New equipment for detection of polymer induced flocculation of cellulosic fibres by using image analysis - application to microparticle systems

The present investigation has shown that the use of image analysis can be a very efficient way to study the state of flocculation of cellulosic fibres . By an FFT analysis of the grey-values of the collected images, of the flo wing fibres, it was possible to evaluate both a degree of flocculation of t he fibres and an average diameter of the formed flocs. Calibration with mod el flocs correlated very well with earlier published data.Investigations re garding flocculation of unbleached cellulosic fibres caused by a microparti cle based retention aid, i.e. a combined addition of a high molecular mass cationic polyacrylamide (C-PAM) and a bentonite clay, and a site blocking p olymer (SBP) (a dimethylamine epichlorohydrine condensate) were also conduc ted. The results from these measurements show that a preadsorption of the S EP to a surface coverage of 50% of the fibres (i.e. of its saturation adsor ption) resulted in a higher degree of flocculation upon addition of the C-P AM of the microparticle based flocculant. This is probably due to a more ex tended conformation of the C-PAM out from the surface of the cellulosic fib ers. These results were also in accordance with earlier published theories. A simultaneous addition of SEP and C-PAM in the microparticle system was n ot as efficient, regarding flocculation, as a pre-adsorption of the SEP. Th is can be explained by the fact that the way that both the SEP and the C-PA M are adsorbed is affected by the way the polymers are added. In accordance with earlier publishd data the results indicate that the adsorption of SEP is strongly affected by the presence of the C-PAM.The results nevertheless show that an addition of a SEP has a positive effect on microparticle base d retention aids.Finally the present results clearly demonstrate that the p olymer addition levels in flocculation studies (which are relevant for prac tical use) are comparably low compared with saturation adsorption on the fi bres and the difference in flocculating ability of differently charged C-PA M is small, compared with their corresponding saturation adsorption. Furthe r investigations in this area are strongly recommended. (C) 2000 Elsevier S cience B.V. All rights reserved.