Different Adhesive Types & How to Use Them
Types & How to Use them
There are many different types of adhesives, each for specific conditions & applications, and there are multiple factors to consider when choosing the correct product. Adhesives can be categorized in different ways, according to their chemical composition, physical form, classification, or load-bearing capability.
This article will discuss different categories and how to use each of them.
ADHESIVES BY CHEMICAL COMPOSITION
Different adhesives can be categorized by their chemistries. Below are a few examples of available chemical compositions.
Epoxy adhesives
Epoxies are a type of structural adhesive. They are highly temperature and solvent resistant and can be structurally bonded to most types of materials, such as metals, ceramics, wood, and plastics.
Polyurethane adhesives
Polyurethanes are polymer-based adhesives used for constructions requiring high-strength bonding and permanent elasticity. They are often offered as two-part adhesives and have many uses. Unlike epoxy adhesives, they require moisture to set, which means they can be used for projects where other types of glues are often unsuitable.
Polyimide adhesives
Polyimides are one-part synthetic polymers that usually contain solvents. They are known for their strength, heat, and chemical resistance, as well as performance in extremely high temperatures, as high as 500 degrees Celsius. They are offered in two formulations, thermoset, and thermoplastic, and are often used for coating or electronic insulation.
ADHESIVES BY PHYSICAL FORM
Adhesive physical form affects product application. Adhesives can be spread manually or using tools and equipment.
Below are the different physical forms available.
Paste
Adhesive pastes are often high in viscosity, thereby making them difficult to spread during the curing period. They are ideal for adhesions requiring gap filling and are usually applied with the use of tools, such as a caulking gun.
Liquid
The liquid is the most common form of adhesive. They are one of the easiest to apply but can leak or sag during the curing process. They often take longer to cure but can be applied in thin layers to help this process.
Film
Adhesive films are available in rolls or pre-cut lengths or shapes, providing easy application. They are available in thicknesses between 2 and 8 mm for different applications.
Pellets
Adhesives in the form of pellets are typically hot melt or thermosetting adhesives. These must usually be inserted into a hot melt gun or melted and sprayed.
ADHESIVES BY CLASSIFICATION
Adhesives are also classified by structure:
Hot melt
Hot melt adhesives are brought to liquid form with heat and can be used to coat entire surfaces before the adhesive cools into a solid polymer. Many industrial sectors appreciate them for their eco-friendliness, safety, and shelf life. Different types of hot melt adhesives include EVA-based, APAO-based, and those that ar. Polyurethane hot melts are also available but don’t have the same properties as standard hot melt adhesives.
Reactive hot melt
Unlike non-reactive hot melt, reactive hot melt adhesives generate additional chemical bonds after the solidification process. This results in stronger adhesion once cured, expanded bonding as well as higher resistance to moisture, heat, and chemicals.
Thermosetting
Thermosetting adhesives are usually available in two-part forms. Resin and Hardener are mixed to obtain the desired setting time. The resin and hardener can be used in the one-part form, however, these aren’t as common because they must be stored in low temperatures. Storing them in high temperatures can cause the desired reaction to occur prematurely, resulting in a much lower shelf life. Pot life is an important property of thermosetting adhesives. It refers to how long a two-part adhesive will efficiently bond after the mixture. A product with a short pot life will harden too quickly, leaving insufficient time to complete the job. Meanwhile, a long pot life can delay the setting time and slow the assembly process.
Pressure-sensitive
Adhesives in this category are low modulus elastomers, meaning they do not require much pressure to deform and can be used on wet surfaces. They are durable for light-load applications and are normally purchased as tapes or labels for non-structural applications.
Contact
Contact adhesives are elastomeric and are applied to both items being bonded together. Once the solvent evaporates, the items are brought into direct contact. These types of adhesives are found in rubber cement or countertop laminates.
ADHESIVES BY LOAD-BEARING CAPABILITY
The load-bearing capability of an adhesive indicates how well it can hold different substrates together. They can be separated into three categories.
Structural
Structural adhesives are offered as pastes, liquids, and films. They are strong and usually used below the (Tg), the temperature at which polymer transitions into a soft and rubbery material. Some well-known structural adhesives are epoxies, cyanoacrylates, urethanes, and acrylics.
Non-structural
Non-structural adhesives are used for light loads or in more aesthetic applications. Both non-structural and semi-structural adhesives are much more cost-efficient alternatives to structural adhesives, but they are not suitable for all types of projects. Non-structural adhesives are often used as secondary fasteners in more long-term attachments rather than as the main adhesive.
Semi-structural
semi-structural adhesives are ideal for less critical applications, though they still offer more strength and support than non-structural adhesives. Depending on the project, they can be used to replace either structural or non-structural adhesive applications.
