2.3 Evaluation of Cellulose Ethers and Certain Water-Soluble Synthetic Polymers as Coatings for Conservation Application

Carnegie Mellon Institute

Robert L. Feller
M. Wilt
John Bogaard (since 6/87)
Period of Activity: 6/85 to 6/89

Project Abstract
Cellulose ethers have been used for some time in several branches of conservation, but no systematic study of their permanence or durability has been conducted. This study concentrated on seven classes of cellulose ethers-carboxymethylcellulose, methylcellulose, ethylcellulose, ethylhydroxyethylcellulose, hydroxypropylcellulose, poly(vinylalcohol), polyacrylamide, and poly(vinylbutyral). These classes were evaluated in terms of their thermal, photochemical, and hydrolytic stability. Samples were prepared as powders and as films-with and without a backing material-and subjected to controlled exposures of heat and light. At selected intervals during the experiment, samples were removed and tested for changes in polymer chain length, weight loss, embrittlement, discoloration, peroxide formation, and decreases in solubility.

Major Findings
All these tests taken together provided a relative ranking of these materials in terms of their potential durability in conservation applications. Carboxymethylcellulose and methylcellulose proved to be the most stable, followed by ethylhydroxyethylcellulose and hydroxypropylcellulose.

Although accelerated aging tests were used to obtain relative characteristics of the various coatings, an effort was also made to estimate their potential long-term stability under normal conditions. Some organic soluble cellulose ethers were found to deteriorate so rapidly that they were not recommended for use in conservation, but in general, early estimates of lifetimes of the water-soluble types under normal museum conditions ranged from 42 to 100 years.

Primary Publications
Feller, R. L., and M. Wilt, Evaluation of Cellulose Ethers for Conservation Application, Research in Conservation, Nš 3, The Getty Conservation Institute, 1990.

ABSTRACT-A study of the stability of cellulose ethers has been completed. Information on the use of cellulose ethers by conservators was summarized by reviewing Art and Archaeology Technical Abstracts (AATA) as well as by compiling information obtained by sending a questionnaire to members of the Book and Paper Group of the American Institute for Conservation. Further, the manufacture of cellulose ethers as well as their specifications and typical properties is discussed. Information on the solubility of the ethers as a function of their degree of substitution is presented. Also included is information on the stability of the ethers as reported by their manufacturers and the mechanical properties of cellulose ether films. The ethers were aged in a circulating-air oven or under daylight fluorescent lamps. Formation of peroxides, the intrinsic viscosity, and Brookfield viscosity and the effect of time of aging were determined. Both powders and films were studied. It has been shown that in order of decreasing stability the ethers can be ranked: carboxymethylcellulose, first; methylcellulose and water-soluble ethylhydroxyethylcellulose, second; and hydroxypropylcellulose, third. Estimates of the possible useful life of the various cellulose ethers were made.

Bailie, C., and R. L. Feller, "The Fading of Some Traditional Pigments as a Function of Relative Humidity," Material Issues in Art and Archaeology, Vol. 123, 1988, Proceedings of the Materials Research Society, Spring Meeting, Reno, Nevada, 1988, pp. 287-292.

ABSTRACT-When powerful light sources such as those used in xenon-arc exposures are adapted to test the fading of paints, the influence of relative humidity is frequently masked if not neglected from consideration. As part of a project sponsored by the (Conservation at the Getty) Institute to investigate the effects of humidity and temperature on photochemically induced deterioration, the influence of relative humidity on the rate of fading of a number of traditional artists' colorants was investigated. Paints were formulated in a hydrophobic vehicle (polyvinylacetate) and in the hydrophilic vehicles hydroxypropyl-cellulose and carboxymethylcellulose. The light source was "daylight" fluorescent lamplight "daylight" through ordinary window glass; the colorants, alizarin and carmine lakes, gamboge, and Vandyke brown. Two aspects of the problem are considered: the potential "maximum" effect resulting from conditions close to 0 to 100% RH and the "average increase for a 10% rise in RH" over the wide range of 20 to 80% RH.

Bailie, C., R. M. Johnston-Feller, and R. L. Feller, "Fading as a Function of Relative Humidity of Paints Based on Several Traditional Organic Colorants," Advances in Coating Technology, 31st Annual Technical Conference of the Cleveland Society for Coatings Technology, John Carroll University, University Heights, Ohio, June 1-2, 1988.

ABSTRACT-Humidity is an important factor to be considered in accelerated-aging tests, yet few detailed studies have been made on the effect of relative humidity on the fading of paint systems. Museums are concerned with the potential rate of fading of a number of traditional organic colorants such as carmine and alizarin lakes, Vandyke brown and gamboge. Using ordinary "daylight" fluorescent lamps, one can demonstrate that relative humidity in the range of 20 to 80% noticeably increases the rate of fading of paints containing these colorants to the extent of 4 to 20% for a rise of 10% in RH.

Feller, R. L., "Cellulose Ethers: Chemistry Should Explain Everything," Washington Conservation Guild 5th Meeting 1990-91 Season, February 7.

ABSTRACT-None available.