Identification and comparison of electrical tapes using instrumental and statistical techniques: I. Microscopic...

Area of Science:

• Forensic Science
• Materials Science
• Analytical Chemistry

Background:

• Traditional polyvinyl chloride (PVC) electrical tape comparisons focus on class characteristics like dimensions and texture.
• Existing analytical techniques lack a standardized, optimal scheme for comprehensive tape comparison.
• Developing quantitative methods for sample discrimination is crucial for forensic applications.

Purpose of the Study:

• To establish an optimal analytical scheme for comparing PVC electrical tapes.
• To develop a quantitative method for discriminating between electrical tape samples.
• To apply these methods in forensic case studies.

Main Methods:

• Analysis of 67 black electrical tape rolls from 34 brands using scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS).
• Evaluation of surface topography (roughness, calendering marks) and elemental composition (Mg, Al, Si, S, Pb, Cl, Sb, Ca, Ti, Zn).
• Application of multivariate statistical techniques for quantitative differentiation.

Main Results:

• Observable differences in surface roughness, calendering marks, and filler particle size, even within the same brand.
• Significant variations in elemental composition between brands, potentially linked to manufacture year.
• Successful quantitative differentiation of electrical tapes into 36 distinct classes using multivariate statistics.
• Correct association of questioned tape samples with known exemplars in a single-blind study.

Conclusions:

• SEM and EDS combined with multivariate statistics provide a robust method for quantitative electrical tape comparison.
• The developed analytical scheme can differentiate tapes at a granular level, including within nominal brands.
• This approach has significant implications for forensic science, particularly in linking evidence from improvised explosive devices.