Papermakers are squeezing 1–5 percentage points more yield and faster drainage out of their machines by tuning retention and drainage aids — with first-pass retention gains of 5–20 points and lighter loads on water treatment.
In the wet end of a paper machine, a small dose of the right polymer can move big numbers. Mills report first-pass retention (FPR — the share of fines and fillers captured in the sheet on the first pass) rising 5–20 percentage points with retention aids (www.tissuestory.com), translating to a 1–5% point net yield boost (www.tissuestory.com). That means less valuable fiber and filler washing out with the white water (the recirculating process water), and more product per ton of furnish.
It is not just cost. Indonesia’s pulp and paper sector — 62 companies producing ~12.98 million t/y paper — faces water-use limits of ≤65 m³/ton pulp, 45 m³/ton integrated, and ≥25% reuse (id.scribd.com). Higher wet-end retention directly supports these efficiency goals.
Wet-end additives and yield math
Retention and drainage aids are specialty wet-end additives that flocculate fines (small fibrous particles) and mineral fillers onto the fiber network, sharply increasing first-pass capture of these components. In practice, high retention reduces raw-material loss and lowers white-water solids, easing effluent treatment and enabling faster machine speeds with lower energy use.
Plant surveys of tissue machines found every mill adding retention chemicals saw FPR rise by 5–20 percentage points (www.tissuestory.com). That uplift delivered 1–5% higher fiber‑to‑paper ratio (www.tissuestory.com) — enough in one case to substitute a cheaper fiber for part of the furnish without sacrificing quality. At 10 million t/year capacity, a 2% yield improvement saves 200,000 t fiber (worth tens of millions USD) annually, while also slashing suspended solids in wastewater by a comparable fraction.
Lower solids in recirculating water lighten the load on clarification assets; mills often observe reduced sludge and chemical demand as more fines and fillers end up in the sheet rather than in clarifiers or DAF (dissolved air flotation) units (www.tissuestory.com). In practice, that shows up as less duty on equipment such as a clarifier or a DAF system.
Polymer mechanisms and formation control
The core mechanism is bridging/coagulation: cationic polyacrylamide (CPAM) or polyamine adsorbs to negatively charged fines and fibers to form flocs that are efficiently caught on the wire. The result is uniform filler distribution, reduced two-sidedness, and higher opacity in the sheet (papermaz.blogfa.com). By keeping solids out of the white water, retention programs also reduce clarifier sludge and DAF solids (www.tissuestory.com).
The upside comes with a warning label: a recycled board study found excess dosing degraded tensile strength and surface smoothness (www.mdpi.com). Overdosing creates oversized flocs that make the sheet “chunky” and weak; underdosing wastes raw materials and raises effluent load.
When sourcing the chemistry, papermakers typically classify these additives under coagulants and flocculants. Programs are often paired with mill-procured coagulants or flocculants tailored to furnish and shear conditions.
Drainage acceleration under vacuum
“Drainage aids” are additives that help water escape from the forming web without harming formation. Many cationic polyelectrolytes (e.g., alum, cationic starch, CPAM) play a dual role: by collapsing fiber micro-porosity and releasing bound water, they reduce hydrodynamic drag and shorten table/vacuum times. Properly chosen cationic polymers “decrease the amount of water associated with fiber and fines… resulting in less drag as the water flows through the web” (papermaz.blogfa.com).
Polymers also keep channels open by flocculating fines so they don’t plug the wire (papermaz.blogfa.com). Many mills use a duo‑system: first a cationic coagulant (PDADMAC, polyamine, or CPAM) to grab fines, then an anionic “microparticle” (colloidal silica, bentonite clay, or synthetic latex) to re‑flocculate at a finer scale. Such micro‑flocs drain quickly. In one report, adding 20% filler by weight (as a control) decreased drainage time by about 20% relative to unfilled stock (www.researchgate.net).
Empirical comparisons underline that fit matters: cationic retention aids improved drainage at high shear, while a high‑molecular PEO system was markedly slower (www.researchgate.net). Mills quantify gains via Canadian freeness or vacuum drainage tests; a well‑chosen system might improve Parker return pit water clarity or reduce freeness by 100–300 mL CSF under constant conditions, translating to fewer wet‑end breaks and higher machine efficiencies.
Specialty polymer systems and doses
Cationic polyacrylamides (CPAM) and polyamines (e.g., polyethyleneimine, cationic starch) are the workhorses. For coarse particulate retention, moderately charged CPAM (charge ~3–14 meq/g; 5–15 MDa molecular weight) perform well. For very fine, colloidal fillers, extremely high‑charge polymers (e.g., 60–80% cationic PDADMAC or polyamine resins) can be used at ~10–100 g/t.
Microparticle additives amplify performance. Colloidal silica (SiO₂, <10 nm) or bentonite clays, added after a small cationic polymer dose, create porous, shear‑resistant micro‑flocs. Patents describe typical silica doses of 0.03–0.1% solids on dry stock (300–1000 g/t) (patents.google.com). Latex nanoparticles are also cited in similar roles.
Inorganic and organic drainage aids exist beyond these — including anionic polymers (dextrans, polyacrylates) that disperse fines and starch‑based additives — but the highest performance systems generally combine cationic flocculants with microparticles. At ultra‑hygienic conditions, a shorter retention polymer (e.g., poly(vinylamine)) paired with silica has been shown to achieve very even filler distribution at low dose.
Quantitatively, high‑charge polymers work at low grams per ton, while high‑MW, lower‑charge CPAM are often dosed at 50–300 g/t. Combined systems can cut CPAM dose and conductivity load yet maintain or boost retention; for example, a dual polyamine/silica system might use 200 g/t polyamine + 100 g/t silica, whereas a single CPAM approach might require ~400 g/t for comparable retention. Such reductions mitigate negative impacts on wetting and formation.
Dose optimization and measurement
The target is “just‑right” flocculation: enough to fix fines, but small enough to keep formation even. Without chemical aid, filler retention is often <30–40% in lightweight or recycled furnishes. Adding cationic polymers typically raises filler retention to 60–80% or higher, climbing with dose before plateauing; one study saw ash retention increase steadily to about 400 g/ton before saturation (www.researchgate.net). Another series showed saturation near ~400–600 g/t CPAM (www.researchgate.net).
Excessive flocculation can make initial drainage very fast, yet trap water in large flocs and leave a limp sheet at the couch — in extreme cases, “break like wet tissue” under vacuum (papermaz.blogfa.com). Conversely, modest dosing often improves both formation and strength by refining pore structure; the recycled board study’s lesson: too much polymer hurts tensile strength and smoothness, a modest level helps (www.mdpi.com).
Optimization is empirical: mills titrate polymer charge — e.g., start from a baseline (say 70% ash retained without aid), then add in 50 g/t increments — while tracking FPR and formation on the scanner to find the “sweet spot.” Instrumental tools like dynamic drainage meters, focused beam reflectance, and lab headbox/former rigs help lock in the in‑machine dose. Accurate chemical dosing hardware, such as a dedicated dosing pump, supports these tight windows, where a 10–20% error can move white‑water solids or sheet quality materially.
Drainage aids also require balance. Salts or very high‑charge polymers can over‑collapse fiber structure, creating a waterlogged sheet. Conversely, a subtle addition of anionic polyacrylate (20–50 g/t) can increase table vacuum dewatering by 10–20% without harming formation; overuse risks a decked sheet with free water.
Water, effluent, and compliance economics
The business case adds up quickly. Every percent of fiber saved stays in the market basket: for a 1 million tpy mill, improving overall retention by 5% saves 50,000 t of fiber annually — roughly US$15–20 million worth. High retention also halves total suspended solids sent to clarification in many programs, cutting coagulation costs and sludge disposal; in tissue studies, as FPR rose, clarifier DAF consumption dropped commensurately (www.tissuestory.com).
On‑machine, better drainage shortens downtime and allows higher speeds; tissue case studies also observed lower wet‑end variability and longer felt life when retention aids were used. Tight control is how mills hit these benefits: white‑water turbidity sensors and mass balances (including first‑pass ash retention meters) regulate dosing, with early‑warning systems bumping polymer feed if retention dips. Data analytics — soft sensors on basis weight and moisture — are increasingly used to fine‑tune feed.
Regulatory pressure is rising. Indonesian standards (Kep. Menperin No. 514/2015) mandate aggressive water reuse and low discharge volumes (id.scribd.com). Higher retention and more efficient white‑water loops reduce fresh water per ton. Greater retention concentrates solids in loop water and may require fiercer filtration or clarification, but overall makeup water demand drops — a net positive for “green industry” certifications.
Key outcomes and ranges
- Fibril & filler retention: Gains of +5–20 percentage points FPR are common (www.tissuestory.com); filler retention with aids often reaches >80%.
- Yield improvement: Corresponds to 1–5% higher production yield (www.tissuestory.com), with proportional raw‑material savings.
- Drainage rate: Proper aid systems can reduce white water volume by ~10–20% or more, and shorten vacuum times (e.g., 20% less drain time with 20% filler; www.researchgate.net).
- Balance/formation: Optimal dosing ensures uniform sheets; overdose forms oversized flocs and hurts strength/smoothness (www.mdpi.com; www.researchgate.net).
- Water/effluent: Increased retention reduces suspended solids in effluent, aiding compliance (aligning with Indonesia’s ≤45–65 m³/t water targets; id.scribd.com).
Chemical supply and integration notes
Retention and drainage programs typically draw on a mill’s broader chemical and water‑treatment toolkits. Where solids removal downstream is needed, operators often coordinate wet‑end chemistry with clarification assets like a DAF unit. For coagulation and flocculation steps, many rely on established flocculant and coagulant supply programs to keep inventories and feed systems aligned with furnish changes.
Sources
Academic studies and industry reports (e.g., papermaking research, TAPPI journals, supplier data) were used to quantify retention/drainage improvements and chemical behavior (www.mdpi.com) (www.researchgate.net) (www.tissuestory.com) (papermaz.blogfa.com) (id.scribd.com). Indonesian industry data and regulations provide local production and water‑use context (id.scribd.com) (id.scribd.com).
