Delamination resistant composites by interleaving bio-based long-chain polyamide nanofibers through optimal control of fiber diameter and fiber morphology

Abstract

In this work an innovative electrospinning system is proposed that simultaneously has an adequate temperature resistance, a high increase in mode I (þ51%) and mode II (þ96%) delamination performance and can be commercially produced. Interleaving nanofibrous veils can potentially solve the issue of the limited delamination resistance encountered in composite laminates, but industrial upscaling has always been impeded by one or more critical factors. These constraining factors include a limited temperature stability of the nanofibers, a lack in simultaneous mode I and II delamination performance increase and the complexity of the electrospinning system because non-commercial polymers or specialty nanofibers (e.g. coaxial) are required. In this paper, a robust electrospinning system is proposed that is the first to overcome all major hurdles to make nanofiber toughening industrially viable. A new class of nanofibers based on biosourced polyamide 11 and its poly(ether-block-amide) co-polymers is used to deal with those shortcomings. The nanofibers have tuneable diameters down to 50 nm and cross-section morphologies ranging from circular to ribbon-shaped. The key to this work is the fundamental underpinning of the toughening effect using a broad range of interleaves with different mechanical and thermal properties, fiber diameters and fiber morphologies, all produced from the same bio-based base polymer. Generally, round and thin nanofibers performed better than larger and ribbon-like fibers. The relationship between the fiber morphology and the delamination performance is further underpinned using detailed analysis of the fracture surface. Ultimately, this results in a range of optimized nanofibrous veils capable of improving the delamination resistance considerably without suffering from the aforementioned drawbacks.

Materials systems for interleave toughening in polymer composites

“…They found nanofibre veils to have a significant effect at the laminate level, as well as on a microscopic and interlaminar level and identified the number of crossings a crack makes through the interlaminar region as the main contributor to composite toughening, since nanofibre bridging zones develop in these regions. As such, we find a broad consensus that nanofibre bridging plays a major role in the toughening of the interlaminar region, though the efficacy of bridging will depend on the mechanical properties of the nanofibre and adhesion between interleaf and matrix [107].…”

Electrospinning based on benign solvents: current definitions, implications and strategies

“…PA11 was successfully electrospun using a mixture of FA : anisole 60 : 40 (v/v) by Meireman et al obtaining nanofibers with an average diameter of 53 ± 10 nm. 58…”

“…57 PA11 was successfully electrospun using a mixture of FA : anisole 60 : 40 (v/v) by Meireman et al obtaining nanofibers with an average diameter of 53 ± 10 nm. 58 2.2.5 Zein. Zein is a class of prolamine protein found in maize, thus being renewable and biodegradable.…”

Effect of solution blown nanofibers on Mode‐I fracture toughness and dynamic mechanical properties of carbon fiber‐reinforced composites

“…The Mode‐I fracture toughness was increased 66%, 51%, and 78% for PVDF, PSF, and their combination, respectively. [ 22 ] In addition to these studies, Meireman et al [ 23 ] used the electrospinning technique to produce nanofibers from polyamide (PA11) and its poly(ether‐block‐amide) (PEBA) copolymers to enhance the fracture toughness of laminated composites. The Mode‐I fracture toughness was increased nearly 51% for both polymer types.…”

“…The level of production rates was claimed as industrial‐scale production. [ 23 ] As an alternative to the electrospinning method, an industrially scalable and cost‐effective nanofiber production technique, solution blowing (SB) is a promising approach that is used to enhance the toughness of composite materials. Rather than electrostatic forces, compressed air is used to form polymer solution into fiber.…”