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.
In this article, we will discuss different adhesive 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.
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.
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.
Polyurethane adhesives, such as the Adbond EX 5690, can be painted for an ideal finish, offer high flexibility and can be used in any weather. This makes polyurethanes ideal for the transport industry.
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.
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 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.
Adhesive films are available in rolls or pre-cut lengths or shapes, provide easy application, and have no pot-life restrictions. They are available in thicknesses between 2 and 8 mm for different applications.
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 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 are pressure-sensitive.
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 a higher resistance to moisture, heat and chemicals.
Thermosetting adhesives are usually available in two-part forms. Resin and Hardener are mixed to obtain a desired setting time. The resin and hardener can be used in 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 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 setting time and slow the assembly process.
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 quite durable for light load applications and are normally purchased as tapes or labels for non-structural applications.
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 adhesives are offered as pastes, liquids and films. They are strong and usually used below their glass transition temperature (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 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 a main adhesive.
Semi-structural adhesives are ideal for less critical applications, though they still offer more strength and support than non-structural adhesives. They can therefore be used to replace either structural or non-structural adhesive applications, depending on the project.
Trust Adfast for high-quality adhesives
In conclusion, there are many different types of adhesives. With their different chemical compositions, forms, classifications, load bearing capabilities, and other properties, choosing the right adhesive for your project may be confusing. Adfast offers a variety of high-quality adhesives for different applications, but most importantly, the technical expertise to guide you in your selection and support your project from beginning to end.
For more information or if you need help choosing the right product for your project, contact us!