AKD (alkyl ketene dimer)
Also: AKD, alkyl ketene dimer
A wax-like internal sizing agent that reacts with cellulose to create a water-repellent fiber surface. Works at neutral pH.
AKD is a wax-like organic molecule that reacts with cellulose hydroxyls to form a covalent bond, leaving its hydrophobic alkyl tail exposed. This gives the paper permanent water resistance at typical addition levels of 0.05 to 0.15% on fiber.
AKD replaced rosin sizing in most modern mills because it works at neutral pH, which also enables the use of calcium carbonate fillers that would dissolve in the older acid system.
Related
- Sizing. The treatment that makes paper resistant to water and aqueous inks. Internal sizing is added to the furnish; surface sizing is applied to the dry sheet.