AUTEX 2021 - 20th WORLD TEXTILE CONFERENCE

AUTEX 2021 – Unfolding the future 1

ELECTROSPUN NANOFIBRES FOR HIGH DELAMINATION RESISTANCE OF FIBRE REINFORCED COMPOSITES Timo Meireman, Lode Daelemans, Wim Van Paepegem, Karen De Clerck(*), Department of Materials, Textiles and Chemical Engineering (MaTCh), Ghent University, Technologiepark 70A, Zwijnaarde B-9052, Belgium (*) Email: Karen.DeClerck@UGent.be

ABSTRACT Fibre reinforced composites are embraced in high-end applications due to their lightweight and high mechanical properties. Yet, the susceptibility to delaminations restricts further weight savings in industry. This is especially true when high interlaminar stresses are present at adjacent plies due to dissimilarities in fibre orientation, fibre material or ply architecture [1,2]. The emerging technology of nanofibre toughening could possibly address this handicap if it were not that up to now industrial upscaling has always been impeded by one or more critical factors. This involves poor temperature stability of the nanofibres, a lack in concurrent gain in mode I and II delamination performance, and the complexity of the electrospinning system [1]. In this work, a robust electrospinning system is proposed that is the first to overcome all major hurdles to make nanofibre toughening industrially viable for a variety of composite interfaces. In addition, the value of fine round nanofibres is underpinned, opposing thicker and flat fibres. MATERIALS AND METHODS Polyamide 11 (PA11) [Sigma Aldrich] & Poly(Ether-Block-Amide) (PEBA) [Arkema] were electrospun with a formic acid – anisole solution and deposited directly onto the glass and carbon fibre plies [1,2]. Composites were made by Vacuum Assisted Resin Transfer Moulding [1,2]. The mode I and mode II interlaminar fracture toughness were respectively evaluated by the Double Cantilever Beam and End Notched Flexure [1,2]. Direct curing at 80°C was compared with a 2-step curing process with a 24h dwell-step at 20°C preceding curing at 80°C. RESULTS AND DISCUSSSION Bio-based PA11 and its PEBA analogues were successfully electrospun with a novel eco-friendly formic acid - anisole solution ensuing a wide range of fibre morphologies (Figure 1c).

Figure 1. The fibre morphology (c) plays a major role in the final interlaminar fracture behaviour (d,e,f) and ultimately to the interlaminar fracture toughness in mode I (a) and mode II (b).

Guimarães, Portugal & Online, 5-9 September 2021

Editors: F. Ferreira, A.M. Rocha, R. Fangueiro, A.Marques, A.Zille 2

The nature of the fibre morphologies largely influences the composite’s fracture behaviour (Figure 1 d,e,f). Fine nanofibres highly increase the mode I (+50%) and mode II (+100%) interlaminar fracture toughness such as shown for PEBA nanofibres in a unidirectional glass fibre (GUD+GUD) composite, while thicker nanofibres and ribbons can even be detrimental (Figure 1 a,b). While some nanofibres (e.g. PCL) fail to toughen composites when time-effective immediate curing at 80°C is applied, PEBA and PA11 nanofibres give rise to similar positive results independent from applying a 1-step or 2-step curing process [1]. High mode I and II gains are noted when dissimilar interfaces are at play (Figure 2). This includes interfaces with adjacent fabrics differing in structural properties [unidirectional (UD) versus woven fabrics (f)], orientation [0° versus ±45°], and material type [glass (G) versus carbon fibres (C)]. Still, the degree of improvement is highly influenced by the interface type as this directly affects the interaction between the propagating crack and nanofibres [2].

Figure 2. All (dis)similar interfaces are highly toughened by interleaving fine PEBA-nanofibres, but the extent of the toughness increase varies depending on the interface type.

CONCLUSION For the first time, the delamination resistance of diverse (dis)similar interfaces is highly increased by nanofibre toughening in mode I (+30–50%) and II (+70–130%) simultaneously, with the nature of the interface architecture largely affecting the degree of improvement. Furthermore, the commercially available PA11-polymer family can be electrospun in an eco-friendly solvent system resulting in nanofibres with adequate temperature stability when curing. ACKNOWLEDGMENT L.D. acknowledges Research Foundation Flanders (FWO.3E0.2019.0043.01). The authors also acknowledge financial support from UGent (BOF 13/24J/020 and BOF.PDO.2015.0028.01). REFERENCES [1] Meireman T., Daelemans L., Rijckaert S., Rahier H., Van Paepegem W., De Clerck K. (2020). Delamination resistant composites by interleaving bio-based long-chain polyamide nanofibers through optimal control of fiber diameter and morphology. ComposSciTechnol, 193. [2] Meireman T., Daelemans L., Van Verre E., Rahier H., Van Paepegem W., De Clerck K. (2020). Nanofibre toughening of dissimilar interfaces in composites, ComposSciTechnol, 195.