Duct tape comes in a wide variety of products for consumer and industrial uses.
Duct tapes consist of three parts: a polymeric (polymer) backing, an adhesive and a fabric reinforcement between the backing and adhesive. The backing of the tape provides the color and is the carrier of the adhesive, giving the tape its tack. The fabric is included to add strength and bulk, as well as to affect its tearing properties.
Duct tape backings are made in a variety of ways, which leads to observed differences between tapes. For example, a duct tape manufacturer may buy the polymeric backing from another company, which produces via a blown film process. These backings appear smooth on both surfaces.
If the backing is made at the tape manufacturing facility, it will likely have dimples or indentations on its surfaces.
Manufacturers can also modify the backing thickness and width.
Backings are usually polyethylene with fillers. Silver is the most common color, provided by aluminum pigments. Some backings have chemicals added to the adhesive side to aid in cohesion of the adhesive to the backing, called the tie layer.
The primary observable differences for adhesives are color and chemical composition. The fabric portion has the greatest number of physical features that researchers can evaluate. Duct tape fabrics tend to be loose weaves or knits. Gennerally, a higher fabric count indicates a higher quality tape.
The yarns, which make up the fabric of the tape, are constructed in several different ways: Twisted, textured/crimped or straight filament, and composed of synthetic – usually polyester – fibers, cotton fibers, or a blend of the two. The fibers will also fluoresce if optical brighteners are present.
As far back as 2005, 150 different reference numbers of duct tape were found in the U.S. That number has undoubtedly grown considerably since, making characterization of these materials crucial to law enforcement efforts.
Researchers conducted a study of 50 duct tapes purchased by the FBI at retail stores and marketed as general purpose or economy grade, and covered a large range of manufacturers and distributors.
Researchers recorded physical characteristics of the tapes 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, yarn composition, fluorescence, and scrim count, or density of the yarns.
For the backing and adhesive color, the observations were conducted with the unaided eye.
Researchers took width measurements with a ruler to the nearest 0.5 mm. To measure thickness of the backing on each sample, researchers removed the adhesive and fabric with hexane or chloroform and placed the backing between the two faces of a digital micrometer.
As a result of these examinations, 99.6% of the possible comparison pairs were classified. The chemical compositions of the backings and adhesives of the remaining indistinguishable samples were subsequently characterized with 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.
HORIBA makes Energy Dispersive X-ray Fluorescence (EDXRF) instruments, including the XGT-9000 X-ray Analytical Microscope, which combines improved sensitivity and new imaging technology with high-speed analysis of foreign materials in one unit.
The XGT 9000 creates an optical image of the sample through its built-in camera, providing further discriminatory information on the duct tape sample.
EDXRF uses the interaction of x-rays with a material to determine its elemental composition. EDXRF is suitable for solids, liquids and powders, and in most circumstances is non-destructive.
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