Why is glue sticky?
Adhesives are substances that make one thing stick to another. White glue and tape are adhesives that companies make for people to get things to stick together. But there are other types of adhesives all around us. When your feet stick to the floor of the movie theater, it is the spilled soda pop that is acting as an adhesive. When your fingers stick together after eating a caramel apple, it is the caramel that keeps them stuck. Some everyday foods work well as adhesives because of the structure of the molecules that make up the substance. Proteins, such as milk and egg yolk, are good for making glue. This is because proteins are often long, branching, stringy chains of molecules. These molecules are mixed into liquids to make glue. When the protein in a liquid is put onto a surface, it moves into the pores and spaces of the material. When the liquid dries, the proteins harden and keep everything that they’ve touched connected. Really smooth surfaces like metal and glass don’t have any
In general, a glue is a chemical compound which contains certain substances that easily bond with other materials. Things like Elmer’s glue harden around surface imperfections on the bonding sufaces of whatever you’re gluing and form bonds with the atoms in those substances. For this reason, many glues don’t work well on metal or smooth surfaces. From Wikipedia: “Cyanoacrylate (Super Glue) 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.
Although there are many ingredients used to make glue, most formulas contain something called polymers. A polymer is a large molecule that often is described as being a long molecular strand, much like spaghetti. Some polymers are naturally “sticky” depending on how they are made. Others require certain ingredients called tackifiers to make them sticky. One of our many challenges here at Elmer’s is to be sure we have exactly the right balance of polymers and tackifiers to create a glue that is sticky and strong.
