University of Central Florida STARS Electronic Theses and Dissertations, 2004-2019 2008 Prevention Of Environmentally Induced Degradation In Carbon/ epoxy Composite Material Via Implementation Of A Polymer Based Coati Bradford Tipton University of Central Florida Part of the Materials Science and Engineering Commons Find similar works at: https://stars.library.ucf.edu/etd University of Central Florida Libraries http://library.ucf.edu This Masters Thesis (Open Access) is brought to you for free and open access by STARS It has been accepted for inclusion in Electronic Theses and Dissertations, 2004-2019 by an authorized administrator of STARS For more information, please contact STARS@ucf.edu STARS Citation Tipton, Bradford, "Prevention Of Environmentally Induced Degradation In Carbon/epoxy Composite Material Via Implementation Of A Polymer Based Coati" (2008) Electronic Theses and Dissertations, 2004-2019 3674 https://stars.library.ucf.edu/etd/3674 PREVENTION OF ENVIRONMENTALLY INDUCED DEGRADATION OF CARBON/EPOXY COMPOSITE MATERIAL VIA IMPLEMENTATION OF A POLYMER BASED COATING SYSTEM by BRADFORD TIPTON B.S Rensselaer Polytechnic Institute, 2000 A thesis submitted in partial fulfillment of the requirements for the degree of Master of Science in the Department of Mechanical, Materials, and Aerospace Engineering in the College of Engineering and Computer Science at the University of Central Florida Orlando, Florida Fall Term 2008 © 2008 Bradford Tipton ii ABSTRACT As the use of fiber reinforced plastics increases in such industries as aerospace, wind energy, and sporting goods, factors effecting long-term durability, such as environmental exposure, are of increasing interest The primary objectives of this study were to examine the effects of extensive environmental exposure (i.e., UV radiation and moisture) on carbon/epoxy composite laminate structures, and to determine the relative effectiveness of polymer-based coatings at mitigating degradation incurred due to such exposure Carbon/epoxy composite specimens, both coated and uncoated, were subjected to accelerated weathering in which prolonged outdoor exposure was simulated by controlling the radiation wavelength (in the UV region), temperature, and humidity Mechanical test data obtained for the uncoated specimens indicated a reduction in strength of approximately 6% after 750 hours of environmental exposure This reduction resulted from the erosion of the epoxy matrix in additional to the formation of matrix microcracks Test data revealed that no further degradation occurred with increased exposure duration The protective coatings evaluated were all epoxy based and included two different surfacing films and a chromate containing paint primer The surfacing films were applied during initial cure of the carbon/epoxy composite laminate, and the chromate containing epoxy based paint primer was applied subsequent to curing the carbon/epoxy composite laminate Although the chromate primer performed well iii initially, degradation of the underlying substrate was detected with extended exposure durations In contrast, the surfacing films provided superior protection against environmentally induced degradation Similar degradation attributes were identified in the surfacing film as observed in the uncoated composite, but the degradation was either confined within the surfacing film layer or only penetrated the very near surface of the carbon/epoxy substrate This limited degradation results in a minimal reduction in mechanical strength iv I would like to dedicate this thesis to my family and to my wife Charlene Without all of your love and support my education would not have been possible v ACKNOWLEDGEMENTS I would like to offer special thanks to my advisor Dr Yong-ho Sohn for his patience and guidance throughout my journey through graduate school I would also like to express my deep gratitude to my colleagues, particularly David Podracky, Amador Motos-Lopez, Ed Jones, Nancy Kozlowski, Tom Chenock, Mike Gordon and Ed Nixon for all of their contributions to this research Additionally, I would like to thank Yali Tang from InterCat for his most beneficial assistance in performing the SEM analysis vi TABLE OF CONTENTS LIST OF FIGURES viii! LIST OF TABLES x! LIST OF ACRONYMS/ABBREVIATIONS .xi! 1.0! INTRODUCTION 1! 2.0! LITERATURE REVIEW 4! 2.1! Chemistry of Epoxy Polymers 4! 2.2! Environmental Degradation of Carbon/Epoxy Composites 13! 2.2.1! Degradation Due to Moisture Exposure 14! 2.2.2! Degradation Due to Ultraviolet (UV) Radiation Exposure 16! 2.2.3! Synergistic Effects of Moisture and UV Radiation 18! 2.3! Mechanisms of Degradation Induced by Exposure to Ultraviolet Radiation 20! 2.3.1! Chemical Reaction Mechanisms 20! 2.3.2! Degradation of the Epoxy Matrix as a Function of Depth 28! 3.0! EXPERIMENTAL DETAILS 30! 3.1! Testing Methodology 30! 3.2! Test Panel Fabrication 31! 3.3! Pre-Exposure Testing 35! 3.4! Accelerated Weathering Exposure Testing 37! 3.5! Post Exposure Testing 39! 3.5.1! Visual Micro-inspection 39! 3.5.2! Mechanical Testing 39! 4.0! RESULTS 42! 4.1! Weight as a Function of Environmental Exposure Duration 42! 4.2! Visual Inspection of Specimens Subjected to Accelerated Environmental Exposure 43! 4.3! Mechanical Test Results 54! 5.0! DISCUSSION 61! 5.1! Environmentally Induced Degradation in Carbon/Epoxy Composite Material 61! 5.2! Prevention of Degradation via Implementation of Polymer Based Coatings 63! 6.0! SUMMARY AND RECOMMENDATIONS 67! 7.0! APPENDIX A: RAW TEST DATA 69! 8.0! APPENDIX B: SUPPORTING DOCUMENATION 80! 9.0! REFERENCES 111! vii LIST OF FIGURES Figure Representation of the Epoxy (a) and the Glycidyl (b) Groups [3] Figure Common Epoxy Synthesis Reaction [3] Figure (a) Tri-functional Epoxy; (b) Tetra-functional Epoxy [3] Figure Epoxy Curing Reaction with Amine Curing Agent [3] 12 Figure Epoxy Crosslinking Mechanism [3] 12 Figure Proposed Mechanism for Photo-Oxidation of TGDDM/DDS Epoxy Polymer Scheme [10] 24 Figure Proposed Mechanism for Photo-Oxidation of TGDDM/DDS Epoxy Polymer Scheme [10] 25 Figure Proposed Mechanism for Photo-oxidation of TGDDM/DDS Epoxy Polymer Scheme [10] 26 Figure Proposed Mechanism for Photo-oxidation of TGDDM/DDS Epoxy Polymer Scheme [10] 27 Figure 10 Carbon/Epoxy Composite Test Panel Cure Cycle 33 Figure 11 Control Test Panels: No Environmental Exposure 34 Figure 12 Fiber Orientation for ASTM 3518 Test Specimen [11] 36 Figure 13 In-Plane Shear Test Specimen Dimensions 41 Figure 14 Percentage Weight Loss as a Function of Accelerated Environmental Exposure Duration 43 Figure 15 Bare Composite (A) No Exposure (B) 1500 Hrs Exposure 44 Figure 16 Chromate Primer Coated Composite (A) No Exposure (B) 1500 Hrs Exposure 44 Figure 17 Surfacing Film A (A) No Exposure (B) 1500 Hrs Exposure 45 Figure 18 Surfacing Film B (A) No Exposure (B) 1500 Hrs Exposure 45 Figure 19 Secondary Electron SEM Images (1000x) of Bare Carbon/Epoxy Composite (A) No Exposure (B) 750 Hrs Exposure (C) 1000 Hrs Exposure (D) 1500 Hrs Exposure 48 Figure 20 Secondary Electron SEM Image (25000x) of Bare Carbon/Epoxy Composite after 1500 Hrs of Environmental Exposure 49 Figure 21 Secondary Electron SEM Images (5000x) of Bare Carbon/Epoxy Composite (A) No Exposure (B) 750 Hrs Exposure (C) 1000 Hrs Exposure (D) 1500 Hrs Exposure 50 Figure 22 Secondary Electron SEM Images (50x) of Bare Carbon/Epoxy Composite (A) No Exposure (B) 750 Hrs Exposure 50 Figure 23 Secondary Electron SEM Image (1000x) of Chromate Primer Coated Carbon/Epoxy Composite (A) No Exposure (B) 1500 Hrs Exposure 51 Figure 24 Secondary Electron SEM Image (1000x) of Carbon/Epoxy Composite Coated With Surfacing Film A (A) No Exposure (B) 1500 Hrs Exposure 51 Figure 25 Secondary Electron SEM Image (1000x) of Carbon/Epoxy Composite Coated With Surfacing Film B (A) No Exposure (B) 1500 Hrs Exposure 52 viii Figure 26 Secondary Electron SEM Image (50x) of Carbon/Epoxy Composite Coated with Surfacing Film A – 750 Hrs Exposure 52 Figure 27 Cross Section Images (50x) of Carbon/Epoxy Specimens coated with (A) Surfacing Film A and (B) Surfacing Film B 53 Figure 28 Ultimate Load vs Exposure Time (A) Bare Composite (B) Chromate Primer Coated Composite (C) Surfacing Film A (D) Surfacing Film B 59 Figure 29 Ultimate Load as a Function of Coating Configuration and Exposure Duration 60 Figure 30 Ultimate Load as a Function of Coating Thickness and Exposure Duration 60 ix 98 99 100 ASTM G 155, 2005, “Operating Xenon Arc Light Apparatus for Exposure of Non-Metallic Materials”[13] 101 102 103 104 105 106 107 108 109 110 9.0 REFERENCES Niu, Michael C.Y Composite Airframe Structures: Practical Design Information and Data Hong Kong: Commilit Press Ltd., 1992 Hoskin, Brian C and Alan A Baker Composite Materials for Aircraft Structures New York, New York: American Institute of Aeronautics and Astronautics, Inc., 1986 Strong, A Brent Composites Manufacturing Materials, Methods, and Applications Dearborn, Michigan: Society of Manufacturing Engineers, 2008 Lofgren, Sean “Global Composites Industry Outlook in 2008 and Beyond: The Composite Products Market Reached $56 billion in 2007.” Rueters February 2008 September 2008 < http://www.reuters.com/article/pressRelease/idUS136283+07Feb-2008+PRN20080207> Kumar, B.G , Singh R.P, and Nakamura T (2002) Degradation of Carbon Fiberreinforced Epoxy Composites by Ulraviolet Radiation and Condensation Jounal of Composite Matrerials, 36(24), 2713-33 Heung K and Urban M (2000) Molecular Level Chain Scission Mechanisms of Epoxy and Urethane Polymeric Films Exposed to UV/H20 Multidimensional Spectroscopic Studies Langmuir, 16(12), 5382-5390 Nakamura, T., Singh, R.P., and Vaddadi, P (2006) Effects of Environmental Degradation on Flexural Failure Strength of Fiber Reinforced Composites Experimental Mechanics, 0, 1-12 Xiaojun L., Zhang, Q., Guojun, X., Guanjie, L (2006) Degradation of Carbon Fiber/Epoxy Composites by XE Lamp and Humidity International Journal of Modern Physics B, 20,25-27, 3686-3691 Mazumdar, Sanjay K Composites Manufacturing Materials, Product, and Process Engineering Boca Raton, Florida: CRC Press LLC, 2002 10 Musto, P., Ragosta, G, Abbate, A., and Scarinzi, G (2008) Photo-Oxidation of High Performance Epoxy Networks: Correlation between the Molecular Mechanisms of Degradation and the Viscoelastic and Mechanical Response Macromolecules, 41, 5729-5743 111 11 ASTM D 3518/D 3518M, 1994, “ In-Plane Shear Response of Polymer Matrix Composite Materials by Tensile Test of a ±45° Laminate”, American Society for Testing and Materials, West Conshohocken, PA 12 ASTM D3039/D3039M, 2007, “Standard Test Method for Tensile Properties of Polymer Matrix Composite Materials”, American Society for Testing and Materials, West Conshohocken, PA 13 ASTM G 155, 2005, “Operating Xenon Arc Light Apparatus for Exposure of NonMetallic Materials”, American Society for Testing and Materials, West Conshohocken, PA 14 ASTM D 7136/D7136M, 2007, “Standard Test Method for Measuring the Damage Resistance of a Fiber-Reinforced Polymer Matrix Composite to a Drop-Weight Impact Event”, American Society for Testing and Materials, West Conshohocken, PA 15 ASTM D 71377137M, 2007, “Compressive Residual Strength Properties of Damaged Polymer Matrix Composite Plates”, American Society for Testing and Materials, West Conshohocken, PA 112 ... Both of these studies indicated that crosslinking and chain scission mechanisms operate in a competing manner during the degradation process Increased crosslinking dominates in the early stages of. .. submitted in partial fulfillment of the requirements for the degree of Master of Science in the Department of Mechanical, Materials, and Aerospace Engineering in the College of Engineering and... instance, increasing the number of bisphenol A units included in the resin molecule depicted in figure 2, will result in an increased resin viscosity and heat distortion temperature Besides changing