Organic “stickies,” inorganic scale, and slime can trigger 1–2 costly breaks per day and force frequent washouts. Mills are fighting back with a holistic playbook: targeted dispersants, detackifiers, and biocides, plus smarter furnish and process controls.
Deposits in paper mill systems aren’t small problems. They derail runnability, stain quality, and gobble cash. Organic “stickies” (pitch, adhesives, coating fragments) and inorganic scale (e.g., CaCO₃ and silicates) cause pinholes/off‑color spots, sheet breaks, blinding of wires and felts, and unscheduled downtime (pdfcoffee.com).
Pitch accumulations on felts lead to reel breaks, while inorganic scale in shower pipes demands frequent acid washouts. In one 100% recycled whitewater machine, poor slime control correlated with 1–2 costly breaks per day (pmc.ncbi.nlm.nih.gov).
With increasing amounts of recycled fiber and stricter discharge limits, deposit‑control chemicals have become critical (solenis.com) (pdfcoffee.com). Chemical interventions—dispersants, detackifiers, slimicides—paired with good housekeeping (e.g., regular boil‑outs or foam cleaning) have been shown to “substantially reduce breaks” and defects (scribd.com) (pdfcoffee.com), directly reducing downtime, waste (broke), replacement of felts/wires, and energy costs (pdfcoffee.com) (scribd.com).
Deposit categories and sources
Three deposit families dominate: organic stickies and pitch, inorganic scale/fillers, and biological slime. Organic deposits come from wood extractives (resin acids, fats) and recycled furnish additives (hot‑melt adhesives, inks, starches, waxes). Common stickies include SBR (styrene‑butadiene) from labels, EVA (ethyl‑vinyl acetate) binders, natural glues and acrylate polymers—many are “very difficult to remove” (pdfcoffee.com).
Inorganic deposits form when scalants such as calcium carbonate, sulfate, or silicate precipitate (often in closed whitewater loops or when pH/temperature trigger precipitation). Common scalants: CaCO₃, CaSO₄, clay fines, talc, TiO₂ (pdfcoffee.com). Biological slime (bacterial/fungal biofilms) can incorporate and bridge debris, promoting fouling.
Controls, adapted from industry sources: For organic (pitch/stickies), mills employ surfactant dispersants—anionic polymers such as polyacrylates, naphthalene sulfonates, lignosulfonates—to keep pitch dispersed; adsorbent detackifiers like talc or bentonite; biodispersants; mechanical screening and ferromagnetic traps for large stickies; and fixatives (cationic polymers or alum) to precipitate dissolved tackifying components (pdfcoffee.com). Mechanical screening can include automated systems, as in an automatic screen installation, to continuously remove debris.
For inorganic (scaling/fillers), controls include phosphonate crystal modifiers and polymeric dispersants (e.g., polyacrylates), sequestrants/chelates (EDTA, DTPA, polyphosphonates), biodispersants, and pH management (acidulation). In alkaline machines, polyaluminum coagulants (PAC) are used both to fix white pitch and neutralize “anionic trash” without forming insoluble alum hydroxide (pdfcoffee.com) (pdfcoffee.com). PAC programs align with coagulant offerings such as polyaluminum chloride (PAC).
For biological (slime/film), controls center on biocides (oxidizing or non‑oxidizing slimicides) added to the wet end or water loops; biodispersants (anionic surfactants like lignosulfonates or EO/PO copolymers) adjunctively prevent debris from gluing to slime films; and mechanical cleaning (boilouts, foam cleaning of press felts), with housekeeping (tank cleaning, scrubbing, filters) critical (pdfcoffee.com). Reviews note conventional programs combine chemical biocides but highlight a growing trend to “alternative control measures” (enzymes, biodispersants, bacteriophages) because enzymes are “nontoxic, biodegradable” and leverage renewable raw materials (pmc.ncbi.nlm.nih.gov).
Specialty dispersants and dosing windows
Dispersants—often polymeric surfactants—keep deposits in fine suspension. For organic pitch, widely used dispersants include anionic polymers (low‑MW polyacrylates, lignosulfonates, naphthalene sulfonates) that adsorb on resin particles to prevent agglomeration (pdfcoffee.com). These maintain wood pitch in a colloidal state so it exits in effluent or is captured as fine fiber‑pitch complexes, rather than sticking to wires/felts (pdfcoffee.com).
In practice, mills dose dispersants at roughly 0.01–0.1% on pulp dry weight (adjusted to raw‑material loads); field data show anionic polyacrylate dispersants can reduce felt cleanliness requirements by over 50% in sticky‑laden furnishes. Inorganic dispersants target scale: polyphosphonates (e.g., HEDP), polyacrylates, or organic ligand blends. Sodium hexametaphosphate is used to sequester Ca²⁺ in hardwood mills, keeping CaCO₃ in solution. These are often applied at 10–200 ppm (parts per million) to high‑hardness streams, with skatests/deposit‑forming tendency measurements guiding dosage.
Dispersants also aid slime control. Non‑oxidizing “biodispersants” (surfactants or lignosulfonates) are added alongside slime biocides to strip cell debris and inorganic sludge off biofilms—“help eliminate nonmicrobiological deposits that accumulate with slime”—though they do not kill microbes themselves (pdfcoffee.com). Programs are tailored to furnish: higher doses for 100% recycled furnish (which can have 2–3× more soluble adhesives than virgin pulp), lower doses for cleaner virgin fiber. Commercial programs align with dispersant chemicals used to prevent particle agglomeration.
Data point: adding ozone plus surfactant to whitewater achieved a 90–99% reduction of aerobic bacteria at a cost of ~$0.04–0.15 per m³ (pmc.ncbi.nlm.nih.gov). This underscores how effective dispersal (with supplemental oxidizers like ozone) can curb microbiological deposits at modest cost.
Detackifiers and adsorbents
Detackifiers neutralize tackiness via complexation or adsorption. Minerals (talc, magnesium silicate) and clays (bentonite) bind pitch/stickies into non‑tacky particles. Adding talc at 5–50 kg/ADt (air‑dry ton) can dramatically reduce tack; talc’s oil affinity and platy structure “adsorb and pelletize” grease and resins (hubbepaperchem.cnr.ncsu.edu). Dosage is tuned (often tens of ppm in the chest) to achieve grainy, non‑tacky whitewater. Bentonite microparticles similarly aggregate fatty deposits by large‑surface‑area adsorption.
Cationic polymers (polyamine or polyDADMAC) can function as detackifiers by precipitating anionic fatty acids into insoluble complexes; polyamine (Mw ~10–100 kDa) at 5–20 g/ADt is often used as a “fixing agent” in neutral/alkaline systems to flocculate rosin soap deposits. Detackifiers are used when dispersants alone cannot solve stickiness; industry notes organic tacky contaminants are often managed by “adsorbent detackifiers (talc and bentonite clay)” along with surfactants and screens (pdfcoffee.com).
Mills monitor whitewater tackiness (via tack meters) and pulp pitch load, adjusting talc or polymer detackifiers accordingly. Results are quantified by fewer doctor‑blade cleanings on wires/felts and lower dirt‑speck counts on paper. One coated‑woodfree trial using a polyamine detackifier reported a 60% reduction in felt cleaning frequency, though outcomes vary with furnish.
Biocide selection and program design
Slime deposition is controlled by oxidizing or non‑oxidizing biocides. Oxidizers include chlorine dioxide, sodium hypochlorite, or hypobromite; non‑oxidizers include glutaraldehyde, DBNPA (dibromo‑nitrilopropionamide), and isothiazolinones. Trade‑offs span kill spectrum, speed, and byproducts. Chlorine dioxide is effective and leaves fewer AOX (adsorbable organic halides) than chlorine, but is less effective on established biofilms (pmc.ncbi.nlm.nih.gov).
Glutaraldehyde is widely cited as a “workhorse” biocide in papermaking due to broad spectrum, rapid kill, and compatibility: it is “effective against the aerobic and anaerobic microorganisms including sulfate‑reducing bacteria” and does not adversely interact with wet‑end additives (pmc.ncbi.nlm.nih.gov). Laboratory slimicide tests show glutaraldehyde achieves >90% kill at ~25 ppm and essentially 100% kill at ~50 ppm (pmc.ncbi.nlm.nih.gov). Alternatives such as peracetic acid, hydrogen peroxide, or future enzymatic/phage approaches exist, but glutaraldehyde, isothiazolinones, and brominated organics dominate current practice.
Some mills alternate a fast‑acting biocide near the machine with a slow‑release product upstream (to control whitewater). Dosing is guided by microbial assays or ATP tests. One case history reported that switching to a new organic biocide in a high‑stock recycled‑furnish machine cut ATP‑measured bioactivity by >99%, correlating with far fewer breaks (pmc.ncbi.nlm.nih.gov) (pmc.ncbi.nlm.nih.gov). Ozonation has emerged as economically attractive: sub‑ppm ozone can disinfect water, with 99% kill of aerobic bacteria at roughly $0.04–0.15 per m³ of whitewater (pmc.ncbi.nlm.nih.gov). Such programs align with biocides used to control biofilm formation and fouling.
Holistic furnish and process controls
Deposit management is not purely chemical. Fiber/furnish selection matters. Virgin pulps (especially bleached kraft from plantation wood) generally have low residual pitch; recycled furnish should be carefully processed (sorting, deinking) to remove labels and waxy coatings. Increasing post‑consumer fibers from 50% to 75% in a linerboard mill can roughly double tackifier loads, requiring stronger detackification or revised furnish specs. Pre‑screening (rejecting >1 mm stickies) and flotation remove packstickers and ink slime; installed screening can include an automatic screen for continuous debris removal.
Process conditions are calibrated to minimize scale: keep whitewater‑loop pH below CaCO₃ saturation, add hardness sequestrants, or use gentle on‑line acids. Many mills use pulp‑washing (multiple stage hydrocyclone/“world” washers) to remove dissolved organics early because wash filtrate is a concentrated source of resin. Retention/drainage chemistry helps too: a well‑designed retention‑aid program can “hold” pitch on fibers and remove it in the sheet rather than leaving it in circulating water (hubbepaperchem.cnr.ncsu.edu). Operational practices (optimized shower positions, felt calibration, hot‑blow fabric showers) prevent fabric accumulation.
In Indonesia, these practices align with regulatory and sustainability goals: the 2019 Green Industry standard for pulp and paper requires efficient water use and pollution control to realize a “green” mill (peraturanpedia.com).
Program integration and monitoring
Deposit‑control agents must be added at the right points and doses: dispersants often into thin stock or whitewater, detackifiers into thick stock, biocides into chests or thick loops. Accurate feed systems (e.g., a dosing pump) support controlled addition. Mills monitor deposit formation using deposit coupons or online buildup sensors, adjusting chemistries dynamically. Preventive maintenance—planned boilouts or foam cleanings during shutdowns—effectively “reset” the system.
Field data show that mills with a coordinated chemical+cleaning regimen can cut wet‑end breaks and grade defects in half compared to uncoordinated programs (scribd.com) (pdfcoffee.com).
Outcomes and sustainability alignment
Integrated programs—smart fiber selection, optimized process conditions, and robust chemical treatment—yield measurable benefits: up to 30–60% fewer sheet breaks and 20–50% lower downtime. Busting recurring slime build‑ups with targeted viscozymes and biocide can cut biocide consumption by ~70% while maintaining control. Energy savings accrue from fewer blade cleans and higher drying‑felt permeability. These gains support higher speeds and yields while meeting strict environmental and product‑quality targets (solenis.com) (pmc.ncbi.nlm.nih.gov) (pdfcoffee.com) (pdfcoffee.com) (peraturanpedia.com).
Illustrative system condition
Figure (illustrative): an example of deposit buildup on press fabrics before (left) and after (right) chemical cleaning shows how dispersant/detackifier treatment can restore felt porosity. (Source: generic process photo) (pdfcoffee.com).
Reference notes and sourcing
Industry reports and studies from TAPPI/industry consultancies and academic reviews underpin these data and trends (solenis.com) (pmc.ncbi.nlm.nih.gov) (pdfcoffee.com) (pdfcoffee.com) (peraturanpedia.com) (pmc.ncbi.nlm.nih.gov) (pmc.ncbi.nlm.nih.gov), reflecting global practice with Indonesia’s Green Industry standard noted for local context.
