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Glues

Historically, glue only refers to protein colloid adhesives prepared from animal tissues, such as hide glue, bone glue, or fish glue. The meaning has been extended to any type of glue-like substances that are used to attach one material to another. Nearly 5,000 years ago, the Egyptians were using hide glue for their furniture adhesive. This is proven by hairs found in Pharaoh's tombs and by stone carvings depicting the process of gluing different woods. Evidence exists that the Sumerians also used glue before the Egyptians did.

Specific substances to which "glue" may refer include:

Cyanoacrylate ("Super Glue", "Crazy Glue")

Cyanoacrylate was discovered during World War II when searching for a way to make synthetic gun-sights (a substitute for spider silk). It did not solve this problem, since it stuck to all the apparatus used to handle it. Later it was developed into a more useful form by the Eastman Kodak company in 1958. The term is now used to refer to a range of adhesives based on similar chemistry.

Medicine

The use of cyanoacrylate glues in medicine was considered fairly early on. Eastman Kodak and Ethicon began studying whether the glues could be used to hold human tissue together for surgery. In 1964 Eastman submitted an application to use cyanoacrylate glues to seal wounds to the United States Food and Drug Administration (FDA). Soon afterward Dr. Coover's glue did find use in Vietnam--reportedly in 1966 cyanoacrylates were tested on-site by a specially trained surgical team, with impressive results. In an interview with Dr. Coover by the Kingsport Times-News, Coover said that the compound demonstrated an excellent capacity to stop bleeding, and during the Vietnam War, he developed disposal cyanoacrylate sprays for use in the battlefield.
"If somebody had a chest wound or open wound that was bleeding, the biggest problem they had was stopping the bleeding so they could get the patient back to the hospital. And the consequence was--many of them bled to death. So the medics used the spray, stopped the bleeding, and were able to get the wounded back to the base hospital. And many, many lives were saved," Coover said.

Properties

In its liquid form, cyanoacrylate consists of monomers of cyanoacrylate molecules. Methyl-2-cyanoacrylate (CH2=C(CN)COOCH3 or C5H5NO2) has a molecular weight equal to 111.1, a flashpoint of 79 ºC, and a density of 1.1 times the density of common water (H2O). Ethyl-2-cyanoacrylate (C6H7NO2) has a molecular weight equal to 125 and a flashpoint of 75 °C.
Generally, cyanoacrylate is an acrylic resin which rapidly polymerises in the presence of water (specifically hydroxide ions), forming long, strong chains, joining the bonded surfaces together. Because the presence of moisture causes the glue to set, exposure to moisture in the air can cause a tube or bottle of glue to become unusable over time. To prevent an opened container of glue from setting before use, it must be stored in an airtight jar or bottle with a package of silica gel.
Another important trait is that cyanoacrylate sets fast, often in less than a minute. A normal bond reaches full strength in two hours, and is waterproof. There are also accelerants that can force cyanoacrylate to set in two or three seconds, at some loss of strength.
Acetone, which is found in nail polish remover, is a commonly available solvent capable of softening cured cyanoacrylate.
Cold temperatures cause cyanoacrylate to become brittle. Cyanoacrylate's bond can be weakened, allowing disassembly, by placing a glued object in a household freezer for several hours.

Uses

Cyanoacrylate is a tenacious adhesive, particularly when used to bond non-porous materials or those that contain minute traces of water. As such it is very good at bonding body tissue, and while this effect can be a nuisance (or even dangerous) for everyday use, it has been exploited for the benefit of suture-less surgery. This technique was shown in the werewolf film Dog Soldiers, where Sean Pertwee's character gets his guts repaired with a large tube of Superglue.
Cyanoacrylates are often used to assemble prototype electronics (see wire wrap), flying model aircraft, and as retention dressings for nuts and bolts. Their effectiveness in bonding metal and general versatility have also made them popular amongst modeling and miniatures hobbyists.
One non-adhesive use for cyanoacrylate is as a forensic tool. Fumes from (warmed) CA can develop latent fingerprints on surfaces. The invisible fingerprint residues react with the CA fumes and atmospheric moisture to become visible and can then be recorded. This technique was shown in the film Beverly Hills Cop II, and occasionally features in the television series CSI: Crime Scene Investigation and its spin-offs.

Epoxy resins

Epoxy or polyepoxide is a thermosetting epoxide polymer that cures when mixed with a catalyzing agent or "hardener". Most common epoxy resins are produced from a reaction between epichlorohydrin and bisphenol-A. The first commercial attempts to prepare resins from epichlorohydrin occurred in 1927 in the United States. Credit for the first synthesis of bisphenol-A based epoxy resins is shared by Dr. Pierre Castan of Switzerland and Dr. S.O. Greenlee in the United States in 1936. Dr. Castan's work was licensed by Ciba, Ltd. of Switzerland and Ciba went on to become one of the 3 major epoxy resin producers worldwide. The epoxy business of Ciba was spun-off and later sold in the late 1990s and is now the Advanced Materials Business unit of Huntsman Corporation of the United States. Dr. Greenlee's work was for a company called Devoe-Reynolds of the United States. Devoe-Reynolds was a player in the early days of the epoxy resin industry, but later sold its business to Shell Chemical (now Resolution Polymers).

Industry

Today the epoxy industry amounts to more than US$5 billion in North America and about US$15 billion world-wide. It is made up of approximately 50 - 100 manufacturers of basic or commodity epoxy resins and hardeners of which the big 3 are Resolution Polymers (formerly Shell; whose epoxy tradename is "Epon"), Dow Chemical (tradename "D.E.R."), & Huntsman Advanced Materials (formerly Ciba; tradename "Araldite"). The other 50+ smaller epoxy manufacturers primarily produce epoxies only regionally (not world-wide), produce epoxy hardeners only, produce specialty epoxies, or produce epoxy modifiers.
These commodity epoxy manufacturers mentioned above typically do not sell epoxy resins in a form usable to most end users, so there is another group of companies that purchase epoxy raw materials from the major producers and then compounds (blends, modifies, or otherwise customizes) epoxy systems out of these raw materials. This class of companies is typically known as "formulators". The vast majority of the epoxy systems sold are produced by these smaller formulators and they account for greater than 60% of the dollar value of the overall epoxy market. There are hundreds of ways that these formulators can modify epoxies — by adding mineral fillers (ex. talc, silica, alumina, etc.), by adding flexibilizers, viscosity reducers, colorants, thickeners, accelerators, adhesion promoters, etc. These modifications are made to reduce costs, to improve performance, and to improve processing convenience. As a result a typical formulator sells dozens, hundreds, or even thousands of formulations — each carefully tailored to the requirements of a particular application or market.
The applications for epoxy based materials are extensive and include coatings, adhesives and composite materials like carbon fiber and glass-reinforced plastic (although polyester, vinyl ester, and other thermosetting resins are also used for glass-reinforced plastic). The chemistry of epoxies and the range of commercially available variations allows cure polymers to be produced with a very broad range of properties. In general, epoxies are known for their excellent adhesion, chemical and heat resistance, good to excellent mechanical properties and very good electrical insulating properties, but almost any property can be modified (for example silver-filled epoxies with good electrical conductivity are widely available even though epoxies are typically electrically insulating).
Epoxies find significant use in many applications including the following:

Paints and coatings

Examples include powder coatings for washers, driers and other "white goods". Epoxy coatings are also widely used as primers to improve the adhesion of automotive and marine paints especially on metal surfaces where corrosion (rusting) resistance is important. Metal cans and containers are often coated with epoxy coatings to prevent rusting especially for foods like tomatoes that are acidic. Epoxy resins are also used for high performance & decorative flooring applications especially terrazzo flooring, Chip Flooring and colored aggregate flooring.

Adhesives

Bostik's 'Titan' waterpoof epoxy is strong enough to withstand the extreme hydrodynamic force transferred from a surfboard fin to the fin mount. This epoxy is not only waterproof but capable of curing underwater. The blue coloured epoxy on the left is still undergoing curing.
Epoxy adhesives are a major part of the class of adhesives called "structural adhesives" or "engineering adhesives" (which also includes polyurethane, acrylic, cyanoacrylate, and other chemistries.) These high performance adhesives are used in the construction of airplanes, automobiles, bikes, golf clubs, skis, snow boards, and many other applications where high strength bonds are required. Epoxy adhesives can be developed that meet almost any application. They are exceptional adhesives for wood, metal, glass, stone, and some plastics. They can be made flexible or rigid, transparent or opaque/colored, fast setting or extremely slow. Epoxy adhesives are almost unmatched in heat and chemical resistance among common adhesives. In general, epoxy adhesives cured with heat will be more heat and chemical resistant than the same formulation cured at room temperature.

Industrial tooling and composites

Epoxy systems are also used in industrial tooling applications to produce molds, master models, laminates, castings, fixtures, and other industrial production aids. This "plastic tooling" replaces metal, wood and other traditional materials and generally improved the efficiency and either lowers the overall cost or shortens the lead-time for many industrial processes. Epoxies are also used in producing fiber reinforced or composite parts. They are more expensive than polyester resins and vinyl ester resins, but generally produce stronger more temperature resistant composite parts.

Electrical systems and electronics

Epoxy resin formulations are also important in the electronics industry and are used in many parts of electrical systems. In electrical power generation, epoxy systems encapsulate or coat motors, generators, transformers, switchgear, bushings, and insulators. Epoxy resins are excellent electrical insulation materials and they protect electrical components from short circuiting, dust, humidity and other environmental factors that could damage the electrical equipment. In the electronics industry, epoxy resins are the primary resin used in overmolding integrated circuits and transistors, and making printed circuit boards. The largest volume type of circuit board - an "FR-4 board" - is nothing but a sandwich of several layers of glass cloth bonded together into a composite by an epoxy resin. Epoxy resins are also used in bonding copper foil to circuit board substrates and are a major component of the solder mask used on many circuit boards.

Consumer and marine applications

Epoxies are sold in many hardware stores - typically as two component kits. They are also sold in many boat shops as repair resins for marine applications. Epoxies typically are not the outer layer of a boat because they are negatively affected by long term exposure to UV light. But they are often used during boat repair and assembly and then are over coated with polyester gel coats or marine varnishes that protect the epoxies from UV exposure. Epoxies are fairly easy to distinguish from polyester thermosets, as commercially marketed epoxy materials typically use 1:1 ratio of resin to hardener, or similar convenient mix ratio, while polyester thermoset materials typically use a ratio of at least 10:1 between resin to hardener (or "catalyst." Also, epoxy materials tend to harden somewhat more gradually, while polyester materials tend to harden more abruptly.
Mucilage

Mucilage is a thick gluey substance, often produced by plants. Mucilage is another term for so called exopolysaccharides. These are sugar substances that cover the outside of, for example, unicellular or filamentous green algae and cyanobacteria. Amongst the green algae especially the group. Volvocales are known to produce exopolysaccharides at least in a certain part of their life cycle.
Exopolysaccharides are the most stabilising factor for microaggregates and are widely distributed in soils. Therefore exopolysaccharide-producing "soil algae" play a vital role in the ecology of the world's soils.
Mucilage is edible, but tastes rather bland. It is used in medicine for its demulcent properties.
Mucilage is also a term for an adhesive composed of a solution of a sticky vegetable product -sometimes the above, but more typically a vegetable gum -- in water, used primarily to seal paper (e.g. postage stamps and envelope flaps)).
Casein glue
Casein is the predominant phosphoprotein found in fresh milk. When coagulated with rennet, casein is sometimes called paracasein. British terminology, on the other hand, uses the term caseinogen for the uncoagulated protein and casein for the coagulated protein. As it exists in milk, it is a salt of calcium.
Casein is not coagulated by heat. It is precipitated by acids and by rennet, a proteolytic enzyme obtained from the stomachs of calves. The enzyme trypsin can hydrolyze off a phosphate-containing peptone.
Casein consists of a fairly high number of proline peptides, which do not interact. There are also no disulphide bridges. As a result, it has relatively little secondary structure or tertiary structure. Because of this, it cannot denature. It is relatively hydrophobic, making it poorly soluble in water. It is found in milk as a suspension of particles called casein micelles which show some resemblance with surfactant-type micellae in a sense that the hydrophilic parts reside at the surface. The caseins in the micelles are held together by calcium ions and hydrophobic interactions.
In addition to being consumed in milk casein is used in the manufacture of adhesives, binders, protective coatings, plastics (such as for knife handles and knitting needles), fabrics, food additives and many other products. It is commonly used by bodybuilders as a slow-digesting source of amino acids.
The isoelectric point of casein is 4.6. The purified protein is water insoluble. While it is also insoluble in neutral salt solutions, it is readily dispersable in dilute alkalis and in salt solutions such as sodium oxalate and sodium acetate.

Polyvinyl acetate (PVA) — white glue and yellow Carpenter's glue (Elmer's glue, Titebond, Lepage)
Polyvinyl acetate or PVA is a rubbery synthetic polymer. It is prepared by polymerization of vinyl acetate. Partial or complete hydrolysis of the polymer is used to prepare polyvinyl alcohol. It was discovered in Germany by Dr. Fritz Klatte in 1912.
PVA is sold, as an emulsion in water, as an adhesive for porous materials, particularly wood. It is the most commonly used wood glue, both as "white glue" and the yellow "carpenter's glue", the former also used extensively to glue other materials like paper and cloth.
It can also be used to protect cheese from fungi and humidity.

Rubber cement
Rubber cement is a common household adhesive, most often used by children due to its low toxicity and ease of cleanup. It is primarily used for glueing various types of paper.
It is made from polymers mixed in a solvent such as acetone or benzene to keep them fluid enough to be used. This makes it part of the class of drying adhesives: as the solvent evaporates, the "rubber" part remains behind forming a strong yet flexible bond.
Rubber cement is used in art applications as unlike water-based casein glues (white or "Elmer's" glue), rubber cement does not shrink much and so does not wrinkle the adhered surfaces. It also does not become brittle like paste does. Rubber cement is safe for use with photographs and specialty papers as it will not cause them to deteriorate over time, a danger associated with many other common adhesives.
The formula for rubber cement varies from brand to brand and has changed over time due to concerns of the toxicity of the chemicals involved, especially in regards to its use by children. Most rubber cement available today is quite safe though. The solvents have also been criticized for potential of abuse as inhalants or at the very least, that they can be a respiratory hazard. For this reason, as with any adhesive, rubber cement should be used in a well-ventilated area.
In the UK, the most common latex-based adhesive 'Copydex' uses an ammonia and water solvent, and needs no special handling, making it very child-friendly. While for this reason it is often given to children, it is also used in artwork, and finds widespread use in light D.I.Y. work such as fixing carpet tiles and repairing upholstery.

Canada balsam
Canada balsam, also called Canada turpentine or balsam of fir, is a turpentine which is made from the resin of the balsam fir.
It is the fir's resin, dissolved in essential oils, and is a viscous, sticky, colourless (sometimes yellowish) liquid, that turns to a transparent yellowish mass when the essential oils have been allowed to evaporate.
Due to its high optical quality, its refractive index (n = 1.55) very close to that of glass, and its purity it is mainly used in optics as an invisible-when-dry glue for glass. It is soluble in xylene, amorphous when dried, and it does not crystallize with age, so its optical properties do not deteriorate.
Some uses include:

• in biology to conserve microscopic samples. The sample is sandwiched between the microscope slide (a glass plate) and the cover plate (a small thin glass plate) and canada balsam is used to glue the arrangement together and enclose the sample to conserve it;
• in optical technology to glue together optical elements such as two prisms to form a beam splitter, or two lenses;
• to fix scratches in glass (car glass for instance) as invisibly as possible.

Postage stamp gum
In philately, gum is the substance applied to the back of a postage stamp to enable it to adhere to a letter or other mailed item. The term is generic, and applies both to traditional types such as gum arabic and to synthetic modern formulations.
The use of gum was part of the original proposal by Rowland Hill, and has been universal from the beginning. There have been a number of stamp types that were issued ungummed, typically due to emergency situations when gum was not available, such as Italy in 1944, Krakow issue of Poland in 1919, Latvia in 1919. Other reasons have included lack of access to gum (the typewritten "Cowries" of 1895 Uganda), extreme tropical climate (1873 Curaçao and Suriname), and intent to sell only to collectors (as with the US "Farley's Follies" souvenir sheets of 1933). The manual gluing-on of postage is such an extreme consumption of time (and "time is money" to businesses with a lot of mail) that these situations are always temporary.
Originally, gumming took place after printing and before perforation, usually because the paper had to be damp for printing to work well, but in modern times most stamp printing is done dry on pregummed paper. There have been a couple of historical instances where stamps were regummed after being perforated, but these were unusual situations.
On early issues, gum was applied by hand, using a brush or roller, but in 1880 De La Rue came up with a machine gumming process using a printing press, and gum is now always applied by machine. The gum is universally spread as uniformly as possible, but a 1946 local issue by the town of Finsterwalde in Germany used an economy process where the back of the stamp had a regular pattern of circular bare patches.
The greatest manufacturing problem of the gumming process is its tendency to make the stamps curl, due to the different reaction of paper and gum to varying moisture levels. In the most extreme cases, the stamp will spontaneously roll up into a small tube. Various schemes have been tried, but the problem persists to this day. In Swiss stamps of the 1930s, Courvoisier used a gum-breaking machine that pressed a pattern of small squares into the gum, resulting in so-called grilled gum. Another scheme has been to slice the gum with knives after it has been applied. In some cases the gum solves the problem itself by becoming "crackly" when it dries.
The appearance of the gum varies with the type and method of application, and may range from nearly invisible to dark brown globs. Types of gum used on stamps include:

• dextrine, produced by heating starch
• gum arabic or acacia gum, derived from the acacia plant
• glue, from gelatin, rarely seen on stamps
• polyvinyl alcohol (PVA)

In recent years, the use of self-adhesive stamps has become widespread. The first use was by Sierra Leone in 1964, and the United States tried it on a Christmas stamp of 1974, although the experiment was judged a failure and not repeated for many years. Traditional gums remain in use, although differentiated by calling them water-activated.
For collectors, gum is mostly a problem. It is rarely of use in differentiating between common and rare stamps, and being on the back of the stamp it is not usually visible. Nevertheless, many collectors of unused stamps want copies that are "mint" or "post office fresh", which means that the gum must be pristine and intact, and they will pay a premium for these. While not so much of a problem for modern issues, the traditional way of mounting stamps in an album was with the use of stamp hinges, and some experts claim that very few unused stamps from the 19th century have not been hinged at some point in their existence. This means that old mint stamps are inevitably under suspicion of having been regummed, and a subfield of forensic philately is the detection of regummed stamps.

 
Model glue (sometimes called "airplane glue") - used for building plastic (polystyrene) models of airplanes, etc.

Adhesives and Glues
Adhesives and glues are substances that are capable of bonding two solid materials together at their surfaces. While they have been used by humans for centuries, it is only in the twentieth century that synthetic adhesives were developed. Archeological evidence suggests that ancient Egyptians used resinous adhesives at least 6,000 years ago. Other adhesives including starch, sugar, casein, bitumen, shellac, pitch and glues made from animals and fish were used around 1500 B.C.. These first adhesives were of natural origin and are still used today in a form that is not substantially different.

The first synthetic adhesive was produced in 1869. This material was incorrectly termed nitrocellulose and was created by a reaction between nitric acid, sulfuric acid, and cellulose. Today, this product is known as cellulose nitrate. In 1912, Leo Baekeland produced phenol-formaldehyde resins, a basic material for many of today=s adhesives. High strength, elastomeric adhesives were available in 1928 when a reaction that produced polychloroprene was developed. Later in the 1930s, pressure sensitive tapes were developed.

The first metal bonding adhesive was developed by Nicholas de Bruyne in 1941. This material was used in the construction of aircraft. Later in the decade, epoxy resin adhesives were introduced. During the 1960s the extremely strong cyanoacrylate adhesives were developed. These products, called super glues, became adhesive when exposed to moisture in the air. Other adhesives that were developed during this time include silicones and anaerobic adhesives. Since that time, most of the advances in adhesive technology have been the result of formulation modifications using varied polymers. In the late 1980s Post-It"! notes were introduced using a microstructured adhesive.

A variety of theories about how adhesives work have been proposed. While none of these satisfactorily describes all aspects of adhesion, they do attempt to explain observed phenomena. The leading theories of adhesion include the diffusion, electrostatic, surface energetics, and mechanical theories.

The diffusion theory states that adhesion is a result of the solubility of the adhesive to the substrate. When the adhesive is applied to the substrate, it is suggested that a solution of the substrate and adhesive is formed if the solubility characteristics are equal. This creates a stable phase that bonds the two surfaces together. While this theory provides some insights, it is mostly applicable to situations in which polymers adhere to each other. It is not applicable to systems where the substrate and adhesive are radically dissimilar.

The electrostatic theory suggests that adhesion is the result of differences in the electronegativities of adhering materials. According to the theory, when two materials are brought into contact there is an amount of electron transfer that occurs. This results in a charge layer being formed which causes the materials to stay together. An example of this theory can be seen when using static electricity to make a balloon stick to a wall.

The surface energetics and wettability theory describes adhesion in terms of intermolecular and interatomic forces. For these forces to have an effect, the adhesive must come in close contact with the substrate. This is only achieved through A wetting of the surface. According to this theory adhesion is a result of bonding across the interface. An example of this theory is chemical adhesion that occurs when the chemical groups from the adhesive covalently bond with those of the substrate. Secondary adhesion occurs similarly through hydrogen bonding.
The mechanical theory describes adhesion in terms of a physical interlocking of the adhesive with the substrate. Mechanical adhesion occurs when the adhesive material flows into and on the microscopically rough substrate surface. This creates a lock and key effect similar to velcro. The viscosity of the adhesive and the contact time with the substrate are important parameters for mechanical adhesion. Viscosity adhesion occurs by restricted movement due to the viscous nature of the substrates.

For a material to be a good adhesive it must has a variety of characteristics. It should have a liquid surface tension that is lower than the wetting tension of the substrate. It should be applied to a surface that is significantly rough to improve adhesion. For polymeric substrates, the adhesive should be somewhat mutually soluble allowing diffusion between the two to occur.

Adhesives can be classified by the type of delivery of the adhesive or by the polymer used in the adhesive. In general, there are five categories of adhesives including structural, natural, pressure-sensitive, hot melt, and solvent-based adhesives.

Structural adhesives are some of the strongest adhesive materials available. They are based on resin systems, typically thermosets, and are meant to serve as permanent bonds. They are supplied as low-molecular-weight polymers that solidify when polymerized. They are sold in a variety of forms including two-part systems, pastes, and films. The most common examples include epoxy resins, acrylic adhesives, phenolic resins, elastomeric adhesives, high-temperature-resistant adhesives, and urethane adhesives.

Epoxy resins are typically based on the polymerization reaction of bisphenol A with epichlorohydrin. The product is sold as a two-part system in which the user applies the epoxy resin, then an amine hardener that causes the resin to cure. Epoxy resins are used in the construction of aircraft and automobiles. They are also a component of plastic cement.
Phenolic resins have been used as adhesives since the early 1900s. They are produced by the polymerization reaction of phenol and formaldehyde. To cure, heat is typically required to drive off excess solvent. This type of adhesive is used in the production of plywood. They also are noted as the most adhesive material to aluminum.

A variety of acrylic adhesives are available. Anaerobic adhesives are unique reactive adhesives. They consist of a mixture of hydroperoxides and dimethacrylates that polymerize in the absence of oxygen. This type of material is useful in anchoring screws and bolts. One of the most famous and strongest acrylic adhesives is Super Glue"!, or Krazy Glue"!. This adhesive is based on cyanoacrylates which spontaneously polymerizes in moist air.
Many structural adhesives that are used for aerospace purposes are lightweight and high-temperature resistant. These are typically resins that have high glass-transition temperatures. An example of this type of adhesive is polyimide that is formed by the polymerization reaction of an aromatic amine with an aromatic anhydride. Since many of the structural adhesives become brittle after they cure, adhesives formulators developed elastomeric adhesives. These materials contain compounds that reduce brittleness without significantly reducing adhesion. This property is useful in applications where vibrational forces can stress adhesives. The final class of structural adhesives is the urethanes. These materials are based on the polymerization reaction of a diol with a diisocyanate. They are primarily sold as two-part structural adhesives. An important application of these kinds of adhesives is in the automotive industry.Polyurethanes are used to bond polyester cords in rubber tires.

Many natural-based adhesives are available. In general, these adhesives are not as strong as the synthetic adhesives. Natural rubber has been used as an adhesive for over 100 years. In 1825, the Macintosh raincoat, which consisted of two layers of cotton bonded by a layer of natural rubber, was introduced.Protein adhesives are used as structural adhesives. They are based on polyamino acids obtained from various animal and plant sources. Curing is typically dependent on heat. Starch-based adhesives are derived from plants. They are primarily used for binding paper and as envelope adhesives. Cellulose is another natural material that provides adequate adhesion. Cellulose nitrate was one of the first modified adhesives produced. It is a general all purpose adhesive which is waterproof and flexible. Modified methylcellulose is used to make wallpaper paste. Other natural adhesives are takifying resins that are derived from coal, petroleum or wood tar.

Pressure sensitive adhesives are polymeric-based adhesives that melt at room temperature. When pressure is applied to the adhesive, they become flowable thereby covering the substrate. As the pressure is removed adhesion takes place. Many tapes use this kind of adhesive material. Pressure-sensitive tape uses a blend of glycerol and abietic acid esters with natural rubber on cellophane. In addition to pressure-sensitive adhesives, hot melt adhesives have been developed. Since thermoplastics melt when heated and reform when cooled, they make good adhesives. This is the principle behind glue guns.Nylon polymers are often used for their formulation.

Solvent-based adhesives work through the action of the substrate or adhesive. The material is put on the substrate and when the solvent evaporates bonding occurs. Adhesion is aided if the solvent interacts with the substrate. An example is model airplane glue that tends to dissolve some of the plastic. This helps to create a solid weld. Latex adhesives are another type of solvent-based adhesive. They are polymeric materials that provide adhesion after their aqueous solvent evaporates. These are the same types of polymers that are used for latex paints. Latex adhesives are used for bonding pile to carpets.

While natural resins dominated the adhesive market years ago, in 1999 they account for less than 10% of the market. Instead elastomers, thermoplastics, and thermosets have the bulk of market share in this three billion-dollar plus market.

     Glues are used in organbuilding to attach one material to another such az wood, metal, plastic, etc.

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