Coagulation polymer

Most suspended solids in water have a surface electrical charge that provides stability to the particles. This ionic charge is usually a negative (—) charge and requires the addition of metal salts or cationic (+) polymer coagulants to destabilize the particles and permit them to agglomerate or come together. 

L. K. Wang, Feasibility Study of Treating Field Military Wastewater by a Process System Including Powdered Carbon Adsorption, Polymer Coagulation, and Diatomite Filtration, US Defense Technical Information Center, Alexandria, VA, ADA077198, June, 1973. 

This method was developed by Zsigmondy in the early part of the last century. A cast polymer solution that consists of polymer and solvent is brought into nonsolvent vapor environment saturated with solvent vapor. While saturated solvent vapor suppresses the evaporation of solvent from the film, nonsolvent vapor diffuses into the film causing polymer coagulation. The formation of the dense skin layer does not occur. Pore sizes are uniform, perpendicular to the membrane surface. 

The fibers did not go into the coagulation bath perpendicularly, but rather in a conical way in a circular motion. This circular motion could be one of the reasons for the angular stress working during the polymer coagulation. 

The chemical structure and molecular weight of the polymer both influence the rate of coagulation and the structure produced. A high molecular weight polymer coagulates more rapidly than one of lower molecular weight. It is found that in a DMF/water system, a polyether-based polymer coagulates more rapidly than a polyester-based polymer of the same urethane content. 

Bone TE 4,4 -Dicyclohexylemethane diisocyanates (HMDI), PCL diol (Mw, 2000 Da), and ethylene glycol (EG) Porous composite scaffolds (PUR blended with hydroxyapatite) (porosity > 70%, pore size 100—400 pm) produced by polymer coagulation combined with salt leaching Ryszkowska et al. (2010)... 

Low molecular weight polymers (coagulants used to enhance the runnability of the paper machine are also added here). 

Where multiple chemicals are used, the order and tuning of chemical addition can be critical. For instance, polymer coagulation aids are sometimes used with alum. Many operators report the order of addition (polymer before or after alum addition) has an effect on performance. Some operators even express the importance of the time between adding the two chemicals. These chemical addition details need to be explored at each site. Jartestingis sometimes effective when comparing these variations. Only promising treatment sequences (from jar testing) are then evaluated in the plant full-scale. 

Fig. 9. Effect of the solvent-coagulant miscibility on polymer structure, (a) ei 2 = 0, Oj) ei 2 = 0.5, (c) i 2 = 0.77, and (d) 1-2 = 1.5. The structures are for a coagulation time t = 0 02 s except (d) which is for t = 0.03 s. All the other parameters are the same as in Figure a The extent of shrinking of the polymer-coagulant interfaces with respect to their initial positions have not been represented. Courtesy of Journal of Polymer Science.

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