Abstract
Like acrylics and alkyds, polyurethanes (PUs) represent an important class of industrial paints adopted by 20th and 21st artists; primarily by those creating outdoor painted sculptures (OPS). Because PU coatings offer a compromise between aesthetic and performance expectations, unachievable with other types of paints, they are commonly recognized as the most appropriate option for painted artworks intended for an outdoor setting. However, the PU class includes various systems and subgroups possessing very different properties. Through the FTIR-ATR study of 137 PU coating references from the Getty Conservation Institute (GCI) reference collection, this paper outlines the differences and the similarities existing, in terms of the composition, of two package solvent-borne, two package water-borne, one package water-borne and fluoropolymer polyurethanes. The comparison of the obtained FTIR-ATR results allowed determining markers helpful to discriminate specific PU subgroups by means of ATR-FTIR spectroscopy. The goals of this paper are to provide to the conservation professionals a better understanding of the versatility and diversity of PU coatings and to facilitate the identification of the various types initially used by the artists.
Highlights
As part of the outdoor sculpture research project at the Getty Conservation Institute (GCI) [1], nearly two hundreds reference samples of industrial paints, used for making and/or conserving modern outdoor painted artworks, were collected
Representing 85% of the build collection, PU coatings appeared by far as the most significant class of industrial paints related to outdoor painted sculptures (OPS)
Two package solvent‐borne PU (2KSBPU) Activators The FTIR spectra obtained from three different Imron activators (FG1333, FG1633 and FG0162) exhibit similar IR features identifying Hexamethylene diisocyanate (HDI) isocyanurate, a trimer with a cyclic structure, see Fig. 1, widely used as precursor in the PU coating industry
Summary
As part of the outdoor sculpture research project at the GCI [1], nearly two hundreds reference samples of industrial paints, used for making and/or conserving modern outdoor painted artworks, were collected. Representing 85% of the build collection, PU coatings appeared by far as the most significant class of industrial paints related to OPS (outdoor painted sculptures). Many outdoor artworks from the late twentieth century have originally been painted with polyurethanes, and PU topcoats and clear coats appear as the favored option in case of a full repainting of exterior sculptures. Isocyanates are highly reactive chemicals containing the functional group –N=C=O. A large variety of branched or crosslinked polymers may be obtained by adjusting the functionality of the isocyanate or hydroxyl-containing reactant [7]
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