VOLUME 14 ISSUE 7

WHAT’S HAPPENING AT MISSOURI S&T (FORMERLY UMR):

SHORT COURSE DATES

We will be offering "Introduction to Paint Formulation" May 20-24 (Spring 2019). This course is intended to give the person a fundamental knowledge of how to approach a starting formulation and troubleshoot it. This course involves both lecture and laboratory work.

We are also offering a new course, "Coatings Composition and Properties for Sales and Marketing Personnel" March 25-27 (Spring 2019). This course is designed for those in the industry who buy and/or sell raw materials into the coatings market, as well as those who buy or sell coatings or simply use coatings.  The course is intended to help the newer person in the field gain a better understanding of the science behind paint. For more information, including course times and fees, click the course name above.

For more information see our web site at http://coatings.mst.edu and to register contact us at mstformulation@mst.edu or call 573-341-4419. **These courses are held on the Rolla Campus**

ONLINE SHORT COURSE

We are offering "Introduction to the Coating Systems" online short course. This course is targeted for automotive and aviation type OEM companies. This self-paced seminar will cover the painting system from the composition of paints to the evaluation of the dry film.  The pigments, resin, solvents and additives will be discussed including their influence on the coatings performance.  Color measurement, surface profile, and other evaluation criteria will be related to composition.  The importance of surface preparation and other manufacturing criteria will show the system complexity and each step's importance.

We are offering "Surface Defects: Elimination from Human and Process Contaminants" online short course. This course addresses many of the issues in prevention and minimization of defects. The course covers the defects caused by the coatings process, as well as human issues, including personal care product causes. Several of the surface defects are discussed – from basic principles and real world automotive and aircraft examples. The highly practical approach of this course will greatly aid the personnel involved in the painting operation to reduce and systematically approach issues.

EMPLOYMENT TAB

There are no current job openings available. Anyone wanting to have job opening listed, please contact us at (573) 341-4419 or e-mail: mstformulation@mst.edu . You can also write to us at Missouri S&T Coatings Institute, BOM #2, 651 W. 13th St., Rolla, MO 65409-1020. Our web site is http://coatings.mst.edu

TECHNICAL INSIGHTS ON COATINGS SCIENCE

PYROLYSIS – GC IN COATING ANALYSIS

Ashish Zore, Missouri University of Science and Technology

Paint is a complex formulation consisting of polymeric materials compounded with colored or opaque fillers and additives. This makes them difficult to analyze especially when dry. Gas chromatography may seem to be an unlikely tool for the analysis of such materials, however when combined with pyrolysis as a sample introduction technique, they have become a significant tool for paint deformulation. Using a pyrolyzer unit we can fragment the polymers used in the coating system to produce molecules small enough to be compatible with gas chromatography-mass spectrometry (GC-MS) while still being characteristic of the original material. Natural polymers, like plant resins and drying oils, as well as synthetic polymers like polyesters, acrylics and polyurethanes, have been extensively studied, and may be easily differentiated using this technique [1]. This technique has been employed by the FBI and most crime labs for the identification and “fingerprinting” of the paint residue at crime scenes [2][3].

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Scheme 1. Schematic diagram of pyrolysis-GC system [4].

Pyrolysis:

Pyrolysis is the thermal fragmentation of a substance in an inert atmosphere. Larger molecules are reduced into smaller molecules through the breaking of bonds via the use of thermal energy. The use of an inert atmosphere and strict control of temperature and heating time, macromolecular materials can be reduced to smaller molecules in a reproducible fashion. These smaller molecules produced through the action of pyrolysis will form a pattern of separated fragments which when analyzed using a separation technique like GC will provide information about the original molecule. This makes it possible to obtain structural information about high molecular weight compounds. There are three different types of instrumentation available for performing analytical pyrolysis: 1) resistively heated pyrolyzers, 2) Curie point pyrolyzers and 3) furnace pyrolyzers, all of them have their own advantages and disadvantages [5].

It is important to pyrolyze the sample at a set temperature and at a reproducible heating rate for a specific duration to ensure reproducibility of the polymer fragmentation in multiple runs. The pyrolysis temperature should allow complete pyrolysis without causing excessive bond breakage. Excessive fragmentation may destroy discriminating higher molecular weight pyrolyzates and also make the resulting pyrogram very difficult to interpret. In order to check for complete pyrolysis one might re-run the system at a higher temperature with the original sample in place after the initial run has been completed. If peaks are observed, pyrolysis was not complete and a higher temperature has to be used [5]. This process is repeat until complete pyrolysis is reached. The typical temperature for pyrolysis 400-800 °C [4].

Gas Chromatography:

The typical gas chromatograph, as shown in scheme 1, consists of an inlet for sample introduction (in this case, a pyrolyzer port), a temperature controlled oven, an analytical column(s), and a detector(s).

The inlet temperature should be high enough to prevent condensation of pyrolysis fragments but not so high that fragments undergo secondary reactions or column degradation can occur. Typical inlet temperatures range from 200 to 300°C. The choice of oven parameters is critical for the separation of pyrolyzates. Temperature ramps are often utilized due to the wide range of fragment size that are formed by pyrolysis [5].

The most commonly used columns for general Pyrolysis-GC applications are poly-dimethylsiloxane based capillary columns of at least 15 meters in length. The two most common detectors for use with Pyrolysis-GC are the flame ionization detector (FID) and mass spectrometer (MS). The flame ionization detector is capable of detecting a broad range of combustible pyrolyzates while being relatively inexpensive. It also has a large linear dynamic range and can therefore handle a wide range of sample sizes. Mass spectral analysis can be used to extract specific information from the data. Classes of compounds can be selectively viewed and searches for specific compounds are possible through the use of MS [6][7].

Use [5]:

1. Identifications of compounds can be accomplished by comparison to known samples or to a mass spectral library.
2. Single component additives (e.g., plasticizers) can be identified via mass spectral library searches.

Fig 1. Pyrogram of an acrylic copolymer based paint. The main monomers are methyl methacrylate (MMA) and butyl acrylate (BA) [4].

1. Pyrograms can be compared side-by-side or using overlays. For instance, if a customer complaints about a paint sample then it can be verified against the actual paint sample by comparing their pyrograms side by side. Any anomalies or impurities should be detected by this technique. Important factors that one should consider when comparing pyrograms include retention time, shape, relative intensity, or presence/absence of peaks. Pyrograms generated can be used to compare questioned and known paint samples and to identify its components. Many studies on different types of paint and different chemistries have already been done [1].
2. The peaks labeled “Fingerprint fragments” in Fig 1 can be very useful in product quality control analyses.

References:

1. 1.     Paints And Coatings: Pyrolysis: Gas Chromatography, T.P. Wampler, CDS Analytical Inc., Oxford, PA, USA.
2. 2.     Diana M. Wright, Ph.D.; Maureen J. Bradley, Ph.D.; and Andria Hobbs Mehltretter, M.S., J Forensic Sci, March 2013, Vol. 58, No. 2.
3. 3.     J. Zieba-Palus et al., J. Chromatogr. A 1179 (2008) 41–46
4. 4.     Gas Chromatography in Coating Analysis, Francis Acholla, JCT CoatingsTech, March 2005.
5. 5.     SWGMAT: Using Pyrolysis in Forensic Paint Exam, JASTEE, Vol. 5, Issue 1.
6. 6.     Spectral Database for Organic Compounds (SDBS), National Institute of Advanced Industrial Science and Technology (AIST) in Japan. (https://sdbs.db.aist.go.jp)
7. 7.     Mass Spectra of Organic Compounds (SpecData) – Software (www.wiley.com), Alexander Yarkov.