Adhesives come in a variety of chemistries and forms, and each has unique features that are formulated to solve a particular problem or need. Science has allowed for engineering very specific adhesives, and they tend to come in polar opposites: solvent or acrylic, clear or pigmented, removable or permanent.
From epoxy to thread lockers, and everything in between, choosing the correct adhesive for your project comes down to the application it will be used for and the environment in which it will be applied.
To get the best results, ask yourself the following questions before selecting your adhesive:
What surface, container or product will the adhesive be applied to?
Adhesives attach to the surfaces of two substrates, unlike a process that fuses substrates into a unified whole such as welding metal or solvent activation of plastics. In selecting a GlueGun.com adhesive, surface condition must be considered: roughness, smoothness, porosity, coated, uncoated, cleanliness, flexibility, and size of the part. Check out our Surface Preparation Tips and Tricks for adhesive bonding.
Not every adhesive will work on every surface. For example, polyurethane adhesives are an excellent choice for finish carpentry and other woodworking projects, as they provide durability, impact resistance and flexibility in open times.
Pressure sensitive adhesives (PSAs) adhere to most surfaces, and contact adhesives are particularly well-suited in applications where clamping is difficult.
Some adhesives, like epoxies, require thorough surface preparation (cleaning, roughening) in order to adhere properly. MMA's would be better for metal bonding in general because they require little or no surface preparation.
What temperature will the adhesive endure or be exposed to during use, distribution and storage?
Many environmental conditions affect how adhesives cure and perform over long periods of time. One of the most significant environmental factors is temperature. Minor changes in temperature can have major changes in cure speed and storage life of adhesives. Most organic adhesives have maximum continuous operating temperatures and if exposed to higher temperatures for long periods of time their performance drops significantly.
Thermosetting adhesives such as melamine, phenolic and formaldehyde resins form strong bonds and have good resistance to higher temperatures. Silicone adhesives have a high degree of flexibility as well as a very high temperature resistance, making them excellent choices for marine or plumbing applications. As a rule, curing will be slower at lower temperatures and faster at higher temperatures.
Will the adhesive need to be one that forms a strong, permanent bond, or one that allows the joined surfaces to be removed or re-positioned as needed?
Adhesive strength is the interfacial strength between adhesive and substrate, and usually the most important consideration when designing a strong adhesive bonded assembly. However, adhesive strength is not the only factor critical to creating an effective bond. Even when using the world's toughest adhesive, a bond will fail if the adhesive does not bond to the surface of the substrate.
Water-based adhesives are commonly used for laminating, they're also a lower cost alternative to resins. Hot melt adhesives can be melted or softened repeatedly by heat, or set by cooling, which allows for re-positioning during assembly. Often, removable adhesives are used as positioning aids during product build.
Polyurethane hot melt, more commonly known as PUR, is an adhesive that shares many characteristics of traditional glue sticks and bulk hot melt. That said, PUR hot melt is not dispensed in a traditional glue gun and can offer some additional bonding attributes that may fit applications that require a stronger bond or higher endurance to the elements.
Will the adhesive be exposed to high humidity during end use, application or distribution?
Excessive humidity can cause adhesives to become more foamy in appearance or softer in quality. It can also result in film formation in certain curing agents. Some adhesives may not be affected by humidity within a certain range, but if condensation forms on top of a substrate, you can be assured that the bond strength will be negatively impacted.
Moisture and humidity will both have an effect on adhesion performance. Acrylic adhesives have excellent environmental resistance but because they are water-based, they are more susceptible to moisture which affects their application and durability aspects. When it comes to humidity, when it's low, drying is accelerated; when high, drying is slower.
Even after all of these questions are answered, there's no guarantee a particular adhesive will perform exactly as you need it to. Adhesive testing is strongly recommended prior to production or purchase. When testing, some factors affecting bond strength you'll want to consider include:
- Test temperature
- The adhesive contact area
- Type of force applied
- The adhesive's properties
- Adhesion to substrates
- Prior or subsequent exposure to heat or moisture
- Storage, complex and loss modulus
At GlueGun.com we offer quality products and deliver great customer service in equal measure; our experienced professionals guarantee it.
If you have additional questions, or would like more information on the use of adhesives, custom formulations or application products, contact us for more information.