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An adhesive is any substance that, when applied to the surfaces of materials, binds the surfaces together and resists separation. The term "adhesive" may be used interchangeably with glue, cement, mucilage, or paste. Adjectives may be used in conjunction with the word “adhesive” to describe properties based on the substance's physical form, its chemical form, the type of materials it is used to join, or the conditions under which it is applied.

The use of adhesives offers many advantages over other binding techniques such as sewing, welding, bolting, screwing, etc. These advantages include the ability to bind different materials together, the ability to distribute stress more efficiently across the joint, the cost effectiveness of an easily mechanized process, an improvement in aesthetic design, and an increased design flexibility. Disadvantages of adhesive use include decreased stability at high temperatures, relative weakness in bonding large objects with a small bonding surface area, and greater difficulty in separating objects during testing.

Adhesives may be found naturally or be produced synthetically. The earliest use of adhesive-like substances by humans was approximately 200,000 years ago. From then until the 1900's, increases in adhesive use and discovery were relatively gradual. Only since the last century has the development of synthetic adhesives accelerated rapidly, and innovation in the field continues to the present.

History
The earliest use of adhesives was discovered in 2001 in Italy. At this site, two stone flakes partially covered with birch-bark-tar and a third uncovered stone from the Middle Pleistocene era (circa 200,000 years ago) were found. This is thought to be the oldest discovered human use of tar hafted stones.

The birch-bark-tar adhesive is a simple, once component adhesive. Although sticky enough, plant based adhesives are brittle and vulnerable to environmental conditions. The first use of compound adhesives was discovered in Sibudu, South Africa. Here, 70,000 year old stone segments that were once inserted in hafts, covered with and adhesive composed of a combination of plant gum and red ochre (natural iron oxide), were found. Adding ochre to plant gum produces a stronger produce and protects the gum from disintegrating under wet conditions. The ability to produce stronger adhesives allowed middle stone age humans to attach stone segments to sticks in greater variations and led to the development of new tools.

More recent examples of adhesive use by prehistoric humans has been found at the burial sites of ancient tribes. Archaeologists studying the sites found that approximately 6,000 years ago, the tribesmen had buried their dead with food found in broken clay pots repaired with tree resins. Another investigation by archaeologists uncovered the use of bituminous cements in the fastening of ivory eyeballs to statues in Babylonian temples dating all the way back to approximately 4,000 B.C.E.

In 2000, a paper revealed the discovery of a 5,200 year old man nicknamed the "Tyrolean Iceman" or Oetzi preserved in a glacier near the Austria-Italy border. With him were found several of his belongings including two arrows with flint stone arrowheads and a copper hatchet, each with evidence of organic glue use for the connecting of the stone of metal parts to the wooden shafts. The glue was analyzed as pitch, which requires the heating of tar during its production. The retrieval of this tar requires a transformation of birch bark by means of heat, in a process known as pyrolysis.

The first references to adhesives in literature first appeared in approximately 2,000 B.C.E. Further historical records of adhesive use are found from the period starting 1,500 B.C.E. and ending 1,000 B.C.E. Artifacts from this period include paintings depicting wood glueing operations and a casket made of wood and glue in King Tut's Tomb. Other ancient Egyptian artifacts employ the use of animal glue in bonding or lamination. Such lamination of wood for bows and furniture is thought to have extended its life and was conducted with the use of casein (milk protein) based glues. The ancient Egyptians also developed starch based pastes for the bonding of papyrus to clothing and a plaster of Paris like material made of calcined gypsum.

From 1-500 C.E. the Greeks and Romans made great contributions to the development of adhesives. Veneering and marquetry (bonding of thin sections or layers of wood) was developed, the production of animal and fish glues refined, and other materials utilized. Egg based pastes were used to bond gold leaves and various natural ingredients such as blood, bone, hid, milk, cheese, vegetables, and grains were incorporated into glues. The Greeks began the use of slaked lime as mortar and the Romans furthered mortar development by mixing lime with volcanic ash and sand. This material, known as pozzolanic cement, was used in the construction of the Roman Colosseum and Pantheon. The Romans were also the first people known to have used tar and beeswax as caulk and sealant between the wooden planks of their boats and ships.

In Central Asia, the rise of the Mongols in approximately 1000 C.E. can be partially attributed to the good range and power of Genghis Khan's hordes' bows. The bows were constructed with laminated lemonwood and bullhorn bonded by a now unknown adhesive.

In Europe, glue was not widely used until the period 1500-1700 C.E. At this time, now world renown cabinet and furniture makers such as Chippendale and Duncan Phyfe began the use of adhesives in their products. Musical instruments made by Antonio Stradivari are believed to have been laminated with a secret connection, including vernice bianca, a varnish made of acacia gum, honey and egg white.

The development of modern adhesives began in 1690 with the founding of the first commercial glue plant in Holland. This plant produced glues from animal hides.



In 1750, the first British glue patent was issued for fish glue. The following decades of the next century witnessed the manufacture of casein glues in German and Swiss factories. In 1876, the first US patent (number 183,024) was issued to the Ross brothers for the production of casein glue.



The first US stamps used starch based adhesives when they were issued in 1840. The first US patent (number 61,991) on dextrin (a starch derivative) adhesive was issued in 1867.

Natural rubber was first used as material for adhesives starting in 1830. In 1839, Charles Goodyear discovered that a rubber and sulfur mixture, when heated, becomes elastic. This was the first time that a natural chemical was altered to make a plastic with new properties. In 1843, Thomas Hancock named this process vulcanization. In 1862, a British patent (number 3288) was issued for the plating of metal with brass by electrodeposition to obtain a stronger bond to rubber. The development of the automobile and the need for rubber shock mounts required stronger and more durable bonds of rubber and metal. This spurred the development of cyclized rubber treated in strong acids. By 1927, this process was used to produce solvent based thermoplastic rubber cements for metal to rubber bonding.

Natural rubber based sticky adhesives were first used on a backing by Henry Day (US Patent 3,965) in 1845. Later these kinds of adhesives were used in cloth backed surgical and electric tapes. By 1925, the pressure-sensitive tape industry was born. Today, sticky notes, 3m tape, and other tapes are example of PSA (pressure sensitive adhesives).

A key step in the development of synthetic plastics was the introduction of a thermoset plastic known as Bakelite phenolic in 1910. Within two years, phenolic resin was applied to plywood as a coating varnish. In the early 1930's, phenolics gained importance as adhesive resins.

The 1920's, 1930's, and 1940's witnessed great advances in the development and production of new plastics and resins due to the World Wars. These advances greatly improved the development of adhesives by allowing the use of newly developed materials that exhibited a variety of properties. With changing needs and ever evolving technology, the development of new synthetic adhesives continues to the present. However, due to their low cost, natural adhesives are still more commonly used.