A binder or binding agent is a material or substance that holds or draws other materials together to form a cohesive whole through mechanical, chemical, adhesion, or cohesion means. In a more narrow sense, binders are liquid or dough-like substances that harden through a chemical or physical process and bind fibers, filler powder, and other particles. Examples of binders include glue, adhesive, and thickening agents. Mechanical binders include bond stones in masonry and tie beams in timber framing.
Classification
Binders can be classified based on their composition as organic (e.g., bitumens, animal and plant glues, polymers) and inorganic (e.g., lime, cement, gypsum, liquid glass), as well as their properties such as chemical resistance. They can also be classified based on their field of use, such as non-hydraulic, hydraulic, acid-resistant, and autoclavable, based on factors such as chemical resistance and the conditions under which they harden or cure.
Physical properties
The physical properties of binders can vary greatly depending on the specific type of binder and the conditions in which it is used. For example, some binders like cement have high compressive strength but low tensile strength and require reinforcement, while others like resins may be tough and possibly elastic but lack the ability to bear compressive or tensile force. The tensile strength and compressive strength of composite materials consisting of resin as the matrix and fiber as reinforcement can be improved by adding filling material.
Uses
Binders are widely used in various industries and applications, including construction, art, cooking, pharmacology, composites, explosives, rocket fuels, and sintering. Different binders have different physical and mechanical properties and can be used for different purposes. The classification and uses of binders are very important in understanding their application and effects.
Starch as binders
Starch can act as a binder. In cooking, various edible starches such as cornstarch, tapioca flour, and potato starch are used as thickening agents and binders. In pharmaceuticals, some starches like cornstarch and tapioca starch are used as tablet binders. In building construction, starch can be used as a binder in some materials such as papercrete.