Some ways to decrease fibre suspension flocculation and improve sheet formation

Fibre suspension flocculation was studied in a flow loop system, simulating the flow conditions in a modern paper machine headbox. Fibre suspensions were studied using an optical detection method. Images were taken by a high speed video camera with transmitted infra-red laser light pulse illumination after the headbox nozzle. Fibre flocculation was evaluated by power spectrum analysis using the concepts of mean floc size and flocculation index. A refined unbleached softwood kraft pulp suspension was used in this investigation. The effect of a formation aid, anionic polyacrylamide, A-PAM, was studied with different addition levels in the fibre suspensions, showing the effects on decreasing the fibre flocculation and improving the sheet formation. Fibre suspensions were also studied at different medium temperatures and at different fibre concentrations. It was found that a decrease of medium temperature decreases the fibre suspension flocculation. These mechanisms of fibre flocculation reduction were discussed in the paper. The refined unbleached softwood kraft pulp was also used for Studying the effect of a non-ionic polymer, xyloglucan, on fibre suspension flocculation. Xyloglucan is strongly adsorbed on fibre surface decreasing the friction between fibres, therefore, reducing the fibre flocculation in suspensions. The flocculation reduction increased with an increased addition of xyloglucan. The effect of xyloglucan on fibre flocculation was also compared with the effects of cationic polyacrylamide, C-PAM, and anionic polyacrylamide, A-PAM, in the same pulp suspension. A refined ECF (Elemental Chlorine Free) bleached softwood kraft pulp was grafted with carboxymethyl cellulose, CMC, for studying the effects of surface modification in different ionic forms on fibre suspension flocculation. CMC-grafting on fibre surfaces reduced the fibre flocculation in suspensions by decreasing the friction between fibres, and the flocculation reduction was in the order of Na-form > H-form > Ca-form. Hence, charged groups provide an electrosteric barrier, decreasing the friction between fibres, resulting an improved fibre dispersion.