Mechanism of pitch adsorption on carboxy methyl dextran surfaces

The direct adsorption of pitch particles onto pulp fibres was investigated as a pitch control strategy. The affinity of colloidal pitch for carboxyl methyl dextran (CMD) surfaces was studied by surface plasmon resonance (SPR) spectroscopy and optical microscopy. CMD was selected as model surface representing the cellulose and hemicellulose fractions of the pulp fibres. The dynamics of adsorption and desorption of concentration pulses of colloidal pitch on carboxy methyl dextran were followed at the solid-liquid interface in real time by SPR. The parameters investigated were temperature, pitch concentration and sequence of pitch build up. The direct adsorption of pure colloidal pitch onto pulp fibres is not an option for papermaking. This is because of the very low chemical affinity measured between pitch and the model CMD polysaccharide. Virtually no pitch remains adsorbed by chemical interaction on CMD surfaces submitted to low shear. In spite of its low affinity for polysaccharides, colloidal pitch can be carried by fibres as the low desorption rate might not allow full particle desorption during the time frame of the forming process, and some physical entrapment might also occur. Pitch has a stronger affinity for pitch covered surfaces than for polysaccharides.