A Study of the Physical Properties of Acrylic Polymers Commonly Used in Art Conservation Público
Kasavan, Benjamin (Spring 2019)
Abstract
Acrylic polymers, such as A-11, B-72, B-48N, and B-44, are regularly used in art conservation to adhere parts together, to consolidate friable objects, and to coat objects, protecting them from light and water. The effect of the glass transition has previously been found to have a large impact on the working properties of these polymers. Furthermore, recent work has sought to mix B-72 and B-48N together in the hope that the blend would provide better properties than either material on its own.
In this study, I used ellipsometry to study the pure polymers, characterizing how the thickness, refractive index, and thermal expansivity go through the glass transition. By comparing the information gleaned on the pure polymers to the data available in the literature, I was able to determine that B-72, B-44, and A-11 all have relatively small breadths in their glass transitions, with the main difference being the temperature at which they start. B-48N had an extremely broad transition spanning more than twice the temperature range of the other polymers. I also showed that mixing B-72 and B-48N in a 3:1 ratio gave a higher glass transition temperature Tg than pure B-72, with a narrower transition than B-48N. The 1:3 B-72:B-48N mixture of the two polymers gave a Tg that is 5 °C higher than the 3:1 mixture, at the expense of a slightly broader transition, suggesting that this combination may have better stability when the object is exposed to temperatures over 40 °C, as may occur when exposed to direct sunlight.
Table of Contents
1 Introduction and Background | 1
1.1 Art Conservation | 1
1.2 Polymer Properties | 2
1.3 Acrylic Polymers used in Art Conservation | 6
1.4 Goal and Outline of Thesis | 10
2 Optics and Ellipsometry | 11
3 Experimental Methods | 18
3.1 Sample Preparation | 18
3.2 Measuring Refractive Index with Ellipsometry | 18
3.3 Ellipsometry Glass Transition Temperature (Tg) Measurements | 21
4 Results and Discussion | 23
4.1 A-11 | 23
4.2 B-72 | 27
4.3 B-48N | 30
4.4 B-44 | 33
4.5 Comparison of the Pure Polymers | 36
4.6 Mixtures of B-72 and B-48N | 40
4.7 Summary | 47
5 Conclusions | 49
6 Bibliography | 51
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