Interactions between cationic amylose derivatives and a pulp fiber model surface studied by molecular modelling

This study was performed in order to obtain more information about the interactions between pulp fibers and acetylated cationic starch derivatives on a molecular scale. The adsorption of the polymers on the fiber surface was studied by simulating polymers on a fiber model surface at 300 K. Fractional atomic coordinates of regenerated cellulose II were used to generate a cellulose fiber surface model. Carboxylate groups were added on the cellulose surface to represent the anionic charge of pulp fiber which originates from hemicelluloses. Amylose chains cationized and acetylated atom by atom were chosen to represent four different starch derivatives. Atomic charges used in simulations were calculated by a semi-empirical PM3 single point calculation. In addition, the effect of water and counter ions was considered. It was observed that especially cationization, but also the degree of acetylation of the modified amylose chains had an effect on the interaction between the model surface and the polymer. This suggests that ionic interactions were dominant but also electrostatic interactions between OH and acetylated groups were significant in the adsorption process. The force field used and the presence of water molecules and counter ions also affected the adsorption of these polymers on the model surface.