Dynamics of colloidal pitch adsorption at the solid–liquid interface by surface plasmon resonance

Abstract

This study has two objectives. The first is to investigate the direct adsorption of pitch on pulp fibres as a papermaking strategy. The second objective is to evaluate the potential of surface plasmon resonance (SPR) to quantify the adsorption of polydisperse colloids at the solid–liquid interface. The affinity of colloidal pitch for carboxyl methyl dextran (CMD) surfaces was studied by SPR and optical microscopy. The dynamics of adsorption and desorption of concentration pulses of colloidal pitch on carboxy methyl dextran were followed at the solid–liquid interface by SPR. The parameters investigated were temperature, pitch concentration, colloid size and pitch build-up. The direct adsorption of pitch onto pulp fibres was found to be a poor strategy for pitch control in papermaking. This is because of the very low chemical affinity of pitch for polysaccharide surfaces. Pitch can be carried by fibres as the low desorption rate might not allow full desorption during papermaking. Pitch has a stronger affinity for pitch covered surfaces than for polysaccharides and first adsorbs as colloids—not as individual fatty/resin acid molecules. Adsorbed pitch particles then serve as nucleation centres for further pitch adsorption. SPR is a suitable analytical technique to quantify the adsorption dynamics of polydisperse colloids at the solid–liquid interface. The low signal response measured for the larger colloid was explained with the bouncing ball mechanism. A fractionation of the polydisperse colloid was observed, with the small particles being eluded first, followed by the bigger one.