Polyester Film: Determining its Purity for Use in Encapsulation of Collection Materials
Background:
One of the most frequently used housing materials for the protective encapsulation of traditional (paper) materials is film made of the polyester poly(ethylene terephthalate) (PET). The LC Preservation Directorate provides a public service specification (Number 500-511-6/19/02) for PET folders. This specification states that the film must not contain any plasticizers, surface coatings, UV inhibitors, adsorbents, or coloring agents, and it must be guaranteed to be non-yellowing with age. Thus, it is important that all PET film be of high purity without deleterious contaminants.
Contributing Studies:
"Polyester Film Encapsulation." Washington, D.C.: Preservation Office, Library of Congress, 1980.
Hengemihle, Frank H., Lindsey, Norris, and Chandru J. Shahani. Accelerated Aging of Paper Within Plastic Film Envelopes and Cardboard Boxes. In Abstracts of Papers Presented at the Seventeenth Annual Meeting, Cincinnati, Ohio, May 31-June 4, 1989, 59-60. Washington, D.C.: American Institute for Historic and Artistic Works, 1989.
Arnaud, C.H. (cover story interview of Jeanette Adams), "Taking Mass Spec Into The Open: Open-air Ionization Methods Minimize Sample Prep and Widen Range of Mass Spectrometry Applications", Chemical & Engineering News, October 8, 2007 Cover, Vol. 85, Issue 41, pp 13‑18. http://pubs.acs.org/cen/coverstory/85/8541aboutcover.html
Project Description: A manufacturer of PET film opened new factories in China and requested that the LC analyze the film to ensure that it meets LC specifications. Fourier-transform infrared spectroscopy (FTIR) is routinely used for the analysis of PET and other housing materials. In this research, both FTIR and direct analysis in real time mass spectrometry (DART-MS) were used to analyze the PET film.
Outcomes/Findings: The FTIR spectra gave no indication that that the PET film was contaminated with any material that would cause it to fail the LC specifications.
However, analysis by DART-MS revealed that the PET film was contaminated with erucamide [cis-13-docosenamide], which is a slip agent used in the manufacturing of some PET films. This discovery of erucamide led to a mystery: The manufacturer claimed that neither erucamide nor any other amide slip agent had been used in the manufacture of the PET film. The mystery was solved when the LC researcher noted that the PET film had been shipped to the LC enclosed in non-stick, plastic sheet protectors: When the sheet protectors were analyzed by DART-MS, they revealed the presence of erucamide. In contrast, when the LC analyzed new samples of the PET film, sent by the manufacturer enclosed in organic-free aluminum foil, no erucamide was detected.
In summary:
- The LC has concluded that this PET film meets LC specifications and may be used in archival encapsulations.
- Even though samples of the original PET film were not in direct contact with the non-stick, plastic sheet protectors, the PET samples were nevertheless contaminated with erucamide. This reveals that erucamide migrated from the sheet protectors into the PET film through several layers of PET film.
- PET films that contain amide slip agents would not meet LC specifications because: (1) there is a high probability that the amide would migrate from the PET film to the object, which because of oxidation, would most likely result in yellowing of the object over time; (2) the amide and/or its degradation products might contribute to degradation of the object; and (3) there is a high probability that the PET itself would yellow over time.
Support: Library of Congress Preservation Directorate
Acknowledgements: Jeanette Adams has contributed time and expertise in performing this research. Deanna Marcum and Robert Dizard provide continuing support to preservation and conservation efforts.
Update and Images: Jeanette Adams presented this work at the 55th American Society for Mass Spectrometry Conference, 2007.
The top images are the FTIR spectra of (A) reference standard MylarTM D, and (B) the PET film contaminated with erucamide: The FTIR spectra provide no evidence for the presence of erucamide. The bottom images are the DART-MS spectra of (C) reference standard MylarTM D, and (D) the PET film contaminated with erucamide: The presence of erucamide is revealed by the abundant ion of m/z 338