Effect of Different Types of Electrospun Polyamide 6 Nanofibres on the Mechanical Properties of Carbon Fibre/Epoxy Composites

A Review of Electrospun Nanofiber Interleaves for Interlaminar Toughening of Composite Laminates

Recently, polymeric nanofiber veils have gained lot of interest for various industrial and research applications. Embedding polymeric veils has proven to be one of the most effective ways to prevent delamination caused by the poor out-of-plane properties of composite laminates. The polymeric veils are introduced between plies of a composite laminate, and their targeted effects on delamination initiation and propagation have been widely studied. This paper presents an overview of the application of nanofiber polymeric veils as toughening interleaves in fiber-reinforced composite laminates. It presents a systematic comparative analysis and summary of attainable fracture toughness improvements based on electrospun veil materials. Both Mode I and Mode II tests are covered. Various popular veil materials and their modifications are considered. The toughening mechanisms introduced by polymeric veils are identified, listed, and analyzed. The numerical modeling of failure in Mode I and Mode II delamination is also discussed. This analytical review can be used as guidance for veil material selection, for estimation of the achievable toughening effect, for understanding the toughening mechanism introduced by veils, and for the numerical modeling of delamination.

The Mechanical Properties of Nanocomposites Reinforced with PA6 Electrospun Nanofibers

Electrospun nanofibers are very popular in polymer nanocomposites because they have a high aspect ratio, a large surface area, and good mechanical properties, which gives them a broad range of uses. The application of nonwoven structures of electrospun nanofiber mats has historically been limited to enhancing the interlaminar responses of fiber-reinforced composites. However, the potential of oriented nanofibers to improve the characteristics of bulk matrices cannot be overstated. In this research, a multilayered laminate composite was created by introducing polyamide (PA6)-oriented nanofibers into an epoxy matrix in order to examine the effect of the nanofibers on the tensile and thermal characteristics of the nanocomposite. The specimens' fracture surfaces were examined using scanning electron microscopy (SEM). Using differential scanning calorimetry (DSC) analysis, the thermal characteristics of the nanofiber-layered composites were investigated. The results demonstrated a 10.58% peak in the nanocomposites' elastic modulus, which was compared to the numerical simulation and the analytical model. This work proposes a technique for the development of lightweight high-performance nanocomposites.

Evaluation of the Failure Mechanism in Polyamide Nanofibre Veil Toughened Hybrid Carbon/Glass Fibre Composites

The interface of hybrid carbon/E-glass fibres composite is interlayered with Xantu.layr^® polyamide 6,6 nanofibre veil to localise cracking to promote a gradual failure. The pseudo-ductile response of these novel stacking sequences examined under quasi-static three-point bending show a change to the failure mechanism. The change in failure mechanism due to the interfacial toughening is examined via SEM micrographs. The incorporation of veil toughening led to a change in the dominant failure mechanism, resulting in fibre yielding by localised kinking and reduced instances of buckling failure. In alternated carbon and glass fibre samples with glass fibre undertaking compression, a pseudo-ductile response with veil interlayering was observed. The localisation of the fibre failure, due to the inclusion of the veil, resulted in kink band formations which were found to be predictable in previous micro buckling models. The localisation of failure by the veil interlayer resulted in a pseudo-ductile response increasing the strain before failure by 24% compared with control samples.

Study into the Mechanical Properties of a New Aeronautic-Grade Epoxy-Based Carbon-Fiber-Reinforced Vitrimer

The current drive for sustainability demands recyclable matrices for composite materials. Vitrimers combine thermoset properties with reprocessability, but their mechanical performance in highly loaded applications, for instance, composites for aeronautics, is still to be demonstrated. This work presents the complete mechanical characterization of a new vitrimer reinforced with carbon fiber. This vitrimer formulation consists of functional epoxy groups and a new dynamic disulfide crosslinks-based hardener. The testing campaign for the vitrimer composites encompassed tension, compression, interlaminar shear strength (ILSS), in-plane shear (IPS), open-hole tension (OHT) and compression (OHC), filled-hole compression (FHC) and interlaminar fracture toughness tests under mode I and II. Test conditions included room temperature and high temperature of 70 °C and 120 °C, respectively, after moisture saturation. Tension and flexural tests also were applied on the neat vitrimer resin. The results compared well with those obtained for current aeronautic materials manufactured by Resin Transfer Molding (RTM). The lower values observed in compression and ILSS derived from the thermoplastic veils included as a toughening material. This work demonstrates that the vitrimer formulation presented meets the requirements of current matrices for aeronautic-grade carbon-reinforced composites.

Synthesis, Properties, and Selected Technical Applications of Magnesium Oxide Nanoparticles: A Review

In the last few decades, there has been a trend involving the use of nanoscale fillers in a variety of applications. Significant improvements have been achieved in the areas of their preparation and further applications (e.g., in industry, agriculture, and medicine). One of these promising materials is magnesium oxide (MgO), the unique properties of which make it a suitable candidate for use in a wide range of applications. Generally, MgO is a white, hygroscopic solid mineral, and its lattice consists of Mg2+ ions and O2− ions. Nanostructured MgO can be prepared through different chemical (bottom-up approach) or physical (top-down approach) routes. The required resultant properties (e.g., bandgap, crystallite size, and shape) can be achieved depending on the reaction conditions, basic starting materials, or their concentrations. In addition to its unique material properties, MgO is also potentially of interest due to its nontoxicity and environmental friendliness, which allow it to be widely used in medicine and biotechnological applications.

Electrospun PVP/TiO2 Nanofibers for Filtration and Possible Protection from Various Viruses like COVID-19

In this study, TiO2 nanofibers were prepared with Polyvinylpyrrolidone (PVP) polymer using sol-gel method via electrospinning technique. Owing to the advantages of small fiber diameter, tunable porosity, low cost, large surface to volume ratio, structure control, light-weight, and less energy consumption, electrospun nanofibers are evolving as an adaptable material with a number of applications, in this case for filtration and environmental/virus protection. Different samples of TiO2/PVP nanofibers have been prepared by changing the parameters to achieve the best result. As the polymer concentration was increased from 6 to 8 wt.% of PVP, diameter of the resultant fibers was seen to be increased, implying decrease in the pore-size of the fibers up to 1.4 nm. Surface morphology has been checked via Scanning Electron Microscope (SEM) images. Crystalline nature has been analyzed by X-ray Crystallography. Using the Bruanauer-Emmett-Teller (BET) test, surface area and porosity has been checked for the suitable application. The synthesized TiO2/PVP nanofibers have tremendous practical potentials in filtration and environmental remediation applications.

Carrier Fibers for the Safe Dosage of Nanoparticles in Nanocomposites: Nanomechanical and Thermomechanical Study on Polycarbonate/Boehmite Electrospun Fibers Embedded in Epoxy Resin

The reinforcing effect of boehmite nanoparticles (BNP) in epoxy resins for fiber composite lightweight construction is related to the formation of a soft but bound interphase between filler and polymer. The interphase is able to dissipate crack propagation energy and consequently increases the fracture toughness of the epoxy resin. Usually, the nanoparticles are dispersed in the resin and then mixed with the hardener to form an applicable mixture to impregnate the fibers. If one wishes to locally increase the fracture toughness at particularly stressed positions of the fiber-reinforced polymer composites (FRPC), this could be done by spraying nanoparticles from a suspension. However, this would entail high costs for removing the nanoparticles from the ambient air. We propose that a fiber fleece containing bound nanoparticles be inserted at exposed locations. For the present proof-of-concept study, an electrospun polycarbonate nonwoven and taurine modified BNP are proposed. After fabrication of suitable PC/EP/BNP composites, the thermomechanical properties were tested by dynamic mechanical analysis (DMA). Comparatively, the local nanomechanical properties such as stiffness and elastic modulus were determined by atomic force microscopy (AFM). An additional investigation of the distribution of the nanoparticles in the epoxy matrix, which is a prerequisite for an effective nanocomposite, is carried out by scanning electron microscopy in transmission mode (TSEM). From the results it can be concluded that the concept of carrier fibers for nanoparticles is viable.

Rubbery-Modified CFRPs with Improved Mode I Fracture Toughness: Effect of Nanofibrous Mat Grammage and Positioning on Tanδ Behaviour

Carbon Fiber Reinforced Polymers (CFRPs) are widely used where high mechanical performance and lightweight are required. However, they suffer from delamination and low damping, severely affecting laminate reliability during the service life of components. CFRP laminates modified by rubbery nanofibers interleaving is a recently introduced way to increase material damping and to improve delamination resistance. In this work, nitrile butadiene rubber/poly(ε-caprolactone) (NBR/PCL) blend rubbery nanofibrous mats with 60 wt% NBR were produced in three different mat grammages (5, 10 and 20 g/m²) via single-needle electrospinning and integrated into epoxy CFRP laminates. The investigation demonstrated that both mat grammage and positioning affect CFRP tanδ behaviour, evaluated by dynamic mechanical analysis (DMA) tests, as well as the number of nano-modified interleaves. Double cantilever beam (DCB) tests were carried out to assess the mat grammage effect on the interlaminar fracture toughness. Results show an outstanding improvement of G_I,R for all the tested reinforced laminates regardless of the mat grammage (from +140% to +238%), while the effect on G_I,C is more dependent on it (up to +140%). The obtained results disclose the great capability of NBR/PCL rubbery nanofibrous mats at improving CFRP damping and interlaminar fracture toughness. Moreover, CFRP damping can be tailored by choosing the number and positioning of the nano-modified interleaves, besides choosing the mat grammage.

Novel Antibacterial and Toughened Carbon-Fibre/Epoxy Composites by the Incorporation of TiO2 Nanoparticles Modified Electrospun Nanofibre Veils

The inclusion of electrospun nanofiber veils was revealed as an effective method for enhancing the mechanical properties of fiber-reinforced epoxy resin composites. These veils will eventually allow the incorporation of nanomaterials not only for mechanical reinforcement but also in multifunctional applications. Therefore, this paper investigates the effect of electrospun nanofibrous veils made of polyamide 6 modified with TiO2 nanoparticles on the mechanical properties of a carbon-fiber/epoxy composite. The nanofibers were included in the carbon-fiber/epoxy composite as a single structure. The effect of positioning these veils in different composite positions was investigated. Compared to the reference, the use of unmodified and TiO2 modified veils increased the flexural stress at failure and the fracture toughness of composites. When TiO2 modified veils were incorporated, new antibacterial properties were achieved due to the photocatalytic properties of the veils, widening the application area of these composites.

TiO2-Doped Electrospun Nanofibrous Membrane for Photocatalytic Water Treatment

This work has been focused on the one-step fabrication by electrospinning of polyamide 6 (PA6) nanofibre membranes modified with titanium dioxide nanoparticles (TiO₂), where these TiO₂ nanoparticles aggregates could induce a photocatalytic activity. The main potential application of these membranes could be the purification of contaminated water. Thus, it is important to analyse the contaminant degradation capability since in these membranes this is based on their photocatalytic activity. In this work, the effect of the photocatalysis has been studied both on the degradation of an organic model contaminant and on the removal of Escherichia coli and other coliform bacteria. As a result, it was observed that these membranes present excellent photocatalytic activity when they are irradiated under UV light, allowing a 70% reduction of an organic model pollutant after 240 min. In addition, these membranes successfully removed Escherichia coli and other coliform bacteria in artificially inoculated water after 24 h of contact with them. Moreover, the stand-alone structure of the membranes allowed for the reusing of the immobilized catalyst. The experimental evidence indicated that developed nanofibre membranes are a fast and efficient solution for polluted water decontamination based on photocatalysis. Their use could contribute to guarantee a fresh water level and quality, mitigating the water scarcity problem worldwide.