Abinder orbinding agent is any material or substance that holds or draws other materials together to form a cohesive whole mechanically, chemically, byadhesion orcohesion.
More narrowly, binders are liquid or dough-like substances that harden by a chemical or physical process and bind fibres,filler powder and other particles added into it. Examples includeglue,adhesive andthickening.
Examples of mechanical binders arebond stones in masonry andtie beams in timber framing.
Binders are loosely classified as organic (bitums, animal and plantglues,polymers) and inorganic (lime,cement,gypsum,liquid glass, etc.). These can be either metallic or ceramic as well as polymeric depending on the nature of the main material. For example, in the compound WC-Co (Tungsten Carbide used in cutting tools) Co constitutes the binding agent for the WC particles.
Based on their chemical resistance, binders are classified by the field of use: non-hydraulic (gypsum, air-cements,magnesia,hydrated lime), hydraulic (Roman cement,portland cement,hydraulic lime), acid-resistant (silicon fluoride cement,quartz cement), andautoclavable (harden at 170 to 300°С i.e. 8-16 atm pressure and, e.g., compriseCaSiO3 materials).
Some materials labeled as binders such ascement have a highcompressive strength but lowtensile strength and need to be reinforced with fibrous material orrebar iftension andshear forces will be applied.
Other binding agents such asresins may be tough and possibly elastic but can neither bearcompressive nor tensile force. Tensile strength is greatly improved incomposite materials consisting of resin as thematrix andfiber as a reinforcement. Compressive strength can be improved by addingfilling material.
Binders hold together pigments and sometimes filling material to formpaints,pastels, and other materials used for artistic and utilitarian painting. Materials includewax,linseed oil,natural gums such asgum arabic orgum tragacanth,methyl cellulose, orproteins such asegg white orcasein. Glue is traditionally made by the boiling of hoofs, bones, or skin of animals and then mixing the hard gelatinous residue with water. Natural gum-based binders are made from substances extracted from plants.[1] Larger amounts of dry substance are added to liquid binders in order to cast or modelsculptures andreliefs.[2]
Incooking, various edible thickening agents are used as binders. Some of them, e.g.tapioca flour,lactose,sucrose, microcrystallinecellulose,polyvinylpyrrolidone and variousstarches are also used in pharmacology in makingtablets.Tablet binders includelactose powder,sucrose powder,tapioca starch (cassava flour) and microcrystallinecellulose.
Inbuilding construction,concrete usescement as a binder.Asphalt pavement usesbitumen binder. Traditionally straw and natural fibres are used to strengthenclay inwattle-and-daub construction and in thebuilding materialcob which would otherwise become brittle after drying. Sand is added to improve compressive strength, hardness and reduce shrinkage. The binding property of clay is also used widely to prepare shaped articles (e.g. pots and vases) or to bind solid pieces (e.g. bricks).
Incomposite materials,epoxy,polyester orphenolicresins are common. Inreinforced carbon–carbon,plastic orpitch resin is used as a source of carbon released throughpyrolysis.Transite,hypertufa,papercrete andpetecrete usedcement as a binder.
Inexplosives,wax or polymers likepolyisobutylene orstyrene-butadiene rubber are often used as binders forplastic explosives. Forpolymer-bonded explosives, various syntheticpolymers are used.
Inrocket fuels,polybutadiene acrylonitrilecopolymer was used in 1960-70's big solid-fuel boosterrocket fuels.
Organic binders, designed to disintegrate by heat duringbaking, are used insintering.
In theClassical World painters used materials like egg, wax, honey,lime,casein,linseed oil orbitumen as binders to mix withpigment in order to hold the pigment particles together in the formation of paint.[3] Egg-basedtempera was especially popular in Europe from theMiddle Ages until the early 16th century.[4] However, since that time, the binder of choice for paint has beenoil.[5]
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