Determination of the polymer composition of mid-twentieth century purses by Raman spectroscopy

Abstract

A database was constructed of 134 reference plastic samples and their Raman spectra to aid in the rapid and accurate identification of the polymer composition of mid-twentieth century plastic purses and their component parts from the Plastics Artifacts Collection at Syracuse University Libraries. Work began by making and testing the database, which led to the determination that matching artifact spectra to reference sample spectra worked well for artifact spectra having signal-to-noise ratios down to 30:1. This finding allowed for using reduced laser power as necessary to protect delicate and pigmented artifacts. These studies enabled the definitive chemical identification of seven selected artifacts, showing that the majority are composed of single plastics including polystyrene, poly(methyl methacrylate), or cellulose acetate. However, it was discovered that one of the purses was composed of both poly(methyl methacrylate) and cellulose acetate. The compositions of three artifacts of unknown composition were discovered, corrections to the existing records were made for three other artifacts, and the composition of one artifact was confirmed. This decisive study will contribute to the archival processing and preservation of these artifacts.

Non-Destructive Identification and Characterization of Crystopal, A Novel Mid-Twentieth Century Plastic

“…In addition to database matching, a visual inspection of the artifact spectra is required prior to making a conclusive positive identification. For example, in our study of mid-twentieth-century plastic purses [25], the population of the SCOAP library was found to be sufficient for unambiguously identifying their plastic contents. However, at the beginning of this Crystopal study, the first artifact analyzed did not positively match any of the database reference plastics.…”

“…An overview of the artifact analysis process is provided here; however, detailed descriptions of the experimental and data analysis methodologies are provided in a previous publication [25]. Raman spectra were obtained using a B&W Tek iRaman Plus portable spectrometer (B&W Tek, Plainsboro, NJ, USA), which was equipped with a 785 nm laser, a fiber-optic probe with an 85 µm spot size, and a CCD detector with a spectral range of 65-3400 cm −1 and a resolution of 4.5 cm −1 .…”

“…A database of reference spectra was constructed as described previously [25] using the BWID software (B&W Tek, v. 2.03). The same BWID software was used to analyze and match reference spectra to spectra collected from artifacts.…”

“…This result was surprising since library records [14] identify Crystopal as a reinforced polyester, and this closest-match reference polymer lacks an ester functional group while still having a moderate HQI value. In our previous work [25], an HQI value of >90 was used as a cutoff for the first step in establishing a positive match, with a visual inspection always required before a final determination of the polymer identity is made. The visual inspection of the spectra of Artifacts A and B (Figure 1) reveals that these objects are nearly identical in composition.…”

“…The methodology used in this study was previously described and involved the compilation of the SCOAP library of Raman spectra for 134 reference plastics [25]. Raman spectra of artifacts are compared to the reference spectra using data-matching software to help identify their plastic compositions.…”