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Cyanoacrylates are a family of strong fast-acting with industrial, medical, and household uses. They are derived from ethyl cyanoacrylate and related . The cyanoacrylate group in the monomer rapidly in the presence of water to form long, strong chains.
Specific cyanoacrylates include methyl 2-cyanoacrylate (MCA), ethyl 2-cyanoacrylate (ECA, commonly sold under trade names such as "Super Glue" and "Krazy Glue"), n-butyl cyanoacrylate (n-BCA), octyl cyanoacrylate, and 2-octyl cyanoacrylate (used in medical, veterinary and first aid applications). Cyanoacrylate adhesives are sometimes known generically as instant glue, power glue, or super glue. The abbreviation "CA" is commonly used for industrial grade cyanoacrylate.
During the 1960s, Eastman Kodak sold cyanoacrylate to Loctite, which in turn repackaged and distributed it under a different brand name "Loctite Quick Set 404". In 1971, Loctite developed its own manufacturing technology and introduced its own line of cyanoacrylate, called "Super Bonder". Loctite quickly gained market share, and by the late 1970s it was believed to have exceeded Eastman Kodak's share in the industrial cyanoacrylate market. National Starch and Chemical Company purchased Eastman Kodak's cyanoacrylate business and combined it with several acquisitions made throughout the 1970s forming Permabond. Other manufacturers of cyanoacrylate include LePage (a Canada company acquired by Henkel in 1996), the Permabond Division of National Starch and Chemical, which was a subsidiary of Unilever. Together, Loctite, Eastman, and Permabond accounted for approximately 75% of the industrial cyanoacrylate market.HBS, "Loctite Corporation: Industrial Product Group," 15 July 1991, p.3 Permabond continued to manufacture the original 910 formula.
In general, the C=C groups rapidly undergo chain-growth polymerization in the presence of water (specifically ), forming long, strong chains, joining the bonded surfaces together. Because the presence of moisture causes the glue to set, exposure to normal levels of humidity in the air causes a thin skin to start to form within seconds, which greatly slows the reaction; hence, cyanoacrylates are applied as thin coats to ensure that the reaction proceeds rapidly for bonding. Cyanoacrylate adhesives generally have a short shelf life—about one year from manufacture if unopened, and one month once opened, but this can be extended by refrigeration.
Cyanoacrylate glue has a low shearing strength, which has led to its use as a temporary adhesive in cases where the piece needs to be sheared off later. Common examples include mounting a workpiece to a sacrificial glue block on a lathe, and tightening pins and bolts. It is also used in conjunction with another slower, but more resilient, adhesive as a way of rapidly forming a joint, which then holds the pieces in the appropriate configuration until the second adhesive has set.
Cyanoacrylate-based glue has a weak bond with smooth surfaces and as such easily gives to friction; a good example of this is the fact that cyanoacrylates may be removed from human skin by means of abrasives (e.g. sugar or sandpaper).
n-Butyl cyanoacrylate has been used medically since the 1970s. In the US, due to its potential to irritate the skin, the U.S. Food and Drug Administration (FDA) did not approve its use as a medical adhesive until 1998 with Dermabond (2-octyl cyanoacrylate). A 1986 independent study suggests that cyanoacrylate can be safer and more functional for wound closure than traditional suturing (stitches). Although cyanoacrylates are widely used for sutureless wound repair, "existing adhesives still lack sufficient adhesion strength to completely replace sutures and staples."
Some Rock climbing use cyanoacrylate to repair damage to the skin on their fingertips. "Bouldering" . climbingaction.com. Retrieved 19 February 2011.Anahad O'Connor (4 December 2007). "The Claim: Super Glue Can Heal Wounds". The New York Times. Retrieved 19 February 2011. Similarly, stringed-instrument players can form protective finger caps (typically, when they lose their due to inactivity or accidents) with cyanoacrylates. While the glue is not very toxic and wears off quickly with shed skin, applying large quantities of glue and its fumes directly to the skin can cause .
While standard "superglue" is 100% ethyl 2-cyanoacrylate, many custom formulations (e.g. , 91% ECA, 9% poly(methyl methacrylate), <0.5% hydroquinone, and a small amount of organic sulfonic acid, Safety data for ethyl cyanoacrylate from the Physical and Theoretical Chemistry Laboratory of the University of Oxford and variations on the compound n-butyl cyanoacrylate for medical applications) have come to be used for specific applications. Three cyanoacrylate compounds are available as topical skin adhesives: 2-Octyl cyanoacrylate is marketed as Dermabond, SurgiSeal, and LiquiBand Exceed. n-Butyl cyanoacrylate is marketed as Histoacryl, Indermil, GluStitch, GluSeal, PeriAcryl, and LiquiBand. The compound ethyl 2-cyanoacrylate is available as Epiglu.
The ester substituent has several effects upon the biocompatibility of the adhesive. Longer side chains result in higher flexibility of the cured adhesive allowing a better match for the flexibility of skin, and can result in a slower release of formaldehyde after curing. Alkoxy-ethyl substituents have also been investigated and have shown some promise as a medical adhesive.
Cyanoacrylate glue's ability to resist water has made it popular with marine aquarium hobbyists for fragmenting corals. The cut branches of Scleractinia, such as Acropora, can be glued to a piece of live rock (harvested reef coral) or Milliput (epoxy putty) to allow the new fragment to grow out. It is safe to use directly in the tank, unlike silicone which must be cured to be safe. However, as a class of adhesives, traditional cyanoacrylates are classified as having "weak" resistance to both moisture and heat although the inclusion of phthalic anhydride reportedly counteracts both of these characteristics.
Cyanoacrylate glue is also used frequently in aquascaping both freshwater and marine aquariums for the purpose of securing the rhizomes of live plants to pieces of wood or stone. Thin cyanoacrylate glue has application in woodworking. It can be used as a fast-drying, glossy finish. An oil, such as boiled linseed oil, may be used to control the rate at which the cyanoacrylate cures. Cyanoacrylate glue is also used in combination with sawdust (from a saw or sanding) to fill voids and cracks. These repair methods are used on piano soundboards, wood instruments, and wood furniture. Cyanoacrylate glue is also used in the finishing of pen blanks (wooden blanks for turning pens) that have been turned on a lathe by applying multiple thin layers to build up a hard, clear finish that can then be sanded and polished to a glossy finish.
Some hobby applications call for cyanoacrylate glue mixed with inorganic fillers such as baking soda (sodium bicarbonate) and calcium oxide.
The United Kingdom's Health and Safety Executive and the United States National Toxicology Program have concluded that the use of ethyl cyanoacrylate is safe and that additional study is unnecessary. Methyl Cyanoacrylate and Ethyl Cyanoacrylate from inchem.org The compound 2-octyl cyanoacrylate degrades much more slowly due to its longer organic backbone (series of Covalent bond carbon molecules) and the adhesive does not reach the threshold of tissue toxicity. Due to the toxicity issues of ethyl cyanoacrylate, the use of 2-octyl cyanoacrylate for sutures is preferred.
When kept unopened in a cool, dry location such as a refrigerator at a temperature of about 55 °F (13 °C), the shelf life of cyanoacrylate will be extended from about one year from manufacture to at least 15 months. If the adhesive is to be used within six months, it is not necessary to refrigerate it. Cyanoacrylates are moisture-sensitive, and moving from a cool to a hot location will create condensation; after removing from the refrigerator, it is best to let the adhesive reach room temperature before opening. After opening, it should be used within 30 days. Open containers should not be refrigerated. Palm Labs Adhesives: Cyanoacrylate Adhesive Shelf LifeAnother manufacturer says that the maximum shelf life of 12 months is obtained for some of their cyanoacrylates if the original containers are stored at . One manufacturer has given a very detailed explanation in answer to a question about shelf life, including the fact that cyanoacrylate adhesives contain an inhibitor to slow curing in the bottle; the amount of inhibitor affects shelf life (but a glue with more inhibitor can require accelerant to be applied for some applications).
Polymerization is nearly stopped, leading to an almost unlimited shelf life, by storing unopened at , the typical temperature of a domestic freezer, and allowing the contents to reach room temperature before use. Weicon stated in the past "By freezing down to -20°C the adhesives can be stored for a nearly unlimited period", but later product sheets only say that unopened storage at 5°C extends life to 12 months, from 9 months at room temperature. Opening a container while chilled may cause moisture from the air to condense in the container.
As cyanoacrylates age, they polymerize, become thicker, and cure more slowly. They can be thinned with a cyanoacrylate of the same chemical composition with lower viscosity.
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