Competitive adsorption of cationic polyacrylamides with different charge densities onto polystyrene latex, cellulose beads and cellulose fibres

The individual and competitive adsorption of cationic polyacrylamides (C-PA M) with different charge densities (CD), 0.62, 1.4 and 2.9 meq/g, but with similar molecular weights (MW = 4.10(5)) have been investigated The substra tes were monodisperse polystyrene latex (PSL), cellulose beads and cellulos e fibres. A 1:1 mixture by charge or by weight of fluorescently labelled C- PAM with high CD and unlabelled C-PAM with low CD were used for the competi tive adsorption experiments. At a stirring speed of 500 rpm in a standardiz ed for (Britt dynamic drainage jar), the adsorption of these C-PAMs onto PS L and the outermost surfaces of cellulose beads and fibres was very rapid. The amount of adsorbed charges in C-PAMs were similar; regardless of CD, in both the individual and the competitive adsorption experiments, but with a somewhat greater adsorption of C-PAM with low CD because these polymers ha ve longer loops and tails than C-PAM of high CD. The adsorbed amounts of C- PAMs by weight ale roughly inversely proportional to the CD. The results im ply that the adsorption of cationic polymers onto anionic surfaces is gover ned mainly by shear-induced collisions. The amounts of adsorbed C-PAM onto cellulose materials increased with time. The increase was most rapid for th e low CD C-PAM on fibres, because of a rather easy penetration into pores. The preadsorbed C-PAM with higher CD restricted more strongly the further a dsorption of C-PAMs due to a greater blocking effect towards C-PAM in solut ion.