Cyanoacrylate

Cyanoacrylate is the generic name for substances such as ethyl-2-cyanoacrylate, which is typically sold under trademarks like Superglue and Krazy Glue, and 2-octyl cyanoacrylate or n-butyl-cyanoacrylate, which are used in medical glues such as Dermabond and Traumaseal. Cyanoacrylate adhesives are sometimes known as "instant adhesives". The acronym "CA" is quite commonly used for industrial grades.

History
Cyanoacrylate was discovered by Harry Coover at Eastman Kodak during World War II when searching for a way to make plastic gun-sight lenses. It did not solve this problem, since it stuck to all the apparatus used to handle it. It was first marketed to industry as well as consumers in February 1955 as a product called "Flash Glue" which is still available today and now owned by Gary Shipko, president of Super Glue International, a United States based firm. It was patented in 1956 and developed into Eastman 910 adhesive in 1958. The new glue was demonstrated in 1959 on the television show I've Got a Secret when the host Garry Moore was lifted into the air by two steel plates held together with a drop of Eastman 910. Cyanoacrylates are now a family of adhesives based on similar chemistry.

General uses
Cyanoacrylate is a tenacious adhesive, particularly when used to bond non-porous materials or those that contain minute traces of water. It is also very good at bonding body tissue, and while this can be a bothersome (or even dangerous) side effect during everyday use, it has been exploited for the benefit of suture-less surgery.

Cyanoacrylate glue has a low shearing strength, which has also led to its use as a temporary adhesive in cases where the piece can easily be sheared off at a later time. Common examples include mounting a workpiece to a sacrificial glue block on a lathe and also tightening pins and bolts.

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. They are used to re-harden the boxes and shanks of ballerinas' pointe shoes as well.

One non-adhesive use for cyanoacrylate is as a forensic tool. Fumes from warmed CA can develop latent fingerprints on smooth surfaces like glass, plastic, etc. The invisible fingerprint residues react with the CA fumes and atmospheric moisture to form a white polymer (polycyanoacrylate) on the fingerprint ridges and can then be recorded. The developed fingerprints are, on most surfaces (except on white plastic or similar), visible to the naked eye. Non-visible or poorly visible prints can be furthermore enhanced by applying a luminescent or non-luminescent stain. This technique was shown in the films Beverly Hills Cop II, National Treasure, and frequently features in the television series CSI: Crime Scene Investigation and its spin-offs.

Thin CA glue is also used as a wood finish, particularly among woodturners. Its fast drying time and glossy finish make it ideal for small applications which generally look best when glossy (such as pens), although it is messy and somewhat expensive. A common mistake made by novice users is to use an accelerator, which can cloud and thus ruin the finish.

Some climbers use glue to prevent damage to the epidermis.

Medical uses
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 after 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. Harry 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 disposable 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.

The original Eastman formula was not FDA approved for medical use, however, because of a tendency to cause skin irritation and to generate heat. In 1998 the FDA approved 2-octyl cyanoacrylate for use in closing wounds and surgical incisions. Closure Medical has developed medical cyanoacrylates such as Dermabond, Soothe-N-Seal and Band-Aid Liquid Adhesive Bandage.

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 °C, and 1.1 times the density of water. Ethyl-2-cyanoacrylate (C6H7NO 2 ) 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 quickly, often in less than a minute. A normal bond reaches full strength in two hours and is waterproof. Accelerators such as toluidine trigger setting in two or three seconds, with some loss of strength.

Acetone, which is sometimes found in nail polish remover, is a commonly available solvent capable of softening cured cyanoacrylate. Nitromethane is also an excellent solvent. Methylene chloride is the most effective but is toxic.

Low temperatures cause cyanoacrylate to become brittle. Cyanoacrylate's bonds can be weakened (allowing disassembly) by placing a glued object in a household freezer for several hours.

If applied to cotton, cyanoacrylate undergoes an exothermic reaction rapid enough to cause minor burns if spilled on clothing, although this reaction is not powerful enough to be noticeable unless it involves more cyanoacrylate than any non-commercial use would reasonably call for.



Toxicity
Cyanoacrylates bond skin and eyes in seconds. Studies have shown that methyl-2-cyanoacrylate degrades fairly rapidly upon contact with living tissue. This leads to the release of formaldehyde and a toxic response. However, epidemiological studies of individuals working in a plant that manufactures ethyl cyanoacrylate do not indicate a risk to human health. The National Toxicology Program and the United Kingdom Health and Safety Executive have concluded that the use of ethyl cyanoacrylate is safe and that additional study is unnecessary. 2-octyl cyanoacrylate degrades much more slowly due to its longer organic backbone which slows the degradation of the adhesive enough to remain below the threshold of tissue toxicity. Due to these toxicity issues, 2-octyl-cyanoacrylate is used for sutures.

Cyanoacrylates give off vapor which is irritating to eyes, mucous membranes and respiratory system. ACGIH assign a Threshold Limit Value exposure limit of 0.2 parts per million. On rare occasions inhalation may cause asthma. There are a wide variety of adhesives of which different cyanoacrylate formulations may be a component. It is wisest to obtain and consult a manufacturers material safety data sheet for a product in order to consider the specific hazards associated with exposure.

Patent
Alcohol-Catalyzed α-Cyanoacrylate Adhesive Compositions, filed June 1954, issued October 1956