BINDERS
A pyrotechnic composition will usually contain a small percentage of an organic polymer that functions as a binder, holding all of the components together in a homogeneous blend. These binders, being organic compounds, will also serve as fuels in the mixture.
Without the binder, materials might well segregate during manufacture and storage due to variations in density and particle size. The granulation process, in which the oxidizer, fuel, and other components are blended with the binder (and usually a suitable solvent) to produce grains of homogeneous composition, is a critical step in the manufacturing process. The solvent is evaporated following granulation, leaving a dry, homogeneous material.
Dextrine is widely used as a binder in the fireworks industry. Water is used as the wetting agent for dextrine, avoiding the cost associated with the use of organic solvents.
Other common binders include nitrocellulose (acetone as the solvent), polyvinyl alcohol (used with water), and Laminae (an unsaturated polyester crosslinked with styrene -- the material is a liquid until cured by catalyst, heat, or both, and no solvent is required). Epoxy binders can also be used in liquid form during the mixing process and then allowed to cure to leave a final, rigid product. In selecting a binder, the chemist seeks a material that will provide good homogeneity with the use of a minimum of polymer.
In selecting a binder, the chemist seeks a material that will provide good homogeneity with the use of a minimum of polymer. Organic materials will reduce the flame temperatures of compositions containing metallic fuels, and they can impart an orange color to flames if incomplete combustion of the binder occurs and carbon forms in the flame. A binder should be neutral and non-hygroscopic to avoid the problems that water and an acidic or basic environment can introduce. For example, magnesium-containing mixtures require the use of a non-aqueous binder/solvent system, because of the reactivity of magnesium metal towards water. When iron is used in a composition, pretreatment of the metal with wax or other protective coating is advisable, especially if an aqueous binding process is used.