In the early days of manufacturing adhesive compounds, the terms cement, glue, gums, mortars, resins, mucilage, pastes and adhesives and sealants were used in free exchange of one another. It has been within modern times that we have sought to differentiate between sealants and adhesives. This has been a difficult task as most sealants can be adhesives, and most adhesives can be sealants. For example, it is common for polyurethane sealants to have similar strength properties to structural adhesives. China Adhesive Manufacturers have been working towards setting up better definitions for these terms to guide customers as to what they should purchase.
Vulcanized rubber has been used as an adhesive since Thomas Hancock first discovered that the vulcanization process invented by Charles Goodyear created a bond between rubber and metal in 1843. It was used for years as the only practical means to adhere metal to rubber, despite its serious limitations as a thermoplastic.
What we call rubber cement was first used in early rubber-to-metal bonding. This was commonly a simple dispersion of rubber sheeting in benzene, which was later changed to toluene or another solvent. The rubber cement would be put on the metal with a brush and allowed to dry prior to being put in contact with the rubber that was to be bonded with the metal.
Polyvinyl acetate was first used in the 1930’s as a solvent based adhesive. It found itself to be commercially viable in the 1940’s when it was introduced as a way to bond paper and wood. Currently, it is the most widely used ‘white glue’ in the world.
In 1937 acrylic adhesives first appeared on the scene. These are now used in both pressure sensitive and non-pressure sensitive formulations in both emulsion forms and as organic solvents, as monomer and polymer cements, as cyanoacrylates, and many technical adhesive uses. These were in production as adhesives in the 1920’s, started to become useful in the late 1930s, but it was in 1958 when the first acrylic sealant came on the market. This is where some of the confusion as to what was a sealant and what was an adhesive began.
Silicone based adhesives became available commercially in 1944. The 1960’s saw them expand to being used as sealants in the construction industry. They are useful at both low and high temperatures, and can be purchased as solvent based moisture curing adhesives, one-part moisture-curing adhesive and sealant, two-part curing adhesives and sealants, and as pressure-sensitive adhesives.
The biggest part of this confusion between adhesives and sealants stems from the late 1950s and early 1960s. This was when marketing programs that were aimed specifically at the adhesive industry established themselves for raw material manufacturers. Formulators had to have an extensive knowledge of all possible chemical types to sort through all this advertising. Because of this broad knowledge, most formulators had a background in the coatings and rubber industries. This has not changed over time, as almost all synthetic resins used today were previously in the coatings and rubber technology industry. This is what has caused, and what will continue to cause, the confusion and multiple uses of sealants and adhesives.