Duct tapes are an increasingly important class of forensic evidence. This research has studied the value of using x-ray diffraction (XRD) to extend the ability of evidence examiners to gain additional information about a duct tape specimen.

Duct tapes are composed of five different layers. Starting from the non-adhesive side, these layers are the release coating, backing, scrim, primer and adhesive. The release coating assists in reducing unwind tension and preventing the tape from sticking to itself when on a roll. The backing layer serves as a support for the adhesive, and is usually based on polyethylene. The scrim is a layer of fibers either embedded in the backing layer or between the backing and adhesive layers. Primers help attach the adhesive to the backing. Pressure sensitive adhesives are based on polymers such as natural or synthetic rubbers combined with tackifying resins and hydrogenated resins. Pigments and additives are added to the backing and adhesive layers in order to achieve the desired tape characteristics and appearance.

A variety of instrumental methods are used to obtain information for discrimination of pressure sensitive tapes including duct tapes. Research has been reported on the evidential value of a range of physical investigations such as, physical and optical examination of thickness, weight/area, fluorescence, and birefringence, as well as instrumental chemical techniques including UV/VIS, FTIR, XRF, NAA, ICP MS, XRD, pyrolysis-GC/MS and isotope-ratio MS. XRD analyses have been used to identify minerals in duct tape but to date, only limited qualitative XRD information has been used and no systematic investigation of the further uses of XRD analysis and databases has been published.

XRD analysis has the potential to offer a convenient, cost effective and non-destructive method for further characterization of the molecular or atomic make up of the tape layers. The diffractogram contains information about the qualitative and quantitative mineral composition and the crystallinity of mineral species and polymers present.

This research has shown that the use of quantitative XRD analysis of duct tapes can differentiate between some duct tape samples from rolls that cannot be distinguished by current, routine analysis methods.