Question: What is the difference between a hardener, a primer, an accelerator, and an activator for adhesives and sealants?

Answer: This terminology can be confusing because the terms are often used interchangeably between technologies and differently by various manufacturers of the same technology. The term hardener is most often used in two-part epoxy adhesives; most manufacturers call the part that actually contains the epoxy molecule the “adhesive,” and the part that contains the curing agent the “hardener.” Some of these epoxy systems also contain additives in the hardener component to speed up the cure; these are usually called “accelerators” or “catalysts.”

In two-part reactive acrylic adhesives, the terms adhesive and initiator, or a resin and catalyst, are often used interchangeably. The important thing to know is the correct mixing ratio of the two components. These days, it’s usually easier because the adhesive systems come in pre-measured syringe or cartridge containers. Some adhesive systems use so-called “primers” or “activators” that are applied to surfaces before applying the adhesive.

Sometimes the primer will serve to condition the surface and ensure maximum adhesion. A good example of this is the use of organosilane primers, which are used for ensuring good adhesion and bond durability when epoxies, acrylics, or RTV silicones are bonded to glass surfaces.

In other cases, the primer or activator actually is used to speed up the curing of the adhesive. For example, special surface primers have been designed for surface-initiated adhesives (such as cyanoacrylates) to increase the speed of cure when atmospheric humidity is very low or on so-called “inactive” surfaces or low-energy plastic surfaces.

Any views or opinions expressed in this column are those of the author and do not represent those of ASI, its staff, Editorial Advisory Board or BNP Media.