Cooked Soil

Dr. Darren Williams and Ethan Debrosky, Sam Houston State University
And
Ed Kanegsberg and Barbara Kanegsberg BFK Solutions LLC

If you put a few drops of a water-soluble metalworking fluid on a metal surface, it wipes right off. After machining, removing residue of that same oil often requires aggressive cleaning. Why? Because heat, force, and time can change the chemical nature of soils. As part of planning the upcoming Product Quality Cleaning Workshop (scheduled May 13 – 14, 2020), we cooked metalworking fluids. In general, the fluids turned from clear to amber and became sticky. Should you care? Yes! Because we also demonstrated chemical changes. The implications will help you to achieve more effective, profitable critical cleaning processes.

Infrared Fingerprints
FTIR (Fourier Transform Infrared Spectroscopy) is useful in looking at individual organic chemicals and also for looking at changes in mixtures of organic chemicals. In this illustration, we compared the FTIR fingerprints of a metalworking fluid before and after heating.

The fingerprint of the original metalworking fluid is shown at the top (in red). Moving left to right, there are big peaks in the area of about 2900 to 2700 cm-1 with a few little hills starting at about 1800 cm-1.

The infrared fingerprint of the metalworking fluid is very different – and more complex. Look at the lower infrared fingerprint (in blue). Moving left to right, the fingerprint of the cooked metalworking fluid shows peaks at about 2900 – 2700 cm-1. In addition, after cooking there is a new mountain range starting at 1800 cm-1; in this range, we are seeing sort of a “smear,” not distinct peaks. This “smeary” area is what is often found with a mixture of lots of different chemicals.

Sugar, caramel, and implications for cleaning
Why will this matter for critical cleaning? Sugar plus heat results in caramel. Sugar is not complex. Caramel contains thousands of compounds. Caramel has been studied extensively, probably because it is more fun than metalworking fluid. Will cooked metalworking fluid or fluid after machining be more difficult to remove from a surface? Which is easier to remove from a child – sugar or caramel?

About FTIR; Using FTIR
Think of the atoms in a molecule bonded to one another by springs. Each bonded pair vibrates at a characteristic frequency. Collectively, all the atomic vibrations give that molecule a “fingerprint”. An FTIR scan depicts the amplitudes of the various molecular vibrations in the sample on a frequency axis. If there is only one kind of molecule, the fingerprint should be relatively simple. But when many compounds are present, the picture gets muddy.  Based on these FTIR fingerprints, we can’t identify all of the compounds. That would take years of study and the use of complex separation and analytical techniques. It would be more information than we need.

In industry, an analyst might keep FTIR records as part of incoming inspection of critical process fluids. If there is a production problem, a change in the FTIR fingerprint of the critical process fluid tends to indicate a change in the process fluid. In most cases, it would not be necessary to identify all the changes in terms of specific molecules. Just the changes in the FTIR would provide ammunition for complaining to the supplier, overcoming assertions that nothing was changed, and then getting the problem fixed.

References:

Epoxies and Caramel, Clean Source, November 2015.

https://bfksolutions.com/epoxies-and-caramel/

Introduction to FTIR

https://www.thermofisher.com/us/en/home/industrial/spectroscopy-elemental-isotope-analysis/spectroscopy-elemental-isotope-analysis-learning-center/molecular-spectroscopy-information/ftir-information/ftir-basics.html

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