22/23-HS2339 Essentials of Conservation

Question 1

Describe the main uses of solvents in conservation, and what needs to be considered when choosing one

Answer 1

Solvents are used for three main purposes in conservation – for cleaning off contaminants (Durkee 2006), for applying polymers, or for removing polymers. When choosing a solvent there are many properties that must be considered: chemical type and purity, solubility parameters, evaporation rate, toxicity and flammability.

[Velson Horie.Materials for Conservation: Organic Consolidants, Adhesives and Coatings]

Question 2

To understand the interactions of solvents, one can start from the intermolecular forces. The forces acting between solvent and polymer molecules may be divided into three types (3)

Answer 2

a. Dispersion force arises from the movement of electrons around molecules. This is a very weak force and is the only force that holds symmetrical molecules, e.g. methane, together. Very little energy is necessary to separate the molecules, and this accounts for the low boiling point of methane (−164 °C). This force is present in all substances.
b. Polar forces arise from non-symmetrical molecules that have an unbalanced distribution of electrons (dipole moment). This imbalance causes further attraction between the molecules, e.g. chloromethane has a higher boiling point (−24 °C) than methane.
c. Hydrogen bonds are an extreme form of polar attraction and occur when the hydrogen is directly attached to oxygen and nitrogen atoms. The subsequent attraction takes place between, for instance, an oxygen atom of one molecule and the hydrogen atom of another. Methanol has a much higher boiling point (65 °C) than methane or chloromethane.

[Velson Horie.Materials for Conservation: Organic Consolidants, Adhesives and Coatings]