2.13 Evaluation of Parylene C for Conservation Application I.
Accelerated Aging of Modern, Coated Silk

The Getty Conservation Institute

Eric Hansen
William Ginell
Period of Activity: 1985-88

Project Abstract
Same as below.

Primary Publications
Hansen, E., and W. S. Ginell, "The Conservation of Silk with Parylene-C," Paper presented at Division of Cellulose, Paper and Textiles, Symposium on Historic Textile and Paper Materials, American Chemical Society, Los Angeles, California, September 25-30, 1988. Published in American Chemical Society Symposium Series, N 410, Chapter 8, September 1989.

ABSTRACT-Parylene-C is a vapor-deposited, colorless, transparent polymer that may have application in the consolidation of fragile porous and fibrous art objects. Tests were conducted to determine the effects of a 0.75 m Parylene-C coating application on the tensile and appearance properties of modern and historic silk fabrics. Accelerated thermal- and photo-aging of coated and uncoated silk were conducted and aging rates were determined. It was found that the thermal degradation rates of the tensile properties (breaking load, elongation to break, and total energy to break), and the rate of yellowing of modern silk fabric were unaffected by the coating within the measurement error. Photodegradation of coated silk, both in reduction of tensile properties and yellowing of the coating, was evident on exposure to xenon-arc radiation filtered to simulate outdoor exposure to sunlight. Parylene-C film showed color development only on exposure to ultraviolet radiation with wavelengths shorter than 385 nm. The effect of coating structurally strong, modern silk was an increase in tensile strength properties. Coating comparatively weak historic silk, by contrast, did not result in any improvement in elongation but increased the breaking load, energy to break, and the elastic modulus. This method of consolidation may be useful for the treatment of very fragile silk where added strength is the primary consideration and illumination is filtered to eliminate UV radiation.

Hansen, E., "Evaluation of Parylene-C for Conservation Application: I. Accelerated Aging of Modern, Coated Silk," Internal Report, The Getty Conservation Institute, two volumes, 1987.

ABSTRACT-Activation energies (Ea) Activation energies (Ea); for the loss of tensile properties in modern silk are determined from the Arrhenius relationship Arrhenius relationship;. Strength has an Ea of 18 kcal/mole, strain loss an Ea of 15 kcal/mole, and energy to break an Ea of 16 kcal/mole. Half-lives for properties are determined by extrapolation to ambient conditions from testing temperatures of 70 C to 110 C. At a temperature of 150 C, continued color change and extent of tensile loss are not consistent with those at the lower temperatures. Parylene-C has neither a protective nor a harmful effect on the thermal degradation of silk cloth or yarn. Retention of the initial consolidation effect is most evident in the tensile property of greatest importance, energy to break. Upon exposure to a xenon-arc lamp the Parylene coating protects silk tensile strength loss but not against elongation degradation. The degradation of Parylene-C is wavelength dependent and found to be a function of the spectral distribution of the light source. The color that developed during thermal exposure was found to be related to tensile property degradation.

Hansen, E., and H. Sobel, "The Deterioration and Preservation of Silk," Textiles Speciality Group, American Institute for Conservation 20th Annual Meeting, Buffalo, New York, June 2-7, 1992.

ABSTRACT-The factors affecting the preservation of objects made from Bombyx mori silk are reviewed, with particular reference to the reasons that archaeological and historic fabrics have survived. Primary considerations are the amino acid composition and thus the protein conformation of fibroin and sericin. Causes of deterioration are water, oxygen, light, mechanical stress, and biodeterioration. The effects of humidity on hydrogen bonding are highly significant. The rates of deterioration are influenced by the interaction of humidity with oxygen concentration, wavelength distribution of light, additives (dyes or metals used for weighting), and the pH. Hydrolytic processes, deamidization, ammonia loss, and evidence of oxidation or cross-linking serve to differentiate the causes of deterioration. Markers of deterioration include yellowing, fluorescence, and tyrosine modification. The conclusions are presented as a basis for making decisions on what are suitable storage or display environments for silk objects in a wide variety of conditions or states of deterioration.

Hansen, E., and C. Sussman, "Deterioration of Silk: A Selected Bibliography," In-house annotated bibliography, September 1992.

ABSTRACT-The more than one hundred articles in this bibliography have been collected in support of research conducted at the Getty Conservation Institute over the past five years concerning various aspects of the deterioration of silk. The articles relate to the scientific, technical textile, or conservation literature. Although the bibliograpy is selective and not comprehensive, it does have a particular focus: studies on or relating to the deterioration of silk that might be useful in support of technical studies for conservation purposes. The articles were located by searching computerized databases including CAS (Chemical Abstracts Service) and BCIN (Bibliographic Database of the Conservation Information Network) with keywords, and hand-searching published abstracting services such as World Textile Abstracts, in addition to articles from personal files.