several key mechanisms:

(1) Charge neutralization
Most fibers, fillers, and dissolved organic substances in white water are negatively charged. Polydadmac neutralizes these charges, reducing electrostatic repulsion and destabilizing colloids.

(2) Adsorption of anionic trash
Dissolved organic substances such as lignin derivatives, resins, and hemicelluloses are captured by Polydadmac, reducing anionic trash load in the system.

(3) Patch flocculation
Positively charged patches on the polymer surface attract negatively charged particles, forming microflocs that can be removed by sedimentation or filtration.

(4) Floc formation and aggregation
Fine fibers and fillers aggregate into larger particles, improving retention and separation efficiency.

(5) System cleanliness improvement
By removing dissolved and colloidal substances, Polydadmac helps reduce deposits and microbial growth in white water circuits.

4. Application in white water treatment system

(1) White water loop control

Polydadmac is added directly into the white water loop to control dissolved and colloidal contaminants. It helps stabilize system chemistry and reduce buildup of anionic trash.

(2) Save-all systems

In save-all units (disc filters, drum filters), Polydadmac improves recovery of fibers and fillers by enhancing floc formation and retention.

(3) Thickening and clarification

Used in clarification tanks to improve settling of fine particles and reduce turbidity in recycled water.

(4) Headbox approach system

White water treated with Polydadmac is reused as process water, improving fiber distribution and sheet formation consistency.

5. Applications in different paper mill systems

(1) Fine paper mills

Improves retention of fillers and fines, enhancing printability and surface smoothness.

(2) Packaging paper mills

Reduces fiber loss and improves recycling efficiency in kraft and linerboard production.

(3) Tissue paper mills

Enhances cleanliness of white water system and improves softness consistency.

(4) Recycled fiber mills

Helps manage high contaminant loads from wastepaper, including inks, adhesives, and fillers.

6. Advantages of Polydadmac in white water treatment

(1) High retention efficiency
Improves recovery of fibers and fillers from white water.

(2) Reduced raw material loss
Minimizes fiber and filler loss in drainage systems.

(3) Improved water reuse
Enhances clarity of recycled water, reducing freshwater consumption.

(4) System stability
Controls anionic trash buildup and stabilizes process chemistry.

(5) Reduced deposits and fouling
Decreases stickies, pitch deposits, and slime formation.

(6) Improved paper quality
Enhances formation, uniformity, and surface properties of paper.

7. Dosage and influencing factors

Typical dosage ranges:

• 0.01–0.1% (based on dry pulp weight) for white water control
• 1–20 mg/L for system-wide white water treatment
• 5–50 mg/L for high contamination recycled systems

Key influencing factors include:

• Pulp type (virgin or recycled fiber)
• Filler content and type
• White water conductivity and ionic strength
• pH conditions
• Machine speed and retention system design
• Degree of system closure (freshwater vs closed loop systems)

Proper mill trials are essential for optimization.

8. Combination with other chemicals

Polydadmac is often used as part of a retention and white water management system:

(1) Anionic polyacrylamide (APAM):
Enhances floc size and retention efficiency in dual polymer systems.

(2) Microparticle systems (bentonite, colloidal silica):
Improves floc strength and drainage performance.

(3) Starch and sizing agents:
Enhances fiber bonding and paper strength.

(4) Biocides:
Works alongside microbial control agents to maintain system cleanliness.

This integrated approach improves overall white water management performance.

9. Limitations and considerations

(1) Overdosing risk
Excess Polydadmac may destabilize the system and cause poor formation.

(2) Shear sensitivity
Flocs may break under high shear conditions in pumps and pipelines.

(3) System variability
Different paper machines require tailored dosing strategies.

(4) Cost considerations
More expensive than simple inorganic additives but more effective in closed-loop systems.

10. Operational best practices

To achieve optimal performance:

• Conduct regular mill trials
• Monitor white water conductivity and turbidity
• Optimize dosage based on system closure level
• Combine with retention aids for better efficiency
• Avoid overdosing to prevent formation issues
• Maintain stable chemical balance in the white water loop

11. Future trends

The use of Polydadmac in white water treatment is expected to increase due to:

• Increased water recycling in paper mills
• Stricter environmental regulations on wastewater discharge
• Demand for higher machine efficiency and speed
• Growth of recycled fiber-based paper production
• Development of advanced retention and closure systems

Future technologies will focus on higher efficiency, lower chemical consumption, and better integration with digital process control systems.