What Makes Superglue so Super? - University ofjwhitesell.ucsd.edu/documents/What_Makes_Superglue_so_Super.pdf · What Makes Superglue so Super? ... solvent in Aleene's quick dry tacky

What Makes Superglue so Super? Lihong Yang

There is always an advertising of superglue popping up from my memory because I had been watching it when I was a kid. The people applied a line of superglue on the plank, and the next second a motorcycle rushed to the plank and then raised the front wheels toward the plank. And guess what happened? The motorcycle was firmly attached to the plank in a second. Cyanoacrylate (the chemical name of superglue) was first discovered in 1942 in a search for materials to make clear plastic gun sights for the war by Dr, Harry Coover. It didn’t work well for gun sight, but it stuck to everything. Its commercial potential was then used and put on the market in 1958.

Figure 1. Advertising of superglue (Aron Alpha) Figure 2. Gun sight

Superglue definitely deserves its name. A one-quarter-inch bond can hold more than a ton. So, what makes superglue so super?

The main ingredient in superglue is cyanoacrylate. It is an acrylic resin that cures almost instantly just way how the advertising did. Cyanoacrylate is a polymer that consists of monomers of cyanoacrylate molecules. There are two main types of monomers, one is methyl-2-cyanoacrylate (CH2=C (CN) COOCH3 or C5H5NO2) and the other one is ethyl 2-cyanoacrylate (C6H7NO2). They contain several identical functional groups, an ester, a nitrile and an alkene. The only difference between them based on the structure is the substituents of the alkyl group connected to the single bond oxygen of ester, one is methyl group and the other one is ethyl

group. It causes the difference of molecular weight and density. Methyl-2-cyanoacrylate has a molecular weight equal to 111.1 grams per mole. The lowest temperature at which it can vaporize to form an ignitable mixture in air is 79 °C and this point of the volatile material is called a flash point. And methyl-2-cyanoacrylate has a density of 1.1 g/ml, which is slightly higher than water. Ethyl 2-cyanoacrylate has a molecular weight equal to 125 grams per mole and with a flash point of larger than 75 °C. Both of them have the similar chemical properties due to the similar structure. The flash point of seventies degree Celsius indicates that the better temperature to use cyanoacrylate should be under it, which allows superglue to be widely used because it is totally workable in room temperature.

Why does superglue work immediately? Why the motorcycle cannot move once it attaches to superglue? Because cyanoacrylate can undergo a process called anionic polymerization rapidly in the presence of water. It is a process of repeatedly reacting cyanoacrylate molecules together in a chemical reaction to form long and strong polymer chains that join the bonded surface firmly together. “Anionic” specifically indicates the hydroxide ions here, which come from water. The hydroxide ion plays as a nucleophile here, which is an electron-rich group. It can attack the electron-poor alkene group to break the double bond. The carbon now becomes negative charge and it has the same ability and plays the same role as the hydroxide group to attack another alkene group of the new cyanoacrylate molecule. So by repeating this reaction, a polymer of cyanoacrylate can be formed. The only thing that needs to trigger the polymerization is the hydroxide group. It is convenient to obtain the hydroxide group because it comes from water. The object you might wish to glue has at least trace amounts of water one its surface, and also the hydroxide ions can be trapped from air in the form of humidity. Because of this cyanoacrylate is applied thinly and it can ensure that the reaction proceeds rapidly and a strong bond is formed within a reasonable time.

Figure 3. Polymerization of methyl-2-cyanoacrylate

Under normal circumstances, cyanoacrylate is liquid. To facilitate easy handling and to make it look like glue, a cyanoacrylate adhesive is frequently formulated with an ingredient such as fumed silica to make it more viscous or gel-like. Fumed silica is a powder that is produced in a flame. It has an extremely low bulk density and high surface area that help in increasing viscosity. More recently, formulations are available with additives to increase shear strength, creating a more impact resistant bond. The manufacturer adds rubber or other additives to superglues to increase viscosity and make it more gel-like.

What makes superglue different from the other normal glues? White glues, such as Aleene’s that we always used for the handcraft making, bond by solvent evaporation. The solvent in Aleene's quick dry tacky glue is water. So you can see the paper soaked wavy when you apply white glue to it. When the water evaporates, the polyvinyl acetate latex, which is the ingredient of white glue, will spread into a material's crevices to form a flexible bond. Since the water cannot evaporate fast, it takes time to wait for it to dry. So it is not as fast as superglue when it comes to drying. After it dries, you can peel entire glue out of the surface if you apply it

to some smooth surface, such as plastic. Super glue, on the other hand, undergoes a process of anionic polymerization as we mentioned above. Cyanoacrylate molecules start linking up when they come into contact with water, and they whip around in chains to form a durable plastic mesh. The glue thickens and hardens until the thrashing molecular strands can no longer move.

While superglue can fix a broken coffee cup forever, it could also bond the fingers to it. Superglue users have had experiences of superglue attaching to their fingers or so. Here are some tips to get rid off superglue from the skins. Cyanoacrylate is impervious to water, but can be dissolved with an organic solvent, such as acetone. Using this property, it is easy to remove the annoying superglue from the fingers. Some nail polish removers can be used because they contain acetone, but be sure to check the label, since many acetone free products are available and will not work against superglue. It’s also possible to find pure acetone in stores that sell home supplies or art supplies, because acetone is a useful solvent such that it can remove sharpie mark. However, acetone is flammable and toxic, so it’s not a chemical that people want to ingest or inhale. It is absorbed into skin on contact. It dehydrates and defats skin, so it’s better to wash any spill with soap and water and apply a moisturizer, if possible.

There are often incomprehensible plot in some movies. For example, young and dangerous people making fun of someone else’s mouth sealed with superglue. I wonder if I am a victim, I will be worried about how to get rid of the superglue and also whether I will be able to talk again. In real life, it barely happens. However, if someone needs to unstick their lips and here is what they can do. If lips are accidentally stuck together, acetone is not useful here since it’s toxic. But a generous amount of warm water helps and maximum wetting and pressure from salvia from inside the mouth also helps. Then it’s time to try to peel or roll lips apart. Don’t worry about swallowing the minor toxic superglue by accident, because it is almost impossible to swallow the adhesive as a liquid. The superglue adhesive solidifies upon contact with saliva due to moisture and it can adhere to the inside of the mouth. Saliva will lift the adhesive in one to two days and avoid swallowing the adhesive after detachment.

Meanwhile, a feeling of heat can be noticed from the fingertips when superglue drops on it. Because the chemical process of polymerization produces a certain amount of heat during the reaction, it also requires cautions that not to apply too much superglue at once. If a large enough amount of super glue makes contact with the skin, it can actually cause burns. Superglue is not only used for adhesives, its properties are applied to many areas. Since cyanoacrylate 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. For those people after few times of uses of superglue must gain acknowledge from experience that thinner layer bonds more effectively than a thicker one that does not cure properly. For thicker layer, it takes longer time to allow the inner side of the thicker amount of superglue to be dried, which definitely make it lose its one of the main advantages of instant. One of the fancy applications of superglue other than just pasting is the superglue fuming, which is a superglue method to collect fingerprints that shown on some gangster films. In the criminal investigation, the police use smoke of cyanoacrylate to identify potential fingerprints. At first, the item of which the finger print had to be taken was placed in a heated and airtight container. Then, superglues were placed into the container and the cyanoacrylate evaporated. The laboratory personnel used the fan to circulate the cyanoacrylate to spread in the container. Because the fingerprint residue material such as amino acids and glucose will react with the gasification of cyanoacrylate and make fingerprint rendering.

There’re some disadvantages of superglue due to its rapid polymerization. Cyanoacrylate adhesives have a short shelf life if not used that is, about one year from manufacture if unopened, one month if opened. It might also be the reason of the small packaging content of superglues since it’s difficult to store. 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. And the inner superglue generally undergoes the reaction although it is much slower than the surface one. Finally superglue needs to be discarded after only one use because its nozzle is clogged and the content become partially solid. The reaction with moisture can cause a container of superglue which has been opened and resealed to become unusable more quickly than if never opened. Even if the lid is tightened after use, it may not be opened again because the opening of the glue tube and the lid stick to each other so tightly. So looking for a better way to store superglue is important. Here are the tips to minimize this reduction in shelf life cyanoacrylate. Once opened, superglue can be stored in an airtight container with a package of silica gel desiccant, which it’s easy to be obtained from some food packages, in order to reduce the chances to get in touch with water. Another way is to insert a hypodermic needle into the opening of a tube instead of using the cap of superglue. After using the glue, residual glue soon clogs the needle, keeping moisture out. The clog is removed by heating the needle before use.