What happens to an adhesive at low temperatures?
Unlike at high temperatures, an adhesive does not deteriorate (break down chemically) at low temperatures, or even at cryogenic temperatures. Even so, the properties of the adhesive can change dramatically.
The main problem at low temperatures is that the modulus of the adhesive increases. In other words, the adhesive becomes less flexible the lower the temperature. When the adhesive is less flexible it is also automatically more brittle and more sensitive to for example impact and vibrations. The worst case scenario is that the adhesive cracks.
Other negative effects of low temperatures could be that the the adhesion between adhesive and substrate is lowered. De-bonding can even occur.
Which types of adhesives should you use at low temperatures?
Temperatures in the range of a normal winter day is usually no problem to most adhesives, depending on what the joint will be subjected to in addition to the cold.
Since it is above all the modulus that is affected, the adhesive types that exhibit the best results at low temperatures are those with an already low modulus or high flexibility. In many applications, it is important that an adhesive bond remains flexible and that the strength / adhesion is kempt high.
Using a flexible adhesive can also have advantages when the bonded details will be subjected to temperature changes where the thermal expansion differs between two substrates.
Standard silicone grades tend to be able to retain their flexibility down to about -60 ˚C. There are specially formulated silicones that can manage the same even below -100 ˚C.
Epoxy based adhesives are certainly not as flexible as silicones. However, they tend to be both high and low temperature resistant and there are cryogenic adhesives proven to work well in those types of environments as well.
Technical data sheet specifications
Don’t get too hung up on the recommended temperature values stated in the technical data sheet (TDS) of an adhesive. As an example, for Epo-Tek, the minimum operation temperature is specified as -55 ˚C. This is not because something in particular happens at this temperature, but because tests have only been performed down to -55 ˚C.
Many epoxy adhesives can manage much lower temperatures without losing too much adhesion or strength. In fact, there have been some great results even at cryogenic temperatures between -150 ˚C and -273 ˚C (absolute zero). Certain products have even been shown to become stronger at lower temperatures.
As always, you always want to consider that the temperature resistance of an adhesive is not only affected by the temperature itself. Other factors such as exposure time, temperature variations, atmosphere, joint design and mechanical stress also weigh in. In addition, the properties of the cured adhesive can change in certain ways, especially near the limits stated. It is therefore important to verify the temperature resistance for the specific application in question.
Applications requiring cryogenic adhesives
Aerospace, space, refrigerator and freezer equipment, SEM (Scanning Electron Microscope) can require adhesives that function at low or cryogenic temperatures. It can be anything from potting or encapsulation of electronic components, coatings or adhesion of components.
Lower temperature limitations for different adhesive types
General limits for standard grade adhesives:
- Silicone: Standard grades normally between -40 and -60 ˚C.
- SMP polymers: Normally -40 ˚C.
- Epoxy: Standard grades normally -55 ˚C.
- Polyurethane: Normally -40 ˚C.
- Akrylic: Normally -40 ˚C
- Cyanoacrylate: Normally -55 ˚C
- Anaerobic: Normally -55 ˚C
Products developed for extremely low temperatures
Examples of some products developed for extremely low or cryogenic adhesive temperatures are listed below.
Nusil R3-2160: 2-component adhesive / sealant, silicone elastomer. Has performed well in applications down to -140 ˚C.
Nusil R-2949: Thermally conductive 2-component adhesive. Maintains its properties down to -115 ˚C.
Nusil R-2634: Electrically conductive silicone adhesive. Has performed well in applications down to -140 ˚C. Has performed well in applications down to -140 ˚C.
Nusil CV-1144-0: Silicone based low outgassing coating (atomic oxygen) that maintains its properties down to -115 ˚C.
Epo-Tek 301-2: Epoxy adhesive with low viscosity and high shear strength at cryogenic temperatures. Low outgassing.
Epo-Tek 7110: Thermally conductive epoxy adhesive with high shear strength at cryogenic temperatures.