Encapsulation: Past, Present, and Future

FAIN: PR-263932-19

Johns Hopkins University (Baltimore, MD 21218-2608)
Patricia McGuiggan (Project Director: June 2018 to present)

A Tier II project to conduct experimental analyses on polyethylene-terephthalate (PET) encapsulation products used in preserving historical documents, along with the testing of newer encapsulation materials and the execution of a national survey about the number and condition of encapsulated documents in library and archival collections.

The preservation of documents by PET encapsulation is one of the most popular methods of paper conservation. In spite of this, there are concerns regarding whether the PET envelope traps acidic gases naturally produced by paper which might harm the document. We propose measuring the permeation of gases through archival PET as well as the properties of encapsulated papers. We will also survey the encapsulation methods used in libraries and archives in the US and test the condition of naturally aged PET in local libraries. We will also investigate newer, breathable films which might be used for archival storage of paper documents.

Media Coverage

Of Paper and Permeability (Media Coverage)
Author(s): Christen Brownlee
Publication: The Johns Hopkins Whiting School of Engineering Magazine
Date: 8/14/2018
URL: https://engineering.jhu.edu/magazine/2018/05/of-paper-and-permeability/

Associated Products

The breathability of PET to water vapor: Thickness effects (Article)
Title: The breathability of PET to water vapor: Thickness effects
Author: Andrea K.I. Hall
Author: Molly K. McGath
Author: William D. Minter
Author: Patricia M. McGuiggan
Abstract: A model study of the permeation of water vapor through archival polyethylene terephthalate (PET) in the context of encapsulation is reported. Using intentionally wetted paper, the rate of mass loss of a wet, encapsulated paper was measured and found to be 1000 times slower than the rate of mass loss from wetted unencapsulated paper. The results show that water vapor can permeate through the PET film and the measured rate of vapor flux increases with decreasing PET thickness. The measured mass loss from the encapsulate was used to calculate the relative humidity (RH) inside the encapsulate and the moisture content of the encapsulated paper. The moisture content of encapsulated paper was calculated to be slighter higher than the moisture content of unencapsulated paper, which might be due to a modified cellulose network structure caused by the slower mass loss or variability in the paper, or due to condensation of water vapor on the PET within the encapsulate. The results of this paper quantify the movement of water vapor through PET film and provide conservators insight on the microenvironment in their PET enclosures.
Year: 2020
Primary URL: https://doi.org/10.1080/01971360.2019.1603713
Access Model: Subscription
Format: Journal
Periodical Title: Journal of the American Institute for Conservation
Publisher: American Institute for Conservation

Directional dependence of the mechanical properties of aged paper (Article)
Title: Directional dependence of the mechanical properties of aged paper
Author: Sophie Leheny
Author: Thomas C. Robbins
Author: Catherine K. Robbins
Author: Fangyi Zhou
Author: Andrea K.I.Hall
Author: Molly K. McGath
Author: Louise Pasternack
Author: Jay Wallace
Author: Thomas C. O'Connor
Author: Patricia M. McGuiggan
Abstract: Tensile testing
Year: 2021
Primary URL: https://doi.org/10.1016/j.mechmat.2021.104036
Access Model: subscription
Format: Journal
Periodical Title: Mechanics of Materials
Publisher: Elsevier

The Permeability of PET by Formic and Acetic Acid Vapors (Article)
Title: The Permeability of PET by Formic and Acetic Acid Vapors
Author: Patricia M. McGuiggan
Author: Andrea K.I. Hall
Author: Molly K. McGath
Author: Louise Pasternack
Abstract: The permeability of biaxially oriented polyethylene terephthalate, PET, to vapors from 5%, 30% and 100% formic acid solutions as well as the vapor from a 30% acetic acid solution was measured by gravimetric analysis in order to determine the transmission rate of the vapors through PET and ultimately understand the microenvironment that is created inside an encapsulate. The data shows that the permeation of formic acid vapor is at least two orders of magnitude slower than the permeation of water vapor. Measurements of the permeation of 30% acetic acid vapor through PET seemed to be due to the permeation of the water only, and the permeation of the acetic acid, if it occurred, occurred too slowly to be measured. The size of the diffusing molecule determines the permeation. Since the permeability decreases as the size of the diffusing vapor molecule increases, a plot of permeability versus vapor size allows the permeability of various other vapors through PET to be predicted. Colorimetry showed that porous PET allowed ambient vapors to diffuse into the encapsulate and the entire paper within the encapsulate was affected, not only the paper near the holes in the PET.
Year: 2022
Primary URL: https://doi.org.10.1080/00393630.2021.2011685
Access Model: subscription only
Format: Journal
Periodical Title: Studies in Conservation
Publisher: Routledge, Taylor & Francis Group

A Review of the Gas and Vapor Transport Through Single Polymer Films: Implications for Their Use in Book and Paper Conservation (Article)
Title: A Review of the Gas and Vapor Transport Through Single Polymer Films: Implications for Their Use in Book and Paper Conservation
Author: Glenn Gates
Author: Patricia McGuiggan
Abstract: Permeability is broadly defined as the ability of a material to allow the transportation of liquids, gases, or vapors through it. Although numerous references can be found in the literature giving the permeability values of polymers, there is no standard unit of gas or vapor transport, making comparisons difficult. This review summarizes the permeability of single polymer films used in book and paper conservation, specifically addressing the permeability of storage materials and processes such as encapsulation. In particular, the permeability of the polymer films to oxygen, nitrogen, hydrogen sulfide, water vapor, and acetic acid is summarized. The permeability was found to differ by over 7 orders of magnitude when comparing different gases and vapors diffusing through the polymer films. The permeability is dependent on the molecular size of the diffusing gas or vapor, with smaller molecules diffusing faster than larger molecules. In addition, the chemistry of the film plays a role. Hydrophilic polymers have a much greater permeability of polar diffusants such as water vapor than hydrophobic polymers. In addition, the permeation increases significantly with temperature. The review provides data of the permeability properties of the films used by conservators and will enable them to make an informed decision of the best material for their application.
Year: 2024
Primary URL: https://www.degruyter.com/document/doi/10.1515/res-2024-0012/html?recommended=sidebar
Format: Journal
Periodical Title: Restaurator. International Journal for the Preservation of Library and Archival Material
Publisher: De Gruyter

Encapsulation at Fifty Years: Results from a Survey of United States Paper Collections (Article)
Title: Encapsulation at Fifty Years: Results from a Survey of United States Paper Collections
Author: Patricia M McGuiggan
Author: Glenn A Gates
Abstract: A survey of the document preservation technique referred to as encapsulation was conducted of United States institutions with catalogued archives and paper collections. The purpose of this survey was to inform: an estimation of the proportion and type of materials and documents encapsulated, the popularity of various methods and the materials used for encapsulation creation, and the condition of encapsulation materials and encapsulants in collections. The survey responses provided the first data pertaining to the state of encapsulation approximately fifty years after encapsulation for preservation was formally developed. Survey results suggest that: encapsulation is well-established and highly valued in the toolbox of preservation strategies yielded by conservators and collection managers; that most encapsulation construction materials used during the past fifty years evidence few deterioration problems such as yellowing or embrittlement; that it is not a frequent occurrence that conservation treatments like deacidification, washing or the introduction of pollution sorbents is common; and that there is general satisfaction with encapsulation as a preservation method for weakened paper, maps and posters, whether the encapsulation is used in an archival or exhibition environment. Several text responses from survey participants expressed that future research on polymeric material stability and permeability may alleviate some concerns regarding future use of encapsulation.
Year: 2025
Primary URL: https://www.degruyter.com/document/doi/10.1515/res-2024-0013/html
Format: Journal
Periodical Title: Restaurator. International Journal for the Preservation of Library and Archival Material
Publisher: De Gruyter

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