Additives in polymer films perform a plethora of tasks.
This is our sample, one of four raw polymer films taken straight from the production line.
To prepare them for a micro FT-IR measurement, we took the four samples, each with different amount
of UV absorber, cut them into thin strips and mounted them on the microscopy sample holder.
This sample holder is then inserted into the LUMOS II ...
… and a visual overview image of the entire sample area captured for reference.
From left to right, we have films with 0%, 1%,
2.1% and 3.5% of UV absorber content - so we would expect,
that the FT-IR signals get stronger from left to right. Let's put that assumption to the test.
To verify these values qualitatively,
we set 4 to 5 measurement points on each film by clicking on the regions of interest. If needed,
the measurement points can be adjusted after placing them.
We enter the name of the sample and start the measurement.
The system then automatically records the FT-IR spectra at the respective positions.
Due to the sample thickness, the C-H bands of the base polymer pass into
total IR absorption. However, this is not a problem because these bands do not
interfere with the comparatively small signal of the UV absorber.
After having normalized all spectra to equalize any layer thickness offset,
we can integrate the frequency range of the UV absorber peak and view the result.
The scale on the right provides information about the relative intensity. White or red
means a high relative concentration, blue or green a low concentration.
As expected, from left to right, the concentration increases, so far so good.
However, we can do much more with IR microscopy. Assuming that the reference
values given for each film are correct, we can use them to build a method that quantifies the
UV absorber content of any polymer film within the same concentration range.
First, we create an average spectrum from the measurement points of each film ...
... then we take the averaged spectra and enter
the respective UV absorber percentage for each sample …
... select the appropriate frequency range in the
IR spectrum corresponding to the UV absorber content ...
... and save the method to our hard drive.
The program, OPUS, now displays the calibration curve and an acceptable correlation coefficient
of about 0.99. That's about it! Now we can apply the method to our measurement.
On the right side, the scale has now changed, and the values now directly
show the UV absorber percentages. The colors of the measurement points also correspond
to this. Now the method allows us to assess the content of any polymeric film at a single glance.
But if we combine the method with focal plane array imaging it can do even more for us.
To demonstrate, we defined an area of about 3.2 x 3.2 mm on one of the polymer films. Again,
the system automatically collects the data, and when we apply our previously created method,
we can quantify the distribution of UV absorber in the material in one sweep. In this case,
the content doesn’t change too much throughout the film and remains about 3.5 percent.
However, FT-IR imaging reveals that the production process has left fine "streaks" or "lines" with
slightly lower concentration in the material. This is exactly the type of information about
a sample that can provide decisive impulses for process optimization or troubleshooting,
making FT-IR a mighty tool for quality control and development of polymer materials.
Thanks for watching and for more information, check out the video description