AKD Emulsion (Alkyl Ketene Dimer Sizing) Storage & Tank Compatibility

Storing AKD Emulsion (Alkyl Ketene Dimer Sizing)? Start Here

AKD emulsion sizing is a water-based dispersion of alkyl ketene dimer (AKD) wax, the dominant internal sizing agent used to make neutral- and alkaline-pH paper water-repellent. A representative product is a milky, mildly acidic (pH ~3-5) liquid carrying roughly 10-20% AKD wax solids stabilized in water by cationic starch (and often a charge-control agent such as alum or polyaluminum chloride). AKD is cellulose-reactive: at the paper machine it bonds to fiber hydroxyl groups to build hydrophobicity, but in the tank it is essentially inert toward plastics. Because the carrier is water rather than an organic solvent, the emulsion is non-flammable and far gentler on materials than a solvent-borne size. Material of construction (MOC) still matters because the emulsion is sensitive to freezing, heat, shear, and metal-ion contamination, any of which can break the dispersion or hydrolyze the AKD and ruin its sizing efficiency.

Polyethylene (HDPE / XLPE) Compatibility

AKD emulsion sizing is compatible with polyethylene. Although the active ingredient is a reactive wax, the product is a water-continuous emulsion, so the phase contacting the tank wall is predominantly water with a mildly acidic, starch-stabilized character. Polyethylene is inert to water and to dilute aqueous wax/starch dispersions, so standard HDPE and cross-linked (XLPE) tanks rated for water and mild-acid service are appropriate for bulk AKD emulsion storage. A smooth poly interior is an advantage over bare carbon steel: it will not corrode in the acidic aqueous phase and will not shed iron, which would destabilize the emulsion and degrade sizing performance. Practical controls — freeze protection, avoiding heat (which accelerates AKD hydrolysis), gentle low-shear handling, and keeping the product within shelf life — matter more for product integrity than chemical attack on the tank. Always confirm against the specific product SDS and a polyethylene resistance chart.

Material compatibility at a glance

AKD emulsion is a water-continuous wax dispersion, so material selection is governed by the dilute, mildly acidic aqueous phase rather than by solvent attack. Polyethylene (HDPE/XLPE), polypropylene, FRP, EPDM and 316 stainless steel are all suitable. The neat AKD wax is cellulose-reactive but inert to plastics. The real failure modes are emulsion instability — freezing, heat, shear, and metal-ion contamination from bare carbon steel — which break the size and accelerate AKD hydrolysis, so inert plastic or 316 contact surfaces are strongly preferred over bare or 304 steel.

Ratings: S suitable · C conditional / limited · U unsuitable. Verify against the cited resistance charts and your concentration/temperature before specifying.

The safety that actually matters

• Many commercial AKD emulsions are not GHS-classified; representative grades carry at most a mild eye/skin irritation note (H319) — verify on the specific product SDS.
• Non-flammable as supplied because the carrier is water; however the neat AKD wax is a combustible solid (melts ~45-55 °C), so dried residue and any recovered wax should be kept away from ignition sources.
• The emulsion is mildly acidic (pH ~3-5) — avoid prolonged skin/eye contact and wear splash goggles and gloves when handling or transferring.
• Spills are slippery (waxy/starchy) — contain promptly and clean before they dry to a film.
• Protect from freezing and excess heat; both break the emulsion and accelerate AKD hydrolysis, generating fatty-acid byproduct and ruining sizing efficiency.
• Manage broken emulsion, washwater and recovered solids per local regulations; do not flush to storm drains.

Common questions

Can I store AKD emulsion sizing in a poly (HDPE/XLPE) tank?

Yes. It is a water-based emulsion and polyethylene is inert to water and dilute mildly-acidic aqueous wax/starch dispersions, so standard HDPE or XLPE tanks rated for water and mild-acid service are suitable. A poly interior also avoids the iron-contamination and corrosion risks of bare carbon steel.

Why is bare carbon steel a poor choice for AKD emulsion?

The emulsion's aqueous phase is mildly acidic (pH ~3-5) and may carry alum or chloride, which corrodes bare steel. The resulting rust and dissolved iron destabilize the emulsion and can break the size, so use polyethylene, FRP, or 316 stainless steel instead.

What ruins AKD emulsion in storage if not chemical attack on the tank?

Freezing, excess heat, high shear, and metal-ion (iron) contamination. Heat and near-neutral conditions also accelerate hydrolysis of the AKD wax. Use freeze protection, keep it cool, handle gently, and rotate stock within its shelf life.

Is AKD emulsion sizing flammable?

As supplied it is non-flammable because the continuous phase is water. The neat AKD wax itself is a combustible solid that melts around 45-55 °C, so keep dried residue and recovered wax away from ignition sources and confirm the flash point on the product SDS.