Cationic starch is one of the most widely used wet-end in board and paper manufacturing. In multilayer board machines, it plays a crucial role in improving strength, retention, drainage, and surface quality, especially for Virgin and recycled Board.
Proper cooking of cationic starch is as important as correct dosage. Even the best-quality starch will not perform well if it is under-cooked, over-cooked, or degraded by shear. Correct starch preparation ensures maximum strength development, good retention, stable viscosity, and smooth machine operation.
What is Cationic Starch?
Cationic starch is a chemically modified starch carrying a positive charge. Since pulp fibers, fillers, and fines are naturally negatively charged, cationic starch easily attaches to them through electrostatic attraction.
This bonding improves: 1. Fiber-to-fiber bonding, 2. Fines and filler retention, 3. Overall sheet strength and quality.
Uses of Cationic Starch in Board Machine
1. Dry Strength Improvement
Cationic starch increases: 1. Tensile strength
2. Burst strength
3. Internal bonding (Scott bond)
“This is especially important for kraft liner, test liner, duplex board, and FBB, where strength targets must be achieved at lower GSM.”
2. Retention of Fines and Fillers
- Improves retention of fines, fillers, and pigments
- Reduces solids load in white water
- Improves yield and lowers raw material loss
3. Improved Drainage & Run-ability
- Better floc formation when properly dosed
- Stable wet-end chemistry
- Helps machine run smoothly at higher speeds
4. Surface Strength & Printability (Surface Application)
When used at size press or spray:
1. Improves surface strength
2. Reduces picking and dusting
3. Enhances ink holdout and print quality
Cationic Starch Cooking & Preparation Guidelines for Board Machines:
Why Proper Starch Cooking is Important
Correctly cooked starch:
1. Fully gelatinizes starch granules
2. Develops optimum viscosity
3. Improves bonding with fibers and fillers
4. Reduces starch loss to white water
5. Prevents deposits, foaming, and drainage problems
Improper cooking leads to:
1. Poor strength response
2. High starch consumption
3. Dirty wet end and unstable operation
Basic Requirements for Starch Cooking System
- Clean starch preparation tank with agitator
- Hot water / steam heating arrangement
- Temperature control (thermometer or PLC)
- Proper dilution water line
- Transfer pump with low shear design
Step-by-Step Cooking Procedure
1. Prepare Slurry (Make-up Stage)
- Fill the cooking tank with clean, cold or warm water
- Start agitator before adding starch
- Slowly add dry cationic starch powder to water
Recommended slurry concentration:
1. 3–6% solids for wet-end application
2. 6–10% solids for surface/spray starch
“Always add starch into water, never water into starch (avoids lump formation).”
2. Heating & Gelatinization
- Start heating the slurry using steam or hot water
- Raise temperature gradually with continuous agitation
Recommended cooking temperature:
1. Maize-based cationic starch: 90–95°C
2. Tapioca-based cationic starch: 85–90°C
3. Maintain target temperature for 20–30 minutes
4. Ensure slurry becomes clear and viscous
“Proper gelatinization means no white grains or cloudy appearance.”
3. Hold & Maturation Time
- After reaching final temperature, hold the starch at: 80–90°C for 10–15 minutes
- This allows complete swelling and molecular development
Do not over-hold at high temperature, as it may cause:
1. Viscosity breakdown
2. Polymer chain degradation
4. Dilution to Use Concentration
- Dilute cooked starch slowly with clean process water
- Maintain gentle agitation during dilution
Final use concentration:
1. Wet-end dosing: 0.5–2.0% solids
2. Spray starch / size press: 4–8% solids
“Sudden cold-water addition may shock the starch and reduce performance.”
5. Cooling & Transfer
- Cool starch to 60–70°C before dosing
- Use short pipelines and smooth bends
- Avoid high-speed centrifugal pumps (use progressive cavity or low-shear pumps)
Storage & Shelf Life:
1. Use cooked starch within 8–12 hours
2. Maximum holding time should not exceed 24 hours
Keep tank covered to avoid: 1. Microbial growth, 2. Viscosity loss, 3. Bad odor formation- “If storage is required, maintain temperature above 55°C and ensure cleanliness.”
Application Points of Cationic Starch
Application Point Purpose
Thick stock line – Maximum dry strength development
Thin stock line / fan pump inlet – Better retention of fines & fillers
Before head box – Formation and strength balance
Size press / spray starch – Surface strength and printability
“Best practice: Split addition between thick stock and thin stock gives balanced strength and retention.”
Recommended Dosage of Cationic Starc
Dosage depends on furnish quality, recycled fiber %, and board grade.
Application Typical Dose
Wet-end (internal addition) 0.3 – 1.5% on dry pulp (3–15 kg/ton)
Retention focused dosing 0.5 – 1.0%
Surface sizing / spray starch As per surface requirement (lower than wet end)
“Overdosing can cause: Poor drainage, Formation issues, Sticky wet-end conditions.”
Advantages of Cationic Starch
- Improves dry strength properties
- Enhances fines and filler retention
- Reduces fiber loss and improves yield
- Improves formation and machine stability
- Better surface strength and printability
- Lower BOD/COD load in effluent due to higher retention
Disadvantages of Cationic Starch
- Higher cost compared to native starch
- Sensitive to overdosing and charge imbalance
- Cooked starch can degrade under high shear
- Improper cooking leads to poor performance
- May increase drying load when used on surface
Common Problems & Solutions:
Problem Likely Cause Solution
Low strength gain – Under-cooked starch – Increase cooking temp or time
High starch consumption – Poor retention – Improve charge balance
Poor drainage – Over-dosage – Reduce dosage or split dosing
Foaming / odor – Bacterial growth – Improve hygiene, reduce storage time
Nozzle choking – Undissolved particles – Improve cooking & filtrationMaize-Based vs Tapioca-Based Cationic Starch
Both starch types are widely used in board machines. The real performance depends more on degree of substitution (DS) and charge density than on the raw material itself. However, some practical differences exist.
Parameter Maize-Based Cationic Starch Tapioca-Based Cationic Starch
Raw material availability – Widely available, stable supply – Regional availability
Gelatinization temperature – Slightly higher – Lower, easier to cook
Viscosity stability – Moderate – Higher and smoother
Strength development – Excellent dry strength – Comparable if DS is similar
Surface film formation – Good – Very good
Cost – Generally economical – Cost varies by region“Key takeaway: If charge level and cooking quality are similar, both maize and tapioca cationic starch provide almost equal performance in board machines.”
Practical Tips for Board Mills
1. Always maintain consistent starch solids
2. Clean starch system regularly
3. Monitor viscosity daily for consistency
4. Always ensure proper starch cooking (complete gelatinization)
5. Maintain wet-end charge balance when dosing
6. Avoid overdosing—optimize through trials
7. Combine with retention aids for best results
Select starch type based on availability, cost, and application need
Conclusion
Cationic starch is a critical strength and performance chemical in modern board manufacturing. When correctly selected, cooked, and applied, it significantly improves strength, retention, surface quality, and machine efficiency.
Choosing between maize-based or tapioca-based cationic starch should depend on process conditions, cost, and supplier consistency, not just raw material origin.