High Molecular Weight Cationic Polyacrylamide Research Articles

Rheological properties of cellulosic fibre suspensions flocculated by cationic polyacrylamides

Cellulosic fibres in suspension form three-dimensional networks which display shear strength as a result of the mechanical entanglement of flexible fibres. The effect of high molecular weight cationic polyacrylamides of different charge densities on the viscoelasticity of softwood kraft pulp suspensions was investigated by rheological measurements in oscillatory shear as a function of straining frequency, straining amplitude, added amount of cationic polyacrylamide and fibre concentration. The flocculants increased the fibre flocculation and this was shown as an increase in the shear modulus and in the critical strain. The critical strain marks the onset of structural breakdown of the fibre network. The threshold concentration of fibres c ∗ for a measurable shear strength was lower for suspensions flocculated by cationic polyacrylamide. The shear modulus showed a scaling relationship as a function of the fibre concentration in excess of the threshold concentration, c-c ∗ . The effect of a flocculant is suggested to be due primarily to an increase in the number of fibres that are active in the network. The flocculant probably also increases the bonding strength in the fibre-fibre contact points. An attempt is made to discuss the results according to an elastic site/bond percolation concept.

Transfer of cationic polyelectrolytes between cellulosic fibres and calcium carbonate particles

AbstractThe transfer of a high molecular weight cationic polyacrylamide between cellulosic fibres and calcium carbonate particles has been studied in a stirred dispersion. It was found that there is a transfer also at very short times (5 s). The final distribution between fibres and fillers depend on the time the polymer has been adsorbed on the cellulosic fibres before the filler particles are added. If the polymer has been adsorbed a short time on the fibres, it does not have the opportunity to interact with the charges in the porcs of the fibres. The distribution will in this case be given by the outer surface areas of the fibres and fillers respectively since the particles have approximately the same z‐potential. If the polymer has been adsorbed a long time it can interact with more charges on the cellulosic fibre. The final distribution of the polymer between fibres and filler particles is for this case approximately determined by the charges available for interaction as given by the adsorption isotherms. The influence of addition level and stirring rate is in line with these arguments.Hydrodynamic forces have a larger effect on larger particles which leads to faster transfer. A higher electrolyte concentration also seems to facilitate transfer. The reason is most likely that the polymers are less tightly bound to the fibres in this case. It has been shown, by adsorbing the polymer on the filler particles, that there is also a transfer of polymer from filler to fibre.

Adsorption and reconformation of a series of cationic polyacrylamides on charged surfaces

The adsorption and adsorption stoichiometry for a series of high molecular weight cationic polyacrylamides of different charge density on cellulosic fibers are examined as functions of time. The time required for the reconformation of the polymer adlayer is of the order of one minute in all cases, but the results indicate a decrease in adsorption stoichiometry and reconformation rate with increasing polyelectrolyte charge density. Comparison of the adsorption/reconformation rates on cellulosic fibers with those on polystyrene latex shows the process to be more rapid for the latex. This result is attributed primarily to differences in the surface porosity of the substrates.

Graft copolymers of starch and poly(2‐hydroxy‐3‐methacryloyloxypropyltrimethyl‐ammonium chloride). Preparation and testing as flocculating agents

AbstractThe title monomer (I) has been graft polymerized onto whole wheat starch with both ceric ammonium nitrate and ferrous ammonium sulfate–hydrogen peroxide initiation. Three graft copolymers, which contained 4.5, 12.1, and 15.2% grafted poly(I), were characterized as to molecular weight of grafted branches and grafting frequency. Graft polymerization was proved by fractional precipitation. Graft copolymers were tested as flocculating agents for diatomaceous silica and nonmagnetic iron ore. The graft copolymers with 12.1 and 15.2% grafted poly(I) compared favorably in flocculating ability with a commercial high molecular weight cationic polyacrylamide.