Alkyl ketene dimer (AKD) is a less reactive sizing agent.(PART1)

Compared to another commonly used sizing agent, ASA (alkenyl succinic anhydride), AKD has lower chemical reactivity, which offers several advantages. Its low reactivity allows paper mills to directly use pre-formulated AKD emulsions supplied by vendors, eliminating the need for additional preparation during the papermaking process. This not only simplifies the process but also makes AKD particularly suitable for certain demanding paper types, such as milk cartons and other products requiring high water resistance.

Chemical Reaction Characteristics of AKD

AKD's uniqueness lies in its chemical structure. Its sizing effect stems from its reaction with cellulose, forming β-keto ester bonds, thereby creating a hydrophobic layer on the paper fibers. This hydrophobic layer effectively repels water, achieving a water-resistant effect. Furthermore, AKD's hydrophobic reaction products are very stable and do not produce incompletely hydrophobic byproducts like ASA, making AKD more suitable for applications requiring permanent sizing. However, AKD's reaction rate is relatively slow; it typically continues to cure during the storage period after paper production, further enhancing the sizing effect. This "post-curing" characteristic means that paper usually requires a period of storage before use to ensure optimal sizing performance.