Microscopical recognition and characterization of solution dyed fibers

Area of Science:

• Forensic Science
• Materials Science
• Textile Science

Background:

• Solution-dyed fibers, colored during polymer extrusion, are increasingly used in textiles.
• Traditional fiber analysis often overlooks the unique pigment characteristics of solution-dyed materials.
• These pigments offer unexploited microscopic properties valuable for forensic comparisons.

Purpose of the Study:

• To develop a microscopy-based method for identifying solution-dyed fibers.
• To characterize the color and optical properties of pigments within these fibers.
• To provide forensic examiners with a systematic approach for analyzing pigmented fibers.

Main Methods:

• Analysis of 76 synthetic fibers (polypropylene, nylon, polyester, rayon) across various colors and applications.
• Utilized polarized light, fluorescence, and oil immersion microscopy.
• Examined fibers longitudinally and in cross-section.

Main Results:

• A method was developed to recognize solution-dyed fibers and characterize their pigments.
• Fibers contained 1–6 distinct pigments, with 260 pigments identified in total.
• Pigment morphologies varied (angular, elongated, rounded, etc.), and ~40% exhibited fluorescence.

Conclusions:

• The developed microscopy technique enables detailed characterization of pigments in solution-dyed fibers.
• This approach enhances the forensic value of trace evidence derived from synthetic textiles.
• Provides a foundational dataset for exploiting pigment characteristics in casework.