Ask any experienced wet-end operator which additive they would keep if they could only keep one, and many will say cationic starch. It adds strength, holds filler, helps drainage and costs less than most synthetic polymers. But it is also one of the easiest chemicals to waste.
What makes it “cationic”
Ordinary starch carries no charge. Cationic starch is modified so it carries a positive charge. Fibres and fillers in the stock carry a negative charge, so the starch is pulled onto them and stays in the sheet instead of draining away.
The benefits mills see
- Higher dry strength – better tensile, burst and folding, especially useful with recycled fibre.
- Better filler retention – more clay or calcite stays in the sheet, so ash goes up and furnish cost comes down.
- Faster drainage – water leaves the wire more easily, which can mean more speed or less steam.
- Cleaner white water – fewer fines and less load on the ETP.
Where to dose it
Most mills add cooked starch to the thick stock, before the fan pump, so it has time to mix and attach to fibres. Adding it too close to the headbox gives poor mixing; adding it too early can expose it to shear that knocks it off again.
Cooking matters
Cationic starch must be fully cooked to work. Undercooked starch shows up as specks, poor strength and sticky deposits. Follow the supplier’s temperature and time, keep the cooker clean, and use the cooked starch within its shelf life – usually the same shift.
Use cases
- Kraft and liner board – strength from recycled fibre (see kraft paper).
- Writing & printing – filler retention and a firmer sheet.
- Duplex board – ply bond and stiffness (see duplex board).
- Tissue – softness and strength balance at low dosages.
Five common mistakes
- Overdosing. Past a point, extra starch does nothing except load the white water and feed slime.
- Ignoring charge. If anionic trash in recycled stock is high, starch gets “used up” by it. A fixative or PAC may be needed first.
- Poor cooking control. Temperature swings mean strength swings.
- Mixing grades between lots. Different degrees of substitution behave differently; stick to one grade.
- No trial. Always run a new starch on one machine and compare strength and ash before switching.
Pairing with other chemicals
Cationic starch works best as part of a programme: with a retention and drainage aid for fines, dry strength resin where strength is critical, and oxidised starch at the size press for surface strength.
FAQ
Is cationic starch the same as maize starch?
No. Maize starch is the base; cationic starch is chemically modified to carry a charge, which is why it retains so well at the wet end.
What packing do you supply?
Usually 50 Kg bags, with bulk possible for regular volumes.
Want to cut fibre cost without losing strength? Tell us your paper grade and current starch – we will suggest a grade and send a trial quantity. Ask for cationic starch →