Title:

Analyzing Paint Samples That Have Been Exposed to Heat with the ATR-FTIR

Spectrophotometer

Author:

Shubhi Singh

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Abstract:

The aim of this work is to test whether the pigmentation of a particular brand of paint

significantly changes the way that it degrades when exposed to various amounts of heat as

measured by FTIR. In this experiment, I used five different colors of the Behr Ultra Exterior Flat

Matte brand paint: Poppy Seed (dark grey), Firecracker (red), Dark Cobalt Blue (blue), Honey

Locust (yellow), and Coastal Beige (white). Tiles holding samples of these paints were heated

for an hour at various temperatures ranging from room temperature to around 500°C. The

average spectra of each color at each temperature was then calculated and used for comparison.

The study concluded that although the pigmentation of the paint appeared to have no effect on

the way that the paint samples degraded, there were notable changes in the spectra and physical

aspects of the paint that could still be used to identify to what degree a paint sample had been

burning. For instance, a distinctive lack of peaks in the average spectra of all five colors of paint

after they had been heated for an hour at at least 300°C is a clear temperature marker that could

prove useful in in-field applications. Also, all of the paint samples heated at 300°C experienced

browning upon the surface to some degree. Similarly, the pigmentation of each paint sample

bleached to a lighter color after being heated for an hour at 500°C. The paint samples also

became powdery in texture regardless of color after being heated for an hour at 400°C or higher.

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Introduction:

Household fires and cases of arson are unfortunately very common throughout the world.

Often times, it is very hard for response teams to distinguish the exact cause of a fire or to what

temperature it has been burning. If forensic scientists gained information on important

temperature markers that different types of paint produced as they burned, they may soon find a

solution to this problem. I have tested several different colors of a brand of exterior home paint

in order to determine whether or not the pigmentation of the paint outside the house affects how

the paint burns. I hope to find information on how the pigment of paint affects the way that it

will react to different temperatures, which can then be later utilized to help find a more reliable

way of determining at what temperature a fire has been burning from a small sample of paint.

Methods and Materials:

Sample Prep:

Paint samples and small (2x2 in.) ceramic tiles were obtained from Home Depot. The

paint samples were of five different colors of the Behr Ultra Exterior Flat Matte brand: Poppy

Seed (dark grey), Firecracker (red), Dark Cobalt Blue (blue), Honey Locust (yellow), and

Coastal Beige (white). The paint was then applied to the ceramic tiles in thin layers, with each

color painted once onto six different tiles. One tile of each color was then designated to be heated

for a certain amount of time at 100°C intervals (ex. one tile of each color, five tiles total, would

be heated at 100°C, another five would be heated at 200°C, and so on until 500°C) Each tile was

heated for one hour. A separate group of five tiles, one of each color, was left at room

temperature and used as a control group. The temperature of the paint during heating was

measured by a Traceable Dual Laser Thermometer bought from Fisher Science Education. Each

tile was then used to generate an average ATR-FTIR spectrum, which would be compared

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afterwards to other tiles of that respective color that were heated at different °C. The paint on the

tiles was scraped off using a metal scoopula from Fisher Scientific, and transferred onto the

FTIR in small samples.

It should be noted that the oven in our laboratory did not reach temperatures higher than

270°C, so the tiles that were designated to be heated at 300°C or higher were heated over a

Bunsen burner. As a result, all temperature measurements are approximated for 300°C and above

and certain tiles may have been unevenly heated.

Name of Paint Brand/Type of Paint Resin Observed/Stated Color

Poppy Seed Behr UltraExterior Flat Matte

Acrylic Polymer Dark Grey

Firecracker Behr UltraExterior Flat Matte

Acrylic Polymer Red

Dark Cobalt Behr UltraExterior Flat Matte

Acrylic Polymer Blue

Honey Locust Behr UltraExterior Flat Matte

Acrylic Polymer Yellow

Coastal Beige Behr UltraExterior Flat Matte

Acrylic Polymer Off-White

Table 1: Brand of Paint and Color

FTIR Setup:

No. of Scans: 64

Resolution: 8

Data Spacing: 3.857 cm–1

Final Format: Absorbance

Correction: None

Parameter Value

Detector DTGS KBr

Beamsplitter KBr

4

Accessory Smart Golden GlobeTable 2: FTIR Setup

Recommended Range 4000-650 limits

Gain: 8 Autogain

Optical Velocity .6329

Aperture 100Table 3: FTIR Setup (2)

Analysis:

Each of the six samples of blue paint was heated for an hour on a piece of ceramic tile at

varying temperatures. One sample was left at room temperature (26°C). Another was heated at

100°C for an hour, the next at 200°C, and so on for 300°C, 400°C, and 500°C. Each sample was

then used to create an average spectrum that would later be used to compare the paint at varying

temperatures. When analyzed at room temperature and after being heated at 100°C for an hour,

the average spectra of the blue paint consistently shows peaks around 3693.00 cm−1, as well as at

2952.00 cm−1, 1726.00 cm−1, 1448.00 cm−1, and 1090.00 cm−1 (fig.1). The peak at 3693.00

cm−1 signifies hydroxyl bonds. The peaks at both 2952.00 cm−1 and 1448 cm−1 both are

indicators of stretching or bending in C-H bonds within the alkanes of the blue paint. The peak at

1726 cm−1 represents C=O stretching within α or β–unsaturated esters. The peak seen in the

spectra around 1090.00 cm−1 represents C-N stretching in aliphatic amines within the paint.

There was no noticeable color change or difference in physical texture of the blue paint after

being heated at 100°C. This shows that the blue paint is, for the most part, unaffected by being

heated for an hour at 100°C. After being heated at 200°C for an hour, the average spectra of the

blue paint displays a slight shift in the location of the peaks. A new peak has also become visible

at 982.49 cm−1, possibly signifying a stretch in the C–N bonds of aliphatic amines (fig.2). After

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being heated for an hour at 300°C, the average spectra of the blue paint shows a significant

change. Two peaks have disappeared, one in the 1740-1720 cm−1 range, and the other in the

1470-1450 cm−1 range, and a new peak appears. The peak in the 1740-1720 cm−1 range

represents bends in =C–H bonds of alkenes, and the peak in the 1470-1450 cm−1 range signifies

C-H bends in alkanes (fig.3). The new peak is located at 686.51 cm−1, representing C-H bends in

alkynes of the paint. It is at this temperature that the color and texture of the blue paint begins to

change for the first time. The color of the blue paint begins to acquire a brown-green color, and

the paint itself becomes a coarse powder as it is scraped off the tile for analysis. The paint

samples that were analyzed after being heated at 400°C for an hour have an average spectrum

that stays relatively consistent with the average spectra of the blue paint samples heated at 300°C

(fig.4). The pigmentation of the blue paint, however, bleaches to a slightly off-white color. The

paint itself is now also able to be scraped off the tile in the form of a fine powder after being

heated for an hour at 400°C. After being heated for an hour at 500°C, the average spectra of the

blue paint finally loses the peak in the 3690 cm−1 region. The average spectrum retains the peaks

around 973.00 cm−1 and 690.00 cm−1 (fig.5). These peaks are representative of =C-H bends

within alkenes and bending within the C-H bonds of alkynes in the paint sample, respectively.

(fig.1 - average spectra of blue paint at room temp (blue) + 100°C (red))

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(fig.2 - average spectra of blue paint at 200°C (green) + room temperature (red))

(fig.3 - average spectra of blue paint at 300°C (green) + 200°C (red))

(fig.4 - average spectra of blue paint at 400°C (yellow) + 300°C (red))

(fig.5 - average spectra of blue paint at 500°C (blue) + room temperature (red))

Six samples of grey paint were painted onto ceramic tiles and heated for an hour at

varying temperatures up to approximately 500°C. One sample of paint was left at room

temperature, the next was exposed to 100°C for an hour, the next at 200°C for an hour, and so on

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for 300°C, 400°C, and 500°C. The average spectra of each sample was then created in order to

compare the six samples with one another. When scanned on the FTIR at both room temperature

and after being heated for an hour at 100°C, the grey paint consistently showed peaks around

3693.00 cm−1, 2952.00 cm−1, 1725.98 cm−1, 1448.00 cm−1, 1382.00 cm−1, and 1090.00 cm−1.

The peaks seen in the average spectra of the grey paint are incredibly similar to those found in

the blue paint. The peak at 3693.00 cm−1 represents hydroxyl bonds. The peaks at both 2952.00

cm−1 and 1448 cm−1 show stretching or bending in C-H bonds within the alkanes of the grey

paint. The peak at 1725.98 cm−1 represents C=O stretching within α or β–unsaturated esters. The

peak seen in the average spectra of the grey paint at 1382.00 cm−1 is representative of C-H

alkanes. The peak seen in the spectra around 1090.00 cm−1 represents C-N stretching in aliphatic

amines within the grey paint. This shows that the grey paint is more or less unaffected by being

heated at 100°C for an hour. There was also no discernable difference in color or texture of the

grey paint before and after heating at 100°C. At 100°C, however, a peak around 1382.75 cm−1 is

also found (fig.6). At 200°C the average spectra of the grey paint, for the most part, remained

consistent with the averages of the room temperature paint and the grey paint that had been

heated at 100°C. The peak at 1090.00 cm−1 (representing C-N stretching within aliphatic amines)

which is seen in both the room temperature spectra and the 100°C spectra, however, is not seen

in the average spectra of the paint heated at 200°C. A peak at 981.82 cm−1 is visible instead

(fig.7). This peak at 981.82 signifies =C-H bending within an alkene group. A noticeable

difference is seen between the average spectra of the grey paint heated at 300°C and the average

spectra of the grey paint heated at 200°C (fig.8). Most of the peaks have been lost in the average

spectra of 300°C. The two remaining peaks are at 3693.99 cm−1 and 685.73 cm−1. The peak at

685.73 cm−1 represents C-H bending inside of the alkynes of the paint. The color of the grey

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paint also began to turn brown after being heated for an hour. The average spectra of the grey

paint after being heated at 400°C is nearly identical to the average spectra of the grey paint

heated for an hour at 300°C (fig.9). The paint became dark brown in color and very powdery in

texture after being heated for an hour at 400°C. The average spectra of the sample of grey paint

heated at 500°C for an hour loses the peak in the 3690 cm−1 area and only a peak at 692.21 cm−1

is clearly visible (fig.10). The color of the grey paint in this sample became bleached to a very

light grey color, and the paint developed a powdery texture when scraped off the tile.

(fig.6 - average spectra of grey paint at room temperature (green) and 100°C (red))

(fig.7 - average spectra of grey paint at 200°C (green), 100°C (red), and room temperature (light blue))

(fig.8 - average spectra of grey paint at 300°C (blue) and 200°C (red))

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(fig.9 - average spectra of grey paint at 400°C (pink) and 300°C (red))

(fig.10 - average spectra of grey paint at 500°C (blue) and room temperature (red))

Wavelength of Peaks Bond Type

3640–3610 cm−1

3000–2850 cm−1

1730–1715 cm−1

1470–1450 cm−1

1250–1020 cm−1

1370–1350 cm−1

1000–650 cm−1

Hydroxyl bonds

C-H stretch within alkanes

C=O stretch within α, β–unsaturated esters

C-H bending within alkanes

C-N stretching within aliphatic amines

C-H rock within alkanes

=C–H bending within alkenesTable 4: Selected wavelengths and their bonds/functional groups as taken from the University of Colorado at Boulder (Table Of Characteristic IR

Absorptions)

Six samples of red paint were painted onto ceramic tiles and heated for an hour at

different temperatures. One sample was left at room temperature and served as a control group;

the rest were used as experimental groups. The second sample was heated for an hour at 200°C,

the third was heated for an hour at 300°C, and so forth for 400°C and 500°C. The average

spectra of the red paint appears to be nearly the same at room temperature and after being heated

for an hour at 100°C. There are consistent peaks around 3693.00 cm−1, 2952.77 cm−1, 1726.00

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cm−1, 1642.00 cm−1, 1604.00 cm−1, 1448.00 cm−1, 1383.00 cm−1, 1140.00 cm−1, 1090.00 cm−1,

754.00 cm−1, and 690.00 cm−1(fig.11). See Table 5 for peak analysis of selected wavelengths.

The average spectrum of the red paint is very close to those of the grey and blue paint. The peaks

at both 2952.00 cm−1 and 1448 cm−1 show stretching and bending in C-H bonds within the

alkanes of the grey paint. The peaks at 1642.70 cm−1, as well as the peak at 1604.00 cm−1, show

an N-H bend within the amines of the red paint. The peak seen in the average spectra of the red

paint at 1383.00 cm−1 is representative of a C-H rock within an alkane functional group. The

average spectra of the red paint that was heated at 200°C is also very similar to the average

spectra of the red paint at 100°C and 200°C (fig.11). There is no noticeable difference in the

color or texture of any of the three samples of paint. The paint samples that were heated at 300°C

for an hour, however, generated an average spectrum that is significantly different from those of

the lower temperatures. In the average spectra of the red paint heated at 300°C, all but two of the

peaks have disappeared (fig.12). The two remaining peaks are located around 3694.74 cm−1 and

692.09 cm−1. The red paint also begins to turn brown on the surface after being heated for an

hour at 300°C. The spectra remains consistent at 400°C as well (fig.13), but at 500°C the peaks

have shifted. There is a peak visible at 3401.21 cm−1 and 719.65 cm−1 (fig.14). After being

heated for an hour at 400°C, the red paint becomes a dark brown color and develops a powdery

texture. After being heated for the same amount of time at 500°C, the red paint bleaches to an

orange color and becomes very powdery in texture.

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(fig.11 - average spectra of red paint at room temperature (purple), 100°C (green), and 200°C (red))

(fig.12 - average spectra of red paint at 300°C (green) and 200°C (red))

(fig.13 - average spectra of red paint at 400°C (yellow) and 300°C (red))

(fig.14 - average spectra of red paint at 500°C (green) and 400°C (red))

Six samples of white paint were painted onto ceramic tiles and heated for an hour at

different temperatures. One of the samples of white paint was left at room temperature, while the

rest were heated at either 100°C, 200°C, 300°C, 400°C, 0r 500°C. The average spectra of the

white paint samples that were heated at 100°C and 200°C are very similar to the average spectra

of the white paint that was left at room temperature (fig.15). There are characteristic peaks in the

3340.00 cm−1 range, as well as the 2940.00 cm−1, 1724.00 cm−1, 1447.00 cm−1, 1382.00 cm−1,

and 986.00 cm−1 ranges. See Table 5 for peak analysis of selected wavelengths. The peak seen in

the average spectra of the white paint at 1382.00 cm−1 is representative of C-H alkanes. The

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white paint had no discernable changes in color or texture as it was heated at 100°C and 200°C.

After being heated for an hour at 300°C, however, the average spectrum is drastically different

than those of the preceding temperatures. There are only three significant remaining peaks in the

average spectra of the white paint that was heated at 300°C for an hour. These peaks are at

3374.07 cm−1, 1619.09 cm−1, and 994.92 cm−1 (fig.16). After being heated at this temperature,

the white paint begins to turn brown on the surface and has a coarse, powdery texture when

scraped off the tile. After being heated for an hour at 400°C, most of the peaks in the average

spectra of the white paint disappear (fig.17). There is a singular remaining peak around 996.85

cm−1 which appears in the average spectra of the paint heated at 500°C as well (fig.18). The

white paint does not turn brown after being heated for an hour at 400°C, but after being heated

for an hour at 500°C the color yellows slightly. The texture of the powder also turns very

powdery at both 400°C and 500°C.

(fig.15 - average spectra of white paint at room temperature (green), 100°C (light blue), and 200°C (red))

(fig.16 - average spectra of white paint at 300°C (blue) and room temperature (red))

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(fig.17 - average spectra of white paint at 400°C (pink), 300°C (green), and room temperature (red))

(fig.18 - average spectra of white paint at 500°C (green) and 400°C (red))

There were six samples of yellow paint painted onto ceramic tiles. Five of these six

samples were then heated at different temperatures between 100°C and 500°C. One of these

samples was left at room temperature and served as a control group for comparison. The average

spectra of the yellow paint that was left at room temperature is nearly identical to the average

spectra of the paint heated for an hour at 100°C. There are distinct peaks around 2940 cm−1,

1725.00 cm−1, 1672.00 cm−1, 1515.00 cm−1, 1445.00 cm−1, 1383.00 cm−1, 1338.00 cm−1,

1243.00 cm−1, 1139.00 cm−1, and 984.00 cm−1. See Table 5 for peak analysis of selected

wavelengths. The peak at 1672.00 cm−1 is representative of -C=C- stretching within alkene

functional groups. The peaks around 1515.00 cm−1 and 1338.00 cm−1 show that there is

asymmetrical stretching within the N-O bonds of nitro compounds. The peak seen in the average

spectra of the yellow paint at 1383.00 cm−1 is representative of a C-H rock within alkanes. The

spectra of the yellow paint heated at 200°C is also very similar to the average 100°C and room

temperature spectra, however there is a peak at 1336.92 cm−1, still representing stretching within

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the bonds of nitro compounds (fig.19). There is no noticeable change in color or texture of the

yellow paint at any of these three temperatures. The average spectra collected from the paint that

was heated for an hour at 300°C is very different from the average spectra of the yellow paint at

room temperature, 100°C, or 200°C. The only peaks remaining in the average spectra of the

yellow paint are at 3378.35 cm−1, 1612.37 cm−1, and 983.17 cm−1 (fig.20). After being heated

for an hour at 300°C, the surface of the yellow paint begins to turn brown, and the paint becomes

slightly powdery. The average spectra of the yellow paint has only one remaining peak at both

400°C and 500°C. This peak is around 985.86 cm−1 (fig.21). At 400°C the yellow paint begins to

develop a brown-pink color, and is powdery when scraped off the tile. At 500°C the yellow paint

acquires a light brown-pink color and becomes very fine powder as it is scraped off the tile for

analysis.

(fig.19 - average spectra of yellow paint at room temperature (yellow), 100°C (blue), 200°C (red))

(fig.20 - average spectra of yellow paint at 300°C (pink) and room temperature (red))

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(fig.21 - average spectra of yellow paint at 400°C (purple) and 500°C (red))

Results and Discussion:

It appears, for the most part, that all of the paint samples degraded in very similar

fashions, despite any differences in pigmentation. Each color had an average spectrum at room

temperature that was typically identical to the average spectra of the color after being heated for

an hour at 100°C and 200°C. There was also no noticeable change in color or texture of any

color paint after being heated for an hour at 100°C or 200°C. Additionally, in all the colors of

paint there was a significant loss of peaks in the average spectra after being heated for an hour at

300°C (fig.3,8,12,16,20). All samples of paint began to turn brown after being heated for an hour

at 300°C, as well. In some samples, the average spectra of the paint after being heated for an

hour at 400°C were nearly identical to the average spectra of the paint that was heated for an

hour at 300°C. These samples were the blue, grey, and red colored paint. The other two colors,

white and yellow, had average spectra after being heated for an hour at 400°C that exhibited a

loss of multiple peaks in comparison to the average spectra of the paint heated at 300°C. All but

two colors of paint turned brown after being heated for an hour at 400°C; the blue and the white

paint either lightened in color or did not change. After being heated at 400°C, all samples of

paint also began to adopt a powdery texture as they were scraped off the tile for analysis, despite

any variation in their pigmentation. After being heated for an hour at 500°C, the average spectra

of all five colors typically matched their average spectra collected at 400°C. The colors of all the

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samples of paint bleached to a lighter color after being heated for an hour at 500°C, and all the

samples of paint had a very powdery texture when they were scraped off their tiles for analysis.

(fig.22 - average spectra of blue paint (dark blue), yellow paint (purple), red paint (red), grey paint (dark blue), and white paint (green) at room

temperature)

(fig.23 - average spectra of blue paint (blue), white paint (green), grey paint (purple), red paint (dark blue), and yellow paint (red) after being

heated for an hour at 100C)

(fig.24 - average spectra of blue paint (green), red paint (yellow), yellow paint (red), grey paint (light blue), white paint (dark blue) after being

heated for an hour at 200C)

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(fig.25 - average spectra of blue paint (pink), grey paint (dark green), red paint (purple), white paint (light green), yellow paint (red) after being

heated for an hour at 300C)

(fig.26 - average spectra of blue paint (pink), grey paint (dark green), red paint (red), white paint (light green), yellow paint (red) after being

heated for an hour at 400C)

(fig.27 - average spectra of blue paint (light green), white paint (dark blue), yellow paint (red), red paint (yellow), and grey paint (light blue) after

being heated for an hour at 500C)

Conclusion and Topics for Further Research:

In conclusion, it does not appear that the color or pigmentation of the paint samples

significantly affect the way that they degrade when exposed to various amounts of heat.

However, there are clear parallels throughout all of the colors of paint in the way that they

degrade after being heated. For instance, 300°C is a clear temperature marker at which all

samples of paint, regardless of their color, lose multiple peaks in their average spectra.

Additionally, at 400°C and 500°C, the texture of the paint for all five colors becomes powdery as

it is scraped off the tiles, as opposed to peeling off in small pieces. Therefore, despite the

pigmentation not appearing to have any unique effects on the way that the paint samples

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degraded, it is still possible to tell approximately what temperature the paint samples were

burned at through FTIR analysis.

There are many opportunities to expand upon this topic of research. For instance, due to

the limitations of the lab equipment I was able to use, I was unable to heat and therefore analyze

the spectra of paint heated to temperatures higher than 500°C. Also, I performed my experiment

using multiple colors of one type of paint: Behr Ultra Exterior Flat Matte. If this experiment was

reconstructed using paint samples from multiple types of paint; for example, interior paint as

opposed to exterior, glossy paint as opposed to matte, or another brand of paint as opposed to

Behr, the results may differ from what I have concluded in this experiment.

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MOLECULAR SPECTROSCOPIC METHODS AND STATISTICAL DATA ANALYSES

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Meilunas, R., Bentsen, J., & Steinberg, A. (1990). Analysis of Aged Paint Binders by FTIR

Spectroscopy. Studies In Conservation, 35(1), 33. http://dx.doi.org/10.2307/1506280

Rein, A., Higgins, F., & Leung, P. (2015). Handheld FTIR analysis for the conservation and

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4200_FTIR_Art_5990-8739.pdf

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Scientific Working Group on Materials Analysis, 2009. Web. 19 Aug. 2015.

Standard Guide for Using Infrared Spectroscopy in Forensic Paint Examinations. (2009)

(1st ed., pp. 4-7, 16-17). Retrieved from

http://www.swgmat.org/SWGMAT%20infrared%20spectroscopy09-09-2004.pdf

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http://orgchem.colorado.edu/Spectroscopy/specttutor/irchart.pdf

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