ABSTRACT
Cellulose fibres used for papermaking are quite hydrophilic and can be rapidly wetted by water and aqueous liquids such as water-based printing inks. Most pa per and paperboards must be hydrophobized (or sized) to an appropriate degree to suit the end-use requirement of the paper or paperboard (e.g., printing) [1], A commonly used sizing chemical in neutral and alkaline papermaking is AKD, a
mixture of alkyl ketene dimers [2, 3]. The molecular structure of AKD is given below. AKD has two saturated hydrocarbon chains and the lengths of the chains vary typically from Ci6H33 to C2oH4i. AKD is a waxy material with a melting point of about 50°C. The application of AKD at the wet end of a paper machine involves mixing the AKD emulsion with the pulp furnish. The particle size of a commercial AKD emulsion is typically about 0.5 to 2 μιη in diameter. Since the AKD emulsion is stabilized with cationic starch and carries positive charges, the emulsion particles attach to the surfaces of the negatively charged pulp fibres [3]. A strong sizing effect takes place after the sized paper is cured or exposed to an elevated temperature. This temperature is typically between 90 and 120°C in the drying section of the paper machine.
