Glue

Glue is a sticky substance designed to attach one object to another. It can be made from natural substances, but these days is more likely to be synthetic. Glue was invented by the Sumerians and is often made from animals, such as horses.[1] Glues have gotten so strong that some airplanes have their wings completely or partially stuck together with high-strength glues, such as the composite wings introduced to the A-6 Intruder in the SWIP upgrade.

## Contents

* 1 Types
* 1.1 Cyanoacrylate
* 1.2 Polyurethane
* 1.3 Epoxy
* 1.4 Hot glue (polymer)
* 2 References

## Types[edit]

There are many kinds of glues. These include the following types, but there are many different bases and variations.

### Cyanoacrylate[edit]

Cyanoacrylate (C5H5NO2) glues are one of the most popular types of glue in use today. This type of glue is best known as "Super Glue," although other brand names exist, such as Krazy Glue.[2] Super Glue bonds surfaces together through a process called anionic polymerization, which basically means that when exposed to water, the glue molecules link together into chains, forming a microscopic plastic mesh. This is an exothermic reaction, so particularly when large amounts are used, the glue can heat up significantly as it cures.[3] There are multiple variations, but this is a synthetic glue composed of acrylic resin, which offers a high tensile strength but low impact strength. This type of glue works very well with plastics and synthetic rubber, but also works on many other materials, such as fabrics and hardwood. Liquid Super Glue can be dissolved in acetone, but once it cures, this solvent no longer has an affect.[4]

### Polyurethane[edit]

Polyurethane adhesives such as "Gorilla Glue"[5] have also become quite popular, as they offer a strong bond between surfaces, even when there are small gaps. This makes it ideal for wood, fabrics, and ceramic, although it also can work with many other materials, such as metals, plastics, glass, sand, and rubber. Liquid polyurethane glues can generally be removed using mineral spirits or acetone, but once cured, these will no longer work.[6]

### Epoxy[edit]

Epoxies are used somewhat less commonly by individuals, but offer a strong bond for many different surfaces. They are therefore quite popular in industry and manufacture. Epoxy is typically sold in two parts; One part is polyepoxide, the other part is a curing agent or another resin. Each part remains viscus for a long time by itself. When used, the two parts are mixed together, and it quickly solidifies. While curing, the monomers in the polyepoxide will bond in a network of ether.[7] There are many varieties of epoxy glues, offering a wide range of strengths and cure times. Some are also designed to cure while in very wet environments.[8]

### Hot glue (polymer)[edit]

Hot glue is a polymer-based glue which is popular for crafts. Various formulations exist, but in general, polymers are heated to 250°F (low temperature formulas) or 380°F (high temperature formulas) at which point it becomes a highly viscus liquid. It is then applied to two or more surfaces that are to be connected, and allowed to cool. As the glue cools, it becomes a solid again, thus holding the desired objects in place relative to each other. Hot glue does not offer a particularly strong bond in most cases, but it can be used to permanently attach things like paper and paperboard. It excels at filling gaps, and thus bonding irregular surfaces together, at least temporally.[9]

## References[edit]

1. ↑ https://slate.com/human-interest/2012/02/what-do-horses-have-to-do-with-glue.html
2. ↑ http://www.krazyglue.com/about-us
3. ↑ https://home.howstuffworks.com/question695.htm
4. ↑ https://www.adhesives.org/adhesives-sealants/adhesive-selection/types-of-glue-glue-tips
5. ↑ https://www.greaseexpert.com/gorilla-glue-vs-super-glue/
6. ↑ https://www.adhesives.org/adhesives-sealants/adhesive-selection/types-of-glue-glue-tips
7. ↑ https://www.gardenguides.com/12167274-how-does-epoxy-work.html
8. ↑ https://www.mixerdirect.com/blogs/mixer-direct-blog/how-does-epoxy-work
9. ↑ https://www.adhesives.org/adhesives-sealants/adhesive-selection/types-of-glue-glue-tips