Glue Types: Understanding Different Adhesives

How are sellotape (Scotch tape), duct tape, stick glue, wood glue, and superglue different? All the types of glue have different chemical components and they are different in the way that they dry. They also stick or don’t stick to different things. Adhesive tape is called sellotape in the UK and Scotch tape in the US and Canada. Both are brand names and I will probably use the words interchangeably.

The glue on sellotape is called pressure-sensitive adhesive. It was invented by a man called Richard Drew, who was working for 3M. A lot of adhesives have been invented by people working for 3M, postits being one of them. He actually came up with masking tape before he invented Scotch tape. He was trying to make an adhesive tape that could be used on the surface of cars when they were being painted, and then peeled off with no damage. After he had masking tape down, he invented a clear tape that he called Scotch tape. The adhesive on the tape is called pressure-sensitive adhesive because it sticks using a physical reaction and not a chemical one, like other glues. The adhesive contains silicone, acrylic, rubber, and a resin to make it tacky. When you put the tape on to another surface, there are two processes that make the tape stick. The first is called wetting. The surface molecules of the tape are very loose and when the tape comes into contact with a surface, the molecules enter that material and sink below the surface, creating a bond. The second thing is something called Van der Waal’s forces. You might remember this. We looked at it when we were finding out how lizards can climb walls. Van der Waal’s forces are a weak attraction between two molecules, holding them together, but not strongly enough that the bond can’t be broken.

Duct tape sticks in the same way as sellotape, but its bond is much stronger. It uses more rubber than sellotape, which gives it a stronger and longer lasting bond. The adhesive layer is thicker than sellotape as well. Another feature duct tape has is a layer of cotton (or polyester these days) at the back of the adhesive. This gives the tape a lot more strength than sellotape and helps it keep its shape and bond.

Glue sticks come in a tube and you can extend them by twisting the base, similar to a lipstick. They are used for sticking paper, and general craft. They are not very strong adhesives. Glue sticks are made of synthetic water soluble resins, such as polyvinylpyrrolidone (PVP), and fatty acid sodium salt, which is a compound formed when fatty acids are reacted with sodium. Fatty acid sodium salts are used in soap and they give both soaps and glue sticks their shape. The resin is dissolved in water and when you use the glue, the water evaporates, leaving the resin. The glue bonds in two ways. First, there are the same Van der Waal’s forces that we had with basic sellotape. The second is a bond between the polymers. When the water evaporates, it leaves just the polymers in the resin and they start to lock together, getting twisted around the molecules in the thing they are sticking, forming a bond. This bond is not very strong and these kind of glues can be pulled apart fairly easily.

There are many types of wood glues, but the most common, the white glue, is made of something called polyvinyl acetate (PVA). It has polymers that are dissolved in a liquid solvent to keep them apart and to keep the glue pourable. When you spread the glue on a surface, the solvent evaporates leaving the polymers. Wood glue can bond incredibly well because the polymers can sink between the fibers of the wood. When the solvent is gone, the polymers harden and form together in a mesh. This mesh goes into the surface of the wood and makes a bond that is harder than the actual wood itself. If you want to break two pieces of wood that have been glued together apart, you will break the wood more easily than you will break the glue.

Superglue is different to the other glues. Stick glue and wood glue have a solvent that needs to evaporate before the glue can set. Superglue doesn’t need that. Superglue contains a chemical called cyanoacrylate. This chemical starts to polymerize when it comes into contact with water molecules. When there are water molecules, which there are, pretty much everywhere on Earth, including in the air, the cyanoacrylate starts to cure. The polymers in the glue rapidly attach to each other and form a very strong mesh. The glue gets into all of the microscopic pores on the surface of the object and this mesh of polymers sets, creating a bond that won’t break. The process creates heat, which is why your fingers feel warm if you super glue them together, which is something I do on a regular basis. And this is what I learned today.

Sources

https://science.howstuffworks.com/innovation/everyday-innovations/adhesive-tape.htm

https://echotape.com/adhesive-tape-guides/the-complete-technical-guide-to-duct-tape

https://en.wikipedia.org/wiki/Glue_stick

https://en.wikipedia.org/wiki/Wood_glue

https://home.howstuffworks.com/question695.htm