Hotmelt adhesives (HMA), also known as hot glues, are generally 100% solids formulations based on thermoplastic resins. They are solid at room temperature and can be softened, reshaped, and dispensed upon heating above their softening point.
Hot melts can be applied by extruding, rolling, or spraying the adhesive, and manual application is usually done with handheld electrical hot glue guns.
Some hot melt adhesive formulas are very simple and some are extremely complex, but they all typically have four types of ingredients in common: polymers, plasticizers, tackifiers, and antioxidants.
Tackifiers: Tack is the measure of the stickiness of an adhesive, essentially how long the adhesive stays stuck after it is applied.
Polymers: The foundation of an adhesive as it provides both strength and flexibility. These are long, repetitive chains of certain molecules that have different properties based on the length of the chains and the type of the molecule.
Plasticizers: Plasticizers are the most common additive in hot melt. In fact, they are used as a sort of second base polymer to give the hot melt greater flexibility and toughness.
Antioxidants: Hot melt adhesives are prone to degradation if kept at higher-than-recommended temperatures for prolonged periods of time. Antioxidants protect the material from degradation over the period of its shelf life.