CCI Newsletter, No. 27, June 2001

The Science of Conservation: Surfactant Residue and Rinsing Procedures for Historic Textiles

by Season Tse, Conservation Scientist, and Dorit von Derschau, Intern, Conservation Processes and Materials Research Division

Water washing is one of the most effective methods of cleaning historic textiles, and can be improved still further with the addition of detergents to the wash water. However, the long-term effects of detergent residue on textile artifacts are not well known, and are therefore a great concern for textile conservators.

Detergents are formulations of cleaning agents that are made up of the active cleaning ingredient, a surfactant, and various additives. Surfactants (surface active agents) are long-chain organic molecules with an oil-soluble end and a water-soluble end. They improve the cleaning action of water by lowering its surface tension, which allows better penetration of the water into soiled surfaces. The surfactant molecules also form spherical micelles that trap the oily soils, keeping them emulsified and suspended in the water. Additives are included in detergent formulations to enhance the cleaning power of the product; they may include builders to reduce water hardness, stain remover, antiredeposition agents, fillers, and other auxiliaries.

Conservation research into wet-cleaning and detergent use is ongoing in the United Kingdom. The British Museum and the Victoria and Albert Museum have collaborated to study detergent efficacy and impact on historic textiles, and David Howell at Hampton Court Palace and Dr. Christopher Carr at the University of Manchester Institute of Science and Technology have pioneered the use of surface analytical techniques to investigate surfactant residue on light-aged wool fabrics.

CCI is also studying surfactant residue using surface analyses, working in collaboration with Dr. Yves Deslandes and Gerald Pleizier of the Institute of Chemical Process and Environmental Technology of the National Research Council of Canada (NRC). The goal of this small study is to evaluate the usefulness of X-ray photoelectron spectroscopy (XPS) for the detection of surfactant residue, and to look at the effectiveness of various rinsing procedures for different types of surfactants from different types of textiles.

The surfactants being used in the study are sodium dodecyl sulphate (SDS), Synperonic N, Synperonic A7, and saponin; the textiles are silk, wool, cotton, and linen. Each fabric has been rinsed at frequencies ranging from zero to six 10-min rinses. Shake test and UV-visible (UV-Vis) spectrophotometric analyses have been carried out for all the rinse waters; the results from UV/Vis analysis of rinse water were used to quantify the materials washed from the textiles and the detergent rinsed out. XPS analysis of textiles after treatment was done by Gerald Pleizier at NRC; this technique detects surfactant residue by analysing the surface 5-10 nm of the textile fibre for changes in surface atomic composition before and after treatment. Colour measurement (L*a*b*) of textiles after treatment and during light-aging will be used as an indicator of the long-term effect, if any, of detergent residue on textiles.

Results from wash water analyses showed that the shake test is very sensitive and gives results similar to those from UV/Vis spectrophotometry. Early XPS results showed loss of oils and other soluble material from 15-year-old wool test fabric after immersion in water and surfactants. Synperonic A7 proved to be more effective than SDS in removing oily soils from wool.

Research such as this will eventually be able to answer conservators' questions about the long-term effects of detergent residue, and allow them to use detergents more effectively and with greater confidence.