Adsorption of different kinds of cationic polyacrylamides on thermomechanical pulp in the presence of detrimental substances

Different types of polyelectrolytes are commonly used as wet-end additives in paper chemistry in order to improve the retention in the papermaking system. Closing of the water circuits in papermaking processes has made the use of polyelectrolytes more difficult than before because the amount of dissolved and colloidal substances has risen in the system. The adsorption of three commercial cationic polyacrylamides with different molecular weights and cationic charges on a peroxid-bleached thermomechanical pulp was studied. In addition, the effect of dissolved and colloidal substances was investigated. Half of the samples were diluted with deionized water and the other half with a water containing dissolved and colloidal substances. It was found that polyacrylamide with the medium molecular weight bur the lowest cationic charge gave the highest adsorption and polyacrylamide with low molecular weight and high cationic charge gave the lowest adsorption. Dissolved and colloidal substances had a remarkable effect on the adsorption.