Polyelectrolyte Complex Formation between Cationic Fixing Agent and Dissolved Substances in Papermaking

Abstract

Dissolved substances (DS) in papermaking suspension contribute a large portion of negativity to the total dissolved and colloidal substances (DCS). Compared to colloidal substances (CS), dissolved substances are clearly more difficult to be removed by fixing agents (FA). Formation of polyelectrolyte complexes (PECs) between fixing agents and dissolved substances plays a very important role in clarifying the mechanism of a fixing agent acting on DCS. This study, therefore, focused on the characteristics of PECs formed between fixing agents and dissolved substances. Three polyamines (PA) with different molecular weight and slight different charge density were synthesized and used as fixing agents, in four different kinds of water including, two kinds of DCS water separated from a same deinked pulp (DIP) but with different size and distribution of CS particles, and two kinds of DS water modeled by oxidized starch (OS) and hemicelluloses (HC). The formation of PEC in these systems and their corresponding characteristics were characterized using focused beam reflectance meter (FBRM), laser particle size analyzer (LPSA), turbidity meter, and charge detection. From the results, it is concluded that for a given DS component and a certain kind of fixing agent, the formation of DSfixing agent PECs highly depended on the molecular weight of the fixing agent and its dosage. A fixing agent with enough low molecular weight could form big but loose and dispersible DS-FA PECs, increasing its dosage would produce denser and smaller PECs; and a fixing agent with enough high molecular weight could directly form dense PECs, increasing its dosage increased the size of PECs. Depositing DS-FA PECs onto small CS particles also played an important role in forming new CS particles with larger sizes, and in this case, a fixing agent with higher molecular weight tended to produce more large particles.