Self-Assembled NBR/Nomex Nanofibers as Lightweight Rubbery Nonwovens for Hindering Delamination in Epoxy CFRPs

Emanuele Maccaferri; Laura Mazzocchetti; Tiziana Benelli; Tommaso Maria Brugo; Andrea Zucchelli; Loris Giorgini

doi:10.1021/acsami.1c17643

Self-Assembled NBR/Nomex Nanofibers as Lightweight Rubbery Nonwovens for Hindering Delamination in Epoxy CFRPs

ACS Appl Mater Interfaces. 2022 Jan 12;14(1):1885-1899. doi: 10.1021/acsami.1c17643. Epub 2021 Dec 23.

Authors

Emanuele Maccaferri¹, Laura Mazzocchetti^{1

2}, Tiziana Benelli^{1

2}, Tommaso Maria Brugo^{2

3}, Andrea Zucchelli^{2

3}, Loris Giorgini^{1

2}

Affiliations

¹ Department of Industrial Chemistry "Toso Montanari", University of Bologna, Viale Risorgimento 4, 40136 Bologna, Italy.
² Interdepartmental Center for Industrial Research on Advanced Applications in Mechanical Engineering and Materials Technology, CIRI-MAM, University of Bologna, Viale Risorgimento 2, 40136 Bologna, Italy.
³ Department of Industrial Engineering, University of Bologna, Viale Risorgimento 2, 40136 Bologna, Italy.

Abstract

Still today, concerns regarding delamination limit the widespread use of high-performance composite laminates, such as carbon fiber-reinforced polymers (CFRPs), to replace metals. Nanofibrous mat interleaving is a well-established approach to reduce delamination. However, nanomodifications may strongly affect other laminate thermomechanical properties, especially if achieved by integrating soft materials. Here, this limitation is entirely avoided by using rubbery nitrile butadiene rubber (NBR)/Nomex mixed nanofibers: neither laminate stiffness nor glass-transition temperature (T_g) lowering occurs upon CFRP nanomodification. Stable noncrosslinked nanofibers with up to 60% wt of NBR were produced via single-needle electrospinning, which were then morphologically, thermally, spectroscopically, and mechanically characterized. NBR and Nomex disposition in the nanofiber was investigated via selective removal of the sole rubber fraction, revealing the formation of particular self-assembled structures resembling quasi-core-shell nanofibers or fibril-like hierarchical structures, depending on the applied electrospinning conditions (1.10 and 0.20 mL/h, respectively). Mode I and Mode II loading tests show a significant improvement of the interlaminar fracture toughness of rubbery nanofiber-modified CFRPs, especially G_I (up to +180%), while G_II enhancement is less pronounced but still significant (+40% in the best case). The two nanofibrous morphologies (quasi-core-shell and fibril-like ones) improve the delamination resistance differently, also suggesting that the way the rubber is located in the nanofibers plays a role in the toughening action. The quasi-core-shell nanofiber morphology provides the best reinforcing action, besides the highest productivity. By contrast, pure Nomex nanofibers dramatically worsen the interlaminar fracture toughness (up to -70% in G_I), acting as a release film. The achieved delamination resistance improvements, combined with the retention of both the original laminate stiffness and T_g, pave the way to the extensive and reliable application of NBR/Nomex rubbery nanofibrous mats in composite laminates.

Keywords: CFRP; Nomex; delamination; electrospinning; mixed nanofiber; nitrile butadiene rubber; rubber; toughening.