How to Choose a Retention Aid for Different Paper Grades

The most reliable approach is to match the retention system to the grade’s shear and ash/fines load: high-shear grades (tissue, high-speed printing) typically need a microparticle program, while moderate-shear, lower-ash grades often run well with a single cationic PAM (CPAM). If your furnish carries high anionic trash (recycled fiber, coated broke), start with charge control (coagulant) before polymer selection.

▶ What “paper grade” changes in retention chemistry

Different grades are not just different recipes—they create different hydrodynamic and colloidal environments. A retention aid that performs well on a low-shear board machine can fail on a high-shear tissue or coated base machine because flocs break, fines release, and the headbox jet re-disperses aggregates.

Four variables that change the “right” retention aid

• Shear level: higher shear favors dual systems (polymer + microparticle) that rebuild microflocs after shear;
• Ash and fines load: higher filler/fines needs more capture capacity and better drainage balance;
• Anionic trash (charge demand): recycled fiber/coated broke often requires a coagulant before CPAM;
• Formation/optics sensitivity: some grades penalize visible floc (printing, coated) more than others.

Practical rule: if the grade demands both high retention and good formation under high shear, assume you will need a structured program (coagulant and/or microparticle), not just “more CPAM.”

▶ Know your retention aid options and what each does best

“Retention aid” can mean several chemistries. Choosing correctly starts with recognizing what mechanism you need: charge neutralization, bridging, or microfloc structuring.

Common retention aid families

Conclusion: coagulant fixes the chemistry, CPAM builds capture, microparticles protect performance under shear.

▶ A grade-based selection playbook with workable dosage ranges

The ranges below are practical starting points used in many mills. Actual optimum depends on furnish, conductivity, pH, and headbox shear, but these ranges help you begin trials without guessing.

Tissue and towel (high shear, low basis weight)

• Recommended program: moderate-charge CPAM + microparticle to rebuild microflocs after shear.
• Starting dosages (active basis): CPAM 200–600 g/t; microparticle 500–2,000 g/t.
• Watch-outs: overdosing CPAM often shows up as clumpy formation and dusting variability.

Uncoated freesheet and office paper (moderate ash, optics-sensitive)

• Recommended program: CPAM alone for simpler systems; add microparticle when speed/shear or ash increases.
• Starting dosages: CPAM 300–900 g/t; optional microparticle 300–1,500 g/t.
• Target mindset: balance ash retention versus formation/print mottle—small chemical gains can have large quality impacts.

Coated base and LWC (high fines/latex, high anionic trash risk)

• Recommended program: coagulant + CPAM + microparticle to stabilize the wet end and control fines/latex.
• Starting dosages: coagulant 200–1,000 g/t; CPAM 300–1,200 g/t; microparticle 500–2,500 g/t.
• Trial sequence: fix charge first (coagulant), then tune CPAM, then adjust microparticle for drainage/formation.

Containerboard, linerboard, and medium (recycled fiber, drainage-limited)

• Recommended program: coagulant + CPAM is a common baseline; microparticles added when speed and shear climb.
• Starting dosages: coagulant 300–1,500 g/t; CPAM 200–800 g/t; optional microparticle 300–1,500 g/t.
• Success indicator: improved drainage and lower solids load to saveall, without sticky deposition spikes.

These ranges are intentionally conservative. If your system is very “dirty” (high recycled/coated broke), it is usually more effective to increase coagulant modestly and keep CPAM moderate than to push CPAM alone.

▶ How to validate the choice with measurable targets

Retention chemistry should be judged on process metrics, not just “looks better.” Use a short scorecard so you can compare programs across trials and paper grades.

A practical scorecard for most grades

• First-pass retention (FPR): track total and ash FPR separately; ash FPR is often the limiting factor in filled grades.
• White water solids (g/L): a direct indicator of fines/ash escape and save-all loading.
• Drainage proxy: vacuum levels, couch solids, or standardized drainage tests (keeping the consistency of method is more important than the method itself).
• Formation/quality: visual formation index, print mottle, or converting defects (tissue linting, dusting).

Example: what “better” looks like in a short trial

A realistic improvement target for a well-run trial is not “double retention.” It is often: +3 to +8 percentage points in ash retention while holding formation steady, or a measurable reduction in white water solids that lowers save-all load and stabilizes the wet end.

If you see retention improve but formation worsens, the program is likely over-bridging (too much polymer, too high MW, or wrong addition point). If formation improves but retention does not, charge control or microparticle timing may be the missing link.

▶ Addition points and sequencing that prevent grade-specific failures

Many “retention aid doesn’t work” problems are actually application problems. Different paper grades impose different shear histories, so where and when you add chemicals matters as much as which product you choose.

Sequencing rules that work across grades

1. Add coagulant early enough to contact dissolved/colloidal trash (often in machine chest or suction side), but not so early that it is consumed before the headbox.
2. Add CPAM after major dilution/shear points when possible, so you do not “build floc just to break it.”
3. Add microparticle late (commonly before screens/headbox depending on system design) to create shear-resistant microstructure.
4. Change only one variable at a time during trials: dosage, location, or product—not all at once.

For high-shear grades, the objective is controlled microflocculation: small, resilient structures, not large flocs. For optics-sensitive grades, prioritize formation and let retention gains be incremental but stable.

▶ Common mistakes when choosing a retention aid for different paper grades

The same mistake repeats across mills: choosing a retention aid by habit (or vendor label) instead of by grade demands and wet-end conditions.

Mistakes that cost the most in trials

• Increasing CPAM repeatedly when the real issue is high charge demand; the polymer gets “neutralized” before it can bridge.
• Using a very high molecular weight polymer on a grade that is formation-sensitive (printing/coated base), creating visible floc.
• Running microparticles without stabilizing the wet end first; response becomes inconsistent shift-to-shift.
• Judging success only by one metric (e.g., ash retention) while ignoring drainage, deposits, or sheet quality.

A good program for a given grade is the one that improves the scorecard without creating new problems. In practice, stability is often worth more than a slightly higher retention number.

▶Conclusion

To choose a retention aid for different paper grades, start with the grade’s shear and furnish cleanliness: use CPAM alone for simpler, moderate-shear systems; add coagulant when charge demand is high; add microparticles when shear and performance requirements rise. Then validate with a scorecard (ash retention, white water solids, drainage proxy, and formation) and optimize dosing and addition points methodically.