CYCLODODECANE: TECHNICAL NOTE ON SOME USES IN PAPER AND OBJECTS CONSERVATION
IRENE BRÜCKLE, JONATHAN THORNTON, KIMBERLY NICHOLS, & GERRI STRICKLER
In 1995, Hans Michael Hangleiter, Elisabeth Jägers, and Erhard Jägers published an article on a material that they proposed might be important for different conservation specialties. The authors described their search for a binding agent that could be applied as a temporary consolidant during treatments. The ideal agent would have good film-forming properties, low melting point, insolubility in water, solubility in organic solvents, and little or no toxicity. Most important, its application would be easily reversible. Their investigation led them to a series of alicyclic hydrocarbons, compounds of a waxlike consistency that can be melted at temperatures ranging from 35 to 65°C. These materials have as their most important common characteristic the ability to sublime, i.e., to volatilize slowly from a solid directly into a gas under ordinary room-temperature conditions. This characteristic eliminates the need for other chemical or physical means of removal necessary with most other consolidants.
Four similar substances with the abovenoted characteristics, all differing mainly in their melting point temperatures and also in the rate or speed of their sublimation, were discussed by Hangleiter and his coauthors. These are camphene (mp 45–46°C); camphene-tricyclene, a mixture of two hydrocarbon types (mp 35°C); menthol (mp 31–35°C); and cyclododecane (mp 58–61°C). The hydrocarbons, termed by the authors “volatile binders,” can be applied in molten state or can be dissolved in nonpolar solvents such as saturated, aromatic, or halogenated hydrocarbons or petroleum ethers. The sublimation of the binders can be retarded by choosing one with a high melting point, applying it in a molten state, keeping the treated object in a contained environment, and protecting the treated object from exposure to elevated temperatures. Since 1995, several potential uses of volatile binders for situations where temporary consolidation and impregnation of fragile materials or objects are desirable have been proposed and/or tested in treatment:
- Parts of objects such as a flaking paint film or fragile objects such as those commonly uncovered during archaeological excavations can be secured for transport with a volatile binder that can be allowed to sublime once the object arrives in the shelter of the lab (Hangleiter et al. 1995). Wall painting fragments were set in a cyclododecane-impregnated bed of sand; the surfaces of wall paintings were protected with a layer of cyclododecane-impregnated gauze (Hangleiter 1998b).
- Friable substrates such as wall surfaces can be protected during surface cleaning by first impregnating them with a volatile binder. The surface of the substrate then can be cleaned through aqueous or air-abrasive cleaning methods while the consolidant is retained in the substrate and protects it from erosion (Hangleiter et al. 1995). Surface soiling on a tempera painting was removed aqueously after protecting the paint layer with a cyclododecane impregnation (Hiby 1997). An oil painting was impregnated with cyclododecane to prevent polar organic solvents used for varnish removal from penetrating the paint film (Hangleiter 1998b). Glue and casein coatings on wall paintings were removed and/or reduced after the paintings were impregnated with cyclododecane (Hangleiter 1998a).
- In the structural treatment of a historic bridge and the nave walls of a church, cyclododecane protected the historic plaster finishes from being soiled. It also prevented the aqueous consolidant solutions injected into the substrates from migrating to the plaster surface (Hangleiter 1998b).
- The local impregnation of friable mortar with a volatile binder could facilitate the clean removal of test samples (Hangleiter et al. 1995). Friable wall paint layers were excavated in test areas after in situ impregnation with camphene (Hangleiter 1998b).
- Local stains on sample textiles were aqueously removed after protecting the unstained textile areas through impregnation with cyclododecane (Hiby 1997).
These authors did not explore all the compatibilities of the hydrocarbon substances with other materials. They pointed out, however, that the cycloalkanes might interact with nonpolar constituents of paint films or varnishes. Gudrun Hiby (1997), for example, found that cyclododecane altered the appearance of a new acrylic paint film. Nicole Riedl and Georg Hilbert (1998) warned that residues of volatile hydrocarbons may remain for extended periods in the interior of mortar substrates.
The present study continues the exploratory investigations. We chose cyclododecane for our testing because it sublimes slowly, is chemically stable, has no known toxicity, and at present is more readily available than other cycloalkanes. It has been used in the chemical industry as an additive for fragrances and synthetic waxes (DuPont Nylon Intermediates 1998). The chemical properties of cyclododecane have been the subject of numerous scientific studies (e.g., Kolossváry and Guida 1993) and are beyond the scope of this article. Of importance for conservation are the physical characteristics of this substance (Hangleiter et al. 1995; Hiby 1997). Cyclododecane has the low solubility parameter and surface energy values comparable to a hydrocarbon wax. It forms a relatively hard, waxy-looking solid, and it has a boiling point of 243°C and a melting point of 58–61°C. The melted material solidifies quickly upon cooling. It is soluble in nonpolar organic solvents but insoluble in acetone, ethanol, or water, and it is impermeable to acids and bases. It volatilizes slowly; Hans Michael Hangleiter et al. (1995) observed that a solid film sublimed at a rate of 0.03 mm per 24 hours. Our tests showed that a film of ca. 0.08 mm thickness brushed out on glass started to disappear within one day if kept at 20°C and disappeared completely within three days. At 38°C, a film of the same thickness disappeared completely within one day.
We investigated aspects of the application of cyclododecane in two areas of conservation treatment: (1) the isolation of water-sensitive media on paper objects that will undergo aqueous treatment and (2) the protection of the substrate of porous objects that are to be cast for replication using a silicone mold. Mention of related subjects appeared in Geller (1997) and Hangleiter (1998b).