FTIR microscopy in tea bag analysis

FTIR microscopy enables precise analysis of teabag adhesive seals, revolutionizing quality control in the tea industry.

Teabags offer a convenient and efficient way to prepare tea. They simplify the brewing process by containing pre-measured portions of tea leaves. In addition they allow for easy disposal and keep the mess to a minimum.

However, this invention, which probably originated in the Middle Ages, also has its disadvantages. Modern tea bags may contain microplastics or open during the brewing process, causing the tea to float freely in the cup.

Although the latter is less dramatic than microplastics in the environment, it nevertheless is a problem for tea bag manufacturers. But why do teabags open at all? And more importantly, what can the industry do about it?

FTIR microscopy can help in prevent this from happening.

So, let’s talk about „FTeaIR“ ! … don’t get up, I’ll show myself out …

FTIR foils teabag troubles

Generally, there are two different types of tea bags. One is simply folded close and creased using a punching machine, while the other is sealed by a non-hazardous adhesive. The folded ones are quite robust and usually stay intact – in contrast to the glued ones.

Due to problems in production, important adhesive components are sometimes missing or are not well distributed. This subsequently leads to the failing of the adhesive seal. In order to prevent this, it is crucial to regularly assess the quality of the sealing.

FTIR microscopy of teabags is helpful in determining why a teabag may disintegrate.

FTIR microscopy is particularly well suited for this purpose. It enables swift and accurate analysis to verify the presence and proper distribution of essential components required for optimal bonding. By employing FTIR, we can ensure the integrity of tea bags, thus minimizing the risk of disintegration. Let’s have a look at how this works in detail.

FTIR teabag imaging

To perform this analysis, we cut the tea bag to size, clamp it in the micro vice holder and cut it flush with the holder’s surface. After that we insert it into the LUMOS II FTIR microscope.

FTIR microscopy sample preparation.
Right: Teabag pre-cut with scissors. Left: Teabag piece (in micro vice holder) cut flush with a knife

After placing a measurement grid over the sample area we start collecting the raw FT-IR imaging data with a focal-plane array detector (FPA). The next step involves interpreting this data through adaptive chemical imaging, where a single click instantly classifies all the components present in the sample.

By referencing a library, each spectral signal can be assigned to its corresponding ingredient, such as Polylactic acid (PLA) indicated in red, Polyethylene (PE) in yellow, Polyethylene terephthalate (PET) in green, and cellulose represented by blue areas.

FTIR microscopy  imaging of a teabag.

The FTIR imaging data not only shows that all relevant components are present but also that their distribution within the sample is optimal. This batch of tea bags would certainly not disintegrate in the cup!


In conclusion, FTIR microscopy proves to be an invaluable tool for quality checking teabag seals. Its swift and accurate analysis allows for the verification of essential components and their proper distribution, ensuring optimal bonding. By employing FTIR microscopy, manufacturers can identify and address any issues with adhesive seals, ultimately guaranteeing the integrity of teabags and providing consumers with a more reliable and enjoyable tea-drinking experience.

In case you are more interested in the microplastics issue, we recommend reading this blog entry: