Binders water-soluble

Film-forming polymers that are soluble in water have been used in the ceramic industry for many, many years. Those knowledgeable in dry pressing are probably familiar with polyvinyl alcohol. Those versed in extrusion are likely familiar with one or more cellulose ethers. These polymeric binders are widely used to impart strength and stiffness to pressed, extruded, and slip-cast parts. These binders have also been explored for use in tape casting. Slip formulations using water-soluble polymers such as PVA and celluloses, di,i2,i3,i4 well as polyacrylic acid can be easily discovered in published literature. 

The big picture in this case focuses mainly on the ability to plasticize these water-soluble polymers in the desired manner. Many plasticizers have been used and reported for both PVA and cellulose binders, but the vast majority fall into the category of Type II plasticizers. Glycerin and various glycols have been reported, and seen by the authors, to be very effective lubricants in the water-soluble tape casting systems. The earlier section on plasticizers, however, pointed out that while a Type II plasticizer is desired in some cases, the mandatory plasticizing agent found in all tapes is the Type I plasticizer or binder solvent. The requirements of a Type I plasticizer are solution of the binder polymer and low volatility. Water-soluble binders are plasticized (Type I) by water, which satisfies both of these criteria. 

In manufacturing, fluctuations of water content in PVA and/or cellulose tapes can prove costly. Fluctuations in atmospheric humidity/ relative humidity can cause large changes not only in laminatability 

Another potential problem in water-soluble binder systems is the achievement of easily processable viscosities. Celluloses are used as thickeners in some industries (food, pharmaceutical), and they behave similarly in tape casting. PVA slips also tend toward higher viscosities, but not to the extent of celluloses. Reported slip recipes have addressed this thickening effect by using additional water to lower slip viscosities. This results in castable slips, but it also results in wet dry ratios of 6.5 1 or 8 1, or z-dimension shrinkage of 77%P The additional water also results in comparatively low solids to solids plus solvent ratios. Some reported formulations display viscosities of 37,500 mPa-s (cP) at 38.6 wt% solids, 17,800 mPa-s (cP) at 43 wt%, or solids loading as low as 17.3 wt%. The role of pH on the viscosity of the multicomponent slip is not widely reported. 

The last processing problem touched on in this section, but certainly not the last processing problem for these binders, is the removal of trapped air or foam. The combination of low solids loading, high 

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K chlorate and water soluble binder (percentages are not given)... 

Dense, spherical particles with smooth surfaces and diameters of 20 p,m or greater provide the optimal flow behavior. The presence of more than 5% fines (particles less than about 20 fim in diameter) may prohibit flow altogether. Binders and other additives can inhibit proper flow when the temperature exceeds the glass transition point of the additive, and relative humidity cau affect the flow behavior of water-soluble binders. 

Paper. Blue paper can be produced by adding water-soluble iron blue pigment directly to the aqueous phase. Alternatively, a suitable iron blue pigment can be ground together with a water-soluble binder, applied to the paper, dried, and glazed (quantity applied ca. 8% in the dispersion). 

Effervescents comprise a soluble organic acid and an alkali metal carbonate salt. Citric acid is most commonly used for its flavor-enhancing properties. Malic acid imparts a smoother after taste and fumaric, ascorbic, adipic, and tartaric acids are less commonly used [14], Sodium bicarbonate is the most common alkali, but potassium bicarbonate can be used if sodium levels are a potential issue with the formulation. Both sodium and potassium carbonate can also be employed. Other excipients include water-soluble binders such as dextrose or lactose, and binder levels are kept to a minimum to avoid retardation of disintegration. All ingredients must be anhydrous to prevent the components within the formulation reacting with each other during storage. 

Other salts which have been used successfully as water-soluble binders are potassium silicate, sodium phosphate, sodium borate and aluminium phosphate , the last two being the only ones apart from sodium silicate which have apparently been widely used. Their application techniques are similar to those described for sodium silicate. The concentration of molybdenum disulphide in inorganic salt binders is usually between about 20 and 75%. 

Slow continuous addition of water (in case the water-soluble binder is dry mixed) or a binder solution to the mix is a granulation method of choice. " The granulating fluid should be added at a slow rate to avoid local overwetting. ... 

Water-Soluble Binders. Water-soluble binders consist of relatively low molecular mass polymers (M < 10000) (e.g., alkyds, polyesters, polyacrylates, epoxides, and epoxy esters) whose individual molecules dissolve in water due to salt formation involving functional anionic or cationic groups. 

Most water-soluble binders are anionic. They are made water soluble by neutralizing carboxyl groups with ammonia or volatile (generally secondary or tertiary) amines that evaporate during film formation. In cationic binders, salt formation usually occurs between the amine groups of the resin and organic acids (e.g., acetic... 

Water-soluble binders generally contain organic solvent (< 10-15 wt%) that originates from their production via polycondensation or polymerization reactions in an organic medium. They can, however, still be dissolved or diluted with water after neutralization. Anomalous viscosity behavior may, however, arise it is characterized by a viscosity increase on dilution with water due to association of the binder molecules in water (Fig. 3.1) [3.42]. More modern binders are supplied as preneutralized solutions in water and cosolvent. 

Water-soluble binders (e.g., polyesters, polyacrylates) can also be chemically cured with cross-linking agents at elevated temperature (oven drying). These binders can be reacted with water-soluble or water-miscible amino resins (especially fully or partially methylated methoxymethylmelamine resins) or with water-soluble or water-miscible blocked polyisocyanates, which only react after the isocyanate groups have been unblocked. 

Hybrid Systems. Combinations of water-soluble and water-dispersed binders may be used to achieve synergistic effects (e.g., to control the amount of organic solvents or the application behavior). Polymer dispersions or powdered binders may be used as water-dispersible binders [3.43]. The use of polymer dispersions allows the solids content of water-soluble binders to be increased, the level of organic solvents to be reduced, and the physical drying time to be shortened. The use of water-soluble binders provides a broad application spectrum and yields paint films with well-balanced properties. 

As a rule, pigments can easily be dispersed in water-soluble binders because the water-soluble binder molecules promote wetting and stabilization of the pigments. The dispersion and stabilization of pigments in polymer dispersions is, however, more difficult because the dispersions form a continuous phase in water and uniform distribution of the dispersed pigment particles in the paint film is hindered by coalescence of the polymer particles. To overcome such problems new dispersion additives have been developed in recent years. 

More recently, classification according to the paint or lacquer system has come to be preferred. Here, a distinction is made between solvent paints or lacquers (that is, those with organic solvents), low-solvent systems, water-soluble binders, aqueous dispersions, nonaqueous dispersions, and powder coatings. 

Paints and Lacquers with Water-Soluble Binders... 

Practically all binders with hydrophilic groups can be used to manufacture paints and lacquers with water-soluble binders. The hydrophilic groups can be introduced by copolymerization with corresponding monomers during... 

Such products are normally based on cellulosic fibres such as viscose rayon 4iich are wetlaid using a water soluble binder, such as polyvinyl alcohol (PVOH), or can also be wetlaid using high-pressure, water jets (hydroentimglement). 

For pipe construction, steel mandrels are generally used. However, where cylinders or spheres are to be made, an alternative material has to be used so that it can be removed once the resin system has cured. In these cases the mandrel can be made from wax, a low melting metal alloy, or an inert plaster held together with a water soluble binder. Clearly, in these cases the mandrel can only be used once. Material choice for the mandrel will depend on the cure cycle needed for the resin system. 

Soft distemper n. Usually based on whiting, lightly bound with glue, size or other water-soluble binder so that the coating will withstand dry rubbing without disturbance but can easily be removed by water washing. 

Granulation requires the use of binders to form the granules, and make them harder and less likely to fracture. Water-soluble polymers, such as polyvinylpyrrolidone and starches or other polysaccharides, are commonly used to increase the adhesion between particles. Water-soluble binders are used to produce rapid and complete breakup back to the primary particle size. Some surfactants and polymers can also act as binders, especially for mechanical granulation techniques. 

A limited number of NSF specimens were cast crack free using suspensions with and without binder additions. A limited number of water soluble binders or emulsions screened so far did not show any improvement over unbinderized suspension. Green densities in the range 1.8 to 1.95 gm/cc (58 to 60% T.D.) were measured in the cast bars. 

An emulsion, according to its basic definition, is a suspension of one material in a liquid in which it is not soluble. The emulsion as a whole may be considered soluble in another liquid, but in the case of binders for aqueous tape casting, the line of distinction must be drawn between water-soluble binders and emulsion binders. Specifically, a water-soluble binder is a polymer that dissolves in water, and an emulsion binder is a collection of insoluble polymer particles, droplets, suspended in water. As pointed out by Doreau et al., the addition of emulsion binder to a slip is accompanied by an addition of water which is also in that emulsion. An 80 g addition of a 50% active emulsion only puts 40 g of binder (polymer) into the tape. Soluble binders may be added 100% active. The two binder families will be discussed separately in this chapter. Phenomena that are shared by both types of binder will be discussed later. 

There are basically two types of water-based formulations (1) those prepared using emulsion binder systems and (2) those prepared with Water-soluble binder systems. Examples of each are included in this section. 

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