Polyacrylonitrile (PAN)/crown ether composite nanofibers for the selective adsorption of cations

In this study, we prepared electrospun polyacrylonitrile (PAN) nanofibers functionalized with dibenzo-18-crown-6 (DB18C6) crown ether and showed the potential of these fibers for the selective recovery of K+ from other both mono- and divalent ions in aqueous solutions. Nanofibers were characterized by SEM, FTIR and TGA. SEM results showed that the crown ether addition resulted in thicker nanofibers and higher mean fiber diameters, in a range of 138 to 270 nm. Batch adsorption experiments were conducted in order to evaluate the potential of the crown ether modified nanofibers as an adsorbent for ion removal. The maximum adsorption capacity of the crown ether modified nanofibers for K+ was 0.37 mmol g−1 and the nanofibers followed the selectivity sequence of K+ > Ba2+ > Na+ ∼ Li+ for single ion experiments. Adsorption of Ba2+ ions onto crown ether-modified nanofiber was examined by XPS and the results confirmed the adsorption of the ion. Mixed ion adsorption experiments revealed competitive adsorption between K+ and Ba2+ ions for the available binding sites. This effect was not observed for the other monovalent ions present in the solution and exceptionally high selectivities for K+ over Li+ and Na+ were obtained. Also the crown ether modified nanofibers exhibited good regeneration properties and a good reusability over multiple consecutive adsorption–desorption cycles. Electrospinning is thus shown to be a very versatile tool to prepare crown ether functional polymer adsorbents for the selective recovery of ions

Mixed mode delamination in carbon nanotube/nanofiber interlayered composites

Laminated composites mostly suffer from layer separation and/or delamination, which may affect the stiffness, strength and lifetime of structures. In this study, we aim to produce micron-scale thin carbon nanotubes (CNTs) reinforced adhesive nanofibrous interleaves and to explore their effectiveness when incorporated into structural composites. Neat polyvinyl butyral (PVB) and solutions containing low fractions of CNTs from 0.5 to 2 wt.% were electrospun directly onto carbon fiber prepregs. These interlayered laminates were cured above the glass transition temperature (Tg) of PVB to achieve strong interlaminar binding and also to resist crack re-initiation. The effect of CNTs presence and their mass fractions both on total Mixed-Mode I + II fracture toughness (GC) and crack length was investigated under Mixed-Mode I + II loading. Almost 2-fold increase in GC was reported in interlayered composites compared to non-interlayered laminates, associated to toughening effect of adhesive PVB/CNTs nanofibrous interlayers. Furthermore, the post-fracture analysis revealed the aid of CNTs interleaves in retarding delamination and afterward stabilization of crack propagation

Electrically conductive high–performance thermoplastic filaments for fused filament fabrication

Conductive polyetherimide (PEI)-based filaments can fill the gap between the design and manufacturing of functional and structural components through additive manufacturing. This study systematically describes the fabrication of carbon nanotube (CNTs)-reinforced PEI filaments, complemented by a custom-built extrusion process facilitating low weight fraction of nanomaterials. Neat PEI and CNTs/PEI filaments at different CNTs fractions ranging from 0.1 to 7 wt. % were fabricated. Supported by morphology analysis, the rheological percolation was found to be higher (0.25 wt. % CNTs/PEI) than electrical percolation (0.1 wt. % CNTs/PEI) since the system reached an electrical percolation within the formation of a continuous conductive path at lower CNTs loadings. With the 7 wt. % CNTs loading, the highest electrical conductivity of CNTs/PEI filaments was reported as 2.57 × 10−1 S/cm. A 55% enhancement in tensile modulus was achieved when 5 wt. % CNTs were introduced, but in a trade-off in elongation at break ca. 65%

Engineering the Microstructure of Carbon Fiber-Reinforced Polymer Composites by Cellulose Nanocrystal–Carbon Nanomaterials

Carbon fiber reinforced polymer (CFRP) composites suffer from weak interfacial and interlayer bonding, and lack of control on the microstructure formation that has resulted in properties lower than theoretical predictions. Despite the promises, integrating carbon nanotubes (CNTs) and graphene nanoplatelets (GNPs) into CFRPs is challenging because of the need for complicated lab-scale processes and toxic chemical grafting or dispersants that makes conventional means of processing less compatible with existing industrial procedures for large-scale applications. Engineering the CNTs/GNPs nanostructured carbon fiber (CF) fabric through conventionally adopted coating approaches can effectively integrate the nanostructures in CFRPs that allow them to boost their functionality and tailor the microstructure of composite components. Hence, the preparation of homogeneous and stable coating suspensions of CNTs/GNPs without damaging their intrinsic properties and efficiently transferring the nanomaterials on the CF surface is essential to enhance the structural performance of CFRPs. This dissertation explores the scalable fabrication of CNT/GNP integrated CFRPs by coating approach and tests their structural and multifunctional contribution to CFRPs’. Cellulose nanocrystals (CNCs) are used to create hybrid nanostructures with CNTs (CNC bonded CNT) and GNPs that enable stabilization of carbon nanomaterials in nontoxic media, e.g., water, and promote the scalability of the process. This work is composed of three main divisions: First, the atomic level interaction of CNC and CNT/GNP is investigated using both experimental (transmission/scanning electron microscopy (TEM/SEM), atomic force microscopy (AFM), and X-ray photoelectron spectroscopy (XPS)) accompanied with quantum-level calculations (density functional theory (DFT)). Second, CNC bonded CNT/GNPs hybrids are integrated into CFRPs by immersion coating, and their effect on mechanical properties e.g., interfacial and interlaminar performance are articulated. Third, the multifunctionality of the manufactured composites is controlled through engineered sub-micron droplets of CNCCNT/GNP to achieve the desired properties such as electrical and/or thermal properties along with mechanical strength. This dissertation presents new possibilities to precisely control the material microstructure and enables the engineering of the bottom-up manufacturing of hybrid nanostructured composites

Polyacrylonitrile (PAN)/crown ether composite nanofibers for the selective adsorption of cations

In this study, we prepared electrospun polyacrylonitrile (PAN) nanofibers functionalized with dibenzo-18-crown-6 (DB18C6) crown ether and showed the potential of these fibers for the selective recovery of K+ from other both mono- and divalent ions in aqueous solutions. Nanofibers were characterized by SEM, FTIR and TGA. SEM results showed that the crown ether addition resulted in thicker nanofibers and higher mean fiber diameters, in a range of 138 to 270 nm. Batch adsorption experiments were conducted in order to evaluate the potential of the crown ether modified nanofibers as an adsorbent for ion removal. The maximum adsorption capacity of the crown ether modified nanofibers for K+ was 0.37 mmol g−1 and the nanofibers followed the selectivity sequence of K+ > Ba2+ > Na+ ∼ Li+ for single ion experiments. Adsorption of Ba2+ ions onto crown ether-modified nanofiber was examined by XPS and the results confirmed the adsorption of the ion. Mixed ion adsorption experiments revealed competitive adsorption between K+ and Ba2+ ions for the available binding sites. This effect was not observed for the other monovalent ions present in the solution and exceptionally high selectivities for K+ over Li+ and Na+ were obtained. Also the crown ether modified nanofibers exhibited good regeneration properties and a good reusability over multiple consecutive adsorption–desorption cycles. Electrospinning is thus shown to be a very versatile tool to prepare crown ether functional polymer adsorbents for the selective recovery of ions