Background: The use of cellulose acetate to laminate documents for the purpose of preservation was a practice begun in the 1930s by W. J. Barrow. Laminate films contain a high concentration of plasticizers, a dispersant additive included in plastics that increase the plasticity or fluidity of a material. The most common plasticizers are phthalate esters added to poly vinyl choloride materials. The challenge with plasticizers is that they can be released from composite material, a challenge not only for laminates but also for modern materials such as sound recordings. In 1959, studies were conducted indicating that one particular phthalate plasticizer, bis(2-methozyethyl)phthalate, contained in one particular cellulose acetate laminate film (Dupont CA48), can cause the laminate to undergo rapid oxidative degradation.
Contributing Studies:
Barrow, W. J. The Barrow Method of Laminating Documents, Journal of Documentary Reproduction 11 (1939) 147-151.
Scribner, B. W. Protection of documents with cellulose acetate sheeting, NBS Miscellaneous Publication M168, 1941.
Stiber, L. S. Thomas Jefferson's Rough Draft of the Declaration of Independence: the evolving condition of an American icon and implications for future preservation, IPC Conference Papers London (1997) 53-63.
Ormsby, M. Analysis of laminated documents using solid-phase micro-extraction, Journal of the American Institute for Conservation 44 (2005) 13-26.
Project Description: One of the Library’s most significant treasures is Jefferson’s handwritten rough draft of the Declaration of Independence. This document was laminated in 1947 to protect further degradation of the document. Once further information was known about plasticizers in the lamination process, an investigation was undertaken to assess and identify the plasticizers used during the brief period documents were laminated at the Library and other cultural institutions. In 1998, liquid chromatography-mass spectrometry (LC-MS) was used to analyze a piece of the laminate from the Rough Draft. Later, in 2008, direct analysis in real time mass spectrometry (DART-MS) was used. The LC-MS method required extracting the sample, comparing the LC retention time to an analytical standard, and analyzing the low-resolution electron ionization mass spectrum. The DART-MS method involved inserting a small piece of the laminate into the helium stream of the DART-MS, analyzing the fragmentation pattern, and obtaining a high-resolution exact mass elemental formula for each ion.
Findings:
- The LC-MS data showed that the plasticizer was bis(2-methozyethyl)phthalate, confirming that Dupont CA48 was the laminate used for the Rough Draft.
- The DART-MS date likewise showed that the plasticizer was bis(2-methozyethyl)phthalate, confirming the earlier findings.
- The rough draft of the Declaration of Independence is permanently housed in an anoxic encasement to reduce any potential impact from the presence of this material.
- ANOXIC ENCASEMENTS
