Table of Contents
- Flexibility in Adhesives
- When to Use More Flexible Structural Adhesives
- Which Structural Adhesives Are the Most Flexible?
- Highlighted Products
- FAQs
Adhesives can be strong, heat resistant, low odor, and more. What you need will all depend on your application, but flexibility is one important property you may want to explore more.
Flexibility in Adhesives
Flexibility in adhesives is a relative term depending on the type of adhesive. Some types of adhesives are extremely pliable and can change their form drastically without breaking. Laminating adhesives, for example, can be as flexible as fabric. There are also graphic arts adhesives that are very pliable.
On the other hand, some types of adhesives are designed not to bend or stretch as much as other adhesives. Structural adhesives tend to fall into this category. Epoxies, for example, are more rigid on the grand scheme of adhesive chemistries. So, while structural adhesives are not the most flexible of adhesives, flexible structural adhesives refer to structural glues that are formulated to have more flexibility and greater elongation than other most other adhesives of the same chemistry.
An adhesive's flexibilty is used measured by elongation percentage, or its ability to increase in length before failing. Elongation can be tested with a special machine that will slowly stretch the adhesive until it breaks. This machine will measure both the percentage of elongation as well as the amount of force it took to break the adhesive.
When to Use More Flexible Structural Adhesives
Structural adhesives that are flexible have specific uses as this property becomes necessary. In comparison to rigid adhesives, you may want to choose a more flexible structural glue if the bond is for an application with:
- Big temperature fluctuations
- Substrates that expand and contract regularly
- Exposure to a lot of moisture
- Joint movement
- Exposure to frequent vibrations or knocks
- A unique design
Flexible adhesives for structural bonding may have better resistance to temperature fluctuations as well as thermal expansion in the substrates. These types of adhesives also tend to be necessary in applications with moving parts when mechanical bonding is not an option.
Altogether, these properties can translate to use in window bonding, automotive displays, sporting goods, trailers, gap filling, and more. If the adhesive chosen isn't flexible enough for the given application requirements, it could lead to bond failure.
Which Structural Adhesives Are the Most Flexible?
While flexibility can vary greatly from product to product and there is a lot of overlap between adhesive chemistries, there are some types of structural adhesives that generally tend to be more flexible than others.
Two-Part Polyurethanes- These adhesives generally have a higher level of flexibility and elongation than other types of structural adhesives. They are often a good option for applications requiring a high amount of impact resistance and less shear strength.
Acrylates- These adhesives, including methyl methacrylate adhesives (MMAs), are an incredibly diverse group of structural adhesives that can be formulated to have varying levels of flexibility depending on what is desired. In general, they tend to offer a good balance of shear strength and elongation for structural adhesives.
Cyanoacrylates- These products tend to have higher shear strength than elongation percentages compared to other structural adhesives. They are best suited for forming fast and strong bonds, rather than in applications with a lot of movement.
Epoxy Adhesives- Epoxy adhesives generally tend to have the lowest elongation percentage and be the least flexible of the structural adhesives, but they also often have the highest shear strength. They are usually better suited for applications where shear strength is the main priority.
Some Top Flexible Structural Adhesives
When it comes to structural applications, you may want a good combination of flexibility and strength. There are a lot of adhesives on the market that claim to be both, but how do you find the right one for you to get the job done? Our adhesive experts want to help.
If flexibility is a higher priority for your structural application, check out some of our favorite flexible structural adhesives. These products may be on the more flexible side for structural adhesives in general or for their specific adhesive chemistry, and they may be a good choice for your application.
3M Scotch-Weld Flexible Acrylic Adhesive DP8625NS
3M DP8625NS has the flexibility of a sealant but the strength and cure speed of an acrylic. It has an incredibly high level of plasticity with an elongation greater than 200%. Along with being a flexible MMA, the adhesive is also low odor, non-sag, and non-flammable. It can be used to bond dissimilar substrates like metals, plastics, and composite materials with minimal surface preparation. It also has a slow set speed.
3M Scotch-Weld Flexible Acrylic Adhesive DP8610NS
This flexible acrylic adhesive has a 200% tensile elongation at break. Because it is such a flexible glue product, it also helps mitigate bond-line read-through so you can use thin, flat substrates in designs. 3M DP8610NS has an open time between 10 to 15 minutes and a time to structural strength between 25 to 35 minutes. It is also low odor and non-flammable.
3M Scotch-Weld Acrylic Adhesive DP8705NS
Another 3M adhesive with a high elongation is the 3M DP8705NS. Not only is it a highly flexible adhesive for its kind, but also it can maintain its structural strength in temperatures as low as -40°F for applications where cold temperature performance is necessary. It has a non-flammable classification and low odor formulation.
Bostik Pliogrip™ Structural Adhesives
The Bostik Pliogrip 7700 series is a great collection of two-part polyurethane structural adhesives. The series as a whole can bond a broad range of materials, has a non-sag formulation, and is great for gap filling. The elongation of these products ranges anywhere from around 50% (Pliogrip 7715B) to 65% (Pliogrip 7771 & Pliogrip 7773). The different products within the series also have different working times, colors, and cartridges sizes to fill the needs of more consumers. If you are looking for a structural adhesive with a higher elongation and gap filling capabilities, these products may be a good choice.
Let Us Guide You
The best flexible structural adhesive for your application will depend on the environment, substrate materials, cost, and more. That is a lot to consider and there are so many adhesives on the market.
To help you narrow down your choices, our adhesives experts are here to offer their assistance. Just contact us and one of them will reach out to help you find the best adhesive solution for you.
