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This is to certify that the
thesis entitled

THE DEVELOPMENT OF A COMPREHENSIVE SCHEME
FOR THE ANALYSIS OF ELECTRICAL TAPE USING
INSTRUMENTAL AND CHEMOMETRIC METHODS

presented by

AMANDA BETH STURDEVANT

has been accepted towards fulfillment
of the requirements for the

degree In Forensic Science

 

 

 

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THE DEVELOPMENT OF A COMPREHENSIVE SCHEME FOR THE ANALYSIS
OF ELECTRICAL TAPE USING INSTRUMENTAL AND CHEMOMETRIC
METHODS
By

Amanda Beth Sturdevant

A THESIS

Submitted to
Michigan State University
in partial fulfillment of the requirements
for the degree of

MASTER OF SCIENCE
School of Criminal Justice

2005

ABSTRACT
THE DEVELOPMENT OF A COMPREHENSIVE SCHEME FOR THE ANALYSIS
OF ELECTRICAL TAPE USING INSTRUMENTAL AND CHEMOMETRIC
METHODS
By

Amanda Beth Sturdevant

Polyvinyl chloride electrical tape is oflen encountered during explosive
investigations. It may be used in the construction of improvised explosive devices as
wire insulation, for sealing openings, and for various other purposes. If tape is recovered
and submitted as evidence, an analyst may be asked to compare the questioned tape with
a known source. When a physical match of tape ends is not possible, the analyst turns to
comparisons of class characteristics for the purposes of association or elimination. Most
often these class characteristics include physical dimensions, surface texture, and
chemical composition.

This study addresses the need for a comprehensive scheme for electrical tape
analysis and discusses a preliminary evaluation of the methods currently in use. A
physical examination followed by instrumental analysis (ATR-IR, SEM-EDS, HT-GC-
MS, and Py-GC-MS) of 38 rolls of black electrical tape separated the sample set into 18
distinguishable classes. Differences in adhesive formulation, elemental composition, and
plasticizer type were the major characteristics used for differentiation. Py-GC-MS was
found to be the least useful method in electrical tape analysis. Furthermore, the use of
statistical methods such as factor analysis allowed for additional discrimination of tape

samples (21 classes) based on quantitative differences in their chemical composition.

ACKNOWLEDGEMENTS

I would like to thank the School of Criminal Justice and the Forensic Science
Department at Michigan State University (MSU) for support and funding during the last
two years. I would also like to thank the members of my thesis committee, Dr. Steven
Dow from the MSU School of Criminal Justice, Dr. John Goodpaster from the Bureau of
Alcohol, Tobacco, Firearms, and Explosives (ATF), and Dr. Jay A. Siegel from the
IUPUI Forensic and Investigative Sciences Program for taking time out of their busy
schedules to read this work, witness the defense, and provide feedback and suggestions
for improvement. In particular, I would like to extend a special thanks to Dr. Jay A.
Siegel who selected me for this program and encouraged me through the completion of it,
and to Dr. John Goodpaster who Spent endless hours revising this work, completing the
factor analysis portion and explaining the results to me, and tying up many loose ends at
the ATF in my absence.

I also wish to thank Leanora Brun-Conti and Edward Bender from the ATF for
their ideas and support throughout the completion of this project. Also, to Michelle
Reardon of the ATF, thank you for the instructions on how to operate the new high
temperature GC-MS and for allowing us the time to run all the samples for this project. I
also wish to thank the ATF for hiring me as a student assistant and for providing funding
and laboratory space and equipment for the completion of this project. I would also like
to thank John Houle and the staff at the 3M Hutchinson plant in Minneapolis, Minnesota
for providing a tour of their plant, answering many questions about the manufacture and

distribution of electrical tape, and for supplying exemplar rolls of tape for this study.

iii

Finally, I would like to thank all of my friends and family for their endless
support, encouragement, and words of wisdom when I needed them the most and I wish
to extend a special thanks to my parents for always believing in me and allowing me to

follow my dreams...wherever they may take me.

 

iv

TABLE OF CONTENTS

LIST OF TABLES ........................................................................................................... vii
LIST OF FIGURES ......................................................................................................... vii
1. INTRODUCTION ....................................................................................................... 1
1.1 ELECTRICAL TAPE-BACKGROUND AND IMPORTANCE .................. 2
1.2 PREVIOUS STUDIES .................................................................................. 9
1.3 CHALLENGES INHERENT TO POPULATION STUDIES-OUR
APPROACH ........................................................................................................ 14
2. MATERIALS AND METHODS ................................................................................. 22
2.1 MATERIALS AND REAGENTS ................................................................. 22
2.2 INSTRUMENTAL PARAMETERS ............................................................. 22
2.3 SAMPLE PREPARATION ........................................................................... 25
3. RESULTS AND DISCUSSION .................................................................................. 26
3.1 PHYSICAL EXAMINATION OF ADHESIVE COLOR ............................. 26
3 2 ATR-IR .......................................................................................................... 26
3.3 SEM-EDS ...................................................................................................... 39
3.4 FACTOR ANALYSIS OF SEM-EDS DATA ............................................... 45
3.5 HT-GC-MS .................................................................................................... 54
3.6 Py—GC-MS ..................................................................................................... 64
3.7 COMPARISION OF METHODS USING “”H VALUES ............................ 67
4. CONCLUSIONS AND FUTURE WORK .................................................................. 68
4.1 CONCLUSIONS ............................................................................................ 68

4.2 FUTURE WORK ........................................................................................... 71

5. APPENDIX .................................................................................................................. 74

6. REFERENCES ............................................................................................................ 97

vi

LIST OF TABLES

Table 1: Examples of electrical tape components ............................................................ 4
Table 2: Specifications of three brands of 3M electrical tape ......................................... 8
Table 3: Sample set data .................................................................................................. 19
Table 4: Instrumental parameters ..................................................................................... 23
Table 5: Characteristic IR bands for electrical tape ......................................................... 31
Table 6: Overall differentiation based on factor analysis of SEM-EDS data .................. 49

vii

LIST OF FIGURES

Figure 1: Schematic of the entire coating process of electrical tape and detail of the
roll-coating process .................................................................................. 6

Figure 2: 2002 market share data for the five major manufacturers of electrical tape ....16

Figure 3: Overall differentiation based on adhesive color (black or clear) and ATR—IR
analysis of adhesive side .......................................................................... 27

Figure 4: Examples of inter- and intra-roll reproducibility in ATR-IR analysis of adhesive
sides of black electrical tape (Super 88 (2004) and WUL) ...................... 28

Figure 5: Examples of ATR-IR spectra of black electrical tapes with black adhesive
(Super 33+ (2004), Temflex 1700, and Scotch 33) ................................. 32

Figure 6 Examples of ATR-IR spectra of black electrical tapes with clear adhesive
(Duck and Lepage) ................................................................................... 34

Figure 7: Examples of ATR-IR spectra of black electrical tapes with clear adhesive
(Powerworks, Manco, and Champion) .................................................... 36

Figure 8: Examples of ATR-IR spectra of black electrical tapes with clear adhesive

(Frost King and Tartan) ........................................................................... 38
Figure 9: Overall differentiation based on adhesive color and SEM-EDS analysis of
backing side ............................................................................................. 41
Figure 10: Examples of the backing textures of black electrical tapes under 200x
magnification ........................................................................................... 43
Figure 11: Examples of the backing textures of black electrical tapes under 200X
magnification ........................................................................................... 44
Figure 12: Factor analysis plot for tapes with black adhesive ......................................... 47
Figure 13: Factor loadings for tapes with black adhesive ................................................ 48
Figure 14: Factor loadings for tapes with clear adhesive ................................................ 52
Figure 15: Factor analysis plot for tapes with clear adhesive .......................................... 53

Figure 16: Overall differentiation based on adhesive color and HT-GC-MS analysis
of plasticizer extracts ............................................................................... 56

viii

Figure 17:
Figure 18:
Figure 19:
Figure 20:

Figure 21:

Figure 22:

Figure 23:

Figure 24:

Figure 25:

Figure 26:

Figure 27:

Figure 28:

Figure 29:

Figure 30:

Figure 31:

Figure 32:

Figure 33:

Extracted ion chromatograms of Commercial 700 tape ................................. 57

Extracted ion chromatograms of Super 33+ tape ........................................... 58
Extracted ion chromatograms of Temflex 1700 tape ..................................... 59
Extracted ion chromatograms of Scotch 33 tape ............................................ 60
Extracted ion chromatograms of Frost King tape .......................................... 61
Extracted ion chromatograms of 667 Pro Series (top) and Manco (bottom)

tapes ......................................................................................................... 62
Extracted ion chromatograms ofTartan tape ........................ 63
Pyrograms of two samples from the same roll of tape (Super 88(2004))

analyzed on the same day ........................................................................ 64
ATR-IR spectra of black electrical tapes with black adhesive .

(Super 33+ (2001) and Super 88 (2004)) ................................................. 75
ATR-IR spectra of black electrical tapes with black adhesive

(Super 88 (2001) and Commercial 700) .................................................. 76
ATR-IR spectra of black electrical tapes with clear adhesive

(667 Pro Series and WUL) ....................................................................... 77

ATR-IR spectra of black electrical tapes with clear adhesive
(Intertape and Electro Tuft) ..................................................................... 78

ATR-IR spectra of black electrical tapes with clear adhesive
(Shurtape and Bengal) .............................................................................. 79

ATR-IR spectra of black electrical tapes with clear adhesive
(Globe and Vanguard) .............................................................................. 80

Examples of the backing texture of black electrical tapes under 200X
magnification ........................................................................................... 81

Examples of the backing texture of black electrical tapes under 200x
magnification ........................................................................................... 82

Examples of the backing texture of black electrical tapes under 200X
magnification ........................................................................................... 83

ix

 

Figure 34: Weight percentage values of elements for electrical tapes with black

adhesive .................................................................................................... 84
Figure 35: Weight percentage values of elements for electrical tapes with black

adhesive .................................................................................................... 85
Figure 36: Weight percentage values of elements for electrical tapes with clear

adhesive .................................................................................................... 86
Figure 37: Weight percentage values of elements for electrical tapes with clear

adhesive ........................................................................... . ........................ 87
Figure 38: Weight percentage values of elements for electrical tapes with clear

adhesive .................................................................................................... 88
Figure 39: Extracted ion chromatograms of Super 88 tape ............................................. 88
Figure 40: Extracted ion chromatograms of Globe tape .................................................. 90
Figure 41: Extracted ion chromatograms of Bengal (top) and Champion (bottom) tapes
.......................................................................................................................................... 91
Figure 42: Extracted ion chromatograms of Duck tape ................................................... 92
Figure 43: Extracted ion chromatograms of Electro Tuff (top) and Intertape (bottom)

tapes ......................................................................................................... 93
Figure 44: Extracted ion chromatograms of Lepage (top) and Powerworks (bottom)

tapes ......................................................................................................... 94
Figure 45: Extracted ion chromatograms of Shurtape (top) and WUL (bottom) tapes ...95
Figure 46: Extracted ion chromatograms of Vanguard tape ............................................ 96

 

1. INTRODUCTION

The philosophy behind any forensic comparison is to utilize methods that
differentiate samples from a given population to the limit of the sample population’s
heterogeneity. In other words, the set of techniques chosen for a comparison should be
able to distinguish each member of the population from all others that are, in fact,
different. In this way, when two samples are found to have very similar characteristics,
the probability of the two samples sharing a common source is increased relative to the
probability that the two samples are only coincidentally alike. In the case of polyvinyl
chloride (PVC) electrical tape, a successful analytical scheme should discern differences
between samples at a relatively small scale, whether that is a tape manufacturer, brand,
batch, or individual roll. Ironically, an analytical scheme that could discern differences
between samples from the same roll of tape would not be desirable; such a scheme would
make associations between a questioned and known length of tape difficult or even
impossible.

Regardless, it is not possible to truly evaluate the success or failure of an
analytical scheme at meeting this goal without first addressing some problems that are
common to many forensic population studies. These include such issues as poor
understanding of the inherent heterogeneity of the sample population, not ensuring
representative sampling of that population, introducing micro-heterogeneity effects
through insufficient sample sizes or excessively precise methods, using only a limited
number of analytical techniques, a lack of quantitative comparison of results, and failure

to monitor changes in the population.

 

This study addresses the above issues and includes a preliminary evaluation of
some of the techniques used for electrical tape analysis in forensic science laboratories.
This is accomplished by gathering as much information as possible about the
manufacturing process and distribution of electrical tape, obtaining as large a sample set
as possible, avoiding sub-sampling, applying multiple analytical methods to the entire
sample set, quantitatively comparing the distinguishing capabilities of these methods, and
then monitoring changes in the population.

1.1 Electrical Tape: Importance and Background

In a forensic setting, there are several different instances when electrical tape may
be encountered as evidence. The tape can be used to bind victims, to package drugs, or in
the construction of improvised explosive devices (IEDS). In the latter scenario the tape
can be used to secure separate components of the device together, seal openings, insulate
wires, attach the device to the target object, or form a crude container for the explosives
themselves. In any of these cases, questioned fragments of electrical tape recovered from
a scene can be compared to known samples using individual or class characteristics.
Electrical tape is composed of two main layers: backing and adhesive. The backing is
composed of approximately 60% PVC resin and 40% liquid and powder additives that
are included to adjust the physical and/or chemical properties of the PVC. The most
abundant of these additives is liquid plasticizer, generally aromatic or aliphatic in nature,
which creates space between the PVC polymer chains and lowers the inter- and intra-
chain attractive forces, giving the PVC the flexibility and workability that is common to
electrical tape'. Examples of some of the more common plasticizers are listed in Table 1.

The powder additives, such as stabilizers to prevent oxidation and/or degradation, fillers

 

to reduce the overall cost of the tape, colorants, and flame retardants are used in smaller
amounts. Examples of each of these additives are also listed in Table 1.

The two main components of the adhesive layer are an elastomer and tackifier
resins. An elastomer is a natural and/or synthetic rubber polymer, which at room
temperature is capable of recovering its size and shape after removal of a deforming
force]. Tackifier resins improve the stickiness, or tack, of the polymer by lowering its
viscosity and allowing it to form an immediate bond with a surface under low pressurel‘
Common examples of polymers and tackifiers used are listed in Table 1. As in the
backing, there are various other additives that lend certain chemical and physical
characteristics to the adhesive layer. These are also listed in Table 1.

There are two other layers incorporated into electrical tape that are used in such
small amounts that analyzing them is not practical; these are the primer layer and the
release coat. The primer layer is intended to increase the bonding of the adhesive layer
onto the backing and is coated onto the backing prior to adhesive application. The
release coat is sometimes applied to the top side of the backing to aid in the unwinding of

the tape. Examples of these materials are listed in Table 1.

 

Table 1: Examples of electrical tape components‘

 

 

 

 

 

 

 

 

 

Electrical Tape Components Examples
Plasticizer
Aromatic phthalate esters
Aliphatic aliphatic fatty acid esters, alkyl/aryl phosphates,
adipates/sebacates, dialky tin, castor oil
Additives
Stabilizers PbCO}, PbSO4, stearates, dibutyl tin, diphenyl urea
Fillers carbon, TiOz, CaCO3, BaSO4, kaolin
(Ale3’28102'2H20), talc (Mg3Si4010(OH)2),
dolomite (CaMg(CO3)2)
Colorants carbon black, aluminum powder, iron corgrlexes

 

Flame retardants

szO3, chlorinated H-C

 

 

 

 

 

 

 

 

 

Polymer
Natural rubber polyisgrrene
Synthetic rubber polybutadiene
Polyacrylates polybutylacrylate
Copolymers styrene/isoprene, styrene/butadiene
T ackifier resins wood rosin, rosin esters, terpene resins/phenolics,
petroleum based resins
Primer rubber, acrylics, starch, polyamides

 

 

Release coat

 

silicones, waxes, acrylics, polyesters, surfactants,
polyamide

 

 

 

The first process used in the manufacturing of electrical tape is the calendering of
plasticized PVC into a thin film. Calendering is defined as the pressing (of a cloth,
rubber, or paper) between rollers or plates in order to smooth and glaze or to thin into
sheetsz. The PVC resin is thoroughly mixed with the additives and then passed through a
series of nip rollers that press the resin into progressively thinner sheets that are then
cooled and wound onto rolls for future use. At this point, some manufacturers (e. g. 3M)
apply an electrical discharge, a “corona,” to the PVC sheets in order to increase the
surface tension and render the surface more receptive to subsequent coatings. This
process is called a Corona Treatment.

The remainder of the manufacturing process involves the roll coating of various
layers (primer, release, and adhesive) onto the PVC film. This is accomplished by
passing the film between a transfer roller and a pressure roller. The transfer roller is in
constant contact with a pick-up roller that is partially immersed in a solution of the
desired component. The pressure roller is adjusted to control the thickness of the layer.
The PVC film is then passed through an oven to evaporate the solvent. These large
sheets are then sectioned into smaller commercial rolls3. It is important to note that
throughout the entire manufacturing process every piece of machinery that comes into

contact with the electrical tape has potential to leave physical and possibly Visible

’9 ‘6 9

markings on the final product. For example, marks such as striations, “divots, craters,’
and bubbles can be from rollers, cutters, the coating application, and even the winding of
the tape. These markings can sometimes be useful in forensic comparisons (i.e., fast

eliminations based on microscopic backing texture). Figure 1 depicts the manufacturing

process of electrical tape.

 

Release

 

 

 

Prime
Coat l’ Coat

 

 

 

Unwind

 

     

 

‘ Adhesive

 

 

 

 

Rewind

 

 

 

Rolls ready to be shipped

Detail of coating
process /

Pressure
roller

    
  
   
  

   

Transfer
roller

 

Backing
roll

Coating pan

 

Figure 1: Schematic of the entire coating process of electrical tape and detail
of roll-coating process"3

Electrical tape is commercially available in three different grades, depending on
the quality and/or quantity of raw materials used in the manufacturing process. These
grades can be designated as general, mid-range, and premium. Each grade of tape meets
a certain set of standards that affects its suitability for use under various conditions.
Examples include temporary versus permanent application, indoor versus outdoor use,
voltage levels, application temperature ranges, flexibility, tensile strength, and tack. &
Table 2 shows the specifications and working conditions of three grades of 3M vinyl

electrical tape‘.

 

Table 2: Specifications of three brands of 3M electrical tape4

General Use (T egrflex 1700)
Application 0°C-80°C
Temporary applications
Relatively low flexibility
Good initial tack

Agency certified

Mid-range (Highland 700)
Application —10°C-90°C
Permanent Application
Good flexibility

High initial tack

Agency certified

Premium (Super 33+, SgpLer 88)
Application -18°C-105°C
All-weather application
Permanent application

Superior flex/conformability
Excellent initial tack
Multiple-agency certified

 

1.2 Previous Studies

There have been several articles published regarding the forensic analysis of
electrical tape. In 1984 Kee published his work regarding over 100 samples of PVC
adhesive tape that had been received into evidence at the Northern Ireland Forensic
Science Laboratory between 1980 and 1981. He examined many physical properties of
the tapes including their dimensions, surface textures, and edge markings. He used X-
Ray Fluorescence (XRF) and Multiple Internal Reflectance-Infrared Spectroscopy (MIR-
IR), respectively, to study the inorganic and organic components of the backing side of
the tapes. He concluded that by using XRF data to determine the presence and/or
absence of calcitun (a common filler component) and lead (a common stabilizer
component) in the tapes, he could separate the samples into four broad classes. He then
further divided these groups based on the presence and/or relative amounts of other
elements, specifically silicon, antimony, and phosphorous. Using this method, Kee was
able to separate 131 tapes into fifieen different groups based solely on elemental
composition. Using MIR-IR and physical characteristics, two of these groups could be
divided into two smaller groups, resulting in a total of seventeen distinguishable classes3 .

Also in 1984, Keto purchased eighteen rolls of black PVC electrical tape, three
rolls from each of six manufacturers; LePage, Tuck, Manco, Nashua, Vanguard, and 3M.
Based on microscopic examination of the backing, Attenuated Total Reflectance-Fourier
Transform IR (ATR-FT IR) analysis of the adhesive side, and XRF elemental analysis he
concluded that any one of these three methods was sufficient to distinguish each of the
six brands from the other five. He noted that the infra-roll variations were much less than

the inter-roll variations within a single manufacturer and that the 3M tapes produced a

completely unique fingerprint region of the IR spectrum that could not be related to any
of the other brands. This aspect was not further examineds.

In 1988, Williams and Munson analyzed thirty black PVC tapes with pyrolysis-
gas chromatography-mass spectrometry (Py-GC-MS) to evaluate the discriminatory
power of the method. They were able to distinguish twenty-six of the tapes based on
pyrograrn pattern analysis, leaving two pairs indistinguishable. One indistinguishable
pair was found to be from the same manufacturer with the only differences being in the
amount of adhesive applied and the thickness of the backing material used. The tapes in
the other indistinguishable pair had different brand names. Although slight differences
did exist within a single roll, the samples taken from the same roll were still more similar
to each other than to any others in the sample set. All samples recovered and tested post-
blast from an IED could be linked back to the appropriate tape, with only small
differences noted. Finally, Williams and Munson suggest that experiments comparing
multiple rolls of the same type of tape could be helpful in establishing the evidentiary
value of a “match6.”

Merrill and Bartick summarized the FBI’s internal procedure for the analysis of
black plastic tape in 1989. In this document they describe what to look for during the
visual examination of tape, specifically any unique surface features or end marks, and
what chemical analyses should be performed. They suggest analyzing the adhesive side,
backing side, and a cast film of the plasticizer that has been extracted with chloroform by
Internal Reflectance Spectroscopy (IRS) and then searching the library database for
possible matches. From the adhesive side, the rubber component can be identified (most

often as polyisoprene (PIR), polyisobutylene (PIB), styrene/isoprene copolymer (SIR), or

10

 

styrene/butadiene copolymer (SBR)) and the type of plasticizer oil used can be classified
as either aromatic or aliphatic. The type of backing can be confirmed as PVC,
polyethylene (PE), or polypropylene (PP). The plasticizer can be typed as aromatic or
aliphatic from the cast film. They also started analyzing the backing side by XRF but did
not publish any of these results7.

In addition to the above articles regarding the analysis of adhesive tapes, there
have been numerous other studies done applying various forms of pyrolysis to the
analysis of adhesives (polymers). In 1972, Wheals and Noble examined the forensic
applications of Py-GC as it is used in the Metropolitan Police Forensic Science
Laboratory in London, England. They describe the use and benefits of the method in
analyzing paint, adhesives, plastics, synthetic fibers, and soil extracts. They provide
sample pyrograms of an epoxy resin, a polyvinyl acetate copolymer, and a
styrene/butadiene copolymer and conclude that the differences between brands are often
such that a particular product can be identified. They also mention that even though
filled adhesives (tiling cements, ceiling tile adhesives, etc.) often pose problems with IR
spectroscopy, these products can be easily characterized by Py—GC8.

Noble, Wheals, and Whitehouse completed an extensive study on the
characterization of adhesives using Py-GC-MS and IR spectroscopy in 1974. They
analyzed 179 commercially available adhesives in the form of dried films and their
results indicate that all but fourteen of these could be assigned to one of twelve classes of
adhesive, depending on the resin base used in the adhesive. They note that, if minor

variations are examined, different products in the same class can be differentiated so that

11

all products are discriminated and that the fourteen unclassified adhesives are all unique
by both of the methods usedg.

In 1980, Wheals published a review of forensic applications, specifically polymer
analysis, of pyrolysis and other thermal degradation techniques in which be assessed the
merits and limitations of each. He describes the characteristics of the “ideal” technique
for polymer analysis and then discusses the advantages and/or disadvantages of using
various techniques to reach this “ideal.” He includes Py-GC, Py-capillary-GC, multiple
stage Py-GC, Py-MS, thermal gravimetry—MS, laser microprobe mass analysis, and
different pyrolyzer types in this critique. A Wheals then applies his ideas to the analysis of
polymers such as paint (decorative gloss and vehicle), synthetic fibers, adhesives, and
other miscellaneous substances. He refers to his previous work regarding Py-GC
analysis, discussed above, and states that using Py-MS on the same sample set (179
tapes) can provide “rapid adhesive identification” where the mass pyrogram sometimes
yields better qualitative information than the pyrogram or IR spectrum. (This was based
on unpublished work at the Metropolitan Police Forensic Science Laboratory in London,
Englandlo.)

Bakowski, Bender, and Munson analyzed ninety-one adhesives by Py—capillary
column-GC-MS in 1985. The results obtained compared well with those of Noble et. al,
discussed above, in that the adhesives fit into the general categories described therein
with the exception of cyanoacrylic-based adhesives (super- glues) that are a newer group.
Five IEDs were constructed using samples of twenty-four of the original ninety-one
adhesives and nineteen residues were recovered post-blast. These represented thirteen of

the twenty-four types of adhesives used in the construction of the devices. All of these

12

residues could be properly associated to the original adhesive type after searching a
database of composite spectra (correct adhesive was in the top five results of the
search1 1.)

Curry (1987) performed a study on ninety-four household adhesives in the UK.
using Py—MS to accommodate the forensic scientist’s problem of small samples that are
frequently contaminated and of unknown origin and composition. He discusses nine
broad classes of basic polymer resins used in the adhesives and details certain
compounding ingredients included in each. These include the plasticizers, tackifying
resins, anti-oxidants, UV absorbers, processing aids, etc. that can be used to further
discriminate within each group. Data from each group is presented”.

Blackledge published a literature review in 1987 on the characterization of
adhesive tapes in forensic science laboratories that included all of the articles previously
mentioned. One technique that was not discussed in any of these works is fluorescence
spectroscopy but it was examined in a previous study by Blackledge (1984). In it, the
non-adhesive side of beige masking tape was examined and the method could distinguish
between brands of tape and between lots of the same brand of tape. Dichloromethane
extracts of the tapes were also examined and showed the same differentiation”.

In a presentation given at the Midwestern Association of Forensic Scientists Fall
Meeting in Minneapolis, Minnesota in 2001, Smith and Randle discuss the forensic
examination of pressure sensitive tape. In addition to the history and background of
pressure sensitive tapes in general, they detail that of black electrical tape and suggest a
scheme for its analysis: a physical match (if possible), examination of physical

characteristics (surface texture, adhesive color, width, and thickness), F TIR, Py—GC-MS,

13

 

and elemental analysis, polarizing light microscopy (PLM), or fluorescence spectroscopy
as a final step. They diagram the different layers of electrical tape, explain the
composition of each, and give examples of the different components (plasticizers, fillers,
stabilizers, etc.) Also, Smith and Randle suggest different plasticizer extractions for
backings constructed of PVC, PP, or PE and provide a list of “useful IR bands to look for
specific to electrical tape.” Finally, they attach a reference “workbook” containing
examples of IR spectra and pyrograms of plasticizers, backings, adhesives, and standards.
They reference several articles dealing with pyrolysis and elemental analysis of electrical
tape but do not include any detail or references regarding PLM or fluorescence
spectroscopyl.
1.3 Challenges Inherent to Population Studies-Our Approach

One of the biggest challenges in completing a population study is the need for a
detailed understanding of the sample population in question. Before one can even begin
to evaluate the ability of different methods to distinguish members of a population, the
inherent heterogeneity of that population must be fully understood and accepted. In the
case of electrical tape this heterogeneity arises fi'om both chemical composition and
product distribution. However, since most formulations of electrical tape are proprietary
and the manufacturers are not willing to disclose the identity of some of the raw materials
used, knowing the exact chemical makeup of some brands is very difficult, if not
impossible, to do. With regards to distribution, a major tape manufacturer may produce a
batch of tape and market some of the tape using their name. However, they may also sell
part of that same batch to another company that then markets the tape under a different

name. Chemically and physically the two tapes are considered to be the same, while

14

commercially they are different. Therefore, trying to find a method that can distinguish
these two tapes based on physical and/or chemical composition is not possible. Also,
stating that a certain method is not useful in discriminating electrical tapes based on its
inability to distinguish these two particular tapes is not accurate. This is why, prior to
completing any population study, it is crucial to study the factors that affect population
heterogeneity and monitor any changes in those factors over time. This last point ensures
that any results obtained by the study retain their applicability.

Before the start of this project, the members of the research group took several
steps to understand the production and distribution of electrical tape. In September of
2002, ATF representatives toured the 3M Hutchinson plant in Minnesota. Here, they
were guided through the plant by engineers and were able to see the manufacture of vinyl
electrical tapes first-hand. They attended a presentation and received a packet of
information on everything from the history of the company to the manufacture and
packaging of the final products. This particular plant produces both industrial and
electrical vinyl tapes, including those brands that were later obtained as exemplars for
this study (i.e., Temflex 1700, Super 88, and Super 33+). Information on the “global
competitive situation” of vinyl electrical tape as of 2002 was also supplied to the group.
This chart, showing the five major manufacturers of electrical tape in 2002, is shown in
Figure 2. We were also informed that 3M discontinued the use of lead salts in its tapes as

of2001}

15

 

 

2002 Market Share Data

23%-3M
42%-Other
5%-PB

' . "SPA-M116

10%-Scapa

 

 

Figure 2: 2002 market share data for the five major manufacturers of electrical tape4

 

1&1

In addition to making contacts with employees of one of the largest electrical tape
manufacturers in the world, our group was interested in learning as much as possible
about any product specifications unique to certain brands or manufacturers of electrical
tape. The packaging of most brands shows the registered trademark of Underwriters
Laboratories, Inc. (UL). Companies are permitted to use this symbol on products that
have been evaluated by UL and are in compliance with UL’S safety requirements. In
addition, the alphanumeric UL control number (e. g., 206T) and file number (e. g.,
E62265) may be included. Based on conversations with UL, it was discovered that a
particular UL control and file number is indicative of a certain set of specifications that a
product must meet in order to be listed under that number. In the case of electrical tape
this can include such properties as tensile strength and/or working temperatures. What
this means to this study is that if two different brands of tape have the same UL number,
they both must meet some of the same specifications.

An additional amount of insight into the presumptive manufacturer of a tape
sample can be gained by looking at the Universal Product Code (UPC) found on the
packaging. Where such a symbol is available, the first six digits can be converted to a
manufacturer’s code that can then be used to access a manufacturer listing kept by
Uniform Codes Council (UCC); this is generally the true manufacturer, the former name
of the manufacturer, or the distributor of the tape. Overall, by associating the UL and/or
UPC markings in our sample set to a manufacturer of electrical tape, we can conclude
that as of 2004 there were tapes from at least 7 manufacturers in circulation around the
world: 3M, Nitto Denko Corp., Ningbo Sincere Adhesive Products Co., Ltd., Henkel

Consumer Adhesives, Inc., ACI-IEM Technology Corp., Globe Industries, Corp., and

17

Syrnbio, Inc.

Once the requirement of understanding a population is met, the next logical step is
acquiring a sample collection that is truly representative of the population as a whole.
Table 3 lists the brand name and notation, quantity, year acquired, UPC, UL control and
file numbers, and associated manufacturers of the thirty-eight rolls of electrical tape
examined in this study. The nine exemplar rolls are listed first. Overall, this collection
represents twenty different nominal brands and at least seven manufacturers of electrical
tape. It is important to note that the tapes in this sample set were purchased in various
years and stored in different environments; the effects of age and storage conditions on
the physical and chemical composition of electrical tape have not yet been examined.
Therefore, all conclusions and results of this work do not take these factors into account
and should be interpreted as such.

Another problem that ofien arises when analyzing many samples is the tendency
to focus on one or two particular methods of analysis. Sometimes, even when multiple
methods are used, one does not provide any more useful information than another, i.e.,
every method used analyzes the same component of the sample or provides the same
level of discrimination. Therefore, using multiple, orthogonal, methods of analysis is
always important in trying to distinguish samples, especially when attempting to develop
a complete analytical scheme. This study uses five distinct methods to analyze electrical
tape. These include a cursory physical examination of adhesive color (black or clear),
ATR-IR of the adhesive side, scanning electron microscopy-energy dispersive
spectrometry (SEM-EDS) of the backing side, high temperature (HT)-GC-MS of

plasticizer extracts, and Py-GC-MS of the entire tape.

18

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19

‘-

he

No matter what or how many methods are used in analyzing samples, one must
always be sure to avoid sub-sampling a specimen. This means that the methods chosen to
analyze a particular sample must do so at a level where the sample is homogeneous.
Anything, electrical tape included, has a level of micro-heterogeneity. Therefore,
anything, if analyzed at a small enough level, can be eliminated from itself. For example,
when examining questioned and known paint chips, an analyst should not focus the ‘l
examination on a single metallic flake in the color coat while ignoring all the other layers. I ”I

In fact, this would undermine any attempt at comparing the questioned and known

 

samples by not being able to associate the flake to anything other than another flake, let J
alone another layer or sample. It is more important in paint examinations to focus on the
number, order, and overall composition of all the layers present. The five methods
chosen for this particular study each analyze electrical tape at a homogeneous level.
Finally, after an appropriate sample set is acquired and analyzed, one more vital
part of a successful population study is developing a way to compare the results. By
using quantitative in addition to qualitative methods, some of the subjectivity involved in
data analysis can be eliminated and seemingly unrelated data can be directly compared.
For purposes of this study, a value “H” (heterogeneity) was defined to compare the
ability of the methods to distinguish among the tapes in the sample set. This value is the
ratio of the nmnber of distinguishable classes found within a population (D) to the total
number of items in the population (I). For the purposes of this study, I can be either rolls
of tape or nominal brands of tape. The two most extreme examples of this “H” value are
white cotton fibers and nuclear DNA. Since there is essentially only one distinguishable

class of white cotton fibers and an infinite number of items, Hwhite comm fibers would be

20

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DNA
the In:

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effectively 0. On the other hand, with just as many distinguishable classes of nuclear
DNA as there are items, Hnuciw DNA would be essentially 1. Presumably, the H values for
the individual methods and combination of methods used in this study will lie between 0
and l. The closer a method’s H value is to 1, the better it is at distinguishing the tapes in
a population.

Another form of quantitation that is used in this study is that of chemometrics,
specifically factor analysis (FA). This technique is meant to reduce the original observed
variables into fewer composite variables, or factors. These factors accOunt for the inter-
correlations among the observed variables and explain how certain variables are related
to each other. FA is slightly different from principal component analysis; the purpose of
the former is to explain relationships among variables, the purpose of the latter is to
account for the maximum amount of variation in the original data set with the fewest
number of factors, or components. FA is the method of choice if the observed variables
are not error-free, as in the current study”. Specifically, in this study, the variables
analyzed by this method are the weight percentages of various elements as determined by
SEM-EDS; these include Pb, Sb, Ca, and Mg for tapes with black adhesive and Pb, Sb,

Ca, Si, S, and Ti for tapes with clear adhesive.

21

 

IE.- :23“ W. II-l I
no

.‘J
0

USE

2.2

Tabl

2. MATERIALS AND METHODS

2.1 Materials and Reagents

Nine exemplar rolls of black electrical tape were requested and received from the
3M Hutchinson plant in May of 2004. These consisted of three rolls of each of three
different brands (Temflex 1700, Super 33+, and Super 88) of electrical tape from three
different batches. Twenty- nine other rolls of black electrical tape were either purchased
during the summer of 2004 or found in the exemplar room of the Bureau of Alcohol,
Tobacco, Firearms, and Explosives National Laboratory Center (ATF-NLC). The
complete list of all thirty-eight rolls is given in Table 3. The pentane for plasticizer
extractions was supplied by Burdick and Jackson and used as received. Glass vials (4
mL) with PTFE-lined caps and 10 mL disposable syringes were received from Sigma-
Aldrich and used as received. PTFE filters (0.45 pm) were supplied by Whatman and
used as received.
2.2 Instrumental Parameters

The parameters for ATR—IR, SEM-EDS, HT-GC-MS, and Py—GC-MS are listed in

Table 4.

22

Mus

Table 4: Instrumental parameters

ATR-IR

Spectrometer - SensIR Technologies, Travel IR
Sampling — single-bounce horizontal diamond ATR
Beam Splitter — zinc-selenide

Detector — DTGS

# Scans (sample and background) — 16

Resolution — 4 cm'1

Software - OMNIC

SEM-EDS
Scanning electron microscope - J EOL JSM-S910LV
Source — tungsten
Energy dispersive spectrometer
Detector — EDAX SUTW
Analyzer — EDAX Phoenix
Software - EDAX Genesis
Calibration settings:
Al peak Kd reference = 1.486 eV
Cu peak Kr’r reference = 8.040 eV

HT-GC—MS
Gas Chromato graph:
Instrument — Perkin Elmer Clarus 500 GC
Column — HTS (5% phenyl equiv. polycarborane-siloxane) aluminum-clad 25 m,
0.22 m i.d., 0.1 um film
Temperature Pro gram-
Initial temperature = 100°C hold for l min.
Rate = 15°C/min.
Final temperature = 370°C hold for 5 min.
Injector — Programmable temperature vaporizer: heated from 50—480°C, held for
2 min., reduced to 400°C, held for 3 min.
Split ratio— 30:1
Carrier gas — hydrogen, 1 ml/min.
Mass Spectrometer:
Instrument — Perkin Ehner Clarus 500 MS
Analyzer — quadrupole
Ionization mode — EI
Solvent delay — off for 3 min., on from 3-20 min., off from 20-24 min.
Full scan - m/z 50-550
Scan time - .15 s
Inlet temperature — 300°C
Source temperature — 300°C
Electron energy — 70 eV
Software -— Turbomass 5.0

23

 

Ila:

Table 4 (cont’d)

Py-GC-MS
Pyrolyzer — CDS Pyroprobe 2000
Interface temperature = 200°C
Pyrolysis conditions = 850°C for 15 5
Gas Chromatograph — Agilent Technologies 6890N
Column — Supelco MDN-SS capillary column, 30 m x 0.25 mm id. x 0.25 pm
Carrier gas - helium
Split ratio — 20:1
Temperature pro gram-
Irritial temperature = 40°C hold for 1 min.
Rate = 20°C/min.
Final temperature = 300°C hold for 6 min.
Inlet temperature = 300°C
Mass Spectrometer — Agilent Technologies 5973
Analyzer — quadrupole
Ionization mode — EI
Full scan — m/z 10-700
Scan time — .10 s
Inlet temperature -— 280°C
Source temperature — 230°C
Electron energy — 70eV

24

 

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2.3 Sample Preparation

For ATR-IR analysis of the adhesive side, pieces of tape measuring
approximately 2”x 3%” were placed adhesive side down onto the diamond. Each piece
was sampled in three different locations to test reproducibility. Backgrounds were run
after each roll. For SEM-EDS analysis of the backing, pieces of tape measuring
approximately %” x 3A” were placed adhesive side down onto aluminum stubs and .‘l

secured in a stub holder. Three separate stubs were prepared for each roll of tape and

V‘érnr"

each stub was analyzed one time.

 

 

For HT-GC-MS analysis of the plasticizer, pieces of tape measuring
approximately 3/4” x 3A” were folded in half and placed into 4 mL vials. Approximately 4
mL pentane was added to each vial and this was shaken vigorously by hand for
approximately 10 seconds. The solutions were then filtered through 0.45 pm filters
attached to disposable 10 mL syringes into labeled GC vials. Three pieces of tape from
each roll were extracted in this manner. A process blank was also prepared using pentane
in an empty 4 mL vial. Blanks of pentane were run between each sample. For Py-GC-
MS analysis, 0.25 mm squares of tape were cut, adhesive side up, using a scalpel,
tungsten probe, ruler, and stereoscope. These were then placed in a quartz tube
containing a glass wool plug. Three pieces of each of the exemplar rolls were analyzed.
The tube was cleaned after every sample by flash heating to 1000°C for 15 sec and the

wool was changed between rolls. Blanks were run after every sample.

25

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The
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Sam;
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”Pro

3. RESULTS AND DISCUSSION

3.1 Physical Examination of Adhesive Color

Figure 3 shows the separation of the sample set based on adhesive color (black or
clear) and ATR-IR analysis of the adhesive side. It is important to note that all the tapes
with black adhesive are manufactured by 3M. Therefore, this characteristic could be an
effective indicator of the manufacturer of a questioned or known fragment of tape if no
labeling or packaging is available. Also, noting adhesive color can help focus the
investigative collection of exemplars to only those tapes that share this feature with a
questioned sample. Completing this exam takes only a few seconds and it should be one
of the first steps in the analysis of electrical tape.
3.2 ATR-IR

The spectra shown in Figure 4 demonstrate the reproducibility of ATR-IR as it
relates to the adhesive side of electrical tape. The top portion of Figure 4 contains the
overlaid spectra from three rolls of Super 88 (2004) that were received directly from 3M
and are known to have originated from three different batches of tape. The similarity in
the spectra indicates there is little inter-batch variability with this component of the tape.
The bottom portion of Figure 4 contains the overlaid spectra of three different positions
on a single 2” x 3A” sample from a roll of WUL tape. Again, the lack of any significant
differences in the spectra indicates little intra-roll variations in the adhesive. These
spectra are shown as examples of the level of reproducibility achieved for all tapes in the
sample set, both between and within rolls. (Samples from the beginning, middle, and end
of three of the exemplar rolls were compared via ATR-IR and show the same level of

reproducibility; however, this was not tested for all tapes in the sample set.)

26

 

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7
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j Super 88 (2004) (Rolls A, B, C)
i
3:
51
.D
81
3i
<
1
I 3000 2000 1500 1000 650
cm'1
lWUL (Positions 1, 2, 3) f.
i ,3
l l.
l
f l i i

 

 

 

 

 

JR 4
. --- -....-..—-.-_..._.-_-.._..—.» - _ -
.——-—-—-,-
.. — .—
.—- .._.

Absorbance

__————--...—----
...———.._..

 

 

 

 

 

 

 

 

 

I
. .
I
I
I
.
I
I
D
U
I
C
.
‘ WW

3000 2000 1500 1000 650
cm’1

 

Figure 4: Examples of inter- and intra-roll reproducibility in ATR-IR of adhesive sides of
black electrical tape (Super 88 (2004) and WUL)

28

 

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Figure 3 shows the overall differentiation of the sample set based on ATR-IR
analysis of the adhesive side. The tapes are first grouped based on adhesive color,
discussed previously, then by presence and/or absence of major absorbances, and finally
by discemable and reproducible differences in the fingerprint region of the spectra. In
this manner, the twenty nominal brands of tape are separated into ten distinct classes with
four brands of tape being individualized. The goals of this particular analysis are to
classify the general type(s) of plasticizer(s) used in the tape backing as either aliphatic or
aromatic and to possibly gain information about the type of rubber polymer used in the
adhesive. The results obtained relating to the plasticizer type will be compared to the
HT-GC-MS data, as this method is expected to provide more definitive identification of
the plasticizers used in the tapes. Also, since the polymer occurs in very small amounts
relative to the plasticizer that leeches fiom the backing into the adhesive, any absorbances ~
from the polymer are often swamped out by those from the plasticizer. When making
decisions on the location of absorbances, the resolution of the instrument (:t 4 cm") must
be taken into account. Examples of characteristic IR bands common to electrical tape are
listed in Table 5.

As previously stated, all tapes with black adhesive are brands manufactured by
3M and these can be divided into three distinct groups using ATR-IR. The spectra of
Super 33+ (2004), Temflex 1700, and Scotch 33 are shown in Figure 5 to represent each
of these three groups. Notice that all three tapes exhibit a large absorption from carbon
black, which is added to the adhesive, resulting in the appearance of a rising baseline.
This was a feature common to all tapes with black adhesive. Only Super 33+ (2004) has

a small peak just above 3000 cm"1 corresponding to sp or sp2 hybridized carbon-hydrogen

29

ban

(phi

abs-
St;

Int

bonds. Also, note that there are no strong absorbances at 699 cm“1 (styrene) or 740 cm'I
(phthalates) in the spectrum of Super 33+ (2004) or Temflex 1700, while these
absorbances are very sharp in the Scotch 33 spectrum. Temflex 1700 and Scotch 33 have
absorbances at 1270 cm'l, 1120 cm], and 1070 cm"l (phthalates) that are lacking in the
Super 33+ (2004) spectrum. Overall, the spectrum of Scotch 33 has a unique appearance
in that the peaks are more defined (sharper) and more intense, relative to the baseline,
than those of either Super 33+ (2004) or Temflex 1700. All three of these brands Show
characteristic absorbances for the CC stretches of PBR at 910 cm'1 and 965 cm". The
spectra of the other brands of tapes in this group are presented in the appendix as Figures

25 and 26.

30

Table 5: Characteristic IR bands for electrical tape

 

Electrical Tape Component

IR Bands (cm'l)

 

Aromatic Plasticizer (phthalates)

1600, 1580, 650
1270, 1120, 1070 (ester stretches)
1570-1600 doublet (ring-stretching)
1730 (C=O) _
705, 741 (sharp)

 

Aliphatic Plasticizer (adipates)

1375-1400 (hydrocarbons)
1170, 1140 (ester stretches)

 

 

 

 

 

 

1740 (C=O)
PVC 1427, 1251, 960, 690, 635, 615
PBR 965, 910, 775
Natural Rubber 1380, 835, 1660, 570, 1446, 1376
Styrene 699, 760

 

 

31

 

‘. L19. 9 “IdflL'JI'i-II'V
q
i.

 

 

 

 

 

 

 

 

 

 

 

 

1 Super 33+ (2004)
1 965
1 vi:
8:
g,
{21
8.
'94
<.
l 3003
jTemflex 1700 9652 910
11201070 AI
- 1270 >UU
8+
54
p«
‘91.
.D
<.
699
I SCOICII 33 10709 65740N
1120
61 \MKM 910
i l
a 1270
1
2‘? ll 1
. l
3000 2000 I 1500 1000 650

cm'

Figure 5: Examples of ATR-IR spectra of black electrical tapes with black adhesive

(S

uper 33+ (2004), Temflex 1700, and Scotch 33)

32

Figure 6 shows the spectra of two tapes with clear adhesive that could be
individualized by ATR-IR. The most important features in the Lepage spectrum are the
complete lack of any significant peaks in the region from 1360 to 1000 cm”, the lack of a
doublet at 1570 cm", and the position of the C=O stretch at 1740 cm'1 (adipate). All the
other tapes with clear adhesive have at least three significant peaks between 1360 and
1000 cm'1 (1270, 1120, and 1070 cm'l), have a doublet at 1570 cm’1 from phthalate ring
stretching, and the C=O stretch is located at 1730 cm"1 (phthalate). These characteristics
tend to indicate that Lepage contains an adipate plasticizer while all the other tapes with
clear adhesive contain a phthalate plasticizer. However, it is more likely that the
spectrum of Lepage is actually representative of the rubber component(s) (i.e., broad 836
cm‘1 absorbance and OH bends at 1450 and 1375 cm'] indicative of natural rubber,
absorbances at 910 and 965 cm'1 from PBR, and a sharp absorbance at 699cm“l indicative
of styrene) in the adhesive rather than being dominated by absorbances from plasticizer.
The dominant plasticizer absorbance in all of the tape spectra is that at 1730 or 1740 cm'
1; this particular absorbance in Lepage is one of the smallest. Therefore, it is possible that
Lepage contains less plasticizer than all the other brands and/or the particular plasticizer
used does not leech into the adhesive to the same extent. The spectrum of Duck brand
tape exhibits a large absorbance at 1537 cm'1 that no other tape contains. This tape also

contains several other absorbances that are indicative of phthalate plasticizer.

33

1 Duck
‘ 1270 699

‘ 1730
, l
1 1120

1070

 

1537

Absorbance
I
e.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Lepage

1450
‘ l
23*, M I 699
iii rivs
§ 965 836
a l l
J

910

. l... b ‘ l
I 3000 2000 1500 1000 650

cm’1

Figure 6: Examples of ATR-IR spectra of black electrical tapes with clear adhesive
(Duck and Lepage)

34

The three spectra shown in Figure 7 are representatives of groups of tapes with
clear adhesive that could be differentiated by small, yet reproducible, differences in the
fingerprint region of the Spectra. The most significant differences in peak shapes
between Powerworks and Champion occur at 1120 and 740 cm". Notice that there is a
small, distinct, peak at a slightly higher frequency than 1120 cm'1 in the spectrum of
Champion that is lacking in that of Poweerrks. Also, the shoulder at a higher frequency
than 740 cm'1 in Powerworks is not present in Champion’s spectrum. There is also a
difference between these two groups in the ratio of the 910 and 840 cm'1 absorbances. In
Powerworks, the 910 cm'1 absorbance has a greater intensity than the 840 cm'1 peak; in
Champion, this is reversed. The spectrum of the Manco adhesive differs from the other
two in Figure 7 in the region of the 1370 cm'1 absorbance. Both Powerworks and
Champion have multiple peaks in this region; Manco has only a single, sharp, peak.
Manco lacks the shoulder on the 1120 cm'1 absorbance, differentiating it from Champion,
and it has a single peak at 740 cm", differentiating it from Powerworks. These three
spectra also Show that varying amounts of styrene (699 cm") in the adhesive polymer can
be an additional point of comparison between samples. The spectra of the other tapes in

these groups are shown in the appendix as Figures 27-29.

35

l Powerworks 699 5’

l 120
740

L

910

W W ’1‘"

 

‘ Absorbance

 

 

 

 

 

 

 

fin/J WJ

 

 

 

 

 

 

 

 

 

 

 

 

 

] Manco

1120 699
I 740

8—

g‘ 1370

a.

s. l

(I)

.0.

W l
1 120

 

Absorbance
E
2__

 

 

 

 

 

J

 

- LMMJ

3000 2000 "1500 1000 " 650
cm"1

 

Figure 7: Examples of ATR-IR spectra of black electrical tapes with clear adhesive
(Powerworks, Manco, and Champion)

36

The final two classes of tapes with clear adhesive are represented by the two
spectra in Figure 8. The two features that separate these two groups from those
previously mentioned are the small absorbance at a slightly higher frequency than 1450
cm'1 and the Size and shape of the absorbance at 1040 cm". The shoulder on the 1450
cm’1 peak is absent in all other tapes and the 1040 cm'1 peak is smaller. and less defined in
the spectra of Tartan and Frost King than in the rest of the sample set. The 1270 cm'1
absorbance is the distinguishing characteristic between these two groups in the position
of the shoulder relative to the apex of the peak. In the Frost King group, the shoulder is
at a higher frequency than 127 0 cm’1 and in the Tartan group, the shoulder is at a lower
frequency. Again, this particular absorbance is indicative of phthalate plasticizers and
these two groups show that even small differences in type(s) and/or amount(s) of this
component can be detected by ATR-IR. The spectra of the other tapes in these groups

are shown in the appendix as Figures 29 and 30.

37

 

3 Frost King

'4

1270

1450 J/

1040

Absorbance

{H

 

L

 

 

 

 

 

 

 

 

l

1270

 

1450

 

1040

4
SW
_‘—;=—-

Absorbance

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

3000 2000 1500 1000 650
cm'1

Figure 8: Examples of ATR-IR spectra of black electrical tapes with clear adhesive
(Frost King and Tartan)

38

3.3 SEM—EDS

Figure 9 shows the overall differentiation of the sample set based on adhesive
color and elemental composition. These two techniques divided the sample set into nine
distinct classes, individualized four nominal brands (Bengal, Globe, Intertape, and
Powerworks), and separated three nominal brands (Frost King, Super 33+, and Super 88)
into two classes (one with lead (Pb) and/or sulfur (S) and one without). If these particular
classes are now considered to be different nominal brands (the only difference being in
the Pb/S content), the total number of brands in the sample set is increased from twenty
to twenty-three. As in ATR-IR, there was no intra-roll variation observed in SEM-EDS.

All tapes contained carbon (C), oxygen (0), aluminum (Al) (from kaolin), and
chlorine (Cl) (from PVC) and these elements were not included in the differentiation or
later quantitative analysis. The presence and/or absence of Pb, S, magnesium (Mg),
silicon (Si), calcium (Ca), antimony (Sb), and titanium (Ti) were the key characteristics
used to differentiate the tapes. All of these elements are components in commonly used
fillers, stabilizers, and fire retardants in electrical tape (Table l).

The elements Pb and S, and Ca and Sb are included as pairs of elements,
respectively, to account for the overlap of peaks in EDS. Since most of the inorganic
fillers in electrical tape are present in trace amounts, it becomes increasingly difficult to
discern if a peak is from one or both of the overlapping elements. Therefore, to reduce
error, if a small, ambiguous, peak was present at these energies (2.3-2.4 eV for Pb and S,
3.6-4.0 eV for Ca and Sb) both elements were included in the differentiation. If it was a
large peak and clearly identifiable, as is the case for Pb in the tapes with black adhesive,

only a single element is listed. For purposes of factor analysis, both elements were

39

included in all of the quantitation (wt%) and the software was able to determine whether
there was Ca, Sb, Pb, and/or S present and, if so, how much of each.

The most important elements for distinguishing those tapes with black adhesive
were Mg and Pb. The tapes either contained one or the other of these elements, never
both. For example, the rolls of Super 88 and Super 33+ from 2001 contain Pb, while the
rolls from 2004 do not. The reason for this was confirmed after speaking with a 3M
representative, who stated that 3M discontinued the use of lead salts in its electrical tapes
in 2001. For those tapes with clear adhesive the most distinguishing element was Si. The
tapes were firrther divided based on presence/absence of Pb/S; the two rolls of Frost King
were separated at this point in the differentiation. The presence/absence of Ca/Sb and Ti

provided the final level of discrimination.

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41

Not only was SEM-EDS used to analyze the elemental composition of the PVC
backing, but this method also produced a magnified (200X) image of the texture of the
backing. Some examples of the variance observed in the backing texttue are shown in
Figures 10 and 11. These are photos of the backing texture of samples of Bengal,
Commercial 700, Electro Tuff, Frost King, Manco, Powerworks, and Shurtape and can be
considered representative of these brands as there was no significant intra- or inter-roll
variation in texture. Because this is such a subjective tool, it helps to separate the tapes
into groups based on overall texture as smooth or rough, size and number and density of

the inorganic particles, systematic defects, and the presence and/or amount of “bubbles,”

 

(oval indentations) or “craters” (jagged indentations).

As shown in Figures 10 and l 1, these seven brands of tape can be separated into
seven distinct texture groups. There will be no detailed discussion of all the textures
observed (shown in the appendix as Figures 31-33) or exactly how many distinguishable
groups this method could separate the population into, but it is important to note that this
characteristic can provide some discrimination. Specifically, even though Duck, Electro
Tuff, Frost King A, Lepage, Manco, Shurtape, and WUL are all in the same group based
on elemental composition, they can be separated into four groups based on backing
texture; these are Electro Tuff and Lepage, WUL, Shurtape, and Duck, Frost King A, and
Manco. This feature can increase the distinguishing ability of the method, SEM-EDS, as

a whole.

42

 

Bengal Commercial 700

         

.
k-

Electro Tuff Frost King ’

Figure 10: Examples of the backing texture of black electrical tapes under 200x
magnification

43

 

 

      

Powerworks

 

Shurtape

Figure l 1: Examples of the backing texture of black electrical tapes under 200x
magnification

 

3.4 Factor Analysis of SEM-EDS Data

As discussed previously, the purpose of FA is to help explain the relationships
between certain variables. In this study, the variables analyzed were the weight
percentages of the elements detected by SEM-EDS in tapes with both black and clear
adhesive. (The raw data is supplied in the appendix as Figures 34-38.) Since the tapes

could quickly and easily be separated into those with black and those with clear adhesive,

 

it makes sense to analyze each group separately rather than looking for minute chemical F :1

differences, when a clear visual differentiation is already possible. Therefore, the data

 

presented is in two parts and each offers separate and valuable information. . J
Figure 12 is the FA plot for the elemental composition of seventeen rolls
representing seven brands of 3M electrical tape (all with black adhesive.) The axes of
this plot represent the underlying/latent factors that best describe the variance in the
weight percentages (wt %) of Sb, Ca, Mg, and Pb. Factor 1 (F1) is plotted along the x-
axis and represents 86.31% of the variation in the data while Factor 2 (F 2) is plotted
along the y-axis and represents another 13.69% of the variation. Together, these two
factors account for 100% of the variation in the data as well as explain how certain
variables are related to each other. Each point on the graph represents the average for the
three replicates of each roll. The error bars represent the standard deviations in F 1 and
F2 and can be used to determine if two samples are differentiable; if the error bars
overlap it is reasonable to assume that no differentiation can be made. Likewise, if the
error bars do not overlap in either the x or y direction, it is assumed that there is enough

variation in the elemental composition of the tapes to state that they are differentiable;

45

this criteria is the basis for the following discussion about the differentiation of the
sample population based on FA.

In the development of the factors F1 and F2, the algorithm assigns different
loadings, or coefficients, for each variable. Figure 13 shows the factor loadings for each
variable relative to F1 and F2 for the tapes with black adhesive. The farther an element is
displaced along an axis, the greater its effect on the overall value of that factor for each
roll of tape. In this case, Mg and Pb are the two biggest contributors to F1, and Sb, Ca,
Pb, and Mg all contribute to F2.

When comparing the differentiation based on visual inspection of the elements
present or absent (nine groups) to the differentiation based on FA of the raw SEM-EDS
data (eighteen groups), it becomes clear that FA can greatly improve the overall
differentiation of an analytical scheme. Table 5 lists the twelve brands of tape that are
individualized and the eleven brands that are part of six different groups after FA is
incorporated into the SEM-EDS method. Using the nine original groups, the FA plot,
and the raw data, detailed information about what differentiates certain brands of tapes
can be gained; the same information could be surmised manually but would require more

time and difficult manipulations.

46

 

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Factor Loadings (Black Adhesive)
axes F1 and F2: 100%

.0
o:

O
.5
"U
0"

.0
N

0.0 . —- i -— 4*,

F2 (13.69%)

4.5 .1.0 .05 on
F1 (86.31%)

Sb .
Ca.

0.5

1.0

1.5

 

Figure 13: Factor loadings for tapes with black adhesive

48

 

Table 6: Overall differentiation based on factor analysis of SEM-EDS data

BRANDS INDIVIDUALIZED via SEM-EDS-F A

Bengal
Duck
Electro Tuff
Frost King B
Globe
Intertape
Lepage
Manco
Powerworks
Shurtape
Temflex 1700
Vanguard

BRANDS IN GROUPS via SEM-EDS-F A

Comm.700 / Scotch 33
Frost King A / WUL
Super 88 (2001) / Super 33+ (2001)
Super 88 (2004) / Super 33+ (2004)
Tartan / Champion
667 Pro Series / Champion

49

I]
r

With this in mind, looking back at Figure 12, the relationship between certain
elements can be examined. It is known from the raw EDS data that the four brands of
tape to the left of the y-axis contain Pb, the three brands to the right of the y-axis contain
Mg, and none of the brands contain both of these elements. However, the most important
use for such a FA program would be to differentiate two samples that could not be easily
differentiated by human interpretation of the results (i.e., in different groups in Figure 9.)
In the FA plot, Temflex 1700 is clearly separated from Super 88 (2004.) and Super 33+
(2004), and Scotch 33 and Commercial 700 are clearly separated from Super 88 (2001)
and Super 33+ (2001). These differentiations appear to be based on differences in the
amounts of Sb and/or Ca present in the tapes. Specifically, both Super 33+ (2004) and
Super 88 (2004) contain approximately twice the amount of Sb as does Temflex 1700 and
both Super 33+ (2001) and Super 88 (2001) contain slightly more Sb and Ca than do
Commercial 700 and Scotch 33. Overall, FA of four elements in seven of the twenty-
three brands of tape examined in this study was able to create two additional distinct
classes of tapes. However, Super 33+ and Super 88 (2004 and 2001) are still not
differentiable, within the same year, using elemental composition as a comparison.

Figures 14 and 15 show the factor loadings and FA plot for the sixteen brands of
tape with clear adhesive, respectively. The factor loadings plot shows that Pb has the
greatest effect on F1 while Si has the least effect. This plot also shows that Sb has the
greatest effect on F 2, Ca and Pb have the least effect, and Si, Ti, and S all contribute to
F2. Looking at Figure 15, there are several important features to note; all tapes above the
x-axis, except Champion, contain Sb while those below the x-axis do not, Champion is

the only tape that contains Ca and not Si, Intertape is clearly separated fi'om all other

50

brands of tape based on the presence of Ti, and Powerworks and Frost King B are
separated because they do not contain Pb or Ti.

Specifically, noticing that Vanguard is clearly separated from the other three
brands in its original SEM-EDS group, an inspection of the raw data indicates that it does
indeed contain about half the amount of Pb as do Tartan, Champion, and 667 Pro Series.
Also, In the same manner, Shurtape and Lepage both contain Sb and are therefore
separated from the other five brands in their group, but Lepage contains more than twice
as much Pb as does Shurtape, placing it farther to the right on the FA plot. Also, Duck
and Manco contain slightly less Pb than do either Frost King A or WUL, placing them
farther to the lefi on the FA plot; Duck contains slightly more Pb than Manco. The other
separations, involving Frost King A, WUL, Electro Tuff, Manco, Duck, Tartan and 667
Pros Series, can be attributed to differences in the amounts of Ca, Sb, S, Si, and Pb that
are not readily noticeable in the raw data. (It is of interest to note that FA of the SEM-
EDS data was able to separate the two different rolls of Bengal tape when initial
inspection of the SEM-EDS data could not; this is another indication of the ability of FA
to detect subtle differences in relative elemental compositions. This could be the first
instance of variation in batch formulations that contain all of the same major ingredients

in slightly different amounts that are only detectable by quantitation of the data.)

51

 

F2 (31.46%)

1.0
0.8
0.6
0.4
0.2

 

Factor Loadings (Clear Adhesive)
axes F1 and F2: 88.85%

Sb

 

-0.2
-0.4

-O.6
-0.2

 

0.0 0.2 0.4 0.6 0.8 1.0
F1 (57.39%)

1.2

 

 

Figure 14: Factor loadings for tapes with clear adhesive

52

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53

3.5 HT-GC-MS

Figure 16 shows the overall differentiation of the sample set based on adhesive
color and HT-GC-MS analysis of pentane plasticizer extracts. The definitions of the
plasticizer abbreviations and what defines a “base,” “major,” and “minor” component are
listed at the bottom of the figure along with the extracted ion associated with each
plasticizer type. All plasticizers were identified based on standards run under the same
conditions as the samples or a combination of the mass spectrum of the extracted ion and
retention time relative to that of known standards. As Figure 16 shows, the
differentiation of the tapes is based on the relative concentrations of the various
plasticizers present.

Some trace level components were also detected at less than 1% of the base peak
height. Examples included DOA in Duck and DEP and DOP in Super 33+ (2001 and
2004). These components were not included in the differentiation as they may not be
reliably detected in all samples from the same source. These differences could arise from
slight variations in sample preparation, contamination, or the sample size. With case
samples, trace level components can be transferred to electrical tape in any number of
ways and, if the source cannot be determined, this may lead to inconclusive
association/elimination results.

It is important to note that all tapes that contain DOA as either the base or major
component or that contain a major amount of an unknown adipate at 15.4 minutes are
known to be manufactured by 3M and have black adhesive. This indicates that 3M is the
only manufacturer of those represented by the sample set that uses adipates as the main

type(s) of plasticizer. All tapes with clear adhesive have DOP as their base plasticizer

54

and Tartan and Vanguard are the only two tapes in the sample set that show TOTM in the
149, 305 extracted ion chromatograrn.

With regards to the ATR-IR data discussed previously, the class represented by
Super 33+ (2004) lacks the absorbances at 1270, 1120, 1070, and 740 cm" that are
indicative of phthalate plasticizers; however, these tapes also lack any significant IR
absorbances that would be considered indicative of the adipate plasticizers shown in the
HT-GC-MS results. The Scotch 33 brand and the group represented by Temflex 1700 in
ATR-IR have DOP as the base plasticizer by HT-GC-MS and contain most of the
corresponding absorbances by ATR-IR. Most tapes with clear adhesive (all except
Lepage) contain IR absorbances characteristic of aromatic plasticizers and Tartan and
Vanguard are in a separate group by both ATR-IR and HT-GC-MS. However, given that
(according to HT-GC-MS) most of these tapes contain multiple plasticizers of both types,
it makes sense that the ATR-IR data would not be explicitly indicative of one plasticizer
type over another. In this case, HT-GC-MS would be the better choice to assess
plasticizer type as the results are mutually exclusive of each other and not complicated by
multiple components.

Figures 17-23 show the HT-GC-MS extracted ion chromatograms (m/z 129, 149,
and 305) of selected tapes from the groups shown in Figure 16. These are representative
of the replicate samples; the only differences that occurred within brands were at the trace
levels and not considered in the overall differentiation. Each chromatograrn is labeled
with the plasticizer abbreviation defined in Figure 16 and the relative amount of each
plasticizer as base, major, minor, or trace. The extracted ion chromatograms for the other

tape brands are shown in the appendix as Figures 39-46.

55

Black Clear

 

 

Adhesive Adhesive
BaseDOA I Base DNP Base
Maj. X Maj. DOA DOP I 1
Min. I Maj. TOTM Min.
Min- DOP DNP DCI)P Frost King Champion Vanguard WUL
D k T rt
Corlnm. Super 33+ Scotch 33 Globe macaw a an Manco
700 Super 88 Intertape
Lepage
Powerworks
Shurtape

Extracted Ion 129

DOA — bis(2-ethylhexyl)adipate

X — unidentified adipate at 15.4 min.
Extracted Ion 149

DEP — diethylphthalate

DOP — bis(2-ethylhexyl)phthalate

DNP — diisononylphthalate

DDP — diisodecylphthalate
Extracted Ion 305

TOTM — tri(2-ethylhexyl)trimelitate

Base = largest peak height in extracted ion chromatogram
Maj. (major) = less than 100%, greater than 10% of base peak height
Min. (minor) = less than 10%, greater than 1% of base peak height

Figure 16: Overall differentiation based on adhesive color and HT-GC-MS analysis of
plasticizer extracts

56

 

Commercial 700 (129 ion) j

 

 

 

 

 

 

‘ DOABasc
1
5 1
O
. c
1 fl ‘
, 1: 1
1:
3 l
2
xMajor
f 1 1 1
.‘t 6 9 12 15 18
Time (min)
‘7 77 7 7 7 77 7 777 7777777, 77777 77777
‘ Commercial 700 (149 and 305 ions)
DNPMajor
o
O
C
111
'u
C
3 DOPMinor
<
1 . AJAl... .. ..‘4.. 4.1. fl, 7 J . 1.1-1.1.”-.. 7171......1
l
l 3 6 9 12 15 18
| Time (min)
7

 

 

Figure 17: Extracted ion chromatograms of Commercial 700 tape

57

 

 

 

Super 33+ (129 ion)

 

 

 

 

 

 

 

 

6 9 12 15 18

Time (min)

DOABasc

. l

0 l
C
(U

u l

C .

a i

2 1

xMajor 3

l

T ‘ 7 - A i

6 9 12 15 18
Time (min)
Super 33+ (149 and 305 ions)
DNPMinor

8
C
(I
'O
C
3
.D
<

 

 

 

 

Figure 18: Extracted ion chromatograms of Super 33+ tape

58

 

 

Temflex 1700 (129 ion)

DOAMajor

 

 

 

 

 

 

 

 

 

 

 

o
2
a
'u
1:
:1
a
<
(3 6 9 12 15 18
Time (min)
Temflex 1700 (149 and 305 ions)
DNPBasc
8
c
(I
1:
C
a
.e
<
1
i :3 6 9 12 15 18
1 Time (min)

 

Figure 19: Extracted ion chromatograms of Temflex 1700 tape

59

 

 

 

 

 

 

Scotch 33 (129 ion)

 

 

 

 

 

 

 

 

DOAMajor
o
e
r:
a
'e
r:
a
a
<
1' I l
6 9 12 15 18
Time (min)
Scotch 33 (149 and 305 ions)
DNPBase
e
0 I
c
a
u
1:
:1
a
< .
DOPMinor
6 9 12 15 18
Time (min)

 

Figure 20: Extracted ion chromatograms of Scotch 33 tape

60

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Frost King (129 ion)
DOAMinor

O

0

C

(I
3

C

3
.0
< XTrace

1.7 A‘s--37“; “u 7.....477 A-L ---._..___“ 7-_4 .7.1 J 777L77TL7-51-“-7
f 6 9 12 15 18
Time (min)
_ . l.
Frost King (149 and 305 Ions)
DOPBase

0

0

c

(I

1:

C

3

a

<

1 6 9 12 15 18

Time (min)

 

Figure 21: Extracted ion chromatograms of Frost King tape

61

 

3 667 Pro Series (149 and 305 ions) 7

 

 

 

 

 

 

 

 

 

 

 

DOPBasc
o
0
1:
(I
1:
1:
:1
.n
<
i
1
i 6 9 12 15 18
Time (min)
7 7 7 7 7 7 7 7
Manco (149 and 305 ions)
; DOPBase
In
M
0 DDPMinor
0
1:
I!
1:
c
z
.e
<
7- 77 -7- .7 .111 77777
|
6 6 9 12 15 18
|
Time (min)

 

 

 

Figure 22: Extracted ion chromatograms of 667 Pro Series (t0p) and Manco (bottom)
tapes ‘

62

 

 

 

 

 

Tartan (129 ion)

 

 

 

 

 

 

 

 

 

DOAMinor
I

° :'

0

1:

I!
u

C

a
.e
<

13 6 9 12 15 18
Time (min)
T" " ‘ *“ F“ .
; Tartan (149 and 305 lens)
I DOPBase

e

0

c

N

'e

1:

3

.e

< TOTIVIMajor

:3 6 9 12 15 18

 

Time (min)

 

 

Figure 23: Extracted ion chromatograms of Tartan tape

63

Overall, HT-GC-MS has proven to be a very effective method for both
comparison and identification of electrical tape plasticizers. Its high operating
temperatures allow for better chromatography of high molecular weight species, such as
plasticizers. In fact, the normal maximum temperature of a typical GC column is 325°C;
the HT model reaches this temperature at 16 min of a 20 min program. As can be seen by
the HT chromatograms presented here, there are at least two plasticizers that elute very
close to this temperature (TOTM and the unidentified adipate). Also, with the injector at
temperatures of 400°C and above, the initial vaporization of the plasticizers is improved
from that in typical GC-MS.

3.6 Py-GC-MS

Pyrolysis is a well-known and established technique for the analysis of
polymers.6’8'9"0’l 1'12 However, the results of this study raise questions about its suitability
for electrical tape analysis. Given that this particular product is a heterogeneous mixture
of many different components, it is not surprising that any results obtained from the
pyrolysis of electrical tape are difficult to interpret; in this case, inconsistent to the point
of not being able to associate a fragment of tape to the roll from which it is known to
have originated.

Figure 24 shows the pyrograms of two samples of electrical tape taken from the
same roll of tape (Super 88 (2004)) and run sequentially on the same day. The labeled
peaks represent cyclopentanone, a known pyrolysis product of adipates, and various
forms of the intact adipates from the plasticizers in the tape. As is easily observed from
the chromatograms, the ratio of these components to one another is not consistent, even

in samples run sequentially. Also, the abundance of the adipates varies from one sample

64

to another (different ratios of three large peaks labeled). This indicates that the pyrolysis
of these specific components (i.e., the plasticizers) is not reproducible.

The cause for this variation is not yet completely understood but is believed to be
the result of the plasticizers thermally desorbing from the tape at relatively low
temperatures during instrument equilibration and initial pyrolysis. If this is the case,
unless this process can be prevented or controlled, the pyrolysis of an electrical tape
sample will never occur in exactly the same manner and/or produce the same components
in the same abundances. With any method, the more variation observed within a single
source, the less valuable the information obtained in making comparisons between
questioned and known samples. Therefore, Py-GC-MS will not be considered in the

remainder of this work for purposes of electrical tape differentiation.

65

Cyclopentanone
Adipates (e.g. DOA)

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Figure 24: Pyrograms of two samples from the same roll of tape (Super 88 (2004))
analyzed on the same day

66

3.7 Comparison of Methods Using “H” Values

For this study, H can be computed for each individual method (ATR-IR, SEM-
EDS (with and without FA), and HT-GC-MS) as well as for the combination of all three
methods. All that is needed is the number of distinct classes generated by a method, D,
as well as the total number of items in the population, I. Since several nominal brands
are represented by multiple rolls, it is more applicable to define I in terms of brands of
tape, 23 (including the “brands” that were created based on presence/absence of Pb in
SEM-EDS), than in terms of rolls of tape. Therefore, if ATR-IR, SEM-EDS, and HT-
GC-MS have D values of 10, 9, and 8, respectively, and I is set at 23 brands of tape, the
H values for these methods are 0.43, 0.39, and 0.35, respectively; combining the three
methods results in 18 distinguishable groups and an H value of 0.78. However, if FA is
incorporated into SEM-EDS, the D value for this method increases to 18 and H for the
method is now .78; H for the three methods (ATR-IR, SEM-EDS-F A, and HT-GC-MS)
increases to .91 (D=21). It is apparent that using multiple, orthogonal, methods,
including quantitation, provides greater differentiation of this sample population than any

single method.

67

4. CONCLUSIONS AND FUTURE WORK
4.1 Conclusions

Ideally, the techniques employed in a forensic comparison scheme will be able to
differentiate any two samples of a population that are truly different. In order to evaluate
the success of a scheme at achieving this goal several issues must first be addressed. This
study focuses on the forensic analysis of PVC electrical tape and attempts to determine
the set of techniques that is most effective at distinguishing members of the electrical tape
population. This is accomplished by researching and monitoring the electrical tape
market, analyzing a representative population with multiple, orthogonal, methods, and
quantitatively comparing the results.

By making contacts with an electrical tape manufacturer (3M) and product code
companies (UL and UCC), valuable information about the past and current electrical tape
market is obtained. This is that there were five major manufacturers of electrical tape in
2002, 3M discontinued the use of lead salts in its tapes in 2001, and that UL control, UL
file, and UCC numbers can be used to indicate the manufacturer of a roll of electrical
tape. All of this information helped in the collection of a population (thirty-eight rolls)
representing at least seven manufacturers and twenty nominal brands of electrical tape.
The sample collection also contained exemplar samples in order to study intra- and inter-
batch variation.

A cursory physical examination of adhesive color was able to separate the
population into those tapes with clear adhesive and those with black adhesive. ATR-IR
analysis of the adhesive side of the tapes was able to differentiate each. of these two

groups and separate the population into ten distinct spectral classes with four brands of

68

tapes individualized (Scotch 33, Champion, Lepage, and Duck). SEM—EDS analysis of
the backing side divided the population into nine classes of different elemental
composition with four nominal brands individualized (Bengal, Globe, Intertape, and
Powerworks) and three nominal brands separated into those containing lead and those not
(Frost King, Super 33+, and Super 88). Incorporating FA into the SEM-EDS analysis
was able to separate the population into eighteen groups and individualize twelve brands
(listed in Table 5). HT-GC-MS analysis of pentane plasticizer extracts resulted in eight
classes based on the types and relative amounts of plasticizers present with three brands
individualized (Commercial 700, Temflex 1700, and Scotch 33). Unlike some previous
works, this study found that Py-GC-MS is not a very effective method for electrical tape
analysis. The results obtained indicate that one of the most abundant components of
electrical tape, plasticizers, can not be reproducibly pyrolyzed to the point of making
confident associations between questioned and known fragments of electrical tape. The
sample-to-sample and day-to-day variations are such that use of this method should be a
last resort in electrical tape analysis.

Quantitation of the relative abilities of ATR-IR, SEM-EDS-FA, and HT-GC-MS
to distinguish the population resulted in H values of 0.43, 0.78, and 0.35, respectively.
The combination of all three of these methods increased this value to 0.91 , supporting the
idea that using multiple methods of analysis can increase differentiation within a
population. Also, these values can help in developing an overall scheme for electrical
tape analysis by using the methods with the highest H values (most discriminating) in the
beginning of an analysis and the methods with the lowest H values (least discriminating)

at the end of an analysis. However, the amount of sample preparation, time of analysis,

69

and relative destructiveness of each method must also be taken into account. ATR-IR
and SEM-EDS require very little, if any, sample preparation and are relatively quick
analyses while HT-GC-MS necessitates a pentane extraction of the plasticizer and a
twenty minute run on the instrument. With regards to destructiveness, HT-GC-MS
causes the most damage to a sample, SEM-EDS causes limited changes, and ATR-IR is
completely non-destructive.

Therefore, taking all of this into consideration, the results of this study indicate
that although SEM-EDS-F A does provide the most discrimination, the most appropriate
scheme for electrical tape analysis would start with ATR-IR analysis of the adhesive side
due to its lack of sample destruction. After ATR-IR, SEM-EDS-FA analysis of the
backing and HT-GC-MS analysis of plasticizer extracts, the most destructive method, can
provide further differentiation if needed. A more detailed physical examination than was
done in this study, which used only adhesive color, should be completed prior to any
instrumental analyses. This would include width and thickness measurements and
microscopic texture of the backing and adhesive.

Based on the FA results obtained with SEM-EDS data, it is probable that
incorporating such an analysis into other methods can provide greater discrimination as
well as allow for the correlation of data that was previously very difficult, it not
impossible, to relate. Therefore, a more in depth look at factor analysis as a way to
differentiate the electrical tape population is necessary.

Overall, both intra— and inter-brand variation in electrical tape composition was
observed in this study while neither intra-batch (intra-roll) nor inter-batch variation was

observed (excluding the initial Py-GC-MS results). However, given the large error bars

70

for some of the exemplar rolls of tape in FA, there is the possibility that there is a small
amount of intra- and inter-batch variation that could be detected under different
parameters. If this is the case, once detected, the heterogeneity of the population is
increased as is the significance of any association. Problems with this level of detection
arise when different batches from different nominal brands start to overlap (error bars)
and the observed variation would need to be tested using manufacturer exemplars.

Nineteen of twenty-three nominal brands of electrical tape were differentiated
using instrumental and chemometric methods. Three nominal brands (Super 88, Super
33+, and Frost King) were separated into two groups based on the presence/absence of Pb
in SEM-EDS. Super 33+ (2001) and Super 88 (2001) and Super 33+ (2004) and Super
88 (2004) are the only brands of tape that could not be distinguished by the methods used
in this study.

Both of the Super 33+ brands and both of the Super 88 brands were manufactured
by 3M (UL control #539H) and both have the same specifications (Table 2). However,
the overall thickness of the tapes, as labeled, differs by 1.5mil (1mil = .001 inch)
indicating that these two brands of tape are most likely composed of the same raw
materials used in different amounts. Therefore, it is not necessarily a downfall of the
analytical scheme that these two brands of tape could not be differentiated. In fact, even
if thickness measurements were completed prior to any instrumental analyses, the results
obtained would not be heavily relied on when making conclusions about possible origins
of a questioned sample, given the nature of PVC (stretches and changes shape when
used). So, stating that these two brands of tape are indistinguishable is a reasonable

conclusion.

71

4.2 Future Work

The goals of this study were to develop an overall analytical scheme for the
forensic analysis of electrical tape while addressing issues that are often ignored when
completing population studies such as the one at hand. To date, a preliminary analytical
scheme has been developed with instrumental techniques as its base and some important
work has been done regarding an assessment of product codes and the manufacture and
distribution of electrical tape. However, there is more work that can be done in
addressing some issues that were not included in the original project because of either
time constraints or having arisen during the course of the research.

Each step in the proposed scheme has the potential for improvement. Including
width and thickness measurements and a more detailed examination of the backing and
adhesive textures by both stereomicroscopy and SEM-EDS would ensure a complete
physical examination prior to employing any instrumental techniques. Devising a
method to isolate the adhesive and analyzing this portion via ATR-IR would elicit
additional, possible very useful, information on the types of rubbers and tackifiers used in
electrical tape. Adjusting the SEM-EDS parameters so as to increase detection of trace
elements would reduce the ambiguity of elements with overlapping energies and provide
more definitive results in this step of the analysis. Also, decreasing the magnification in
SEM-EDS would analyze larger sections of the tape at once and perhaps eliminate some
of the variation (micro-heterogeneity) in the elemental data obtained (error bars in FA.)
Obtaining and running additional plasticizer standards on HT-GC-MS could aid in the
identification of the adipate that elutes at 15.4 minutes in the 3M tapes. Also, continued

chemometric analysis of the data obtained from each individual method can determine if

72

such analysis is useful for further differentiation of the sample population. Comparing
data from different techniques via chemometrics could be a way to objectively evaluate
relationships within data that were previously undetected.

Just as important as improving the analytical methods used in this project is
continuing to monitor the sample population for changes in composition and/or
distribution so the developed scheme retains its usefulness. This involves making and
maintaining contacts with companies that control these aspects of the electrical tape
population. Also, through these relationships additional exemplars can be obtained and a
more in depth study of inter- and intra- batch variation can be completed. One vital
aspect of forensic analyses that was not examined in this work is that of the applicability
of the scheme to case samples, not just samples collected for the study. To do this, both
pre- and post-use samples of electrical tape must be analyzed so as not to assume that the
chosen scheme is able to differentiate the used samples to the same extent as pristine
samples. Changes in the structural and/or chemical integrity of the tape can occur from
stretching and/or use in an exploding IED; studies analyzing these effects are warranted.
Finally, due to known plasticizer leeching, it is of concern to the researchers of this
project that storage conditions of electrical tape samples may affect the chemical
composition of the samples and hinder forensic comparisons. Because of this, until
firrther work is done to determine if this is indeed an issue, samples of electrical tape
should not be stored in items made from materials containing large amounts of

plasticizers (i.e., plastics).

73

APPENDIX

74

Super 33+ (2001) FM

 

 

 

.1
1 l
J l
l
.‘
,1. J
1'1 I
2‘ . /\.’
or 1 \JV
0 ,.
51 J
vie-1 "'11 ff”
0 / "
.8 "1. "V
4 1 1 ‘1 1'
<4 , ‘ ’1 .
l U
,1
ft
1“. .1 j
l L: i i 11 or 5r
i 1' W ”’4'"
1
1 \ _..J
| :"r
i i‘a m, /
1 7, ‘1 ,1
f” \‘ 1P \1 ’l
1 \\ I 1“,",
r'"-*Mj ‘\' V
1 Super 88 (2004) l\
.1
J
O .
‘5?
‘3
o -1
m
43 .
<
..(
-(

 

 

Figure 25: ATR-IR spectra of black electrical tapes with black adhesive
(Super 33+ (2001) and Super 88 (2004))

75

1 Super 88 (2001)

L

Absorbance

7L

 

 

: Commercial 701 ’1,

Absorbance .

17

7

L

 

 

 

Figure 26: ATR-IR spectra of black electrical tapes with black adhesive 1
(Super 88 (2001) and Commercial 700)

76

4 667 Pro Series

 

 

 

 

 

 

 

 

 

 

 

 

‘.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

J7

‘ Absorbance

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

J
i [J

Figure 27: ATR-IR spectra of black electrical tapes with clear adhesive
(667 Pro Series and WUL)

 

 

 

77

Intertape

77

 

7
E

 

 

.1

1 Absorbance J
S

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

' Electro Tuff

x

 

75——

 

 

Absorbance

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

_T ,_..._,,.‘_1.

Figure 28: ATR-IR spectra of black electrical tapes with clear adhesive
(Intertape and Electro Tuft)

78

' Shurtape f

 

7 71
F
:—

 

 

. Absorbance

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

1 Bengal

Absorbance .

 

75

 

 

 

 

 

 

 

 

 

 

 

 

 

 

W

Figure 29: ATR-IR spectra of black electrical tapes with clear adhesive
(Shurtape and Bengal)

 

 

? M

W

 

79

: Globe

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

' Vanguard

7

. Absorbance

 

 

7
775

 

 

 

 

 

 

 

 

 

 

1.
.1 .
n-
M *7
3 V

Figure 30: ATR-IR spectra of black electrical tapes with clear adhesive
(Globe and Vanguard)

80

 

 

 

 

 

667 Pro Series Cnharnpio

 

Duck ’ Globe

    

Intertape

Figure 31: Examples of the backing textures of black electrical tapes under 200x
magnification

81

   

Lepage I i Scotch 33

         

Super 33+ Super 88

 

Tartan

Figure 32: Examples of backing textures of black electrical tapes under 200x
magnification

82

 

Temflex 1700 Vanguard

 

Figure 33: Examples of the backing textures of black electrical tapes under 200x
magnification

83

 

 

 

 

Sample Element

Temflex Mg 81) Ca
A1 0.20 0.76 0.26
A2 0.16 0.76 0.28
A3 0.19 0.69 0.29
B1 0.23 0.64 0.26
82 0.18 0.67 0.22
B3 0.17 0.49 0.22
C1 0.21 0.76 0.35
C2 0.21 0.72 0.19
C3 0.20 0.68 0.23

Average 0.19 0.69 0.26

Super 88 (2004)

A1 0.25 1 .52 0.52
A2 0.27 1 .50 0.44
A3 0.28 1 .69 0.38
31 0.24 1 .52 0.34
82 0.21 1 .53 0.33
83 0.23 1 .61 0.51
C1 0.23 1 .62 0.48
C2 0.22 1 .81 0.51
C3 0.24 1 .82 0.60

Average 0.24 1 .62 0.46

Super 33 + (2004)

A1 0.28 1 .13 0.25
A2 0.29 1 .75 0.52
A3 0.26 1 .72 0.44
81 0.26 1 .64 0.46
82 0.25 1 .55 0.38
83 0.23 1 .59 0.46
Ct 0.26 1 .46 0.42
C2 0.21 1 .58 0.40
C3 0.27 1 .47 0.74

Average 0.26 1 .54 0.45

Figure 34: Weight percentage values of elements for electrical tapes with black adhesive

84

 

 

 

 

 

Sample Element
"sip" 33+ (2001) 8? __———Ca Pb
1 1.31 1.56
2 1.51 2.14
3 1.50 1.85
Average 1.44 1.85
Super 88 (2001)
A1 0.96 0.27 1.57
A2 0.82 0.22 1.58
A3 1.05 0.27 1.77
B1 1.06 0.26 1.80
B2 0.93 0.25 1.61
B3 1.09 0.25 1.76
Average 0.99 0.25 1 .68
Scotch 33
A1 0.62 0.10 1.74
A2 0.44 0.08 1.76
A3 0.69 0.10 1.85
B1 0.53 0.08 1.33
B2 0.50 0.09 1.50
B3 0.67 0.10 1.71
C1 0.74 0.07 1.74
02 0.70 0.13 1.75
C3 0.81 0.09 1.69
D1 0.55 0.09 1.83
D2 0.64 0.09 1.90
D3 0.65 0.07 1.81
Avegge 0.62 0.09 1 .76
700 Comm
A1 1.49 1.12
A2 1.43 1.31
A3 1.23 1.13
B1 1.34 1.28
82 1.13 1.23
B3 1.06 1.27
Average 1.28 1 .22

Figure 35: Weight percentage values of elements for electrical tapes with black adhesive

85

 

 

 

 

 

Sample Element
Tartan1710 Sb Ca Pb S St
A1 1.04 0.88
A2 1.15 0.89
A3 1.28 0.97
81 0.97 0.74
B2 1.03 0.81
B3 1.03 0.61
Overall 1.08 0.82
867 Pro
1 1.07 0.69 0.14
2 1.07 0.85 0.12
3 1.07 0.91 0.14
Average 1.07 0.82 0.13
Bengal
A1 0.44 0.10
A2 0.50 0.12
A3 0.30 0.12
81 0.61 0.15
B2 0.60 0.11
83 0.58 0.10
Overall 0.51 0.12
Champion
A1 2.82 1.38
A2 2.94 1.18
A3 2.77 1.09
B1 2.70 1.06
B2 2.64 1.33
B3 2.83 1.03
Overall 2.78 1.18
Frost King
A1 1.80 0.78 1.61
A2 1.67 1.11 1.61
A3 1.68 1.32 1.62
B1 1.76
B2 1.65
B3 1.68
Overall 1 .72 1 .07 1 .66

 

 

Figure 36: Weight percentage values of elements for electrical tapes with clear adhesive

86

 

 

 

 

 

 

 

 

 

Sample Element
Globe Sb Ca Pb 8 SI Ti
1 1.09 1 .22 ‘
2 1 .1 1 1 .28
3 1 .16 1 .13
Avegge 1 .12 1 .21
Duck
1 0.69 0.77 1 .02
2 0.81 0.77 1 .03
3 0.72 0.64 0.88
Average . 0.74 0.73 0.98 ,
lnterBlaek
1 0.95 1 .18 0.26
2 1 .03 1 .13 0.22
3 0.96 1 .10 0.21
Average 0.98 1 .14 0.23
LePage
1 1 .50 1 .21 2.16
2 1 .80 1 .55 2.30
3 1 .72 1 .52 2.04
Average 1 .67 1 .43 2.17
Manco
1 1 .22 1 .46
2 1.06 0.53 0.13 1.38
3 1.02 0.47 0.07 1 .36
Average 1.10 0.50 0.10 1.40
Powerw
1 0.82 1 .15
2 0.76 1 .19
3 0.81 1 .15
Average 0.80 1 .16
ShurTape
1 1.54 1.15 0.56 0.11 1.41
2 1.43 1.16 0.69 0.06 1.43
3 1 .31 1.22 0.49 0.07 1 .36
Average 1 .43 1 .18 0.58 0.08 1 .40
Tuffl‘ ape ‘
1 0.89 1 .29 . 1 .02
2 0.97 0.92 1 .01
3 0.88 1 .14 1 .03
Average 0.91 1.12 1 .02

 

Figure 37: Weight percentage values of elements for electrical tapes with clear adhesive

87

 

 

 

Sample Element
Vanguard Sb Ca Pb S Si
A1 1 .17
A2 1 .19
A3 1 .04
B1 1.14 0.42 0.1 1
B2 1 .01 0.49 0.06
B3 1.00 0.39 0.07
Overall 1 .09 0.43 0.08
WUL
1 0.97 0.85 0.14 1.21
2 0.96 0.90 0.12 1 .15
3 1.18 0.68 0.17 1.24
Average 1.04 0.81 0.14 1.20

 

Figure 38: Weight percentage values of elements for electrical tapes with clear adhesive

88

 

 

 

 

Super 88 (129 ion)

 

 

 

 

 

 

 

 

DOABase
0
0
C
N
'U
C
3
.0
< XMajor
1 6 9 12 15 18
Time (min)
Super 88 (149 and 305 ions)
DNPMinor
|
i
0
O
5
'U DEPTracc
C
3
.0
<
3 6 9 12 15 18
Time (min)

 

Figure 39: Extracted ion chromatograms of Super 88 tape

89

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

i Globe (129 ion)
DOAMinor
8
1:
I!
'o
c
a
.o
<
6 9 12 15 18
Time (min)
Globe (149 and 305 ions)
DOPBase
o
2
G
'o
c
:1
n
<
13 £5 9 12 15 118
Time (min)
L

 

 

 

 

 

Figure 40: Extracted ion chromatograms of Globe tape

90

 

 

 

Bengal (149 and 305 ions)

 

 

 

 

 

 

 

 

 

 

 

 

O

8

a

-o

C

3

.o

<

(3 £5 9. 12 115 118

i Time (min)
1 ‘— . . ‘” T
1 Champion (149 and 305 Ions)
‘ DOPBase

O

2

a

U

C

3

.n

<
t
x g g g .2 {a
I Time (min)

 

Figure 41: Extracted ion chromatograms of Bengal (top) and Champion (bottom) tapes

91

 

 

 

 

 

 

Duck (129 ion)

DOATrace

 

 

 

 

 

 

 

 

 

o
2
a
'o
c
3
.o
<
is 6 9 12 15 18
Time (min)
Duck (149 and 305 ions)
DOPBase
8
5
-o
C
3
.o
<
:3 5 9 12 15 18
Time (min)

Figure 42: Extracted ion chromatograms of Duck tape

92

 

 

 

 

 

 

Electro Tuff (149 and 305 ions)

 

 

 

 

 

 

 

 

 

 

 

DOPBasc
\
1
1 o
o
:
fl
1:
c
a
.o
<
f 6 9 12 15 18
Time (min)
lntertape (149 and 305 ions)
DOPBase
4
1 2
i
o
o
1:
u
1::
c
a
.o
<
f 6 9 12 15 18
Time (min)

 

 

 

 

Figure 43: Extracted ion chromatograms of Electro Tuff (top) and Intertape (bottom)
tapes

93

 

T Lepage (149 and 305 ions)

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DOPBasc j

o

o

c

n
u

c

a
a
<

i1 6 9 12 15 18
| Time (min)
Powerworks (149 and 305 ions)
DOPBase

o

O

r:

a

'o

c

a

.o

<

:3 6 9 12 15 18
Time (min)

 

 

 

Figure 44: Extracted ion chromatograms of Lepage (top) and Powerworks (bottom) tapes

94

 

 

Shurtape (149 and 305 ions)

 

 

 

 

 

 

 

 

 

DOPBase
0
0
C
G
'3
C
3
D
<
13 6 9 12 15 18
Time (min)
T" ‘ _ — ‘ .
WUL (149 and 305 Ions)
DOPBasc
‘—
M
0
g DDPMinor
fl
.5
C
3
n
<
13 6 9 12 15 18

 

Time (min)

 

Figure 45: Extracted ion chromatograms of Shurtape (top) and WUL (bottom) tapes

95

 

 

 

Vanguard (129 ion)

DOAMinor

 

 

 

 

 

 

 

 

 

 

 

 

O
0
C
1!
'3
C
3
.0
<
:3 5 7 9 11 13 15 17 19
Time (min)
Vanguard (149 and 305 ions)
DOPBasc
a l
0
C
N
'O
C
3
.n
< TOTMMajor
3 5 7 9 11 13 15 17 19
Time (min)

 

Figure 46: Extracted ion chromatograms of Vanguard tape

96

 

REFERENCES

97

10.

11.

12.

6. REFERENCES

Smith, Jenny M. and William A. Randle, “Introduction to Forensic
Examinations of Pressure Sensitive Tape.” Workshop-Midwestern
Association of Forensic Scientists, Minneapolis, MN, September 24, 2001.

Merriam-Webster’s Online Dictionary

Kee, T.G., “The Characterization of PVC Adhesive Tape.” Proceedings of the
International Symposium on the Analysis and Identification of Polymers, FBI
Academy, Quantico, VA, July 31-Aug 2, (1984) 77-85.

3M Hutchinson plant, Minneapolis, MN-John Houle

Keto, R.O., “Forensic Characterization of Black Polyvinyl Chloride Electrical
Tape.” Proceedings of the International Symposium on the Analysis and
Identification of Polymers, FBI Academy, Quantico, VA, July 31-Aug 2,
(1984) 137-143.

Williams, ER. and TD. Munson, "The Comparison of Black
Polyvinylchloride (PVC) Tapes by Pyrolysis Gas Chromatography.” J oumal
of Forensic Sciences, JFSCA, Vol. 33, No. 5 (1988) 1163-1170.

Merrill, RA. and EC. Bartick, “Procedure for the Forensic Analysis of Black
Plastic Tape.” Internal FBI Document, FBI Forensic Science Research Unit,
Quantico, VA, Jan. 1989.

Wheals, BB. and W. Noble, “Forensic Applications of Pyrolysis Gas
Chromatography.” Chromatographia, 5 (1972) 553-557.

Noble, W., Wheals, BB, and Whitehouse, M.J., “The Characterisation of
Adhesives by Pyrolysis Gas Chromatography and Infrared Spectroscopy.”
Forensic Science, 3 (1974) 163-174.

Wheals, B.B., “Review-Analytical Pyrolysis Techniques in Forensic Science.”
Journal of Analytical and Applied Pyrolysis, 2 (1980/1981) 277-292.

Bakowski, N.L., E.C. Bender and TD. Munson, “Comparison and
Identification of Adhesives Used in Improvised Explosive Devices by
Pyrolysis-Capillary Column Gas Chromatography-Mass Spectrometry.”
Journal of Analytical and Applied Pyrolysis, 8 (1985) 483-492.

Curry, C.J., “Pyrolysis-Mass Spectrometry Studies of Adhesives.” Journal of
Analytical and Applied Pyrolysis, 11 (1987) 213-225.

98

13.

14.

Blackledge, R.D., “Tapes with Adhesive Backing; their Characterization in
the Forensic Science Laboratory.” Conference Proceeding-Appl. Polym. Anal.
Charact., (1987) 413-421.

http: //www. utexas. edu/cc/docs/stat53. html, “Factor Analysis Using SAS
PROC Factor” June 26,1995.

99

   

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