Every tonne of fines and filler that goes through the wire and into the white water is money you have already paid for. On many smaller machines, first-pass retention sits well below where it could be – and nobody notices until the ETP bill or the ash test says so.
What a retention aid does
A retention and drainage aid is usually a long-chain polymer. It bridges fine particles together and onto fibres, so they stay in the sheet as it forms. Because the fines are tied up, water drains faster too.
Signs you need one (or a better one)
- White water looks cloudy and solids keep rising.
- Ash in the sheet is lower than the filler you are adding.
- The machine is drainage-limited – you cannot go faster without wet sheet breaks.
- The ETP is struggling with suspended solids.
Benefits
- More filler in the sheet – lower furnish cost per tonne.
- Faster drainage – higher speed or lower steam on the dryers.
- Cleaner system – less build-up in tanks, fewer deposits and breaks.
- Lighter load on effluent treatment.
Where to add it
Most retention aids go in late – after the last pressure screen, close to the headbox – because shear breaks the bonds they form. Dosing too early is the most common reason a good product “does not work.”
Making it work with the rest of the wet end
Retention aids work best on a clean, balanced system:
- Use cationic starch first for strength and part of the retention.
- Control anionic trash in recycled stock with PAC or a fixative.
- Keep alum dosing steady if you run rosin sizing.
- Control slime with an antislime agent – biofilm upsets charge.
Use cases
- Kraft paper and corrugated grades on recycled fibre.
- Writing and printing papers with high filler loading.
- Duplex board where drainage limits speed.
Quick trial plan
- Measure white water consistency and sheet ash for one week.
- Start at a low dosage near the headbox.
- Step up slowly, watching formation – too much retention aid can flocculate the sheet.
- Compare speed, steam and ash before and after.
Want to check your retention programme? Share your machine, furnish and current chemicals – we will recommend a grade and arrange a trial. Get in touch →