Hydrolysis of Micron Alkylketene Dimert Particles Under Alkaline Conditions

D. Ravnjak, A. Može and I. Plazl

Abstract
The hydrolysis of alkylketene dimer (AKD) in a diluted dispersion was studied under alkaline conditions. The dispersion consisted of particles with 1 #m in diameter with the reaction product forming a porous insoluble layer on the particle surface. The shrinking core model (SCM) for particles of unchanging size is proposed for describing the overall rate of hydrolysis reaction. The model assumes a process controlled by a surface reaction on the boundary between unreacted AKD core and outer ketone layer, with no significant transport phenomena due to the small particle dimensions and porous structure of the reaction product layer on the particle surface. Under conditions studied (at pH 10.3), where the concentration of OH– ions is in excess compared to the AKD concentration and in the temperature range between 40 and 60 "C, the proposed model is in good agreement with experimental data. A temperature dependence of reaction rate was tested and the apparent activation energy was calculated as well. Compared to the activation energy for reaction between AKD and cellulose, AKD hydrolysis can represent an important competitive process that significantly influences the sizing efficiency.

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Keywords
Alkylketene dimer, hydrolysis, unreacted-core model, shrinking core model, Reaction kinetics, sizing, papermaking