Flocculants (Clarifiers)
Flocculants are additives for coalescing suspended colloidal particles into aggregates which, in turn, precipitate out of suspension. (RDC 3/26/2009)
Flocculation, in the field of chemistry, is a process where colloids come out of suspension in the form of floc or flakes. The action differs from precipitation in that, prior to flocculation, colloids are merely suspended in a liquid and not actually dissolved in a solution. In the flocculated system there is no formation of a cake since all the flocs are in the suspension. (Wikipedia, Flocculants, 1/10/2011)
“Coagulants heretofore employed are typically salts of inorganic multivalent cations, A. L. Logothetis, Prog. Polym. Sci, 14, 251-296 (1989). These include aluminum salts such as aluminum sulfate, alums such as potassium aluminum sulfate, calcium salts such as calcium chloride and calcium nitrate, and magnesium salts such as magnesium chloride, magnesium sulfate, and magnesium nitrate. While these salts work very well as coagulants, residual amounts of these salts remain in the polymer. The presence of these salts renders these polymers unsuitable for use in contamination-sensitive applications such as seals in semiconductor manufacture. Thus, it would be desirable to find other coagulants effective for use in the emulsion polymerization of fluoroelastomers.”
“Salts of univalent cations, such as sodium chloride, have been proposed as coagulating agents for the manufacture of fluoroelastomers. Residual amounts of these salts are considered relatively innocuous in some end use applications. However, excessively large amounts of salts of univalent cations are required to fully coagulate the fluoroelastomer. The resulting polymer is difficult to fully dry. In addition, the large amounts of these salts that are needed to coagulate the polymer require large and expensive water treatment facilities. “
“The use of organic coagulants is another method to avoid polymer contamination. Residual amounts of organic coagulants will not contaminate semiconductor processes and in any case may volatilize out of the polymer during the curing process. U.S. Pat. No. 3,598,794 discloses polyamines as coagulants for fluoroelastomers. Addition of a polyamine to a fluoroelastomer dispersion forms a gel that can be separated from the aqueous phase. Washing of this gel, however, is difficult and residual polyamine that remains in the fluoroelastomer interferes in the curing operation.”
(Lyons, US Patent 7,816,468; 10/19/2010)
Recent US Patents
10/19/2010
7,816,468
Coagulation of fluoroelastomer dispersions with polyethylene oxide
Lyons of DuPont, Delaware isolated fluoroelastomer gum or crumb is from fluoroelastomer dispersions by the addition of a water-soluble polymeric coagulating agent. This coagulating agent is either a homopolymer of ethylene oxide (CH2.CH2.O--) or a copolymer of ethylene oxide. Specific examples of such copolymers include, but are not limited to ethylene oxide-propylene oxide copolymers and ethylene oxide-butylene oxide copolymers.(RDC 1/24/2011)
Recent Journal Articles
Characterization of cationic polyacrylamide-grafted starch flocculant synthesized by one-step reaction
(1261–1266)Journal of Applied Polymer Science 123 #2 (2012)
Cao et al ofBeijing University of Chemical Technology, China, prepared cationic polyacrylamide-grafted starch (St-g-CPAM) flocculant by using corn starch and acrylamide (AM) as monomers, dimethyl diallyl ammonium chloride (DMDAAC) as cationic monomer through solution polymerization. The results show that the optimal conditions of the polymerization are as follows: the concentration of ceric ammonium nitrate is 0.5%, the reaction temperature is 60°C, the concentration of total monomer is 20%, and the monomer ratio between AM and DMDAAC is 7 : 3. The flocculation capability was characterized by turbidity reduction. (RDC 10/12/2011)
Dual-polymer flocculation with unmodified and ultrasonically conditioned flocculant
(128-138) Chemical Engineering and Processing 50, #1 (2011)
Lemanowicz, Gierczycki and Al-Rashed, Poland and Kuwait showed that ultrasonic conditioning may be an effective alternative for a dual-polymer flocculation where two different flocculants are used. In some cases the mechanical strength of flocs, created by combination of unmodified and conditioned polymers, was improved which resulted in reduction of time needed to achieve the steady state of the system. (RDC 2/11/2011)
Preparation of amphoteric polyacrylamide flocculant and its application in the treatment of tannery wastewater
(518–523)Journal of Applied Polymer Science 120 #1 (2011)
Zhu, Zhang and Li of Shaanxi University of Science and Technology, China synthesized amphoteric polyacrylamide (AmPAM) emulsion, as an environmental friendly flocculant for the tannery wastewater by two phase aqueous polymerization. (RDC 1/10/2011)