Aggregation Process and Mechanism of Pitch Deposits with Ca2+ in Papermaking White Water

Chen Chen, Chun-Jian Wang, Hui Xu, Hong-Qi Dai

Abstract


The lipophilic colloidal substances (CS) in papermaking white water mainly originate from sizing agents applied during paper manufacturing operations and wood extractives, such as resin acids and fatty acids. In this study, the aqueous dispersions of sodium resinate and sodium stearate were used to simulate the colloidal substances concentrated in white water. The aggregation process and mechanism of pitch deposits developed from soluble colloidal particles were investigated by the determination of turbidity and zeta potential of colloidal substances simulacra dispersions as a function of Ca2+ concentration, as well as through morphological observation, structural characterization, and contact angle measurement of calcium-induced pitch deposits. The results showed that the micelles with hydrophilic groups extending in the water could be formed when the colloidal substances accumulated to a certain concentration. The Ca2+ can exchange Na+ of colloidal substance micelles, and hydrophobic pitch deposits can then be produced by either particle-particle collision or “layer by layer” adsorption with addition of Ca2+, or by both of the mechanisms mentioned above. The complete destabilization of the colloidal substance simulacra occurred when the Ca2+ concentration reached 5 mmol/L. The initial contact angles of water on the surfaces of calcium resinate and calcium stearate discs were 90.2° and 96.0°, respectively.

Keywords


Colloidal substances; Ca2+; Pitch deposits; Aggregation process and mechanism

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