Technical Guide: Paper Chemicals for Deinking, Sizing & Defoamers

Deinking chemistry essentials

Recycled fibre lines need collectors and dispersants matched to ink type and separation method (flotation vs washing). Key application notes:

• Keep flotation foam within the window that carries ink without excessive reject fibre
• Avoid carryover surfactant levels that later fight sizing or create wet-end foam
• Re-screen chemistry when ONP/OMG/mixed office ratios change

Defoamers without collateral damage

Defoamers protect washers, chests, and the paper machine, but misplaced silicone or oil antifoams can:

• Suppress flotation efficiency upstream
• Contribute to deposits on felts and wires
• Interfere with sizing development

Prefer the lowest effective dose at the true entrainment point. Chemistry family (silicone, oil, EO/PO) should match temperature and furnish—not only price.

Sizing after recycled fibre

Internal and surface sizing must overcome variable anionic trash and residual surfactants. Application practice:

1. Stabilize first-pass retention and charge before chasing Cobb with more size
2. Confirm size emulsion quality and shear history
3. Use size-press programmes to fine-tune printability after base sheet hydrophobicity is set
4. Audit recent defoamer and deinking changes whenever Cobb drifts

Bleaching aids linkage

Where brightness is critical, bleaching aids and metal control protect peroxide efficiency. Residual metals and poor washing after deinking raise bleach demand—fix pulp cleanliness before increasing chemical load.

Mill trial protocol

1. Baseline foam maps, Cobb, brightness, and break rate
2. Change one chemistry family per trial window
3. Inspect deposits and flotation yield daily during trials
4. Lock SOPs only after two stable production campaigns

Troubleshooting matrix

• High foam on machine + poor deink yield: Check antifoam addition points vs flotation needs
• Rising Cobb after furnish change: Revisit sizing dose and anionic trash
• Brightness dip: Metals, washing, then bleaching-aid package

Conclusion

Deinking, defoamers, and sizing must be qualified together against the mill’s fibre and water reality. Use the paper chemicals hub and companion how-to on applying paper chemicals for addition-point detail. Esteem’s technical team can help sequence trials so foam control does not erase deinking gains or sizing results.