Quantifying Dialkyl Ketone Accumulation Impact on Press Felt Dewatering Efficiency in Short Fibre Furnishes
Dialkyl ketone deposition drops press felt voidage and raises water contact angles, reducing press exit dryness by 1 to 3% in hardwood furnishes.
Wax
Dichloromethane extractions of blinded pickup felts taken from high-speed hardwood machines show dialkyl ketone concentrations ranging from 12.4 to 48.7 milligrams per gram of dry textile fibre. The neutral ketone fraction consists of 16-hentriacontanone and 18-pentatriacontanone, generated by the decarboxylation of hydrolyzed alkyl ketene dimer sizing agents. In short fibre furnishes dominated by bleached eucalyptus kraft pulp, specific surface area runs between 3.8 and 5.2 square metres per gram.
Unadsorbed emulsion droplets encounter elevated concentrations of colloidal fines, inorganic carbonate fillers, and dissolved anionic trash. The colloidal particles carry unreacted sizing agent into the press nip rather than fixing it to the fibre wall.
The operational takeaway centers on press solids. Every 10 milligrams of dialkyl ketone deposited per gram of outer nylon batt reduces press exit dryness by 0.6 to 1.1 percentage points under steady nip loading. On an 800-tonne-per-day line running copy paper at 1,150 metres per minute, that loss forces an immediate evaporative penalty in the dryer section.
The primary mechanism involves wetting alterations: dialkyl ketone lowers the surface free energy of polyamide 6 and polyamide 6,6 filaments from 46 millinewtons per metre down to 24 millinewtons per metre. The dynamic contact angle between process water and the textile monofilaments shifts from 32 degrees to 104 degrees, suppressing capillary penetration during the 1.8 to 3.2 millisecond nip dwell.
Hydrophobic deposition on outer batt fibres raises dynamic contact angles past one hundred degrees, halting dynamic capillary absorption.
Hardwood fines accelerate compound pickup. In bleached acacia and eucalyptus stocks, parenchymal cells and vessel elements generate a substantial fines fraction passing a 200-mesh screen (ISO 5269). These small particles exhibit high specific surface areas and capture excess cationic promoter resins.
When sizing emulsion retention falls below 82 percent in the wet end, unbonded ketone dimers circulate through the short white water loop. Thermal exposure at the headbox (typically 48 to 55 degrees Celsius) and alkaline pH conditions (7.8 to 8.4) hydrolyze the lactone ring into an unstable beta-keto acid. Decarboxylation follows rapidly, leaving the insoluble, wax-like ketone.
- Unretained sizing emulsion migrates through the forming fabric directly into the white water silo.
- Decarboxylation kinetics transform beta-keto acids into solid ketones at temperatures above forty-five degrees.
- Hardwood parenchyma cells carry sticky hydrophobic clusters into the press section through mechanical entrapment.
- Shear forces within the press nip smear softened ketone deposits across the structural pores of the nylon batt.
Chemical suppliers attribute persistent dewatering declines to inadequate cationic starch retention rather than sizing recipe over-addition.
Batt
Polyamide filaments forming the active face of a press textile depend on calibrated void geometry to receive hydraulic flow under mechanical pressure. Modern press clothing features multi-axial base structures layered with needle-punched webs of polyamide 6 and polyamide 6,6 fibres ranging from 3.3 to 22 dtex. Under continuous cyclic loading at 1,000 kilonewtons per metre in an extended nip shoe press, clean textiles maintain void fractions between 42 and 48 percent.
When dialkyl ketone aggregates coat the monofilaments, void spaces clog with low-surface-energy solids. Capillary suction collapses under hydrophobic coating.
Does Hydrophobic Contamination Drive Premature Batt Compaction?
Accumulation of fatty ketones within the interstitial spaces alters mechanical stress distribution across the textile. Instead of pure elastomeric deflection followed by spring-back in the expanding nip phase, the coated synthetic fibres experience plastic deformation. The hydrophobic matrix glues adjacent filaments together, resisting high-pressure needle shower penetration and preventing full thickness recovery.
Permeability losses concentrate on the sheet-contact face.
Under twenty kilonewtons per square metre differential pressure, air permeability drops by sixty percent within twelve operational days (ISO 9237).
Water escapes through the open base. However, when the face layer seals, hydraulic pressure within the nip rises sharply, driving sheet rewetting during the nip exit phase. In short fibre furnishes, where web tensile strength before drying remains fragile (0.45 to 0.70 kilonewtons per metre), hydraulic backpressure produces micro-crushing along the sheet surface.
| Felt State | Extractable Ketone (mg/g) | Air Permeability (cfm/sq ft) | Void Volume (%) | Exit Sheet Solids (%) |
|---|---|---|---|---|
| Unused Baseline | 0.0 | 52.4 | 46.2 | 45.8 |
| Ten Operating Days | 8.6 | 38.1 | 39.5 | 44.9 |
| Twenty Operating Days | 19.4 | 24.3 | 33.1 | 43.7 |
| Thirty Operating Days | 37.8 | 14.2 | 27.8 | 42.1 |
Felt caliper drops under continuous compaction. As mechanical thickness decreases from 3.2 millimetres down to 2.1 millimetres, the dynamic void volume no longer accommodates peak hydraulic discharge from the wet web. Water forced out of the eucalyptus furnish hits the sealed batt surface, bounces, and returns to the sheet interface.
A clogged face layer turns mechanical compression into sheet distress.
Steam
Boiler output responds directly to moisture swings entering the cylinder drying line. Press dewatering operates at high energetic efficiency, consuming between 15 and 25 kilowatt-hours of electrical drive energy per tonne of displaced water. Evaporative thermal drying requires roughly 1.2 to 1.5 tonnes of low-pressure steam per tonne of water evaporated.
When dialkyl ketone deposition reduces press solids out of the second nip from 45.0 percent down to 42.5 percent, incoming moisture ratio jumps from 1.22 to 1.35 kilograms of water per kilogram of dry fibre.
Do Extended Nip Loadings Counteract Wax Accumulation?
Machine superintendents often raise shoe press hydraulic loading to bridge dewatering gaps. Moving from 800 kilonewtons per metre to 1,050 kilonewtons per metre temporarily recovers 0.8 percent sheet solids on virgin stock. However, when dialkyl ketone resides in the textile interior, excessive pressure compacts the batt permanently, compounding dewatering resistance.
Dryer cans demand additional boiler pressure.
Every percentage point lost at the press discharge demands an additional four percent thermal drying capacity downstream.
Evaporation costs surpass press mechanical dewatering. The worked economics prove severe when calculated across continuous production. Take a paper machine outputting 35 metric tonnes per hour of 75 gsm uncoated woodfree copy sheet derived entirely from bleached birch and eucalyptus kraft pulp.
- Operating speed stabilizes at 1,100 metres per minute across a 6.8-metre trimmed web width.
- Initial sheet solids exit the second press nip at 45.2 percent under virgin felt conditions.
- Blinded textile solids drop to 42.6 percent following four weeks of high dialkyl ketone deposition.
- Water evaporation burden increases from 42.4 tonnes per hour up to 47.1 tonnes per hour.
- Additional thermal demand requires 6.1 tonnes of dry saturated steam per operating hour.
| Parameter | Clean Baseline | Mild Deposition | Severe Deposition | |
|---|---|---|---|---|
| Press Exit Dryness (%) | 45.2 | 43.8 | 42.6 | |
| Sheet Water Ratio (kg/kg) | 1.212 | 1.283 | 1.347 | |
| Hourly Evaporation (t/h) | 42.42 | 44.91 | 47.15 | |
| Specific Steam Consumption (t/t paper) | 1.57 | 1.66 | 1.75 | |
| Daily Thermal Premium (USD) | 0 | 2,688 | 5,124 | |
| Assumes natural gas generated steam at 32.00 USD per metric tonne landed cost and continuous 24-hour operation. | ||||
Mill production schedules face hard limits when dryers reach pressure maximums, forcing machine operators to slash line speed and sacrifice salable daily tonnage.
Assay
Quantitative isolation of neutral fatty ketones requires rigorous extraction chemistry paired with chromatography. Standard Soxhlet extraction using dichloromethane (ISO 14453) removes total extractable organics, including processing oils, free fatty acids, silicone defoamers, and dialkyl ketones. Dichloromethane extraction isolates the neutral fraction.
Unrefined gravimetric weighing overstates ketone deposition by including synthetic base-fabric processing lubricants. Accurate isolation isolates the ketone carbonyl.
Infrared spectra confirm the ketone carbonyl. Fourier-transform infrared spectroscopy (FTIR) identifies the aliphatic ketone absorption band at 1,715 cm⁻¹, clearly separated from the 1,735 cm⁻¹ ester carbonyl of unhydrolyzed sizing agent and the 1,640 cm⁻¹ secondary amide peaks of the nylon textile. Gas chromatography with flame ionization detection (GC-FID) quantifies the exact split between palmitone (derived from C16 palmitic chains) and stearone (derived from C18 stearic chains).
Standard procurement contracts mandate that extractable neutral organics remain below fifteen milligrams per gram of textile batt over four operating weeks.
Diagnostic verification follows a sequenced operational flow:
- Textile core extraction retrieves three 50-millimetre diameter samples across the cross-machine profile during planned maintenance shutdowns.
- Solvent washing in boiling dichloromethane under reflux conditions for six hours isolates non-polar deposits.
- Silica gel fractionation separates polar fatty acids from non-polar dialkyl ketones using hexane and diethyl ether eluting solvents.
- Chromatographic quantification identifies individual ketone species against pure 16-hentriacontanone reference standards.
- Permeability mapping correlates localized ketone accumulation against on-machine microwave moisture profiles.
Gas chromatography separates the homologues cleanly. When laboratories employ non-polar capillary columns (such as 100 percent dimethylpolysiloxane, 30 metres length, 0.25 millimetres internal diameter), stearone elutes at 285 degrees Celsius without decomposition. Palmitone solidifies near sixty degrees Celsius.
Purchase specifications requiring compliance with TAPPI T 204 omit chemical identification unless the buyer explicitly inserts an annex binding the laboratory to chromatographic separation of neutral ketones.
Solvent
Remediation of contaminated press fabrics requires precise chemical conditioning matched to the melting points of long-chain aliphatic ketones. Palmitone melts between 58 and 63 degrees Celsius, while stearone liquefies between 68 and 73 degrees Celsius. Cold washing cycles fail completely; unheated wash water solidifies the compounds into adhesive smears that plug deep base voids.
Continuous conditioning slows organic deposit accumulation.
Alkaline washes strip the nylon batts. High-pressure oscillating showers delivering concentrated sodium hydroxide solutions (pH 11.0 to 11.5) at temperatures exceeding 60 degrees Celsius saponify associated fatty acids and disperse inorganic carriers. Synthetic non-ionic surfactants featuring low hydrophilic-lipophilic balance (HLB 8 to 11) penetrate the wax layer, emulsifying neutral ketones without hydrolyzing the nylon textile bonds.
Batch boiling dissolves the fatty ester.
Chemical maintenance programs run into practical machine floor barriers. High concentrations of aromatic or chlorinated solvents damage polyurethane doctor blades, dissolve roll cover bonding adhesives, and generate volatile organic emissions that violate occupational safety standards. Machine operators rely instead on micro-emulsion cleaners containing ethoxylated fatty alcohols paired with organic solvents derived from orange terpenes or glycol ethers.
These formulations soften wax accumulations during five-minute creep-speed shutdown washes.
The unresolved question remains whether wet-end chemical control using high-charge, low-molecular-weight polyamines can trap hydrolyzed dialkyl ketones onto eucalyptus fibres before they leave the wire, or whether mechanical felt conditioning will always bear the burden of sizing inefficiencies.