Kinetics of colloidal alkylketene dimer particles deposition on pulp fibers

For achieving a certain level of hydrophobicity in paper, sizing agents are added to the paper stock. In alkaline papermaking system, sizing is often performed by the use of alkylketene dimer (AKD)-type sizing agents. Although the key factor for developing sizing properties in paper is the reaction between AKD and cellulose during drying, good retention of size particles in the paper web is required as a prerequisite for later reaction. A mathematical model based on particle collision frequency is used for the description of deposition kinetics of colloidal alkylketene dimer particles on pulp fibers. Modified Langmuir equation was used to describe the retention process in terms of surface coverage, attachment, and detachment rate constants. The values for equilibrium retention predicted by the model are in good agreement with experimental data. The analysis of surface charge in the system also suggests that the extent and efficiency of collisions between colloidal AKD size particles with fibers are one of the key factors for successful retention. Influence of shear on the retention process was also studied.