Coagulation molecular weight determination

Organic polymeric coagulants and flocculants (or polyelectrolytes) are polymers of repeating monomer units held together by covalent bonds and are available in many hundreds of permutations, in such a variety of molecular weights, ionic charges, physical form, etc., that it has become the province of experts in this field to determine the precise product or combination of products most suitable for any specific purpose. 

Determination of Viscosity Number and Average Molecular Weight of Polymers. The polymers were dissolved and coagulated several times in order to remove the emulsifier. The intrinsic viscosity was then determined with an (Jbbelohde viscometer. Normally we measured values of 7/ p/c at different concentrations [rj] was then determined by graphical extrapolation at concentration zero. 

Fig. 8 illustrates the effect of the change in molecular weight distribution of HS in model water. Over 50% of HS2 (Fig. 2) can be taken for fulvic acid. The dose of 25 mg/L was determined by the same procedure used for Fig. 4. Fig. 8 is comparable to Fig. 6 with respect to optimal coagulant dose. The comparison of Fig. 6 with Fig. 8 reveals a lowered ability of separation of coloured substances... 

The molecular-weight distribution can, at least in principle, be determined by the cloud-point titration or turbidimetric titration method. In turbidimetric titration, a precipitant is added continually, with stirring, to a very dilute ( 0.01 %) solution, and the increase in turbidity is observed as a function of the quantity of precipitant added. The turbidity curve which is obtained is a qualitative measure of the molecular weight distribution. These curves are difficult to evaluate quantitatively, however, since the turbidity continually changes because of the coagulation of the droplets during titration. The turbidity is therefore not entirely due to the molecular weight and concentration of the macromolecule. 

As shown by Eq. (15) and (17), the tensile elastic behaviom of fibers made from lyotropic polymers is determined by the chain modulus e the shear modulus go and the orientation parameter . As has been discussed in Sect. 2 and 3, the latter is determined by the persistence length, the molecular weight, the polymer concentration and the temperature of the liquid crystalline solution, and furthermore by the spinning and coagulation conditions. 

The structure produced and the properties of the resulting sheet material are determined by the composition, molecular weight and concentration of the polymer, the choice of pore former, its concentration and particle size, the presence of non-removable additives, and the coagulation conditions. 

The described method was used to measure cohesive force under applied shear between individual cotton fibers in aqueous solution and in solutions of polyethyleneimine (PEI), which is a common papermaking coagulant with a molecular weight of around 60,000 Da. The fiber thickness as determined by microscopy was 10 pm, and the compression load was varied between 0.057 and 1 g, with a minimum of 30 measurements conducted at each load. 

Figure 3.5 shows the curve for an experiment carried out with a membrane obtained with 20% polysulfone in dimethyl formamide (DMF) and precipitated in a coagulation bath composed of 50% water and 50% DMF. The test fluid was obtained by mixing six dextrans of different molecular weights (17, 40, 70, 100, 200, 500 kDa) from Leuconostoc (Fluka). The concentration of each one in solution was 1.0 g/L. From the curve obtained, a MWCO of 28kDa could be determined. Transmembrane pressure (driving force) was set to 9 bar. 

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