ADHESIVES: Intro

ADHESIVES

Understanding adhesives: What diff erent types are available?

Adhesives are materials capable of fastening or binding two surfaces. Also called glues, sealants, and cement, adhesives work by surface attachment but without altering these surfaces. An adhesive’s ability to hold fast and bond to a surface is critical. However, those features are not the sole determinant of performance. An ability to bond to dissimilar materials, form crystalline or reliant structures, and bond quickly or slowly are also important considerations. The good news is there are many adhesives available tailored to several applications. The bad news is there’s no one adhesive ideal for all applications. Knowledge of the attributes and shortcomings of adhesives is required to choose wisely. The fi nal application must also be considered, including the environment or conditions it will be subject to. Compared to other joining methods — such as mechanical fastening or welding — adhesives can o er several advantages. They can reduce the time and cost of assembly, improving stress distribution. They can lengthen the working time, allowing for adjustments during assembly. They can also add performance by reducing assembly noise, for example. Some adhesives are rigid and tough when cured, while others are soft and fl exible. Some form permanent bonds, while others o er impermanent bonds that be undone without damage to the substrates. Typically, adhesives are more di cult to disassemble than mechanical fasteners. The reliability and durability of adhesives continue to improve, but failures still happen. There is no single, universal adhesive. The ideal adhesive choice requires knowledge of the surfaces to be joined. Surface preparation is essential and primers or other surface treatments often maximize bond strengths.

Adhesives can be classifi ed in several ways, such as reactive or non-reactive. Reactive adhesives require a chemical reaction to form a bond. Non-reactive adhesives require no chemicals but might undergo a physical change during bonding. Examples include hotmelt, pressure-sensitive, and solvent-based adhesives. Reactive adhesives raise the bar on performance substantially but are nothing new. In fact, some ancient adhesives take advantage of chemical reactions during curing. Modern reactive adhesives are thermoset polymers, where a chemical reaction is responsible for curing the adhesive. Typically, two components are mixed to start the curing. Some adhesives also rely on reactants, such as water. It’s wise to learn thoroughly about adhesives before selecting a formulation for any application.