Types of Binders

Sodium alginate Synthetic polymers Wet mixing 1-3 Water 3-5 

Freshly prepared starch paste is used at a concentration of 5-25% (w/w) in a tablet granulation. Relatively soft and friable granules are produced when starch paste is used as a binder. Consequently, it yields tablets that disintegrate readily. During the wet-massing process, high viscosity of the starch paste can sometime make it difficult to evenly distribute the binder in the powder blend. 

Gelatin is a mixture of purified protein fractions obtained by partial add hydrolysis (Type A gelatin) or alkali hydrolysis (Type B gelatin) of animal collagens. It is insoluble in cold water and in alcohol, but is soluble in hot water. In hot water, gelatin forms a gel on cooling to 35-40°C. At temperatures 40°C, the system exists as a solution. Therefore, the gelatin solutions must be used when warm to avoid gel formation. 

Acacia is a natural gum obtained from the acacia trees. It is a complex, loose aggregate of sugars and hemicelluloses. It is commercially available in a powdered form, a granular form, or as a spray-dried product. As a tablet binder, it is used in an aqueous solution or added in dried form prior to moistening with water. Acacia forms very hard tablets, which disintegrate slowly. Aqueous solutions are susceptible to bacterial and enzymatic degradation. It is incompatible with amidopyrine, cresol, phenol, ethanol, ferric salts, and a number of other substances. Acacia, which was widely used in the past as a tablet binder, is rarely used today, in favor of one of the many synthetic polymers. 

Tragacanth is a naturally occurring dried gum. It poses similar problems as those of acacia. Dry addition to the blend followed by addition of water works better than addition of the solution, because it is difficult to prepare and use the mucilage. 

---

Most pigments can be used in any type of binder therefore, paints cannot be identified by pigment type alone. For example, micaceous iron oxide pigment is traditionally in an oil-based binder but is being increasingly used in epoxies, etc. In the paint coating film, the pigment content may vary from 15 to 60 per cent. In the special case of zinc rich primers, it is over 90 per cent. 

The most important component in the majority of paints is the binding medium, which determines the physical and chemical properties of the paint. Blends of binding media are often used to impart specific properties to the dry paint film or to suit a particular application method. The compatibility of chemically different types of binders is an important factor to be taken into account by the paint formulator. These properties will be modified, however, to a greater or lesser extent by the nature and quantity of the other components, more especially the pigment. The general characteristics of various binding media are given in Table 14.2. 

Type of binder Mode of drying Solvents Acid resistance Alkali resistance Water resistance Solvent resistance Exterior weathering resistance Special features... 

Silicate binders are used in conjunction with zinc powder to give paints of excellent corrosion resistance. The organo-silicates, e.g. ethyl orthosilicate, are most commonly used. The full potential of this type of binder has probably not yet been exploited. 

The paint technologist entrusted with the task of formulating a paint to meet a specified set of conditions must first decide what type of binders he should use and the type of solvent blend that this will require. In the particular case of a finish, he must then select the pigments most likely to give the required colour, bearing in mind any limitations imposed by his choice of binder system or by the conditions to which the paint will be subjected. 

Structure for double-base propellants shown in Fig. 6.3. Thus, the burning rate of AP composite propellants depends largely on the particle size of AP.F b the mass fraction of AP, and the type of binder used.F.i i... 

The burning rates of AP composite propellants are not only dependent on the AP particles, but also on the binder used as a fuel component. There are many types of binders, with varying physicochemical properties, as described in Section 4.2. The... 

Various types of binders are used to formulate AP composite propellants. Binders such as HTPB and HTPE decompose endothermically or exothermically at the burning surface. The burning rates of AP composite propellants thus appear to be dependent on the thermochemical properties of the binders used. Figs. 7.17 and 7.18 show In r versus In p plots for AP composite propellants made with five differ-... 

The effects of four types of binders, HTPS, HTPE, HTPA, and HTPB, on the burning rates of HMX composite propellants are shown in Fig. 7.33. The physicochemi-... 

Though the physicochemical properties of HTPE and HTPS are different, both are subject to a similar super-rate burning effect. However, the magnitude of the effect is dependent on the type of binder used. As in the case of double-base propellants, the combustion wave structures of the respective propellants are homogeneous, even though the propellant structures are heterogeneous and the luminous flames are produced above the burning surfaces. 

The burning rates of AP-RDX composite propellants are dependent on the physicochemical properhes of the AP, RDX, and fuel used, such as particle size, as well as on mixture raho and the type of binder. The results of burning rate measurements are reported in AlAA Paper No. 81-1582.125] Various combinahons of AP and RDX parhcles are used to formulate AP-RDX composite propellants, as shown in Table 7.6.125] pjjg particles incorporated into the propellants have bimodal combinations of sizes, where large RDX particles (RDX-I), small RDX particles (RDX-S), large AP particles (AP-I), and small AP particles (AP-S) are designated by d, d, dj, and da, respectively. HTPB binder is used in all of the propellants shown in Table 7.6. 

Use in a wide range of pharmacopoeial tests. In practice commercial plates may be used which contain a different type of binder The same types of applications as silica G where visualisation is to be carried out under UV light Identification of tetracyclines... 

Binder Different binders have different binding properties and the concentration of an individual binder may have to be changed to obtain similar binding of primary particles. Thus, the type of binder, and binder content in the formulation and concentration of the binder have major influence on granule properties. These properties include friability, flow, bulk density, porosity, and size distribution. 

Wise and Rocchio [32] have discussed the processing techniques for LOVA formulations which invariably depend on the type of binder. The polybutadiene-based formulations referred to as cured systems, are processed through a solventless process whereas formulations based on cellulose derivatives and thermoplastic elastomers as binders are processed by a solvent process similar to standard NC propellants. In conclusion, LOVA formulations offer unique propulsion systems for tanks with the potential to offer high energy and low vulnerability. 

In the paint and coating industries, iron oxide pigments can be incorporated in many types of binders. Some reasons for their wide applicability in this sector are pure hue, good hiding power, good abrasion resistance, and low settling tendency. Their high temperature resistance allows them to be used in enamels. 

With a consumption of about 150 000 t/a carbon blacks are the most important pigments used in the printing-ink industry. The required properties of the pigment black vary rather widely, depending on the printing process and the type of binder. 

A highly concentrated dispersion of carbon black is first prepared with a portion of the binder and solvent. The viscosity of this concentrate is a function of the particle size, structure, and surface chemistry of the black, the type of binder and its interaction with the pigment black, and the proportions of black, binder, and solvent. The final paint is made from the concentrate by adding more binder and solvent, its carbon black concentration is 3-8% referred to the solids content. Wetting agents are sometimes added to improve dispersibility and prevent flocculation. A number of concentrates for paint manufacture e.g., carbon black-nitrocellulose chips or carbon black -alkyd resin pastes, can be obtained from paint producers. 

Paints are often classified by the type of binder they include. The most common classifications (with percent of total coatings used m 1985) are Latexes (31%) waterborne (10%) noil-aqueous dispersions (2%) solvent-borne (55%) and one hundred percent sohds coatings (2%) A small volume of paint is made with silane binders. 

---