Design and Construction of a Tensile and Shear Strength Testing Apparatus to Study the Addition of Fumed Silica to the Acrylic Adhesive B-72 Used in Art Conservation Pubblico

Abstract

The field of art conservation adds fumed silica (FS) to acrylic adhesives in order to improve their rheological properties during application. However, little is known about how this added FS may alter the polymer’s material properties. Since 1986, when Stephen Koob published an article on how to make the acrylic B-72 easier to work with, which included adding 0.1 wt% FS to the application solvent, B-72 has become very popular in the conservation community. Paraloid B-72 is a copolymer of methyl methacrylate and ethyl methacrylate, with 2.2 wt% butyl methacrylate. In polymer materials engineering, nanoparticles (NPs) are often added in small quantities to increase the modulus and improve strength of the polymer material. These polymer nanocomposites (PNCs) are used today in a wide variety of applications, yet the underlying scientific mechanism by which these nanometer sized particles act to reinforce the material are unclear. While early theoretical work suggested that adding NPs to polymers should increase their glass transition temperature Tg when attractive interactions exist, current experimental work often shows that the average Tg of the polymer matrix is not altered. We confirm this finding for our system via ellipsometry measurements of the glass transition temperature Tg of neat B-72 and B-72 with 0.2 wt% FS (relative to the dried polymer). We then designed and built the Conservation Adhesive Tensile-to-Shear (CATS) tester to determine the fracture stress of adhesives used in art conservation. We determine that the CATS tester produces reproducible data, and obtained preliminary data that suggests that adding fumed silica to B-72 does increase its tensile fracture stress.

Table of Contents

TABLE OF CONTENTS

Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . vi

List of Tables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . x

List of Figures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xi

Chapter 1: Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

1.1 Motivation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

1.2 Goals of Thesis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

Chapter 2: Materials and Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

2.1 Materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

2.1.1 Polymer Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

2.1.2 Polymers in this Study . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

2.1.3 Fumed Silica . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

2.2 Weight Percent Conventions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

Chapter 3: Relevant Literature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

3.1 Polymer Nanocomposites . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

3.1.1 Property Changes in Materials with the Addition of Nanoparticles . . . . . 14

3.1.2 Bound Polymer Layer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

3.1.3 The Importance of Solvents . . . . . . . . . . . . . . . . . . . . . . . . . . 18

3.2 Art Conservation Literature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

3.2.1 Effect of Fumed Silica on Material Properties of Polymers Used in Art Conservation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

3.2.2 Effect of Drying Time on Fracture Strength . . . . . . . . . . . . . . . . . 21

3.2.3 The Importance of Solvents . . . . . . . . . . . . . . . . . . . . . . . . . . 23

3.2.4 Shear vs Tensile Stress . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

Chapter 4: Experimental Methods: Ellipsometry . . . . . . . . . . . . . . . . . . . . . . 26

4.1 Ellipsometry Theory . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

4.2 Ellipsometry Sample Preparation and Procedure . . . . . . . . . . . . . . . . . . . 30

4.2.1 Sample Preparation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

4.2.2 Measurement Procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

Chapter 5: Results and Discussion of Ellipsometry Measurements . . . . . . . . . . . . 33

5.1 Ellipsometry Measurements of B-44 . . . . . . . . . . . . . . . . . . . . . . . . . 33

5.2 Ellipsometry Measurements of B-72 with Different Amounts of Added Fumed Silica 36

Chapter 6: Design of the Conservation Adhesive Tensile-to-Shear (CATS) Tester . . . . 42

6.1 Initial Tests to Determine Design Specifications for the Conservation Adhesive Tensile-to-Shear (CATS) Tester . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42

6.1.1 Sample Creation and Testing . . . . . . . . . . . . . . . . . . . . . . . . . 43

6.1.2 Results from Initial Testing . . . . . . . . . . . . . . . . . . . . . . . . . . 45

6.2 Design of the CATS Tester . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50

6.3 Design of the Drying Rack . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54

6.4 Experimental Procedure for the CATS Tester . . . . . . . . . . . . . . . . . . . . . 55

6.5 Initial Testing with the CATS Tester . . . . . . . . . . . . . . . . . . . . . . . . . 56

Chapter 7: Conclusions and Future Work . . . . . . . . . . . . . . . . . . . . . . . . . . 62

7.1 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62

7.2 Future Work . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69

About this Honors Thesis

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School	Emory College
Department	Physics
Degree	B.S.
Submission	Honors Thesis
Language	English
Research Field	Physics, Condensed Matter Physics, General Art History
Parola chiave	polymer Conservation B-72
Committee Chair / Thesis Advisor	Connie Roth, Emory University
Committee Members	Effrosyni Seitaridou, Emory University Renee Stein, Emory University

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