A STUDY OF ACRYLIC DISPERSIONS USED IN THE TREATMENT OF PAINTINGS
Michael C. Duffy
2 LITERATURE REVIEW
THE PRIMARY SOURCE FOR INFORMATION on acrylic polymers and their properties remains Robert Feller's “Polymer Emulsions,” first published in 1966 and included as an appendix in the pioneering On Picture Varnishes and Their Solvents (1985). This study includes fundamental information on polymer emulsions, such as manufacturing methods, drying phenomena, and film formation. Physical properties such as minimum film forming temperature (MFT) and glass transition temperature (Tg) are also noted for some acrylic copolymer emulsions. Feller's study is essential reading before undertaking further research into acrylic dispersions.
A review of recent conservation literature in AATA revealed the first mention of polymer dispersions used as lining adhesives in an article by Mehra published in 1972.2 Mehra's study on the use of Plextol B500 as a lining adhesive included data on peel strength and sheer strength. In articles published in 1974 and 1975 Mehra described the use of Plextol B500 in conjunction with a low pressure cold-lining table he had developed.3 Other practical applications of polymer dispersion adhesives were addressed by Volkmer et al.4 Accelerated aging of acrylic dispersion Plextol D360 was done in 1976 by Ketnath, but apparently no test results were reported.5
Not until 1984 were comprehensive test results of these materials published in the conservation literature. Howells et al. examined the aging properties of 14 different dispersions and considered weight change, color change, solubility, tensile mechanical properties, response to heat, and pH changes.6 They found that the most significant changes occurred with thermal aging as opposed to natural, sunlight, and fluorescent aging. DeWitte's study demonstrated that certain dispersion additives sometimes influence the physical properties of a synthetic resin.7 These articles are useful precedents because they begin to examine the long-term stability of these materials being used by conservators today. In addition, Falvey8 and Barclay9 have published case studies in which the application of acrylic dispersion adhesives has been useful in treating difficult problems.
There is much useful information published outside the conservation literature. Excellent information on polymer dispersions can be obtained from Martens' Emulsion and Water–Soluble Paints and Coatings. For information on adhesives and adhesive theory, Wake's Adhesion and the Formulation of Adhesives and Shield's Adhesives Handbook are indispensable. The most current information on advancements in industry can be found in journals such as Colloid and Polymer Science.