Molecular Network Development of a Thermosetting Epoxy-Amine Polymer

132 Pages·2017·4.71 MB·English

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Dissertations
Spring 5-2012
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Christopher Michael Sahagun
University of Southern Mississippi
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Sahagun, Christopher Michael, "Molecular Network Development of a Thermosetting Epoxy-Amine
Polymer" (2012). Dissertations. 827.
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The University of Southern Mississippi

MOLECULAR NETWORK DEVELOPMENT OF

A THERMOSETTING EPOXY-AMINE POLYMER

by

Christopher Michael Sahagun

Abstract of a Dissertation
Submitted to the Graduate School
of The University of Southern Mississippi
in Partial Fulfillment of the Requirements
for the Degree of Doctor of Philosophy

May 2012
ABSTRACT

MOLECULAR NETWORK DEVELOPMENT OF

A THERMOSETTING EPOXY-AMINE POLYMER

by Christopher Michael Sahagun

May 2012
Epoxy-amine resins find wide application as the matrix material of high
performance polymer composites due to their favorable mechanical properties, thermal
properties and solvent stability. These properties are derived from the complicated,
highly crosslinked molecular network that is characteristic of these thermoset polymers.
The connectivity of the molecular network has a strong influence on the physical
performance of the finished part. Non-homogeneity in the network structure can degrade
these favorable properties through the introduction of low-energy pathways for solvent
penetration or fracture propagation. This work examines nanoscale variation in the
crosslink density of the epoxy-amine network. Specific attention is paid to the influence
of cure temperature on the network-building reaction and the subsequent effect on the
architecture of the crosslinked molecular network. Thermal, rheological and
spectroscopic techniques are used to monitor key chemical and structural changes during
network growth. Atomic force microscopy is used to understand nanoscale fracture
behavior in terms of the low energy pathways that result from a non-homogeneous
distribution of crosslink density. The influence of processing-induced changes in
molecular connectivity is discussed in terms of observed nanoscale morphology and
fracture properties of the cured material.
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COPYRIGHT BY

CHRISTOPHER MICHAEL SAHAGUN

2012

The University of Southern Mississippi

MOLECULAR NETWORK DEVELOPMENT OF

A THERMOSETTING EPOXY-AMINE POLYMER

by

Christopher Michael Sahagun

A Dissertation
Submitted to the Graduate School
of The University of Southern Mississippi
in Partial Fulfillment of the Requirements
for the Degree of Doctor of Philosophy

Approved:

____________Sarah Morgan ____________
Director

____________Sergei Nazarenko_________

____________James Rawlins____________

____________Daniel Savin_____________

____________Jeffrey Wiggins___________

____________Susan A. Siltanen_________
Dean of the Graduate School

May 2012
ACKNOWLEDGMENTS
I gratefully acknowledge the unconditional support provided to me by my major
research advisor, Dr. Sarah Morgan, and I am especially grateful for the countless
opportunities she provided for me as her student.
I also wish to extend my gratitude to my doctoral committee, Dr. Sergei
Nazarenko, Dr. James Rawlins, Dr. Daniel Savin, and Dr. Jeffrey Wiggins. I would also
like to thank Diane Rawlings, Stephen Christensen and Terry Schneider from The Boeing
Company for helpful advice regarding the needs of the aerospace community.
I would also like to acknowledge the contribution of Katrina Knauer who spent an
entire summer with me analyzing data from rheological experiments.
Additionally, I wish to thank the Office of Naval Research as the primary funding
source for this research through award number N00014-07-105 as well as the National
Science Foundation for providing me with financial support through Igert award
0333136.

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TABLE OF CONTENTS

ABSTRACT........................................................................................................................ii

ACKNOWLEDGMENTS..................................................................................................iii

LIST OF TABLES...............................................................................................................v

LIST OF ILLUSTRATIONS..............................................................................................vi

CHAPTER

I. INTRODUCTION.......................................................................................1

II. THE EPOXY-AMINE MOLECULAR NETWORK................................10

III. NON-HOMOGENEITY IN THE EPOXY-AMINE NETWORK............39

IV. FRACTURE PATHWAY AS AN INDICATOR OF
UNDERLYING NETWORK STRUCTURE............................................51

V. EXPERIMENTAL DETAILS...................................................................58

VI. THE TIME-TEMPERATURE TRANSFORMATION BEHAVIOR
OF THE EPOXY-AMINE NETWORK....................................................69

VII. TOPOLOGY OF THE EPOXY-AMINE NETWORK.............................80

VII. THE HETEROGENEOUS NATURE OF THE
EPOXY-AMINE MOLECULAR NETWORK.........................................92

IX. CONCLUSIONS.....................................................................................113

X. RECOMMENDATIONS FOR FUTURE WORK..................................115

REFERENCES................................................................................................................117

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LIST OF TABLES
Table
1. Initial molar concentrations, molar absorptivities and wavenumbers of the
absorption bands used to quantify NIR spectra for the sample cured at
150°C.....................................................................................................................65
2. Rate of development of linear and branch/crosslink segments during the pre-
gelation stage of cure as determined by rate of production of secondary amine
and rate of production of tertiary amine................................................................90

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LIST OF ILLUSTRATIONS

Figure

1. Model Homogeneously and Non-Homogeneously Crosslinked
Molecular Networks.................................................................................................7

2. Molecular Structure of the Diglycidyl Ether of Bisphenol-A
and 3,3’-diaminodiphenyl Sulfone.........................................................................15

3. Epoxy-Amine Network Building Reactions..........................................................17

4. Space filling Models of Epon 828/3,3’-diaminodiphenyl Sulfone........................23

5. Theoretical Time-Temperature Transformation Diagram.....................................26

6. AFM Topographic and Phase Images of a Variety of Epoxy-Amine
Networks................................................................................................................45

7. Three Dimensional Projection of AFM Topographic Data of the Fracture
Surface of a Crosslinked Epoxy and a Thermoplastic Polystyrene.......................47

8. Molecular Structure of Diglycidyl Ether of Bisphenol-A
and 3,3’-Diaminodiphenyl Sulfone........................................................................59

9. Tan δ as a Function of Cure Time..........................................................................72

10. Glass Transition Temperature as a Function of Cure Time...................................74

11. Cure Time Required to Reach the Gel Point for a Series of Temperatures...........76

12. Cure Time Required to Reach the Onset of Vitrification for a Series
of Temperatures.....................................................................................................76

13. Illustration of Two Different Modes of Potential Network Growth......................82

14. Near-Infrared Spectra of Stoichiometric Epon 828/DDS Mixtures
as a Function of Cure Time....................................................................................84

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