Mechanism and Catalysis of Oxidative Degradation of Fiber-Reinforced Epoxy Composites
Carbon fiber-reinforced polymer (CFRP) materials are widely used in aerospace and recreational equipment, but there is no efficient procedure for their end-of-life recycling. Ongoing work in the chemistry and engineering communities emphasizes recovering carbon fibers from such waste streams by dissolving or destroying the polymer binding. By contrast, our goal is to depolymerize amine-cured epoxy CFRP composites catalytically, thus enabling not only isolation of high-value carbon fibers, but simultaneously opening an approach to recovery of small molecule monomers that can be used to regenerate precursors to new composite resin. To do so will require understanding of the molecular mechanism(s) of such degradation sequences. Prior work has shown the utility of hydrogen peroxide as a reagent to affect epoxy matrix decomposition. Herein we describe the chemical transformations involved in that sequence: the reaction proceeds by oxygen atom transfer to the polymer’s linking aniline group, forming an N-oxide intermediate. The polymer is then cleaved by an elimination and hydrolysis sequence. We find that elimination is the slower step. Scandium trichloride is an efficient catalyst for this step, reducing reaction time in homogeneous model systems and neat cured matrix blocks. The conditions can be applied to composed composite materials, from which pristine carbon fibers can be recovered.
KeywordsRecycling Epoxy Composites Carbon fiber Depolymerize Catalysis
Financial support from the USC Zumberge fund, the M.C. Gill Composites Center at USC, the National Science Foundation (CHE-1566167), and George Olah’s Hydrocarbon Research Foundation are gratefully acknowledged. We thank the NSF (DBI-0821671, CHE-0840366) and the NIH (S10 RR25432) for NMR spectrometers.
- 3.Campbell FC (2006) Manufacturing technology for aerospace structural materials. Elsevier, LondonGoogle Scholar
- 5.European Parliament, Council of the European Union. (2000) Directive 2000/53/EC of the European Parliament and of the Council; OJ L 269:L0053; 2013Google Scholar
- 8.Shibata K, Nakagawa M (2014) CFRP Recycling technology using depolymerization under ordinary pressure. Hitachi Chemical Technical Report No. 56Google Scholar
- 9.Maekawa K, Shibata K, Kuriya H, Nakagawa M (2011) Proceedings of 60th the Society of Polymer Science Japan Annual Meeting, p 6Google Scholar
- 13.Hudson A, Betz D, Kühn FE, Jiménez-Alemán GH, Boland W (2013) Methyltrioxorhenium. In Fuchs PL (ed) Encyclopedia of reagents for organic synthesis. Wiley, New YorkGoogle Scholar