Adhesive Testing | Strengthening the Bonds

Adhesives are everywhere and so is adhesive testing. They are in planes, your car, your phone and basically found anywhere. Often high-performance glues yield significant advantages compared to nails, bolts and screws.

One example for this is the aircraft industry. By replacing traditional rivets with epoxies, drag was significantly reduced while fuel efficiency improved greatly. However, „glueing“ is not limited to engineering applications. “Superglue“, or cyanoacrylate, is well known for its rapid bonding of wounds in medical use.

As adhesives can cover more and more applications, the applied mixtures increase in complexity. Because of that, a safe and easy technique is needed for adhesive testing, to guarantee a good bonding result. So, did you know?

FTIR is the powerhouse of adhesive analysis

Sounds bold? Holds true. Let’s look at two examples of adhesive testing.

Example #1: Studying curing kinetics

Deep insights into an adhesive’s reaction kinetics are for instance crucial to optimize manufacturing processes. In addition, it helps to determine when the next production step can be started.

Figure 1. Temporal progression of the intensity of C-O-C group (green curve) and the C-H group at C=C double bond (pink curve)

So, we took a standard epoxy glue, irradiated it with UV light to start the curing process. The reaction was monitored by ATR FTIR. The starting material has a characteristic carbon double bond, which is replaced by a carbon oxygen bond during the reaction. With FTIR, we can monitor how much of each bond is in our sample and thus, follow the chemical processes.

In Figure 1 we follow the progression of these two bonds and their IR intensity during the experiment. While the carbon double bond (violet) vanishes, the carbon oxygen bond (green) rises. The reaction then slows down after 20 seconds and eventually comes to a halt.

From this plot, the reaction rates of functional groups can be easily determined providing information about the reaction mechanism.

And what about cleaning?

Cleaning of “super glue” can be “super annoying”. But if you are using ATR to follow the hardening of adhesives, you don’t have to worry about this. The monolithic diamond of the Bruker Platinum ATR accessory shown in Figure 2 is exceptionally sturdy. It allows to remove hardened epoxy easily and safely. If you don’t know about ATR, you should check our tutorial video on YouTube.

Close-up image of a monolithic diamond embedded in the Platinum ATR accessory.
Figure 2. Monolithic diamond in the Platinum ATR accessory

Example #2: Failure Analysis

The presence of glues often leads to unexpected product failures. Therefore, root cause analysis is one of the challenging tasks in adhesive quality control.

Particles and other contaminations find their way into production processes and might ruin the bonding results. If such a problem occurs, IR microscopy can be of great service. Figure 3 shows the analysis of an unknown crystalline contamination within an adhesive layer, carried out with Bruker’s LUMOS II. Our easy-to-use OPUS software quickly displays the spectrum of the adhesive layer and that of the contamination. By comparing the spectra with a database, you can easily identify the contamination.

Figure 3. Left: Spectra of the hardened adhesive (blue) and a crystalline contamination (red). Right: Superimposed chemical image on top of the visual microscopic image of an adhesive layer.

But wait! There is more!

In addition, the software not only allows you to identify contaminations and defects. By superimposing the chemical data onto the visual image, we get find out where the issue is located.

If you focus on incoming goods inspection, the ALPHA II is the right choice for you. Its identification and verification tools boost your analytical confidence, enabling you to efficiently test any material.

On our YouTube channel, we have many videos showing its ease-of-use, why not check it out? Here is the analysis of additives in a plastic piece.

Get the best results in adhesive testing – stick to Bruker

In conclusion, you can see, Bruker’s FTIR equipment is excellent for analyzing a wide variety of adhesives. In this article, we showed how to find potential flaws and study UV curing kinetics. With our easy-to-use technology and innovative software, you can be sure to strengthen your customer bonds.