The breathability of PET to water vapor: Thickness effects

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.

RESUME

Un modèle d’étude de la perméabilité de la vapeur d’eau à travers le polyéthylène téréphtalate (PET) de qualité conservation dans le contexte de l’encapsulation est présenté. La vitesse de perte de masse d’un papier humide encapsulé, intentionnellement humidifié, a été mesurée et s’est avérée être 1.000 fois plus faible que la vitesse de perte de masse d’un papier humidifié non encapsulé. Les résultats montrent que la vapeur d’eau peut pénétrer à travers le film de PET et que plus l’épaisseur de PET est fine, plus la vitesse du flux de vapeur mesurée est grande. La perte de masse mesurée de la capsule a été utilisée pour calculer l’humidité relative (HR) dans la capsule et la teneur en humidité du papier encapsulé. La teneur en humidité du papier encapsulé a été mesurée comme étant légèrement supérieure à la teneur en humidité du papier non encapsulé, ce qui pourrait être dû à une modification de la structure réticulaire de la cellulose causée par une plus lente perte de masse ou une irrégularité du papier, ou à la condensation de vapeur d’eau sur le PET à l’intérieur de la capsule. Les résultats de cet article quantifient le mouvement de vapeur d’eau à travers le film de PET et permettent au restaurateur d’avoir un aperçu du microenvironnement à l’intérieur des conditionnements en PET. Traduit par Elsa Thyss.

RESUMO

Um estudo modelo da permeação do vapor d'água através do polietileno tereftalato (PET) arquival no contexto do encapsulamento é relatado. Usando papel intencionalmente úmido, a taxa de perda de massa de um papel encapsulado úmido foi medida e verificou-se ser 1000 vezes mais lenta do que a taxa de perda de massa do papel não encapsulado úmido. Os resultados mostram que o vapor d'água pode permear através do filme PET e a taxa medida do fluxo de vapor aumenta com a diminuição da espessura do PET. A medida da massa perdida do encapsulado foi usada para calcular a umidade relativa (UR) dentro do encapsulado e o conteúdo de umidade do papel encapsulado. A quantidade de umidade do papel encapsulado foi calculada para ser levemente mais alta do que a quantidade de umidade do papel não encapsulado, o que pode ser devido à estrutura em rede de celulose modificada causada por uma perda mais lenta de massa ou variação no papel, ou devido à condensação do vapor d'água sobre o PET dentro do encapsulado. Os resultados desse artigo quantificam o movimento de vapor d'água através do filme PET e fornecem aos conservadores uma visão do microambiente nas suas embalagens de PET. Traduzido por Sandra Baruki.

RESUMEN

Se informa sobre un estudio modelo de la permeación del vapor de agua a través del tereftalato de polietileno (PET - siglas en inglés) de óptima calidad, en el contexto de la encapsulación. Usando papel humedecido intencionalmente, se midió la tasa de pérdida de masa de un papel mojado, encapsulado y se encontró que era 1,000 veces más lento que la tasa de pérdida de masa de papel humedecido no encapsulado. Los resultados muestran que el vapor de agua puede penetrar a través de la película de PET y la velocidad de flujo de vapor medida aumenta al disminuir el espesor del PET. La pérdida de masa medida del encapsulado se usó para calcular la humedad relativa (HR) dentro del encapsulado y el contenido de humedad del papel encapsulado. El resultado del cálculo muestra que el contenido de humedad del papel encapsulado fue mayor que el contenido de humedad del papel no encapsulado, lo que podría deberse a una estructura de la red de celulosa modificada causada por la lenta pérdida de masa o variabilidad en el papel, o debido a la condensación del vapor de agua sobre el PET dentro del encapsulado. Los resultados de este documento cuantifican el movimiento del vapor de agua a través de la película de PET y brindan a los conservadores información sobre el microambiente en sus sobres/fundas de PET. Traducción: Amparo Rueda.

KEYWORDS:

• Encapsulation
• permeation
• PET
• polyethylene terephthalate
• conservation

Disclosure statement

William Minter is owner of William Minter Bookbinding & Conservation, Inc. which supplies ultrasonic welders for conservation.

ORCID

Andrea K. I. Hall http://orcid.org/0000-0003-1670-091X

Molly K. McGath http://orcid.org/0000-0001-9352-7394

William D. Minter http://orcid.org/0000-0002-5678-8234

Patricia McGuiggan http://orcid.org/0000-0003-3001-3163

Additional information

Funding

This work was supported by The Andrew W. Mellon Foundation: [Grant Number Renewed Support for Heritage Science for Conservation] and The National Endowment for the Humanities [Grant Number PR-2639-19].

Notes on contributors

Andrea K. I. Hall

Andrea K. I. Hall is a Senior Research Specialist at Heritage Science for Conservation in the Department of Conservation and Preservation at Johns Hopkins University where she is working on physical property testing of heritage materials, environmental monitoring, studying conservation testing and treatment methods, and material deterioration. Hall has a background as a conservation specialist and a materials scientist. She received her Master of Science in Engineering from Johns Hopkins University in 2016. Hall obtained her Bachelor of Science in biology at Bowling Green State University and studied the conservation of art and artifacts at Studio Art Centers International in Florence, Italy. Email: [email protected]

Molly K. McGath

Molly K. McGath received her Ph.D. from the Department of Materials Science and Engineering at the University of Arizona. She was an Andrew W. Mellon Postdoctoral-Fellow in Heritage Science for Conservation within the Department of Conservation and Preservation at Johns Hopkins University with research focused on environmental monitoring, evaluation of past conservation treatments and methods, and deterioration of organic materials in the library, archive and museum environments. She has been a researcher at the Smithsonian Institution’s Museum Conservation Institute and the Freer Sackler, as well as at the National Gallery of Art in Washington, DC, and is currently a conservation scientist at The Mariners’ Museum and Park, Newport News, VA, USA. Email: [email protected]

William D. Minter

William D. Minter is currently senior book conservator for The Pennsylvania State University Libraries. Previously, he worked with the post-doctoral fellows, researchers, and conservators in the Heritage Science for Conservation project at Johns Hopkins University. And during this time, he has maintained a private-practice book conservation business in Woodbury, Pennsylvania. Bill has always been interested in the science of book conservation. Email: [email protected]

Patricia M. McGuiggan

Patricia M. McGuiggan obtained her Ph.D. in Chemical Engineering from the University of Minnesota. During her Ph.D., she was a research scholar in the Applied Mathematics Department at the Australian National University. She spent 3 years as a postdoctoral fellow at the University of California, Santa Barbara with Professor Jacob Israelachvili. She has worked at 3M, W.L. Gore & Associates, and the National Institute of Standards and Technology. She is currently an associate research professor in the Department of Materials Science and Engineering at Johns Hopkins University and is P.I. of the Heritage Science for Conservation Program in the Department of Conservation and Preservation at JHU. Email: [email protected]