There are many emulsion polymers on the market today and they can be customized to meet any water or wastewater treatment need. Depending on your application, you may need a cationic (positive charge), anionic (negative charge), or nonionic (neutral charge) emulsion polymer. In most water and wastewater applications, the particles in the water will have a negative surface charge so you will use a cationic or positively-charged emulsion polymer.
Emulsion polymers are shipped as a thick, concentrated, viscous solution and in this form the polymer is referred to as being “neat.” This neat polymer solution needs to be “made down” or diluted in order for the polymer chains to unravel or uncoil. This is done simply enough, but often incorrectly, with water, to a solution strength of 1% or less. The key to the proper dilution of an emulsion polymer is that the introduction of water must be done quickly and completely under high mix conditions while at the same time providing low shear conditions. Static mixers have been designed that do allow the dilution to occur quickly and efficiently. The series of pictures below attempts to portray how the millions and millions of polymer strands, tightly bound up or coiled in the neat solution, begin to unravel when mixed with water.
Consider that Figure 1 represents the neat polymer solution before it has been blended with water to form a 1% solution. In the neat form, the polymer consists of long, tightly coiled strands.
Figure 1: The “Neat” Emulsion Polymer Solution
With the rapid addition of a small quantity of polymer into a larger volume of water, the tightly coiled polymer strands begun to unravel and unwind as shown in Figure 2, which depicts a “linear” polymer. You can compare the uncoiling of the linear in Figure 2 with a “cross-linked” polymer uncoiling in Figure 3. Generally, you would tend to use a cross-linked polymer when biological solids are involved and a linear polymer or a slightly cross-linked polymer when dealing with inorganic solids such as catalyst fines.
Figure 2: The “Neat” Linear Emulsion Polymer Solution Beginning to Uncoil With the Addition of Water
Note the smaller strands branching off the larger or main strands of polymer in Figure 3. These branches represent portray the “cross-linking” component of some emulsion polymers. The degree of cross-linking can range anywhere from 0% to 60% with 0% characterizing a linear polymer rather than a cross-linked polymer. The cross-links add structural integrity to the polymer improving its functionality in high-shear conditions such as dewatering sludge on belt filter press or in a centrifuge.
Figure 3: The Unfolding and Uncoiling of a Cross-Linked Polymer
In Figure 4 you can see a “close-up” view of a single strand of polymer uncoiling when added to water. You can also see the smaller strands or cross-links of polymer that will connect to other polymer strands to form a strong web providing strength and many, many points of contact for trapping solids.
Figure 4: Close-up of a Polymer Strand Uncoiling with Slight Cross-Links
The uncoiling of the main polymer strands occurs quickly with the full development of the cross-links taking somewhat longer. In Figure 5 you can see the original thickness in the polymer is gone due to lengthening and stretching caused by the reaction of the polymer with water.
Figure 5: Cross-Linked Polymer Strands Lengthening, Stretching, and Uncoiling
The interwoven polymer strands and bonds form a network that is surprisingly strong and highly resistant to the shear forces present in various sludge dewatering operations. This network is portrayed in Figure 6.
Figure 6: Interwoven Polymer Strands
In Figure 7 you can contrast a highly cross-linked polymer to a lesser degree of cross-linking shown in Figure 6. The end result is that the polymer now has many millions of positively-charged attachment points to attract and attach to the negatively-charged particles in the water or wastewater.
Figure 7: Highly Cross-Linked Emulsion Polymer