How to Apply Paper Chemicals in Pulp & Papermaking

Map chemicals to the process train

Start with a simple process map: pulping / deinking → washing → bleaching → stock preparation → wet end → size press → coating (if any). Assign each foam, deposit, brightness, Cobb, and drainage complaint to a control point. Buying chemistry without an addition-point plan is the fastest way to overspend and create deposits.

1. Pulp / recycled fibre: Contaminant control, deinking, foam, and metal management
2. Bleach plant: Brightness, peroxide stability, chelation
3. Paper machine: Drainage, retention support chemistry interactions, wet-end foam, sizing
4. Size press / coating: Surface strength, printability, optical properties

Defoamers: dose at the source

Defoamers should knock down foam where air is entrained—not only where foam is visible in a chest. Typical practice:

• Identify primary foam generators (washers, screens, cleaners, headbox approach)
• Select chemistry compatible with temperature, pH, and furnish (silicone vs oil vs EO/PO)
• Start at the low end of the recommended range; raise only against measured foam or entrained air
• Watch for deposit formation, felt filling, and sizing interference after dose changes

In flotation deinking, preserve process foam needed for ink removal while controlling nuisance foam elsewhere—coordinate with deinking surfactants rather than flooding the circuit with antifoam.

Sizing chemicals: internal then surface

Sizing programmes balance sheet hydrophobicity, runnability, and print performance:

Internal sizing

1. Confirm furnish pH window and alum / retention co-chemistry where used
2. Ensure emulsification / dispersion quality of the size emulsion
3. Control addition point relative to shear and retention aids
4. Cure / development time must match machine speed and drying profile

Surface sizing

1. Set size-press solids and viscosity for uniform film
2. Match starch / synthetic package to Cobb and pick targets
3. Monitor press picking and dusting after grade changes

Bleaching aids: protect brightness development

Bleaching aids and related peroxide stabilizers / chelant programmes reduce catalytic decomposition and fibre damage:

• Measure incoming metals; set chelant strategy before raising peroxide
• Stabilize pH and temperature in the bleach stage
• Use brightener / OBA programmes only after base brightness is under control
• Track residual peroxide and brightness gain per kg chemical

Deinking and recycled furnish notes

Recycled mills should sequence collector / dispersant chemistry with flotation air rates, then confirm that residuals do not sabotage wet-end sizing. Defoamer choice after flotation must not collapse useful foam in the cell while still protecting washers and the machine. Cross-check with the paper chemicals hub when changing recovered-fibre mix.

Best practices

• One change at a time—dose or addition point, not both
• Log furnish, water hardness, and temperature with every trial
• Inspect felts, wires, and chests for deposits after chemistry shifts
• Align wet-end and size-press SOPs with quality lab Cobb / brightness methods
• Qualify dual sources only after matched performance data

Troubleshooting

Persistent foam

Cause: Wrong addition point, underdose, or incompatible chemistry.

Solution: Move feed closer to entrainment, re-screen chemistry, check for surfactant overload from upstream.

High Cobb / weak sizing

Cause: Poor size emulsion, wrong pH, retention conflict, or defoamer interference.

Solution: Audit size quality, addition order, and recent antifoam changes.

Brightness shortfall

Cause: Metal catalysis, unstable peroxide, or insufficient bleaching aid.

Solution: Improve chelation / stabilization before increasing bleach load.

Conclusion

Applying paper chemicals well means treating the mill as a connected system: foam control, sizing, and bleaching aids must be dosed at the right points with documented process windows. Esteem Industries provides practical support across pulp and paper chemistries for mills that need reliable runnability and sheet specs. Reach our technical team for addition-point reviews and grade trials.