Polyvinyl acetate

Polyvinyl acetate is a versatile synthetic polymer used widely as an adhesive. It is known by many common names, including white glue, wood glue, or carpenter's glue. In the United States, it is frequently called Elmer's Glue. This substance belongs to the polyvinyl ester family and is classified as a thermoplastic. A thermoplastic is a type of material that can change its shape when heated. Polyvinyl acetate is particularly effective at sticking to porous materials. These are substances like wood, paper, and cloth that contain tiny openings.

The chemical structure of polyvinyl acetate is defined by the formula (C4H6O2)n. It is created through a process called free-radical vinyl polymerization. This process uses a monomer, which is a single building block, called vinyl acetate. In the past, manufacturers produced this monomer by adding acetic acid to acetylene. They used a mercury(I) salt as a catalyst to make the reaction happen. Today, the process is different and more modern. Makers primarily use the palladium-catalyzed oxidative addition of acetic acid to ethylene. This method uses a metal called palladium to help the chemical reaction occur.

Polyvinyl acetate has several distinct physical properties and forms. The degree of polymerization, which describes the length of the molecular chains, typically ranges from 100 to 5000. Its glass transition temperature, the point where it changes from hard to soft, is between 30 and 45 °C. This temperature depends on the molecular weight of the substance. Often, the glue is sold as a dispersion in water, which is also called an emulsion. In these mixtures, polyvinyl alcohol is added as a protective colloid to keep the particles stable.

Chemical reactions can change how polyvinyl acetate behaves in different environments. Its ester groups are sensitive to base hydrolysis. This means that in alkaline conditions, the substance slowly converts into polyvinyl alcohol and acetic acid. If you add boron compounds, such as borax or boric acid, to a polyvinyl alcohol dispersion, a unique reaction occurs. The boron causes the molecules to cross-link, which means they tie together into a web. This creates thick, tacky precipitates often used to make toys like Slime or Flubber.

The history of this polymer began in Germany in 1912. A scientist named Fritz Klatte is credited with its discovery. He filed for a patent in 1913 and received several others in 1914. His work helped pave the way for the massive industrial use of adhesives we see today. Later, the chemical properties of polyvinyl acetate helped shape modern science. For example, the way it could be turned into polyvinyl alcohol through saponification provided a clue to Hermann Staudinger. He used these observations to help develop his famous theory regarding macromolecules.

Because it is considered a food-safe material, polyvinyl acetate has many surprising applications. It is used in food packaging and even serves as a gum base in chewing gum. You can find it as a coating layer on Gouda cheese or as an adhesive for cigarette paper. It is also used for much larger tasks, like acting as a primer for drywall. In the paper industry, it is used in coatings, paints, and as a binder for materials like filter paper and sanitary napkins. It can even be used as a wallpaper adhesive or for bookbinding.

However, the strength of this glue can sometimes cause unexpected problems. In the 20th century, it was used on the Archimedes Palimpsest, an ancient manuscript. The glue was so strong that it actually held the parchment together more tightly than the parchment itself. This made it very difficult for scientists in the 21st century to separate the pages for imaging and preservation.

Additionally, the material can be degraded by nature. While many microorganisms can break it down, filamentous fungi are the most common cause of damage. Other organisms like bacteria, algae, yeasts, and lichens can also degrade the polymer over time.