Plasticizer and Binder Mixing

Before embarking on the procedures for adding the plasticizer(s) and binder, it is important to point out that the order in which you add the organics to the mill is almost as critical as the materials themselves. The dispersant, which is dissolved in a solvent or solvents, is 

This is like putting a clump of particles inside a bag, sealing it shut, and then trying to get the particles apart. While it is possible to break the agglomerate within the bag, all pieces of that agglomerate still remain within the bag until the bag is broken. 

After the dispersion milling process is complete—that is, after 24 or more hours of milling—the mill is opened and the plasticizer or plasticizers are poured onto the top of the slip. Most plasticizers are liquids and quite fluid, and therefore this is not a complicated procedure. The plasticizer or plasticizers form a thin film on the surface of the slip in the mill. The weighed quantity of binder, either in powder form or dissolved in one or both of the solvents, is then added to the layer of plasticizer(s). Usually the binder is more soluble in the plasticizer(s) than it is in the solvent(s), so it is good practice to introduce the binder to the plasticizer first. Remember from Chapter 2 that the whole point of the Type I plasticizer is to react with (dissolve) the binder. The plasticizer wets the binder if it is in powder form and aids in the dissolution process. It is also good practice to make sure that the binder, if in powder form, is stirred into the slip mixture before the mill is sealed and returned to the rollers. We have found large clumps of undissolved binder after 12 hours or more of mixing if we didn t follow this simple procedure. 

Usually about 12 hours are required for the complete dissolution of the binder and reaction of the binder with the Type I plasticizer (see the definition of a Type I plasticizer in Chapter 2). If the binder is pre-dissolved in a solvent mixture and the Type I plasticizer is added 

Once the plasticizer(s) and binder(s) have been mixed into the slip formulation, it is ready for precasting conditioning and characterization. 

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