"Effect of Washing on Plastic Bag Surface Composition and Color" by Katelyn Haas

Abstract

Plastic is prevalent in each aspect of everyday life. Due to its regular use and pervasiveness, plastic is a type of evidence that persists at a crime scene. The color and chemical signature of a plastic can be used to identify a potential common source of the bag and aid in the investigation of a crime. Plastic trash bags, composed of low-density polyethylene, colorants and/or coatings, are a common plastic submitted for analysis. However, pretreatment of the plastic in the lab before analysis (i.e. washing away debris) could alter the color and chemical signature. A deeper understanding of the extent of these observed changes is required.

In this study, two brands of black plastic trash bags were subjected to sequential washings with water along or with water and soap. Colorimetry quantitatively assessed the color of the bags after each washing while Fourier Transform Infrared (FTIR) Spectroscopy assessed the chemical composition. Measurements were taken to assess variations within bags, across bags, across brands, and between washings. The colorimetry data indicated no significant or consistent changes in color resulted from repeated washing with either water alone or water and soap. Visual overlays of FTIR spectra suggested minute differences in the chemical signature, so the spectra were subjected to further statistical analysis using a spectral angle contrast ratio (SCAR) analysis. This revealed some variations are large enough to provide confidence in the observed differences and provide a foundation for comparison between crime scene and potential source bags.

Semester/Year of Award

Fall 2024

Mentor

Cynthia J. Kaeser Tran

Mentor Department Affiliation

Chemistry

Access Options

Open Access Thesis

Degree Name

Honors Scholars

Degree Level

Bachelors

Department

Chemistry

Share

COinS