CPGAN #040 37 Rubber Duck Deformulation · CPGAN #040 37 Rubber Duck Deformulation ©Cambridge...

CPGAN #040

37 Rubber Duck Deformulation

©Cambridge Polymer Group, Inc.(2016). All rights reserved

56 Roland Street, Suite 310 ∙ Boston, MA 02129 ∙ Office (617) 629-4400 ∙ Fax (617) 629-9100 ∙ [email protected] ∙

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Summary

Poly(vinyl chloride) (PVC) is a popular polymer that achieves much of its popularity as a result of the wide

range of flexibilities that can be gained with plasticizers. In this application note, we examine the

properties of a common PVC blend before and after accelerated aging, and under extreme environmental

conditions, and review the chemical changes within the material. The source of the PVC blend was from a

rubber duck.

Impact testing indicated no changes after aging, with only the sub-ambient (liquid nitrogen-cooled) sample

breaking during the test. An examination of the fracture surfaces of the sub-ambient impact tested duck,

along with manually notched and torn aged and unaged ducks at room temperature, showed typical brittle

fracture surfaces in the sub-ambient impact testing, and the same ductile tear behavior in both aged and

unaged ducks. Extraction analysis with chromatography showed that the ducks contained multiple

plasticizers, namely citrate and phthalate-based plasticizers. One plasticizer in particular was present more

in the aged sample than the unaged sample, although this is likely to be due to inter-duck variability rather

than an aging by-product.

Background

Poly(vinyl chloride) has been in use for over a century. Its water repellency and high flexibility (in some

forms) made it a suitable replacement for natural rubber, and it quickly became a highly used water

repellent coating for fabrics and for wiring insulation. Part of the popularity of this material stems not so

much from the polymer chain itself, but the range of properties that are attainable by judicious

plasticization of the vinyl polymer. By selecting smaller molecules that are compatible with the polymer,

the flexibility of the articles made from this material can be tuned from rigid to floppy, and everywhere in

between. As a go-to material for soft “rubber like” materials, it became the third most widely produced

synthetic polymer (after two of our other favorites, polyethylene and polypropylene). However, recently it

has received unfavorable press related to perceived issues from the plasticizer additives. Here, we review

the chemical composition of one form of plasticized PVC using Fourier transform infrared spectroscopy

(FTIR). We also examined the aging behavior of the material using an ASTM accelerated aging standard

test (F2003) commonly used in the biomedical industry, followed by impact testing the aged and unaged

samples. We examined the fracture surfaces of specimens that were notched and manually fractured, as

well as the impact tested ducks, with scanning electron microscopy (SEM), while also looking for fillers

with energy dispersive spectroscopy (EDS). Lastly, we performed extraction and chromatography

experiments to identify the type of plasticizers used in the PVC and to examine change products due to the

aging process.

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Summary ........................................................................................................................................................ 1

Background.................................................................................................................................................... 1

Samples .......................................................................................................................................................... 2

Procedure and Results ................................................................................................................................... 2

FTIR compositional analysis ................................................................................................................... 2

Accelerated aging per ASTM F2003 ....................................................................................................... 4

Impact testing ........................................................................................................................................... 4

Fracture surface analysis using SEM ..................................................................................................... 5

Extraction, deformulation and aging products using GCMS and LCMS ........................................... 7

Samples

Samples were novelty toys in the shape of rubber ducks.

Procedure and Results

FTIR compositional analysis

Spectra were gathered from three locations on both the aged and unaged duck. The spectra were obtained

from the outside surface, inside surface, and cross-sectional surface of each duck. The sample was placed

under the Varian 610-IR microscope portion of a Varian 640-IR spectrometer, which had been aligned and

calibrated according to CPGSOP0076. The collection parameters are listed below:

Aperture size: 200 µm

Verification: Polystyrene

Number of scans: 32

Purge: Nitrogen

Scan rate: 20 kHz

Slices from each duck were obtained using a clean razor blade for each location. The spectrometer was

equipped with a germanium crystal to perform attenuated total reflectance (ATR). The crystal was placed

on the surface of each sample to scan an area approximately 500 µm in diameter. The resulting spectra

were compared to the Biorad Know-It-All Spectral Database in an attempt to identify the material. The

spectral data base showed the best match for the bulk of the material (cross-section and inside surface) is a

thermoplastic polyester (Figure 1 and Figure 2). The outside surface was best matched to a modified

polyvinyl chloride (Figure 3). This structure is unexpected, with the material anticipated to be a PVC.

Figure 4 through Figure 6 compare the different sample locations for the unaged and aged ducks.

Figure 1: Comparison of unaged cross-section (black line) with best match from the Biorad spectral

library (orange line), a thermoplastic polyester.


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Figure 2: Comparison of unaged inside surface (black line) with best match from the Biorad spectral

library (orange line), a thermoplastic polyester.

Figure 3: Comparison of unaged outer surface (black line) with best match from the Biorad spectral

library (orange line), modified polyvinyl chloride (PVC).

Figure 4: Comparison of unaged (blue) and aged (green) cross-sectional surfaces.


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Figure 5: Comparison of unaged (blue) and aged (purple) inside surfaces.

Figure 6: Comparison of unaged (blue) and aged (teal) outside surfaces.

Accelerated aging per ASTM F2003

One rubber duck was heated to 70 ºC for a duration of two weeks in an oxygen atmosphere (73±1 psi) per

ASTM F2003-02. After aging the duck was stored in a bag for further testing.

Impact testing

Three impact tests were performed on ducks using an Instron/CEAST 9050 impact tester with an 11 J

hammer. Aged and unaged ducks were tenderly folded and mounted into the Izod vice jaws such that the

impact hammer would strike the duck approximately between the eyes. Neither the unaged nor aged ducks

cracked, tore, or appeared otherwise damaged by impact testing. Subsequently, the unaged duck was

doused with liquid nitrogen while mounted in the impact tester vice, then immediately tested with the 11 J

hammer, resulting in shattering of the frozen duck into numerous pieces (see Figure 7).


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Figure 7: Images LN2-cooled duck immediately before (left) and after impact (right).

Fracture surface analysis using SEM

Fracture surfaces were generated manually in the aged and unaged ducks using notching with a razor blade

and pulling opposite sides of the notch in tension to generate tears in the duck. These tears, as well as a

brittle fracture surface created using impact testing the LN2-cooled duck, were examined using SEM. The

LN2 impact specimens (see Figure 8) were characteristic of a brittle fracture. The aged and unaged control

ducks yielded essentially similar images, with a clean region from a razor notch followed by regions of

high deformation in a plastic tearing mode (Figure 9 and Figure 10). There is no evidence of a surface

coating differentiated from the bulk, as would be implied by the FTIR data. This observation is reinforced

by the EDS analysis (Figure 11) which observes chlorine throughout the sample (although it does appear to

suggest relatively less carbon in the bulk, as in on the surfaces

Figure 8: Fracture surface of LN2-cooled duck at 69X run under Extended Pressure mode (no

coating)


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Figure 9: Fracture surface of unaged duck at 81X run under Extended Pressure mode (no coating).

The initial razor blade pre-notch is shown in the bottom of the image.

Figure 10: Fracture surface of aged duck at 81X run under Extended Pressure mode (no coating).

The initial razor blade pre-notch is shown in the bottom of the image.


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Figure 11: EDS map and spectral comparisons of interior and exterior surface and two different

scans of the fracture surface (bulk). Taken using Extended Pressure mode (no coating) on the LN2

fractured sample.

Extraction, deformulation and aging products using GC-MS and LC-MS

Aged and unaged duck samples were cut into the small pieces, weighed into the round bottom flasks and

extracted with boiling isopropanol (IPA) for 6 hours. At the end of extraction, flasks were cooled down to

ambient temperature, IPA was decanted to pre-weighed beakers and dried to a constant weight. The weight

of extracts from each sample constituted approximately 41 %. Dried extracts were reconstituted in IPA to

approximately 1.5 mg/mL concentration and analyzed by gas chromatography with mass spectroscopy

(GC-MS) and liquid chromatography with mass spectroscopy (LC-MS).


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GC-MS analysis was performed on an Agilent 6890/5973 GC-MS system under the following conditions:

Instrument: Agilent 6890 GC

Capillary Column: Phenomenex ZB-5ms, 30 m x 0.25 mm I.D., 0.25 m film thickness

Carrier: Helium, 1.0 mL/min constant flow

Injector: Inlet Temperature: 250 °C

Injection: 1 μL

Mode: Split (5:1 split ratio)

Oven Program: Initial temperature 50 °C, hold 2 min, ramp 10 ºC/min to 315 ºC, hold

10 min at 315 °C

Solvent Delay: No delay

5973 MSD Detector: EI Scan Mode, m/z 30-550

A blank injection of IPA was performed in between each sample. The NIST spectral library database (NIST

MS search 2.0) was used for compound identifications. Mass spectral measurements were performed by

taking the mass spectrum at the apex of each peak and subtracting the mass spectrum at the base of the

peak.

An overlay of total ion chromatogram for aged (black line) and unaged (blue line) duck sample (blue) is

shown in Figure 12 and compounds identified in the extracts of both samples are presented in Table 1.

Compounds detected in significant quantities were plasticizers based on citric acid derivatives (BC and

TBA) and phthalate plasticizers (DEHP and DOTP). Interestingly, TBA and DEHP were detected only in

the extract of an aged sample. Identification of phthalates DEHP and DOTP was confirmed by GC-MS

analysis of reference samples.

Table 1: Compounds identified by GC-MS in the extracts of aged and unaged duck sample.

Retention

time

[min] Compound Formula

Match

factor

CAS # or

NIST # Unaged Aged

15.63

Propanoic acid, 2-methyl-, 1-

(1,1-dimethylethyl)-2-methyl-

1,3-propanediyl ester C16H30O4 716 74381-40-1 + +

18.84 1-Hexadecanol C16H34O 877 36653-82-4 + +

21.47

1-Propene-1,2,3-tricarboxylic

acid, tributyl ester C18H30O6 845 7568-58-3 - +

21.72 Butyl citrate (BC) C18H32O7 918 77-94-1 + +

22.28 Tributyl acetylcitrate (TBA) C20H34O8 929 77-90-7 - +

24.28

Phthalic acid, di(6-methylhept-

2-yl) ester C24H38O4 850 377973 - +

24.66

Bis(2-ethylhexyl) phthalate

(DEHP) C24H38O4 954 117-81-7 - +

26.24 Dioctyl terephthalate (DOTP) C24H38O4 936 6422-86-2 + +


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Figure 12: An overlay of total ion chromatogram for aged (black line) and unaged (blue line) duck

sample (blue). BC and DOTP were detected in the extracts of both samples, but DEHP and TBA

were detected only in the extract of aged sample.

LC-MS analysis was performed using an Agilent 1100 HPLC system equipped with an Agilent G1354A

Quaternary Pump, G1322A Micro Degasser, G1313A Autosampler, G1316 Column Compartment,

G1315A Diode Array Detector (DAD), G1956B MSD, and a Polymer Laboratories 2100 ELSD. The test

conditions were as follows:

Column: Kinetex EVO C18 100Å (150 x 4.6mm)

Mobile Phase: A: Water + 0.1% Formic Acid

B: Methanol + 0.1% Formic Acid

Flow Rate: 0.5 mL/min

Injector: Injection Volume: 10 μL

Temperature: Column Temperature: 40 °C

DAD: Wavelength: 273 nm (Bw 4nm), Reference 360 nm (Bw 80nm)

Peakwidth: >0.01 min

Slit Width: 4 nm

MSD: Detector mode: API-ES

Polarity: Positive

Scan Range: 50-1000 m/z

Fragmenter: 110 V

Gas: 350 °C Nitrogen, 13.0 L/min, 35 psig

VCap: 3500 V

DOTP DEHP TBA

BC


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Mobile Phase Gradient: Time [min] %A %B

0.00 60 40

0.50 60 40

5.00 1 99

30.00 1 99

30.50 60 40

35.00 60 40

A set of plasticizer reference standards was tested under the same conditions as the test samples to evaluate

the performance of the system to separate these compounds and to allow for confirmation of plasticizer

identity based on retention time. Figure 13 shows a mixture of seven plasticizers run at a concentration of

100 ppm in isopropyl alcohol (detection by UV at 273 nm). Note that diisononyl phthalate and diundecyl

phthalate are mixtures of isomers, which are partially separated by the chromatographic conditions used

here, and which partially co-elute with adjacent plasticizers. However, it is possible to separate the

characteristic signals for these compounds by mass spectral detection, specifically by extracting a

characteristic ion (e.g. the hydrogen or sodium adduct of the molecular ion) from the total ion

chromatogram recorded by the mass spectrometer. An example of this process is shown in Figure 14

below.

The MSD chromatogram for the unaged duck sample is shown in Figure 15, and the aged duck sample is

shown in Figure 16. Trace amounts of DEHP were observed in the unaged duck sample, while substantially

more DEHP was observed in the aged duck sample. Similar quantities of DOTP were observed in both

unaged and aged duck samples. This confirms the GC-MS result of substantial DEHP quantities present in

the aged duck only. It is not immediately apparent why this plasticizer would only be present after aging as

there is no clear mechanism for the conversion of DOTP to DEHP (through a degradation pathway or

otherwise). Further testing is necessary to determine whether this difference is due to duck-to-duck

variability, heterogeneity on the surface of each duck, or due to some other reason.


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Figure 13: Seven plasticizers run at a concentration of 100 ppm in isopropyl alcohol. Detection by UV

at 273 nm. Note that diisononyl phthalate and diundecyl phthalate are mixtures of isomers, which are

only partially separated by the chromatographic conditions used here.

Figure 14: Mixture of seven plasticizers at a concentration of 100 ppm in isopropyl alcohol. Detection

by MSD in positive mode. Shown is the total ion chromatogram (front blue trace) and extracted ions

corresponding to the hydrogen or sodium adduct of each phthalate. From front to back:

Blue = Total Ion Chromatogram

Red = 391 – [M+H]+

for Bis(2-ethylhexyl) phthalate

Green = 413: [M+Na]+

for Dioctyl Terephthalate

min9 10 11 12 13 14 15

mAU

-1250

-1000

-750

-500

-250

0

250

500

DAD1 A, Sig=273,4 Ref=360,80 (U:\MARKETI...\PHTHALATES FEB 18_2016 2016-02-18 20-58-39\201602180000012.D) DAD1 A, Sig=273,4 Ref=360,80 (U:\MARKETI...\PHTHALATES FEB 18_2016 2016-02-18 20-58-39\201602180000013.D) DAD1 A, Sig=273,4 Ref=360,80 (U:\MARKETI...\PHTHALATES FEB 18_2016 2016-02-18 20-58-39\201602180000014.D) DAD1 A, Sig=273,4 Ref=360,80 (U:\MARKETI...\PHTHALATES FEB 18_2016 2016-02-18 20-58-39\201602180000015.D) DAD1 A, Sig=273,4 Ref=360,80 (U:\MARKETI...\PHTHALATES FEB 18_2016 2016-02-18 20-58-39\201602180000016.D) DAD1 A, Sig=273,4 Ref=360,80 (U:\MARKETI...\PHTHALATES FEB 18_2016 2016-02-18 20-58-39\201602180000017.D) DAD1 A, Sig=273,4 Ref=360,80 (U:\MARKETI...\PHTHALATES FEB 18_2016 2016-02-18 20-58-39\201602180000018.D)

min10 20 30 40 50

0

1000000

2000000

3000000

4000000

5000000

*MSD1 TIC, MS File (U:\MARKETING\APPLICATION NOTES\DUCK DEFORMULATION\DATA\HPLC\PHTHALATES FEB 18_2016 2016-02-18 20-58*MSD1 391, EIC=390.7:391.7 (U:\MARKETING\APPLICATION NOTES\DUCK DEFORMULATION\DATA\HPLC\PHTHALATES FEB 18_2016 2016-02-*MSD1 413, EIC=412.7:413.7 (U:\MARKETING\APPLICATION NOTES\DUCK DEFORMULATION\DATA\HPLC\PHTHALATES FEB 18_2016 2016-02-*MSD1 247, EIC=246.7:247.7 (U:\MARKETING\APPLICATION NOTES\DUCK DEFORMULATION\DATA\HPLC\PHTHALATES FEB 18_2016 2016-02-*MSD1 279, EIC=278.7:279.7 (U:\MARKETING\APPLICATION NOTES\DUCK DEFORMULATION\DATA\HPLC\PHTHALATES FEB 18_2016 2016-02-*MSD1 419, EIC=418.7:419.7 (U:\MARKETING\APPLICATION NOTES\DUCK DEFORMULATION\DATA\HPLC\PHTHALATES FEB 18_2016 2016-02-*MSD1 475, EIC=474.7:475.7 (U:\MARKETING\APPLICATION NOTES\DUCK DEFORMULATION\DATA\HPLC\PHTHALATES FEB 18_2016 2016-02-*MSD1 547, EIC=546.7:547.7 (U:\MARKETING\APPLICATION NOTES\DUCK DEFORMULATION\DATA\HPLC\PHTHALATES FEB 18_2016 2016-02-

Bis(2-ethylhexyl)

phthalate, MW: 390.56

Diallyl Phthalate,

MW: 246.26 Dibutyl Phthalate,

MW: 278.34

Diisononyl

Phthalate, MW:

418.61

Dioctyl Terephthalate,

MW: 390.56 Diundecyl phthalate,

MW: 474.72

Trioctyl Trimellitate,

MW: 546.78


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Magenta = 247 [M+H]+

for Diallyl Phthalate

Tan = 279 [M+H]+

for Dibutyl Phthalate

Purple = 419 [M+H]+

for Diisononyl Phthalate

Black = 475 [M+H]+

for Diundecyl phthalate

Dotted Blue = 547[M+H]+

for Trioctyl Trimellitate

Figure 15: Unaged duck sample, detection by MSD. Shown are the total ion chromatogram (blue

trace), extracted ion 391 corresponding to the hydrogen adduct of DEHP, and extracted ion 413

corresponding to the sodium adduct of DOTP (green trace).

min11.5 12 12.5 13 13.5 14 14.5

0

250000

500000

750000

1000000

1250000

1500000

1750000

2000000

MSD1 TIC, MS File (U:\MARKETING\APPLICATION NOTES\DUCK DEFORMULATION\DATA\HPLC\PHTHALATES FEB 18_2016 2016-02-18 20-58 MSD1 391, EIC=390.7:391.7 (U:\MARKETING\APPLICATION NOTES\DUCK DEFORMULATION\DATA\HPLC\PHTHALATES FEB 18_2016 2016-02- MSD1 413, EIC=412.7:413.7 (U:\MARKETING\APPLICATION NOTES\DUCK DEFORMULATION\DATA\HPLC\PHTHALATES FEB 18_2016 2016-02-


MW: 390.56

Bis(2-ethylhexyl)



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Figure 16: Aged duck sample, detection by MSD. Shown are the total ion chromatogram (blue trace),

extracted ion 391 corresponding to the hydrogen adduct of DEHP, and extracted ion 413

corresponding to the sodium adduct of DOTP (green trace).

min11.5 12 12.5 13 13.5 14 14.5

0

500000

1000000

1500000

2000000

2500000

MSD1 TIC, MS File (U:\MARKETING\APPLICATION NOTES\DUCK DEFORMULATION\DATA\HPLC\PHTHALATES FEB 18_2016 2016-02-18 20-58 MSD1 391, EIC=390.7:391.7 (U:\MARKETING\APPLICATION NOTES\DUCK DEFORMULATION\DATA\HPLC\PHTHALATES FEB 18_2016 2016-02- MSD1 413, EIC=412.7:413.7 (U:\MARKETING\APPLICATION NOTES\DUCK DEFORMULATION\DATA\HPLC\PHTHALATES FEB 18_2016 2016-02-

Bis(2-ethylhexyl)



MW: 390.56


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