This document summarizes a study that characterized various recycled carbon fibers and compared them to virgin carbon fibers. It analyzed the chemical, morphological, and mechanical properties of recycled carbon fibers from different sources using SEM imaging, XPS analysis, tensile testing, and single fiber composite testing. The main findings were that recycled carbon fibers exhibited minimal changes in diameter, surface pitting or texture, favorable surface chemistry for bonding, high strength and modulus retention compared to virgin fibers, and in some cases increased adhesion in single fiber composite tests. The study demonstrated a methodology for effectively evaluating recycled carbon fibers and showed they can retain high performance after recycling.

1. A Comparison of Chemical, Morphological, and Mechanical Properties of Various Recycled Carbon Fibers Joseph Heil, D. Litzenberger, M. Hall, R. Clearfield, Dr. Jerry Cuomo NC State University Pete George & William L. Carberry The Boeing Company 1

2. Preview How to study recycled carbon fibers Fiber type & source material Results Conclusion 2

3. Sample Codes 3

4. Characterization Methods 4

5. Testing Matrix 5

6. SEM-Fiber Diameter Standard Modulus Image Analysis software used to measure fiber diameter 6

7. SEM-Fiber Diameter Overall no dramatic reductions Variation between fiber lots 7 IM T800s IM Hexcel IM7 * Most significant change ~8% diameter decrease

9. Char

10. Grooved surfaceDiameter : Virgin > Recycled Virgin IM7

14. 13 A-RCF9 T300 SM Fibers Thick crenulations, considerable junk on surface Striations more evident than virgin fiber Virgin – characteristic striations A- Cured Trim Scrap A & B reclaimed by Milled Carbon Diameter: A>B>C B- Uncured Trim Scrap C-V T300H

15. SEM Discussion Minimal changes in diameter Pitting observed on IM fibers Difficult to identify surface material SEM analysis is informative & efficient 14

16. XPS Discussion Used to determine atomic percentages % bonding Significant surface activity for chemical bonding Activity comparable to unsized virgin fiber 15

21. Fibers remain stiff after recycling19

22. Tensile Test Summary Strength retention: <0.25in: 90% ~1in: 80% 2+in: 60%-70% Modulus increases with gauge length High modulus retention Flaw distribution sensitivity 20

25. Acknowledgments The Boeing Company Milled Carbon Ltd (Recycled Carbon Fiber Ltd.) Adherent Technologies Dr. Anil Netravali IMST-NCSU Ka Wong & Chuck Mooney- NCSU AIF 23

26. Toray T800s (IM) 24 Reclaimed by Milled Carbon V T800s Uncured a) Characteristic air gap spun precursor b) Residue noticeable on surface. Similar to residue found on recycled T700G. Diameter : Virgin > Recycled

28. V AS4 most representative

30. RCF show mostly carbon & oxygen

31. Surface chemistry is more variable