Forensic Analysis and Discrimination of Duct Tapes*€¦ · Duct tape backings can be made in a...
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JASTEE, Vol. 3, Issue 1 Mehltretter & Bradley: Duct Tape Andria H. Mehltretter 1 , M.S. and Maureen J. Bradley 2 , Ph.D. Forensic Analysis and Discrimination of Duct Tapes* ABSTRACT Duct tape is a common type of evidence submitted to forensic science laboratories, due to its potential for use in illicit activities. In this study, eighty-two commercially available duct tape samples were analyzed and compared to evaluate the significance of a failure-to-discriminate result. Samples were first evaluated through examination of their physical characteristics, including, but not limited to, backing color, backing surface features, fabric pattern, scrim count, and general description of the yarns. As a result of these examinations, 99.6% of the possible comparison pairs were discriminated. The chemical compositions of the backings and adhesives of the remaining indistinguishable samples were subsequently characterized through the use of Fourier transform infrared spectroscopy, X-ray diffractometry, and scanning electron microscopy with energy dispersive spectroscopy, with additional pairs discriminated at various stages. The overall discrimination power of this series of examinations was 99.8%. Each of the remaining pairs of indistinguishable samples likely shares a common manufacturing source. Keywords: forensic science, trace evidence, duct tape, discrimination, stereomicroscopy, Fourier transform infrared spectroscopy, X-ray diffractometry, scanning electron microscopy / energy dispersive spectroscopy 1 Corresponding author: Federal Bureau of Investigation, Laboratory Division, 2501 Investigation Parkway, Room 4220, Quantico, VA 22135 2 Federal Bureau of Investigation, Laboratory Division, Quantico, VA *This work has been presented in part at the American Academy of Forensic Sciences 58 th Annual Meeting. Seattle, WA. 2006. This is the FBI Laboratory Division’s publication number 12-02. Names of commercial manufacturers are provided for identification only, and inclusion does not imply endorsement of the manufacturer, or its products or services, by the FBI. The views expressed are those of the authors and do not necessarily reflect the official policy or position of the FBI or the U.S. Government. Page 2 of 49
Transcript of Forensic Analysis and Discrimination of Duct Tapes*€¦ · Duct tape backings can be made in a...
JASTEE, Vol. 3, Issue 1 Mehltretter & Bradley: Duct Tape
Andria H. Mehltretter1, M.S. and Maureen J. Bradley2, Ph.D.
Forensic Analysis and Discrimination of Duct Tapes*
ABSTRACT
Duct tape is a common type of evidence submitted to forensic science laboratories, due to its potential for use in illicit activities. In this study, eighty-two commercially available duct tape samples were analyzed and compared to evaluate the significance of a failure-to-discriminate result. Samples were first evaluated through examination of their physical characteristics, including, but not limited to, backing color, backing surface features, fabric pattern, scrim count, and general description of the yarns. As a result of these examinations, 99.6% of the possible comparison pairs were discriminated. The chemical compositions of the backings and adhesives of the remaining indistinguishable samples were subsequently characterized through the use of Fourier transform infrared spectroscopy, X-ray diffractometry, and scanning electron microscopy with energy dispersive spectroscopy, with additional pairs discriminated at various stages. The overall discrimination power of this series of examinations was 99.8%. Each of the remaining pairs of indistinguishable samples likely shares a common manufacturing source. Keywords: forensic science, trace evidence, duct tape, discrimination, stereomicroscopy, Fourier transform infrared spectroscopy, X-ray diffractometry, scanning electron microscopy / energy dispersive spectroscopy
1 Corresponding author: Federal Bureau of Investigation, Laboratory Division, 2501 Investigation Parkway, Room 4220, Quantico, VA 22135 2 Federal Bureau of Investigation, Laboratory Division, Quantico, VA *This work has been presented in part at the American Academy of Forensic Sciences 58th Annual Meeting. Seattle, WA. 2006. This is the FBI Laboratory Division’s publication number 12-02. Names of commercial manufacturers are provided for identification only, and inclusion does not imply endorsement of the manufacturer, or its products or services, by the FBI. The views expressed are those of the authors and do not necessarily reflect the official policy or position of the FBI or the U.S. Government.
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JASTEE, Vol. 3, Issue 1 Mehltretter & Bradley: Duct Tape INTRODUCTION
A wide variety of tapes are available to the consumer, and as a result, many different types can be used in the commission of a crime. In fact, tapes are routinely examined by forensic laboratories in investigations involving kidnappings and homicides and construction of improvised explosive devices. One of the most frequently encountered types of tape submitted to North American forensic laboratories is duct tape. Duct tapes are composed of three constituents: a polymeric backing, an adhesive, and fabric reinforcement (scrim) between the backing and adhesive. The backing of the tape provides the color and acts as a carrier for the adhesive, which in turn provides the tack to the tape. The fabric is included to add strength and bulk to the tape as well as to affect its tearing properties. The design and construction of a duct tape depends on its specifications, its commercial end use, the processes available at the manufacturing facility, and the raw materials available. Duct tape backings can be made in a variety of ways, which leads to observed differences between tapes. A duct tape manufacturer may purchase the polymeric backing from another company, which produces it via a blown film process. Such backings appear smooth on both surfaces. If the backing is made at the tape manufacturing facility, it is likely to have dimples or indentations on its surface(s), which can arise from the rollers (calenders) or the fabric when it is added. Depending on the tape specifications and procedures at the plant, the backing thickness and width can also be modified. Regarding their composition, backings are usually polyethylene with fillers. Silver is the most common color of duct tapes, and the silver color is provided by aluminum pigments, either throughout the entire thickness of the backing or in one or more layers in the backing. Some backings have different chemicals (e.g., acrylates) added to the adhesive side to aid in cohesion of the adhesive to the backing. This is called the “tie layer.” The primary observable differences for adhesives are color and chemical composition, which generally are related characteristics. The color is determined by the elastomer (i.e., different natural rubber sources have different colors) and/or the pigments/fillers (e.g., titanium dioxide will whiten adhesives). Natural rubber-based adhesives are typically made/mixed on-site at the tape manufacturing plant, and synthetic (e.g., styrene-isoprene-styrene, acrylic) adhesives can either be prepared on-site or purchased (1). The fabric portion has the greatest number of physical features that can be evaluated. Duct tape fabrics (scrim) tend to be loose weaves (plain weave) or knits (weft-insertion). In this fabric, yarns run along the length of the tape and across the width: the former are called warp or machine direction yarns and the latter are called weft or fill yarns. The scrim count (density of these yarns) is measured by counting the number of yarns per inch in each direction. Generally, a higher scrim count indicates a higher quality of tape. The warp and fill yarns can be constructed in several different ways: twisted, textured/crimped, or straight filament, and
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JASTEE, Vol. 3, Issue 1 Mehltretter & Bradley: Duct Tape composed of synthetic (usually polyester) fibers, cotton fibers, or a blend of the two. The fibers of the yarns may also exhibit fluorescence if optical brighteners are present. As of 2005, there were well over 150 different reference numbers of duct tape found in the United States, produced by approximately four or five manufacturers (1). Because of all the variations possible, duct tape comparisons can be valuable evidence in criminal investigations, and forensic laboratories have been conducting these examinations for decades (2-17). Their value was documented in a 1998 study by Smith in which fifty-one duct tape samples were analyzed and compared (7). The study demonstrated variability in construction and composition between manufacturers and even within the same manufacturer. This study aimed to expand on Smith’s study and to evaluate the significance of failing to differentiate samples. The techniques used in this evaluation were physical examinations, Fourier transform infrared spectroscopy (FTIR), X-ray diffractometry (XRD), and scanning electron microscopy with energy dispersive spectroscopy (SEM/EDS). Although additional techniques can be applied to duct tape analysis, based on the discrimination obtained through the reported combination of techniques, this analytical scheme is routinely employed in the authors’ laboratory. MATERIALS AND METHODS Tape Collection The tape collection for this study consisted of 82 samples purchased by the FBI between 1993 and 2005 at common retail stores and marketed as general purpose or economy grade, and covered a range of manufacturers and distributors. The same tapes were reported on in a previous study (10). Table 1 provides the available manufacturer/product information. Once tapes are manufactured, many of them are sold to various distributors, who may resell them under different brand names or labels (1). As a result, different rolls of a single duct tape product may be labeled and packaged in more than one way. Physical examinations Physical characteristics of the tapes were recorded during visual and stereomicroscopical evaluations. The characteristics observed included backing and adhesive color, backing surface features and layer structure, width, and backing thickness. The fabric characteristics observed were weave/knit pattern, yarn description (e.g., twisted), yarn composition (e.g., synthetic or cotton), fluorescence, and scrim count. For the backing and adhesive color, the observations were conducted with the unaided eye. Only distinct color differences of the adhesives were considered significant, due to the typical
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JASTEE, Vol. 3, Issue 1 Mehltretter & Bradley: Duct Tape condition of adhesives in casework samples (i.e., contamination by dirt or body fluids). Surface features of the backings were observed unaided and with a stereomicroscope and were described as smooth or dimpled (calendering marks). To determine the layer structure of the backings, thin cross-sections were taken and viewed with transmitted light (10). Width measurements were taken with a ruler to the nearest 0.5 mm. To measure thickness of the backing on each sample, the adhesive and fabric were removed with hexane or chloroform and the backing was placed between the two faces of a digital micrometer. A minimum of ten areas were measured, and the values were recorded to the nearest 0.05 mil (1 mil = 1/1000 inch) and averaged. A significant difference between pristine tapes (not stretched, deformed, or highly contaminated) is generally considered to be a width difference greater than 1.0 mm (personal communication with Mark Byrne, Technical Manager at Shurtape Technologies, on December 9, 2011) or a thickness difference greater than 10% (personal communication with Jerry Serra, consultant, on December 30, 2011). To best visualize the fabric, the adhesive was removed with hexane or chloroform. The weave/knit pattern and general yarn description were observed by stereomicroscopy. For the latter, the yarns were documented as twisted, textured, or straight filament. Using transmission microscopy, the yarns were classified as being synthetic, cotton, or a blend of synthetic and cotton fibers. Yarn fluorescence was observed under long wave UV light (λ = 366 nm). The scrim count was measured using a ruler, counted per square inch, and recorded as number of warp yarns / number of fill yarns. Scrim counts of +/-1 are generally acceptable in the manufacturing of duct tape products (personal communications with Jerry Serra and John Johnston, consultants, on March 27, 2012), so for this study, a count difference of +/-1 in either direction did not result in samples being discriminated. In other words, a significant difference was considered to be a count difference of two or more in either the warp or fill direction. Additional fabric/fiber examinations are generally conducted in the authors’ laboratory in casework, but for this study, examinations were limited to those described. FTIR Adhesive samples were smeared onto either one diamond window of a compression cell (Thermo Scientific, Waltham, MA) or a KBr disc and analyzed in the transmission mode using a Continuum microscope attached to a Nicolet Nexus 670 or 6700 FTIR E.S.P. spectrometer with a MCT/A detector (4000-650 cm-1) (Thermo Nicolet, Madison, WI). The resolution was 4 cm-1, the aperture was approximately 100x100 μm, and the number of scans was 128.
Backing samples were cleaned with hexane and each side of the backings was analyzed using a Dura SamplIR ATR (SensIR Technologies, Danbury, CT) attached to a Nicolet Magna 560 FTIR
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Tabl
e 1.
Sam
ple
Info
rmat
ion
and
Phys
ical
Cha
ract
eris
tics
Tape
N
umbe
r M
anuf
actu
rer /
Pro
duct
B
acki
ng
Col
or
Bac
king
Su
rfac
e Fi
lm T
hick
ness
(m
ils)
Wid
th
(mm
)
Bac
king
La
yer
Stru
ctur
e
(Mic
rosc
opy
only
)
Adh
esiv
e C
olor
Sc
rim T
ype
Yar
n D
escr
iptio
n
(w -
f)
Scrim
C
ount
(w
/f)
Fluo
resc
ence
Y
arn
Com
posi
tion
(w
- f)
1 PE
Tar
paul
in R
epai
r Tap
e si
lver
di
mpl
ed
5.3
48.0
si
ngle
be
ige
plai
n w
eave
tw
iste
d tw
iste
d 35
/ 29
no
ne
synt
hetic
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tton
synt
hetic
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tton
2 C
ante
ch
silv
er
smoo
th
3.3
48.0
si
ngle
of
f whi
te
wef
t in
serti
on
filam
ent
text
ured
19
/ 8
none
sy
nthe
tic
synt
hetic
3 3M
Hom
e an
d Sh
op
silv
er
smoo
th
2.6
48.0
cl
ear,
silv
er,
clea
r be
ige
plai
n w
eave
te
xtur
ed
text
ured
24
/ 7
none
sy
nthe
tic
sunt
hetic
4 3M
Pro
fess
iona
l HV
AC
si
lver
sm
ooth
2.
7 49
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clea
r, si
lver
, cl
ear
beig
e pl
ain
wea
ve
text
ured
te
xtur
ed
29 /
8 no
ne
synt
hetic
sy
nthe
tic
5 3M
Tar
tan
Util
ity
silv
er
smoo
th
2.0
48.5
cl
ear,
silv
er,
clea
r be
ige
plai
n w
eave
te
xtur
ed
text
ured
20
/ 7
none
sy
nthe
tic
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hetic
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ther
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lver
sm
ooth
3.
1 48
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r, si
lver
, cl
ear
beig
e pl
ain
wea
ve
text
ured
te
xtur
ed
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10
none
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tic
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hetic
7 Fi
x-It
silv
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dim
pled
5.
1 48
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sing
le
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r pl
ain
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ve
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ted
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ted
19 /
9 w
& f
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lar T
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pl
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14
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ve
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14
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1 48
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thin
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and
silv
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off w
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w
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19 /
8 no
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sy
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tic
14
3M H
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and
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ooth
3.
0 50
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ain
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ve
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ted
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10
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tic-
cotto
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15
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17
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and
M
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th
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51.0
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lig
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plai
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f sy
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tic-
cotto
n
18
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tipur
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mpl
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50.5
lig
ht si
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d m
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m
silv
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med
ium
gr
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plai
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tw
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d te
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13
w
synt
hetic
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tton
synt
hetic
19
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Gen
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Pur
pose
700
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silv
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dim
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3 49
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si
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m
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m
gray
pl
ain
wea
ve
twis
ted
text
ured
19
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w
synt
hetic
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tton
synt
hetic
20
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hua
Gen
eral
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pose
285
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silv
er
smoo
th
2.2
48.5
si
ngle
w
hite
pl
ain
wea
ve
twis
ted
text
ured
20
/ 8
w
synt
hetic
-co
tton
synt
hetic
Page 6 of 49
JASTEE, Vol. 3, Issue 1 Mehltretter & Bradley: Duct Tape
Tabl
e 1.
Sam
ple
Info
rmat
ion
and
Phys
ical
Cha
ract
eris
tics
(con
tinue
d)
Tape
N
umbe
r M
anuf
actu
rer /
Pro
duct
B
acki
ng
Col
or
Bac
king
Su
rfac
e Fi
lm T
hick
ness
(m
ils)
Wid
th
(mm
)
Bac
king
La
yer
Stru
ctur
e
(Mic
rosc
opy
only
)
Adh
esiv
e C
olor
Sc
rim T
ype
Yar
n D
escr
iptio
n
(w -
f)
Scrim
C
ount
(w
/f)
Fluo
resc
ence
Y
arn
Com
posi
tion
(w
- f)
21
Nat
iona
l 181
-6
silv
er
smoo
th
2.2
49.5
si
ngle
w
hite
pl
ain
wea
ve
twis
ted
text
ured
20
/ 8
w
synt
hetic
-co
tton
synt
hetic
22
Anc
hor P
rem
ium
Gra
de 9
602
silv
er
smoo
th
2.7
51.0
si
ngle
m
ediu
m
gray
w
eft
inse
rtion
fil
amen
t te
xtur
ed
19 /
8 w
& f
synt
hetic
sy
nthe
tic
23
Tape
-It
silv
er
smoo
th
3.5
48.5
si
ngle
m
ediu
m
gray
pl
ain
wea
ve
twis
ted
text
ured
20
/ 8
w
synt
hetic
-co
tton
synt
hetic
24
Out
door
Res
earc
h G
ear -
REI
31
300
silv
er
smoo
th
4.7
19.0
si
ngle
m
ediu
m
gray
pl
ain
wea
ve
twis
ted
text
ured
20
/ 11
w
sy
nthe
tic-
cotto
n sy
nthe
tic
25
tesa
si
lver
sm
ooth
2.
7 52
.0
sing
le
light
gra
y pl
ain
wea
ve
twis
ted
twis
ted
22 /
10
w &
f sy
nthe
tic-
cotto
n sy
nthe
tic-
cotto
n
26
tesa
Gen
eral
Pur
pose
214
10
silv
er
smoo
th
2.2
49.0
si
ngle
lig
ht g
ray
plai
n w
eave
tw
iste
d tw
iste
d 23
/ 10
w
& f
synt
hetic
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tton
synt
hetic
-co
tton
27
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Ene
rgy
Savi
ng 1
241N
si
lver
sm
ooth
2.
2 51
.0
sing
le
beig
e w
eft
inse
rtion
fil
amen
t te
xtur
ed
19 /
10
w &
f sy
nthe
tic
synt
hetic
28
Silv
er C
law
147
12
silv
er
smoo
th
2.1
38.0
si
ngle
lig
ht g
ray
wef
t in
serti
on
filam
ent
text
ured
19
/ 8
w &
f sy
nthe
tic
synt
hetic
29
Man
co In
dust
rial 3
158
silv
er
dim
pled
5.
1 48
.5
sing
le
beig
e pl
ain
wea
ve
twis
ted
text
ured
30
/ 15
w
sy
nthe
tic-
cotto
n sy
nthe
tic
30
Man
co In
dust
rial 3
157
silv
er
smoo
th
2.6
48.0
si
ngle
m
ediu
m
gray
pl
ain
wea
ve
twis
ted
filam
ent
24 /
12
w
synt
hetic
-co
tton
synt
hetic
31
Serv
iSta
r Pro
fess
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l 333
32
silv
er
dim
pled
4.
7 50
.5
sing
le
off w
hite
pl
ain
wea
ve
twis
ted
filam
ent
25 /
12
w
synt
hetic
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tton
synt
hetic
32
Prid
e-C
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lver
di
mpl
ed
6.1
48.5
si
ngle
w
hite
pl
ain
wea
ve
twis
ted
twis
ted
34 /
30
none
sy
nthe
tic-
cotto
n sy
nthe
tic
33
Uni
ted
Util
ity F
D18
145
silv
er
smoo
th
2.1
46.0
si
ngle
lig
ht g
ray
wef
t in
serti
on
filam
ent
text
ured
19
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tic
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hetic
34
Man
co E
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me
Duc
k Ta
pe
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nt
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ge
smoo
th
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red
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ed in
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ckin
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ngle
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plai
n w
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tw
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d tw
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tton
35
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hor C
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7.
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r and
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te
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ted
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ured
20
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tton
synt
hetic
Page 7 of 49
JASTEE, Vol. 3, Issue 1 Mehltretter & Bradley: Duct Tape
Tabl
e 1.
Sam
ple
Info
rmat
ion
and
Phys
ical
Cha
ract
eris
tics
(con
tinue
d)
Tape
N
umbe
r M
anuf
actu
rer /
Pro
duct
B
acki
ng
Col
or
Bac
king
Su
rfac
e Fi
lm T
hick
ness
(m
ils)
Wid
th
(mm
)
Bac
king
La
yer
Stru
ctur
e
(Mic
rosc
opy
only
)
Adh
esiv
e C
olor
Sc
rim T
ype
Yar
n D
escr
iptio
n
(w -
f)
Scrim
C
ount
(w
/f)
Fluo
resc
ence
Y
arn
Com
posi
tion
(w
- f)
37
Clin
g-A
us R
B45
si
lver
di
mpl
ed
4.8
48.0
si
ngle
of
f whi
te
plai
n w
eave
tw
iste
d te
xtur
ed
30 /
15
w
synt
hetic
-co
tton
synt
hetic
38
Clin
g-A
us R
B51
si
lver
di
mpl
ed
4.0
48.0
sing
le,
poss
ibly
de
lam
inat
ing
dow
n ce
nter
beig
e pl
ain
wea
ve
twis
ted
twis
ted
29 /
14
none
sy
nthe
tic
synt
hetic
39
Uni
ted
Dol
lar G
ener
al 2
33
silv
er
smoo
th
2.7
47.5
si
ngle
lig
ht g
ray
wef
t in
serti
on
filam
ent
text
ured
19
/ 12
no
ne
synt
hetic
sy
nthe
tic
40
Inte
rtape
691
0 si
lver
sm
ooth
2.
2 47
.5
sing
le
light
gra
y w
eft
inse
rtion
fil
amen
t te
xtur
ed
19 /
8 no
ne
synt
hetic
sy
nthe
tic
41
Tyco
Nas
hua
FR33
3 si
lver
w/
writ
ing
smoo
th
3.3
48.5
si
ngle
, but
pr
inte
d lig
ht g
ray
plai
n w
eave
tw
iste
d tw
iste
d 23
/ 18
w
& f
synt
hetic
-co
tton
synt
hetic
42
Man
co S
kinn
y si
lver
di
mpl
ed
5.3
19.0
si
ngle
be
ige
wef
t in
serti
on
filam
ent
text
ured
26
/ 10
no
ne
synt
hetic
sy
nthe
tic
43
Wal
mar
t Mai
nsta
ys P
roje
ct
silv
er
smoo
th
1.9
48.0
si
ngle
ta
n pl
ain
wea
ve
twis
ted
text
ured
18
/ 9
w
synt
hetic
-co
tton
synt
hetic
44
Fros
t Kin
g si
lver
sm
ooth
2.
2 48
.5
sing
le
light
gra
y pl
ain
wea
ve
filam
ent
text
ured
23
/ 10
no
ne
synt
hetic
sy
nthe
tic
45
Tape
-It D
60
whi
te
smoo
th
1.9
47.5
si
ngle
be
ige
plai
n w
eave
fil
amen
t te
xtur
ed
23 /
10
none
sy
nthe
tic
synt
hetic
46
Anc
hor P
ocke
t Duc
t Tap
e si
lver
sm
ooth
2.
4 50
.5
sing
le
tan
wef
t in
serti
on
filam
ent
text
ured
19
/ 12
no
ne
synt
hetic
sy
nthe
tic
47
Inte
rtape
w
hite
sm
ooth
2.
2 49
.0
sing
le
light
gra
y w
eft
inse
rtion
fil
amen
t te
xtur
ed
19 /
8 no
ne
synt
hetic
sy
nthe
tic
48
Inte
rtape
Pro
Gra
de 9
602
silv
er
smoo
th
2.6
47.0
si
ngle
lig
ht g
ray
wef
t in
serti
on
filam
ent
text
ured
19
/ 12
no
ne
synt
hetic
sy
nthe
tic
49
Pact
ape
A92
10
red
smoo
th
2.5
49.0
si
ngle
lig
ht g
ray
plai
n w
eave
tw
iste
d tw
iste
d 23
/ 17
w
& f
synt
hetic
-co
tton
synt
hetic
-co
tton
50
Ace
All
Purp
ose
4289
7 si
lver
di
mpl
ed
4.5
47.5
si
ngle
be
ige
wef
t in
serti
on
filam
ent
text
ured
19
/ 8
none
sy
nthe
tic
synt
hetic
51
Ace
Pro
Gra
de 4
2911
w
hite
sm
ooth
2.
6 49
.5
sing
le
off w
hite
pl
ain
wea
ve
twis
ted
text
ured
25
/ 12
w
sy
nthe
tic-
cotto
n sy
nthe
tic
52
Hom
e H
ardw
are
- Can
ada
silv
er
smoo
th
2.0
49.5
si
ngle
ta
n pl
ain
wea
ve
twis
ted
filam
ent
18 /
9 w
sy
nthe
tic-
cotto
n sy
nthe
tic
53
Tago
- C
anad
a si
lver
sm
ooth
2.
2 48
.0
sing
le
off w
hite
pl
ain
wea
ve
twis
ted
twis
ted
19 /
10
w &
f sy
nthe
tic-
cotto
n sy
nthe
tic-
cotto
n
Page 8 of 49
JASTEE, Vol. 3, Issue 1 Mehltretter & Bradley: Duct Tape
Tabl
e 1.
Sam
ple
Info
rmat
ion
and
Phys
ical
Cha
ract
eris
tics
(con
tinue
d)
Tape
N
umbe
r M
anuf
actu
rer /
Pro
duct
B
acki
ng
Col
or
Bac
king
Su
rfac
e Fi
lm T
hick
ness
(m
ils)
Wid
th
(mm
)
Bac
king
La
yer
Stru
ctur
e
(Mic
rosc
opy
only
)
Adh
esiv
e C
olor
Sc
rim T
ype
Yar
n D
escr
iptio
n
(w -
f)
Scrim
C
ount
(w
/f)
Fluo
resc
ence
Y
arn
Com
posi
tion
(w
- f)
54
Ren
frew
- C
anad
a si
lver
sm
ooth
2.
2 48
.5
sing
le
off w
hite
pl
ain
wea
ve
twis
ted
twis
ted
20 /
10
w &
f sy
nthe
tic-
cotto
n sy
nthe
tic-
cotto
n
55
Hen
kel -
Duc
k si
lver
w/
whi
te o
n un
ders
ide
smoo
th
3.1
50.5
w
hite
, silv
er,
clea
r be
ige
wef
t in
serti
on
filam
ent
text
ured
19
/ 8
none
sy
nthe
tic
synt
hetic
56
Adv
ance
Tap
es
silv
er
dim
pled
4.
8 50
.0
sing
le
beig
e w
eft
inse
rtion
fil
amen
t te
xtur
ed
19 /
15
none
sy
nthe
tic
synt
hetic
57
Prid
e D
olla
r Gen
eral
bl
ack
smoo
th
6.1
48.0
si
ngle
w
hite
pl
ain
wea
ve
twis
ted
twis
ted
34 /
30
none
sy
nthe
tic-
cotto
n sy
nthe
tic-
cotto
n
58
Pact
ape
A92
10
teal
sm
ooth
2.
2 51
.0
sing
le
light
gra
y pl
ain
wea
ve
twis
ted
text
ured
20
/ 9
w
synt
hetic
-co
tton
synt
hetic
59
Inte
rtape
AC
50
blac
k sm
ooth
6.
4 48
.0
clea
r, bl
ack,
cl
ear
light
gra
y pl
ain
wea
ve
twis
ted
twis
ted
38 /
20
w &
f sy
nthe
tic-
cotto
n sy
nthe
tic-
cotto
n
60
Fros
t Kin
g T9
03
silv
er
smoo
th
1.8
51.0
po
ssib
le th
in
clea
r lay
er
light
gra
y pl
ain
wea
ve
text
ured
tw
iste
d 17
/ 9
none
sy
nthe
tic
synt
hetic
-co
tton
61
Shur
tape
si
lver
sm
ooth
2.
6 48
.5
sing
le
off w
hite
pl
ain
wea
ve
twis
ted
text
ured
28
/ 12
w
sy
nthe
tic-
cotto
n sy
nthe
tic
62
Pana
cea
6003
1 gr
een
smoo
th
5.0
6.0
sing
le
off w
hite
pl
ain
wea
ve
twis
ted
text
ured
(2
0) /
11
w
synt
hetic
-co
tton
synt
hetic
63
Tape
-It D
A10
si
lver
sm
ooth
2.
7 48
.0
sing
le
light
gra
y pl
ain
wea
ve
twis
ted
twis
ted
18 /
7 w
& f
synt
hetic
-co
tton
synt
hetic
64
Tape
-It D
A10
w
hite
sm
ooth
2.
2 48
.5
sing
le
off w
hite
pl
ain
wea
ve
filam
ent
text
ured
22
/ 9
none
sy
nthe
tic
synt
hetic
65
tesa
Gen
eral
Pur
pose
214
02
silv
er
smoo
th
1.9
48.5
si
ngle
lig
ht g
ray
plai
n w
eave
tw
iste
d tw
iste
d 22
/ 10
w
& f
synt
hetic
-co
tton
synt
hetic
-co
tton
66
tesa
Gen
eral
Pur
pose
214
02
silv
er
smoo
th
2.0
48.5
si
ngle
lig
ht g
ray
plai
n w
eave
tw
iste
d tw
iste
d 22
/ 10
w
& f
synt
hetic
-co
tton
synt
hetic
-co
tton
67
Duc
tTite
, Tite
Seal
si
lver
sm
ooth
3.
0 50
.5
sing
le
light
gra
y pl
ain
wea
ve
twis
ted
twis
ted
23
/ 12
w &
f sy
nthe
tic-
cotto
n sy
nthe
tic-
cotto
n
68
Tuck
ST4
4 ca
mou
flage
sm
ooth
3.
3 49
.5
beig
e, c
amo
prin
t lig
ht g
ray
plai
n w
eave
tw
iste
d tw
iste
d 3
6 / 2
4 w
& f
synt
hetic
-co
tton
synt
hetic
-co
tton
69
Tyco
960
763
cam
oufla
ge
smoo
th
2.4
48.5
ca
mo
film
, cl
ear
med
ium
gr
ay
plai
n w
eave
tw
iste
d te
xtur
ed
20 /
14
w
synt
hetic
-co
tton
synt
hetic
70
Cam
o D
uct T
ape
8220
ca
mou
flage
sm
ooth
2.
4 48
.5
cam
o fil
m,
clea
r m
ediu
m
gray
pl
ain
wea
ve
twis
ted
text
ured
2
0 / 1
4 w
sy
nthe
tic-
cotto
n sy
nthe
tic
Page 9 of 49
JASTEE, Vol. 3, Issue 1 Mehltretter & Bradley: Duct Tape
Tabl
e 1.
Sam
ple
Info
rmat
ion
and
Phys
ical
Cha
ract
eris
tics
(con
tinue
d)
Tape
N
umbe
r M
anuf
actu
rer /
Pro
duct
B
acki
ng
Col
or
Bac
king
Su
rfac
e Fi
lm T
hick
ness
(m
ils)
Wid
th
(mm
)
Bac
king
La
yer
Stru
ctur
e
(Mic
rosc
opy
only
)
Adh
esiv
e C
olor
Sc
rim T
ype
Yar
n D
escr
iptio
n
(w -
f)
Scrim
C
ount
(w
/f)
Fluo
resc
ence
Y
arn
Com
posi
tion
(w
- f)
71
Uni
ted
3958
57
silv
er
smoo
th
1.8
51.0
si
ngle
m
ediu
m
gray
pl
ain
wea
ve
text
ured
tw
iste
d 18
/ 9
non
e sy
nthe
tic
synt
hetic
-co
tton
72
Uni
ted
10s2
sh
silv
er
smoo
th
4.2
51.5
cl
ear a
nd
silv
er
med
ium
gr
ay
plai
n w
eave
tw
iste
d te
xtur
ed
20 /
10
w
synt
hetic
-co
tton
synt
hetic
73
Vic
tor v
302
blac
k sm
ooth
1.
8 49
.5
sing
le
light
gra
y pl
ain
wea
ve
twis
ted
twis
ted
19 /
9 w
& f
synt
hetic
-co
tton
synt
hetic
-co
tton
74
True
Val
ue D
uck
Mul
ti U
se A
ll Pu
rpos
e si
lver
di
mpl
ed
4.8
47.5
th
in c
lear
an
d si
lver
of
f whi
te
wef
t in
serti
on
filam
ent
text
ured
19
/ 8
none
sy
nthe
tic
synt
hetic
75
Hen
kel -
Duc
k dx
660
silv
er
dim
pled
3.
9 48
.0
sing
le
off w
hite
pl
ain
wea
ve
filam
ent
text
ured
20
/ 7
none
sy
nthe
tic
synt
hetic
76
Gen
eral
Pur
pose
- C
hina
si
lver
sm
ooth
6.
0 48
.0
sing
le
whi
te
pla
in
wea
ve
twis
ted
twis
ted
36 /
32
w &
f sy
nthe
tic-
cotto
n sy
nthe
tic-
cotto
n
77
Inte
rtape
All-
wea
ther
si
lver
sm
ooth
2.
2 48
.5
sing
le
beig
e w
eft
inse
rtion
fil
amen
t te
xtur
ed
19 /
9 no
ne
synt
hetic
sy
nthe
tic
78
Inte
rtape
Util
ity
silv
er
smoo
th
2.0
48.5
si
ngle
of
f whi
te
wef
t in
serti
on
filam
ent
text
ured
19
/ 9
none
sy
nthe
tic
synt
hetic
79
Mad
e in
Pol
and
silv
er
dim
pled
5.
5 46
.5
sing
le
whi
te
pla
in
wea
ve
text
ured
te
xtur
ed
27 /
11
none
sy
nthe
tic
synt
hetic
80
Man
co U
tility
dx6
60
silv
er
dim
pled
3.
0 48
.0
sing
le
beig
e pl
ain
wea
ve
filam
ent
text
ured
2
0 / 7
no
ne
synt
hetic
sy
nthe
tic
81
3M H
ome
Off
ice
silv
er
smoo
th
2.7
48.5
cl
ear,
silv
er,
clea
r of
f whi
te
plai
n w
eave
te
xtur
ed
text
ured
25
/ 7
none
sy
nthe
tic
synt
hetic
82
3M H
ome
and
Shop
si
lver
sm
ooth
2.
5 48
.0
clea
r and
si
lver
of
f whi
te
plai
n w
eave
te
xtur
ed
text
ured
25
/ 7
none
su
nthe
tic
sunt
hetic
Page 10 of 49
JASTEE, Vol. 3, Issue 1 Mehltretter & Bradley: Duct Tape
JASTEE, Vol. 3, Issue 1 Mehltretter & Bradley: Duct Tape (Thermo Nicolet, Madison, WI) with a DTGS KBr detector (4000-650 cm-1). The resolution was 4 cm-1, and the number of scans was 32.
XRD
Samples were prepared in two ways: intact and backings only (following removal of adhesive and scrim). Each was mounted on a silicon wafer in a sample holder. Analysis was performed on a PANalytical X’Pert Pro MPD X-ray diffractometer (Westborough, MA), with Cu Kα radiation, operated at 45kV and 40 mA, scanning continuously between 8 and 80° 2Θ with a step size of 0.0170° 2Θ, and using a 10 mm beam mask. Total analysis time was approximately 8 minutes.
SEM/EDS
Backing samples were attached to a pyrolytic carbon planchet using their own adhesives, grounded with carbon paint, and carbon coated by vacuum evaporation. Adhesive samples were smeared onto a pyrolytic carbon planchet and carbon coated by vacuum evaporation. Analysis was performed using a tungsten filament source on either a JEOL JSM-6300 (JEOL, Peabody, MA) SEM with an Oxford ISIS L300 EDS (Oxfordshire, United Kingdom) or a Camscan MV2300 (Tescan, Cranberry Township, PA) with a 4pi Analysis EDS (Durham, NC). SEM conditions were as follows: a magnification of approximately 50X, working distance of approximately 15 mm, take-off angle of approximately 30°, and accelerating voltage of 25 kV. Both EDS systems were operated with a dead time of approximately 30% and live counting time of 200 s.
Data Evaluation
For the physical characteristics, the data was entered into Microsoft® Excel and sorted according to the various characteristics. Samples that remained indistinguishable were analyzed and compared by FTIR, with data review by two examiners. Samples that continued to be indistinguishable were analyzed and evaluated by both XRD and SEM/EDS.
Discrimination Calculations
The total number of comparison pairs possible from a population of 82 samples is 3321,
calculated with the formula 2)1( −nn
, where n is the number of samples (18). Following the physical examinations and the entire analytical scheme, the number of comparison pairs for each indistinguishable group was calculated using the same formula and subsequently summed across the groups to provide the total number of indistinguishable pairs. The percentage of pairs that were discriminated, which is equivalent to the discrimination power (DP), was then calculated as follows:
DP = % of pairs discriminated =
Page 11 of 49
JASTEE, Vol. 3, Issue 1 Mehltretter & Bradley: Duct Tape
100% x ⎟⎟⎠
⎞⎜⎜⎝
⎛−
pairscomparisonofnumbertotalpairsishableindistinguofnumber1
An example follows in the results of the physical examinations section.
RESULTS
Microscopical examinations and physical examinations
The physical characteristics observed/measured for these samples are detailed in Table 1. Most of the tape samples had backings that were silver in color, but black, white, and camouflage were also observed for several tapes. The adhesives covered a range of shades of white, gray, and beige. Roughly three-quarters of the tape backings had smooth surfaces and one-quarter had dimpled surfaces. Figure 1 depicts one example of each. Most of the tape widths were between 47.5 and 51.0 mm; the narrowest and widest widths were 6.0 mm and 76.0 mm, respectively. The range of backing thicknesses was from 1.8 to 7.7 mils. Nearly three-quarters of the tape backings appeared single-layered when a cross-section was viewed (10).
Figure 1: Sample 11 (left) has a smooth backing surface, and Sample 12 (right) has a dimpled backing surface.
A variety of fabrics was also observed. About 75% of the tapes had a plain weave pattern, with the remaining being weft-insertion. For the former, an over-under pattern is observed, whereas for the latter, a chain-stitch pattern can be seen. In the tapes with a plain weave pattern, a variety of different combinations of twisted, textured, and straight filament yarns was apparent. Figure 2 shows the difference between plain weave and weft-insertion, with three examples of plain weave construction. Yarn composition and fluorescence both varied with no obvious correlation between them. The fabric characteristic that varied the most was scrim count, ranging from 17/9 or 18/7 to 68/44, with many possible combinations in between. Half
Page 12 of 49
JASTEE, Vol. 3, Issue 1 Mehltretter & Bradley: Duct Tape of the warp values were between 18 and 20, and half of the fill values were between 8 and 10; the warp count was always higher than the fill count.
Figure 2: Four different scrim patterns, oriented so that the warp yarns run left to right. Clockwise from top left: plain weave with twisted yarns in both directions (Sample 67), plain weave with twisted yarns in the warp direction and straight filament yarns in the fill direction (Sample 52), plain weave with textured yarns in both directions (Sample 4), and weft‐insertion (Sample 40).
Due to the variety of combinations of the aforementioned characteristics, there were only eight groups of samples that remained indistinguishable following comparisons of the physical features of these tapes. The eight groups were as follows: 3 and 81; 12 and 31; 13 and 74; 26, 65, and 66; 39 and 48; 40, 77, and 78; 45 and 64; and 53 and 54. This resulted in 12 total pairs of indistinguishable samples, with a discrimination power (DP) of 99.6%, calculated as follows:
Page 13 of 49
JASTEE, Vol. 3, Issue 1 Mehltretter & Bradley: Duct Tape
⎥⎥⎥⎥⎥⎥⎥⎥⎥⎥
⎦
⎤
⎢⎢⎢⎢⎢⎢⎢⎢⎢⎢
⎣
⎡
⎟⎟⎟⎟⎟
⎠
⎞
⎜⎜⎜⎜⎜
⎝
⎛−
+−
+−
+−
+−
+−
+−
+−
−×3321
2)12(2
2)12(2
2)13(3
2)12(2
2)13(3
2)12(2
2)12(2
2)12(2
1%100
FTIR
The adhesives and backings of any samples that remained indistinguishable in observed and measured physical properties were compared by FTIR. As a result, Samples 12 and 31 were differentiated from each other, and Sample 78 differed from Samples 40 and 77. As seen in Figures 3 and 4, respectively, the differences could be attributed to the presence of kaolin in the adhesive of Sample 12, and the presence of dolomite versus calcite in the adhesives of 78 and 40/77. The rest of the adhesive samples remained indistinguishable after FTIR spectroscopy. None of the samples in these groups were discriminated by ATR analysis of the backing.
Figure 3: FTIR spectral overlay of two adhesives that differ. The peaks present in Sample 12 (3700‐3600 and 1100‐1000 cm‐1 ranges) that are absent in Sample 31 are due to kaolin.
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JASTEE, Vol. 3, Issue 1 Mehltretter & Bradley: Duct Tape
Figure 4: FTIR spectral display of two adhesives that are indistinguishable and one that differs. Calcite peaks are observed at 875 and 711/712 cm‐1 in Samples 40 and 77, and dolomite peaks are observed at 881 and 729 cm‐1 in Sample 78.
XRD
The remaining indistinguishable samples were compared by XRD, which successfully discriminated two additional pairs: Samples 39 and 48 and Samples 53 and 54. XRD analysis indicated the presence of talc in the backings of Samples 48 and 54, but not in Samples 39 and 53. Figure 5 demonstrates this difference for Samples 39 and 48.
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JASTEE, Vol. 3, Issue 1 Mehltretter & Bradley: Duct Tape
Figure 5: XRD diffraction patterns of two backings that differ. The peaks present in Sample 48 (top) that are absent in Sample 39 (bottom) are due to talc (T). Polyethylene (P) and calcite (C) are observed in both samples.
SEM/EDS
The same samples that were compared by XRD were also compared by SEM/EDS, but no discriminating characteristics were readily observed.
Figure 6: SEM/EDS spectral overlay (displayed in square root scale) of the backings of Samples 39 and 48, demonstrating that magnesium (Mg) is not readily apparent in Sample 48, despite talc being a major component of the XRD pattern. Mg would be observed to the left of aluminum (Al).
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JASTEE, Vol. 3, Issue 1 Mehltretter & Bradley: Duct Tape Overall Discrimination
Following all examinations, seven pairs (five groups) of samples remained indistinguishable: 3 and 81; 13 and 74; 26, 65, and 66; 40, 77; and 45 and 64. The resulting overall discrimination was calculated as 99.8%.
Of the samples that were not discriminated, one pair was from the same manufacturer: Samples 40 and 77 were both Intertape products.
Samples 45 and 64 were both distributed by Tape-It, which reportedly does not manufacture the duct tape it distributes (personal communication with Arnold Rabinowitz, President of Tape-It, Inc., on April 20, 2011). It is quite possible that these tapes share a common manufacturer, but this information is not known.
Regarding Samples 13 and 74, one was made by Shurtape and the other was labeled as True Value, which does not make its own tape products; Shurtape is known to have manufactured tapes for True Value (personal communication with Mark Byrne, Technical Manager at Shurtape Technologies, Inc., on October 20, 2010).
One pair of samples (3 and 81) was labeled as 3M products (from Canada), and 3M is known to be both a duct tape manufacturer and distributor. Likewise, tesa [sic] is a known manufacturer and distributor, and Samples 26, 65, and 66 are all tesa-labeled tapes. Therefore, the samples within each of these latter two groups could have come from the same source.
DISCUSSION
The comparison of the physical characteristics of duct tape yielded an impressive discrimination power of 99.6%. Therefore, the vast majority of unrelated tapes were discriminated at the physical examination stage. Most of these characteristics can be evaluated with simple laboratory tools: a microscope, scalpel, tweezers, ruler, and solvents.
Tape products change over time due to market demands, supplier sources, and manufacturing trends. Therefore, it should be noted that while the characteristics observed for this sample set are quite diverse, the trends observed for these samples might differ for another sample set or another time frame.
Although more complicated than a simple physical characteristic evaluation, FTIR is a widely available technique that is relatively easy to use. For this sample set, FTIR yielded additional discrimination following physical examinations. As a stand-alone technique, it is expected that FTIR would have a relatively high discrimination power. Due to the amount of information available on a very small amount of sample, FTIR would be quite valuable if a tape’s condition limited the physical features available for evaluation.
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JASTEE, Vol. 3, Issue 1 Mehltretter & Bradley: Duct Tape Few laboratories use XRD in duct tape examinations, primarily due to availability, but the technique has proven to be simple and reliable in the authors’ laboratory. The presence of talc in the backing was the only way two pairs of samples were discriminated using this suite of analytical techniques. XRD can distinguish between the rutile and anatase forms of titanium dioxide, and between calcite and dolomite, all of which are common duct tape pigments/fillers. Further, as demonstrated in this study, XRD can detect talc (a magnesium silicate) in instances where Mg is not readily observed by SEM/EDS; refer to Figures 5 and 6. In these ways, XRD has clearly differentiated samples where other techniques have not.
Although SEM/EDS did not add additional discrimination to this particular study, the authors believe that this result says more about the sources of the samples than the discrimination ability of SEM. The authors’ experience suggests that taken alone, SEM/EDS is very discriminating. In fact, the authors’ laboratory uses SEM/EDS in conjunction with the fabric characteristics to initially narrow down potential manufacturers in duct tape sourcing examinations.
Regarding sourcing, manufacturing and distribution channels make describing a potential source roll to investigators nearly impossible, even when a single manufacturer has been determined. In most instances, a particular manufacturer can be identified, but the source roll could have a number of different brand names or labels, and would be widely available in the marketplace. Occasionally, an atypical tape is examined and the list of potential suppliers is more limited.
Since duct tape products are mass-produced, there could be many other rolls (hundreds of thousands) that have the same physical and chemical properties as the two samples being compared. Despite this, a duct tape comparison in which samples remain undifferentiated still has probative value due to the large number of possible combinations of characteristics and compositions available: the number of duct tape rolls that would differ from those in question is far greater than the number of rolls that would be indistinguishable.
In this study, most of the samples were successfully discriminated, demonstrating that common laboratory techniques are capable of a high degree of discrimination. Since 99.8% of samples were ultimately discriminated, 99.6% by physical characteristics alone, samples that remain indistinguishable following all examinations likely share a manufacturing source.
Acknowledgments
The authors wish to thank Jennifer Gauntt, Roger Keagy, Preston Lowe, and Dennis Ward for their assistance in analyzing these samples and Diana Wright for her insightful comments on the manuscript.
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JASTEE, Vol. 3, Issue 1 Mehltretter & Bradley: Duct Tape REFERENCES
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JASTEE, Vol. 3, Issue 1 Mehltretter & Bradley: Duct Tape 13. Scientific Working Group on Materials Analysis (SWGMAT). Guideline for the forensic
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Additional information and reprint requests: Andria Mehltretter, M.S., F-ABC Forensic Examiner/Chemist Federal Bureau of Investigation Laboratory Division 2501 Investigation Parkway, Room 4220 Quantico, VA 22135
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