A New Analytical Technique to Identify Surface Treatments of a Single Fiber

The use of fibers -- for example rug fibers--as evidence in court has been long-established as a type of associative evidence. Chemical analysis of the fibers added evidential value to fibers by providing identification and classification based on fiber composition. However, the current methods mostly focus on characterization of fiber cores.

The ability to distinguish between fiber surface modifications- -for example those associated with stain resistance-- would add increased evidentiary value by providing the ability to better differentiate between variants of, for example, rugs, cloths, etc. The applicant proposes to develop such an ability using a mass spectrometry technique that differentiates between the composition of fiber cores and surface modifications.

"Note: This project contains a research and/or development component, as defined in applicable law," and complies with Part 200 Uniform Requirements - 2 CFR 200.210(a)(14). nca/ncf

The goal of this proposal is to develop a technique to distinguish between single fibers based on their surface coatings. The use of fibers as evidence in court has been long-established as a type of associative evidence. Chemical analysis of the fibers has added significant evidentiary value to fibers by providing identification and classification based on fiber composition. However, the current methods mostly focus on characterization of fiber cores. The ability to distinguish between fiber surface modifications significantly increases their evidentiary value. Many chemical fiber surface modifications are currently used to impart certain functionalities such as stain resistance. Among the surface coatings, fluorinated polymers are common as they provide both water and oil repellence. These coatings are often very thin, and the fibers found as evidence are typically small, making chemical identification a challenging analytical task. Techniques such as surface-sensitive attenuated total reflectance FT-IR and energy dispersive x-ray spectroscopy have been unsuccessful for identification of these modifications. A promising approach is pyrolysis-GC-MS. The application of high temperature in the absence of oxygen breaks the polymer into smaller pieces for detection by GC-MS. The fragmentation pattern depends on the original structure of the polymer. Therefore, the fragments can be used to identify the chemical nature of the coating. However, the sensitivity in this approach is too low for practical applications, requiring a 30-mm^2 piece of fabric. A major reason for low sensitivity is that the large mass of the fiber core masks the signal produced by the thin polymer coating. To enable differentiation between types of fluorinated polymer coatings at the single fiber level, this proposal will employ a new analytical technique, plasma-assisted reaction chemical ionization (PARCI)-MS, eliminating the interference from fiber core in detection of pyrolysis products. The proposed pyrolysis-GC-PARCI-MS technique selectively detects elemental fluorine in pyrolysis products of the fiber separated by GC, revealing fiber surface information in pyrograms. The high sensitivity of GC-PARCI-MS at low pg level for fluorine will enable single fiber analysis. Moreover, the technology can be expanded to detection of other halogenated additives in fibers. Considering the prevalence of fluorinated coatings and other halogenated additives in textiles, this technique is expected to significantly enhance the value of fiber analysis, providing forensic investigators with more evidence to perform their roles in the justice system. ca/ncf