Chitosan-Graphene Oxide Dip-Coated Polyacrylonitrile-Ethylenediamine Electrospun Nanofiber Membrane for Removal of the Dye Stuffs Methylene Blue and Congo Red.

Textile wastewater accommodates many toxic organic contaminants that could potentially threaten the ecosystem if left untreated. Methylene blue is a toxic, non-biodegradable, cationic dye that is reportedly observed in significant amounts in the textile effluent stream as it is widely used to dye silk and cotton fabrics. Congo red is a carcinogenic anionic dye commonly used in the textile industry. This study reports an investigation of methylene blue and Congo red removal using a chitosan-graphene oxide dip-coated electrospun nanofiber membrane. The fabricated nanocomposite was characterized using Scanning Electron Microscopy (SEM), FT-IR Spectroscopy, Raman Spectroscopy, UV-vis Spectroscopy, Drop Shape Analyzer, and X-ray Diffraction. The isotherm modeling confirmed a maximum adsorptive capacity of 201 mg/g for methylene blue and 152 mg/g for Congo red, which were well fitted with a Langmuir isotherm model indicating homogenous monolayer adsorption.

Removal of Methylene Blue and Congo Red Using a Chitosan-Graphene Oxide-Electrosprayed Functionalized Polymeric Nanofiber Membrane.

Untreated textile effluent may contain toxic organic pollutants that can have negative impacts on the ecosystem. Among the harmful chemicals present in dyeing wastewater, there are two frequently used organic dyes: methylene blue (cationic) and congo red (anionic). The current study presents investigations on a novel two-tier nanocomposite membrane, i.e., a top layer formed of electrosprayed chitosan-graphene oxide and a bottom layer consisting of an ethylene diamine functionalized polyacrylonitrile electrospun nanofiber for the simultaneous removal of the congo red and methylene blue dyes. The fabricated nanocomposite was characterized using FT-IR spectroscopy, scanning electron microscopy, UV-visible spectroscopy, and Drop Shape Analyzer. Isotherm modeling was used to determine the efficiency of dye adsorption for the electrosprayed nanocomposite membrane and the confirmed maximum adsorptive capacities of 182.5 mg/g for congo red and 219.3 mg/g for methylene blue, which fits with the Langmuir isotherm model, suggesting uniform single-layer adsorption. It was also discovered that the adsorbent preferred an acidic pH level for the removal of congo red and a basic pH level for the removal of methylene blue. The gained results can be a first step for the development of new wastewater cleaning techniques.

Electroless plating of premetalized polyamide fibers for stretchable conductive devices.

A new approach was used to produce electrically conductive polyamide yarns, employing an electroless plating technique, which involved stabilizing silver nanoparticles on the surface of the yarn using Sn2+. First, the [Ag(NH3)2]+ complex was reduced using Sn2+ to produce silver nanoparticle seed layers on the fiber surface, followed by a formaldehyde reduction. The nucleation and growth of silver nanoparticles on the fiber surface were observed through SEM images, demonstrating varying degrees of silver deposition depending on the silver concentration. This deposition variation was confirmed through XRD patterns, TGA data and UV-vis spectra. Additionally, XPS characterization showed the evolution of the chemical state of silver and tin during the silver reduction process. Electrical resistance revealed that the resistance per unit length of the yarn ranged from 3 ± 0.3 Ω cm-1 to 70 ± 6 Ω cm-1, depending on the silver concentration. The resulting silver-plated yarn was incorporated into a stretchable device, demonstrating stable resistance over multiple cycles. This method of fabricating conductive yarn has the potential to open up new possibilities in the design and manufacture of stretchable conductive devices for flexible electronics.

Utilizing peptidic ordering in the design of hierarchical polyurethane/ureas.

One of the key design components of nature is the utilization of hierarchical arrangements to fabricate materials with outstanding mechanical properties. Employing the concept of hierarchy, a new class of segmented polyurethane/ureas (PUUs) was synthesized containing either a peptidic, triblock soft segment, or an amorphous, nonpeptidic homoblock block soft segment with either an amorphous or a crystalline hard segment to investigate the effects of bioinspired, multiple levels of organization on thermal and mechanical properties. The peptidic soft segment was composed of poly(benzyl-l-glutamate)-block-poly(dimethylsiloxane)-block-poly(benzyl-l-glutamate) (PBLG-b-PDMS-b-PBLG), restricted to the ß-sheet conformation by limiting the peptide segment length to <10 residues, whereas the amorphous soft segment was poly(dimethylsiloxane) (PDMS). The hard segment consisted of either 1,6-hexamethylene diisocyanate (crystalline) or isophorone diisocyanate (amorphous) and chain extended with 1,4-butanediol. Thermal and morphological characterization indicated microphase separation in these hierarchically assembled PUUs; furthermore, inclusion of the peptidic segment significantly increased the average long spacing between domains, whereas the peptide domain retained its ß-sheet conformation regardless of the hard segment chemistry. Mechanical analysis revealed an enhanced dynamic modulus for the peptidic polymers over a broader temperature range as compared with the nonpeptidic PUUs as well as an over three-fold increase in tensile modulus. However, the elongation-at-break was dramatically reduced, which was attributed to a shift from a flexible, continuous domain morphology to a rigid, continuous matrix in which the peptide, in conjunction with the hard segment, acts as a stiff reinforcing element.

Scalable Textile Manufacturing Methods for Fabricating Triboelectric Nanogenerators with Balanced Electrical and Wearable Properties.

Triboelectric nanogenerators (TENGs) are foreseen as a leading candidate to harvest mechanical energy from ambient sources such as human body movements. However, wearable TENGs, which are used for this purpose, require adequate wearability for long durations, in addition to sufficient electrical outputs. So far, it has been difficult to achieve this through the predominantly plastic-based wearable TENGs constructed using conventional nanogenerator fabrication methods. This Article evaluates the use of textile materials and scalable fabrication techniques to develop TENGs targeting balanced electrical and wearable properties. The fabrication process is conducted using yarn-coating, dip-coating, and screen-printing techniques, which are common textile manufacturing methods, and converted into fabrics using flat-bed knitting, resulting in TENGs with improved wearable and electrical performances. The electrical properties (open circuit voltage (V oc), short circuit current (I sc), and short circuit charge (Q sc)) and wearable properties (air permeability, stretch and recovery, and moisture management) of these structures are evaluated, during which the yarn-coated TENG resulted in maximum electrical outputs recording V oc ≈ 35 V, I sc ≈ 60 nA, and Q sc ≈ 12 nC, under mild excitations. In terms of wearability, the yarn-coated TENG again performed exceptionally during the majority of tests providing the best moisture management, air permeability (101 cm3/cm2/s), and stretch (∼75%), thus proving its suitability for wearable TENG applications.

Towards Truly Wearable Systems: Optimizing and Scaling Up Wearable Triboelectric Nanogenerators.

Triboelectric nanogenerator (TENG) is an upcoming technology to harvest energy from ambient movements. A major focus herein is harvesting energy from human movements through wearable TENGs, which are constructed by integrating nanogenerators into clothing or accessories. Textile-based TENGs, which include fiber, yarn, and fabric-based TENG structures, account for the majority of wearable TENGs, with many designs and applications demonstrated recently. This calls for a comprehensive analysis of textile-based TENG technology, and how the state-of-the-art device optimization concepts can be deployed to construct them efficiently. Concurrently, how advanced engineering concepts and industrial manufacturing techniques, which are bound with fiber, yarn, and fabric-related developments, can be applied into the TENG context for their output enhancement is still under investigation. Herein, we fill this vital gap by analyzing the state-of-the-art developments, upcoming trends, output optimization strategies, scalability, and prospects of the textile-based TENG technology, presenting a textile engineering perspective.

All-organic, conductive and biodegradable yarns from core-shell nanofibers through electrospinning.

Electrically conductive and biodegradable materials are desired for a range of applications in wearable electronics to address the growing ecological problem of e-waste. Herein, we report on the design and fabrication of all-organic, conductive and biodegradable nanofibrous core-shell yarn produced by in situ polymerization of aniline on the surface of electrospun poly(ε-caprolactone) nanofibers. The effect of concentration of aniline monomer on the morphology and resistivity of deposited polyaniline layer was investigated. The electrical resistance changed almost instantaneously with the strain for multiple stretch and recovery cycles. This rapid and sensitive response to mechanical loading and unloading is promising to validate the possibility of using the conductive yarns as strain sensors for monitoring human motion. Increasing the number of plies of yarn to three resulted in a three-fold reduction of the resistance. The twisted plied yarns were incorporated into fabric by stitching to demonstrate their use as a wearable electrode for capacitive sensors. This approach presents an early step in realizing all-organic conductive biodegradable nanofibrous yarns for biodegradable smart textiles.

Injectable Highly Loaded Cellulose Nanocrystal Fibers and Composites.

Cellulose nanocrystals (CNC)/poly(ethylene oxide) (PEO) composite fibers were successfully produced in situ by injection into a hydrophobic solvent. Using a similar principle, a single step manufacturing method of injectable composites was developed by injection of a CNC solution into a hydrophobic resin. Molecular orientation and deformation of the fibers and composites were obtained using Raman spectroscopy. CNCs were found to be highly aligned along the fiber's axes, as confirmed by 2-fold symmetry of polar plots and second and fourth order orientation parameters. A shift in the position of a characteristic Raman band, initially located at ∼1095 cm-1, corresponding to vibrations of the cellulose backbone polymer chains was followed under tensile deformation. Using this shift, it was possible to estimate the fiber modulus as being ∼33 GPa, which is remarkably high. Stress transfer between the hydrophobic resin and the injected CNC fibers was quantified in this new type of composite using a modified shear-lag theory showing that appreciable reinforcement occurs. Our approach presents a new way to introduce highly loaded CNC fibers in situ into a composite structure.

Tunable Mechanics in Electrospun Composites via Hierarchical Organization.

Design strategies from nature provide vital clues for the development of synthetic materials with tunable mechanical properties. Employing the concept of hierarchy and controlled percolation, a new class of polymer nanocomposites containing a montmorillonite (MMT)-reinforced electrospun poly(vinyl alcohol) (PVA) filler embedded within a polymeric matrix of either poly(vinyl acetate) (PVAc) or ethylene oxide-epichlorohydrin copolymer (EO-EPI) were developed to achieve a tunable mechanical response upon exposure to specific stimuli. Mechanical response and switching times upon hydration were shown to be dependent on the weight-fraction of MMT in the PVA electrospun fibers and type of composite matrix. PVA/MMT.PVAc composite films retained excellent two-way switchability for all MMT fractions; however, the switching time upon hydration was decreased dramatically as the MMT content was increased due to the highly hydrophilic nature of MMT. Additionally, for the first time, significant two-way switchability of PVA/MMT.EO-EPI composites was achieved for higher weight fractions (12 wt %) of MMT. An extensive investigation into the effects of fiber diameter, crystallinity, and MMT content revealed that inherent rigidity of MMT platelets plays an important role in controlling the mechanical response of these hierarchical electrospun composites.

Effect of stiffness of micron/sub-micron electrospun fibers in cell seeding.

The objective of this study was to develop a predictive model for cell seeding depth in electrospun scaffold as a function of fiber stiffness. Electrospun scaffolds (micron and submicron) and 3T3 fibroblasts are used as scaffold-cell systems under vacuum seeding conditions. Atomic force microscopy is used to determine the Young's modulus (E) as a function of fiber diameter. A higher E value led to a lower depth of cell seeding (closer to the surface) indicating that nanofibrous scaffolds offer higher resistance to cell movement compared to microfibrous scaffold. An energy balance model was developed to predict cell seeding depth as a function of E for various vacuum pressures. Experimental data was used in the model to extract unknown parameters to predict cell seeding depth as a function of vacuum pressure for different stiffness scaffolds.

Influence of secondary structure and hydrogen-bonding arrangement on the mechanical properties of peptidic-polyurea hybrids.

Bio-inspired materials design is an important strategy used in the fabrication of tunable and mechanically enhanced polymeric systems. An important aspect of bio-inspiration is to understand how components, such as hierarchy and self-assembly, affect the properties of the designed materials. In this investigation, we explore the use of polypeptide secondary structure and hydrogen bonding arrangement, in order to determine their effects on the thermal and mechanical properties of fully synthetic peptidic polyureas. Specifically, we incorporate either short ß-sheet forming peptide blocks of poly(ß-benzyl-l-aspartate)5 or poly(ε-carbobenzyloxy-l-lysine)5 or longer peptide blocks of poly(ß-benzyl-l-aspartate)20 or poly(ε-carbobenzyloxy-l-lysine)20 as α-helix forming domains into non-chain extended polyureas based on 1,6-hexamethylene diisocyanate and poly(dimethysiloxane). Secondary structure was found to be influenced by the weight fraction of peptide, e.g. increasing peptide weight fractions increased sheet or helical ordering. Additionally, the polyurea microstructure was comprised of nanofibrils with a secondary structure dependent fiber width, attributed to the peptidic motif alignment within the nanothreads. Analysis of the thermomechanical and tensile response revealed multiple trends, such as increased toughness attributed to ß-sheet ordering and increased modulus with increased peptide weight fraction. It is anticipated that this observed interplay between peptide organization and mechanics will be applicable to engineering and biomaterial development due to the simplicity of the synthetic protocol and the promising mechanical tunability guided by the peptide segment.

All-Organic, Stimuli-Responsive Polymer Composites with Electrospun Fiber Fillers.

Stimuli-responsive materials are desired for a wide range of applications. Here, we report the design and fabrication of all-organic, stimuli-responsive polymer composites using electrospun nanofibers as the filler. The incorporation of 4 wt % of filler into the polymer matrix increased the tensile storage modulus by 2 orders of magnitude. Upon exposure to water, the filler fibers plasticize and no longer provide mechanical reinforcement. The tensile storage modulus subsequently diminishes 2 orders of magnitude to the value of the neat matrix polymer.