Which of the following best describes the role of a hardener in adhesives?

A hardener plays a crucial role in the curing process of adhesives, particularly in systems that require a chemical reaction for hardening, such as epoxies or polyurethanes. When a hardener is added to an adhesive, it reacts with the adhesive's resin component to form a rigid structure. This curing reaction transforms the adhesive from a liquid or semi-liquid state to a solid state, providing the necessary mechanical properties for strong bonding.

This process is essential because it determines the effectiveness and stability of the adhesive bond once applied. Without a hardener, many adhesives would remain in a malleable or unbonded state, which would fail to achieve the intended strength and durability. Thus, the role of a hardener is integral to developing a successful and lasting bond in various applications, making it a fundamental aspect of adhesive technology.