Considerations for temperature resistant adhesives

How elevated temperatures a temperature resistant adhesive can withstand depends, among other things, on which type of chemistry the adhesive is based on. Organic adhesives such as epoxies, cyanoacrylates, acrylates, polyurethanes, light curing adhesives and anaerobic adhesives begin to deteriorate around 250 – 300 ˚C. Silicones can withstand degradation up to 350 ˚C. BUT – there is a difference between deterioration temperature and the temperature resistance in an application.

The strength of an adhesive bond is generally reduced the higher the ambient temperature. This is the case even at temperatures below the degradation temperature. Then add the fact that synergy effects may occur. For example, there can be a substantial difference between an adhesive joint that is exposed to 100 ˚C and a joint exposed to 100 ˚C while simultaneously being immersed in a solvent.

You will often in the technical data sheet for an adhesive find two different specification for temperature resistance. First, it is the suggested operating temperature which an adhesive joint is expected to withstand for a longer period of time. Then there is the suggested intermittent operating temperature which is the temperature which the adhesive is to be expected to withstand for a shorter while, a peak temperature if you will.

In some cases, it can also be important that an adhesive can withstand temperature cycling with quick changes.

In technical data sheets, it is not usually the degradation temperature that is stated. The temperature resistance actually refers to the temperature at which a specific adhesive joint (two specified materials bonded with the adhesive in question in a certain manner) retains a certain strength.

Choosing a temperature resistant adhesive

To choose an adhesive for details or constructions that need to have high temperature resistance, it can be a good idea to prepare by considering the following:

• Find out which temperatures the adhesive needs to withstand and for how long. Will this temperature be in combination with anything else that may weaken adhesive joint; mechanical loads, chemicals?
• Define other important qualities such as which materials the adhesive needs to have adhesion to, mechanical properties, colour, approvals/certifications or other requirements.
• Decide how you want to set up your gluing process. Will it be manual, semi-manual or fully automatic?

Which types of adhesives can withstand the highest temperatures?

The answer is that it depends on what kind of temperatures we are talking about. Within each category of adhesives, there are more temperature resistant adhesive grades than the standard ones. You will find some examples below.

Among the most temperature resistant adhesives, there is silicone and epoxy. They can withstand up to 300 ˚C for longer periods of time. Generally, higher temperature resistance will be achieved if the adhesive is heat cured.

The most temperature resistant type of adhesive is ceramic adhesive. These can withstand up to 3000 ˚C. However, ceramic adhesives are very stiff and brittle which limits their use mechanically.

Examples of a few common adhesive products with especially high temperature resistance (there are many options, so ask us for more):

Nusil R-2160, 2-compoonent silicone adhesive, 315 ˚C

Sealtite 210, 1-component silicone adhesive, 350 ˚C

Permabond ET5411 2-component epoxy adhesive, 230 ˚C

Epo-Tek 353ND 2-component heat curing epoxy, 250 ˚C continuously, 350 ˚C intermittent

Permabond HM165 Anaerobic thread sealant, 230°C

Permabond 920 Cyanoakrylate, 250 ˚C

Epo-Tek H74 Thermally conductive epoxy adhesive, 250 ˚C continuously, 350 ˚C intermittent

How is the thermal resistance of an adhesive determined?

The temperature resistance of an adhesive is determined by testing the strength of an adhesive joint at different temperatures. Hence, the result is specific for a certain substrate (material that is being glued) and using a specific method in which for example the size and shape of the bond are defined. It is therefore a good idea to be careful when comparing two different brands of adhesives or using the values on the technical data sheet as the absolute truth. You always have to verify the results in your specific application!