Microstructure and Mechanical Properties of Al-Si Alloys Produced by Rapid Solidification and Hot Extrusion

The paper presents the results of tests of rapid solidification (RS) aluminum alloys with the addition of silicon (5%, 11%, and 20%). Casting by melt-spinning on the surface of an intensively cooled copper cylinder allowed to obtain a metallic material in the form of flakes, which were then consolidated in the process of pressing and direct extrusion. The effect of refinement on structural components after rapid solidification was determined. Rapidly solidified AlSi materials are characterized by a comparable size of Si particles, regardless of the silicon content, and the shape of these particles is close to spheroidal. Not only Si particles are fragmented, but also the Al-Si-Fe phase, which also changed its shape from irregular with sharp edges to regular and spherical. The melt-spinning process resulted in a fine-grained structure compared to materials obtained by gravity-casting and extrusion. The influence of the high-temperature compression test on the mechanical properties of rapidly solidified materials was analyzed, and the results were compared with those of gravity-cast materials. An increase in strength properties was found in the case of the AlSi5 RS alloy by 20%, in the case of AlSi11RS by 25%, and in the case of the alloy containing 20% Si by as much as 86% (tensile test). On the basis of the homogeneity of the particle distribution determined by the SEM method, it was found that rapid solidification is an effective method of increasing the strength properties and improving the plastic properties of Al-Si alloys.

Nano-Structured Ridged Micro-Filaments (≥100 µm Diameter) Produced Using a Single Step Strategy for Improved Bone Cell Adhesion and Proliferation in Textile Scaffolds

Textile scaffolds that are either 2D or 3D with tunable shapes and pore sizes can be made through textile processing (weaving, knitting, braiding, nonwovens) using microfilaments. However, these filaments lack nano-topographical features to improve bone cell adhesion and proliferation. Moreover, the diameter of such filaments should be higher than that used for classical textiles (10−30 µm) to enable adhesion and the efficient spreading of the osteoblast cell (>30 µm diameter). We report, for the first time, the fabrication of biodegradable nanostructured cylindrical PLLA (poly-L-Lactic acid) microfilaments of diameters 100 µm and 230 µm, using a single step melt-spinning process for straightforward integration of nano-scale ridge-like structures oriented in the fiber length direction. Appropriate drawing speed and temperature used during the filament spinning allowed for the creation of instabilities giving rise to nanofibrillar ridges, as observed by AFM (Atomic Force Microscopy). These micro-filaments were hydrophobic, and had reduced crystallinity and mechanical strength, but could still be processed into 2D/3D textile scaffolds of various shapes. Biological tests carried out on the woven scaffolds made from these nano-structured micro filaments showed excellent human bone cell MG 63 adhesion and proliferation, better than on smooth 30 µm- diameter fibers. Elongated filopodia of the osteoblast, intimately anchored to the nano-structured filaments, was observed. The filaments also induced in vitro osteogenic expression, as shown by the expression of osteocalcin and bone sialoprotein after 21 days of culture. This work deals with the fabrication of a new generation of nano-structured micro-filament for use as scaffolds of different shapes suited for bone cell engineering.

Structure-Property Relationship in Melt-Spun Poly(hydroxybutyrate-co-3-hexanoate) Monofilaments

Poly(hydroxybutyrate-co-3-hexanoate) (PHBH) is a biodegradable thermoplastic polyester with the potential to be used in textile and medical applications. We have aimed at developing an upscalable melt-spinning method to produce fine biodegradable PHBH filaments without the use of an ice water bath or offline drawing techniques. We have evaluated the effect of different polymer grades (mol% 3-hydroxy hexanoate, molecular weight etc.) and production parameters on the tensile properties of melt-spun filaments. PHBH monofilaments (diameter < 130 µm) have been successfully melt-spun and online drawn from three different polymer grades. We report thermal and rheological properties of the polymer grades as well as morphological, thermal, mechanical, and structural properties of the melt-spun filaments thereof. Tensile strengths up to 291 MPa have been achieved. Differences in tensile performance have been correlated to structural differences with wide-angle X-ray diffraction and small-angle X-ray scattering. The measurements obtained have revealed that a synergetic interaction of a highly oriented non-crystalline mesophase with highly oriented α-crystals leads to increased tensile strength. Additionally, the effect of aging on the structure and tensile performance has been investigated.

Structural Analysis of Melt-Spun Polymer-Optical Poly(Methyl Methacrylate) Fibres by Small-Angle X-ray Scattering and Monte-Carlo Simulation

The structural properties, mainly the spatial variation of density and chain interaction, of melt-spun polymer optical fibres (POFs) are investigated by small-angle X-ray scattering (SAXS) and compared to Monte-Carlo polymer simulations. The amorphous PMMA POFs had been subjected to a rapid cooling in a water quench right after extrusion in order to obtain a radial refractive-index profile. Four fibre samples with different processing parameters are investigated and the SAXS data analysed via Guinier approach. Distance-distribution functions from the respective equatorial and meridional SAXS data are computed to extract the fibres’ nanostructures in the equatorial plane and along the fibre axis, respectively. Temperature profiles of the cooling process are simulated for different locations within the fibre and taken as input for Monte-Carlo simulations of the polymer structure. The simulation results agree with the SAXS measurements in terms of the cooling profile’s strong influence on the structural properties of the fibre: slower cooling in the centre of the fibre leads to stronger interchain interaction, but also results in a higher density and more homogenous materials with less optical scattering.

Inhomogeneity and Anisotropy in Nanostructured Melt-Spun Ti2NiCu Shape-Memory Ribbons

Ti₂NiCu exhibits outstanding properties, such as superelasticity. Recently, its functional properties were also demonstrated on the nanoscale, a fact that makes it the preferred choice for numerous applications. Its properties strongly depend on the manufacturing route. In this work, phase analysis, inhomogeneity, and texture of melt-spun Ti₂NiCu ribbons were investigated using X-ray diffraction. Initially, the ribbons are amorphous. Passing an electric current result in controlled crystallization. Ribbons with 0%, 60%, and 96% crystallinity were studied. Both B2 austenite and B19 martensite phases were observed. Using grazing incidence X-ray diffraction, the inhomogeneity across the thickness was investigated and found to be substantial. At the free surface, a small presence of titanium dioxide may be present. Pole figures of 60% and 96% crystallinity revealed mostly strong fiber <100>_B2 texture in the thickness direction. These observations may be inferred from the manufacturing route. This texture is beneficial. The inhomogeneity across the thickness has to be considered when designing devices.

Melt-Spun Fibers for Textile Applications

Textiles have a very long history, but they are far from becoming outdated. They gain new importance in technical applications, and man-made fibers are at the center of this ongoing innovation. The development of high-tech textiles relies on enhancements of fiber raw materials and processing techniques. Today, melt spinning of polymers is the most commonly used method for manufacturing commercial fibers, due to the simplicity of the production line, high spinning velocities, low production cost and environmental friendliness. Topics covered in this review are established and novel polymers, additives and processes used in melt spinning. In addition, fundamental questions regarding fiber morphologies, structure-property relationships, as well as flow and draw instabilities are addressed. Multicomponent melt-spinning, where several functionalities can be combined in one fiber, is also discussed. Finally, textile applications and melt-spun fiber specialties are presented, which emphasize how ongoing research efforts keep the high value of fibers and textiles alive.

Enhanced Thermoelectric Performance of Bi0.46Sb1.54Te3 Nanostructured with CdTe

Cd-containing polycrystalline Bi_0.46Sb_1.54Te₃ samples with precisely controlled phase composition were synthesized by conventional melting-quenching-annealing technique and a melt-spinning method. The pseudo ternary phase diagram for Cd-Bi/Sb-Te in the region near Bi_0.46Sb_1.54Te₃ was systematically studied. Cd serves as an acceptor dopant contributing holes, whereas for samples doped with CdTe, the combined effects of the substitution of Sb/Bi with Cd and the formation of Sb/Bi_Te antisite defects leads to the increase in hole concentration. Moreover, upon doping with Cd, the lattice thermal conductivity decreases significantly owing to the intensified point defect phonon scattering. The sample with Cd content of 0.01 attains the maximum ZT of 1.15 at 425 K. The utilization of melt-spinning method brings about the in situ nanostructured CdTe and grain size refinement, which further reduce the lattice thermal conductivity while preserving excellent electrical performance. As a result, a higher ZT of 1.30 at 425 K is realized with CdTe content x = 0.005.

Pragmatic Approach to Design Silicon Alloy Anode by the Equilibrium Method

Silicon fascinates with incredibly high theoretical energy density as an anode material and considered as a primary candidate to replace well-established graphite. However, further commercialization is hindered by the abnormal volume changes of Si in every single cycle. Silicon embedded in a buffer matrix using the melt-spinning process is a promising approach; however, its metastable nature significantly reduces the microstructure homogeneity, the quality of the composition, and, therefore, the electrochemical performances. Herein, we developed a new approach to design a high-performance Si-alloy with improved microstructure uniformity and electrochemical properties. Namely, annealing at a certain temperature of the melt-spun amorphous alloy ribbon allowed us to evenly distribute Si nanocrystallites in the microstructure with control of average grain size. As a result, the Si-alloy electrode delivers an initial discharge capacity of 900 mAh g^-1 and exhibits a high coulombic efficiency of >99% from the second cycle with a capacity retention of ∼98% after 100 cycles. This study provides powerful insights and evidence for the successful application of the proposed approach for commercial purposes.

Effect of the Ionic Liquid Structure on the Melt Processability of Polyacrylonitrile Fibers

The production of high-strength carbon fibers is an energy-intensive process, where a significant cost involves the wet or dry-spinning of polyacrylonitrile (PAN) fiber precursors. Melt-spinning PAN fibers would allow for significant reduction in the production cost and production hazards. Ionic liquids (ILs) are an attractive fiber-processing medium because of their negligible vapor pressure and low toxicity. In addition, they are carbon-forming precursors; upon carbonization, residual ILs can enhance the carbon yield, although primarily useful for plasticized melt-spinning of PAN precursor fibers. In this research, we investigated the influence of the molecular structure of ILs and the control of plasticizing interactions with PAN during melt-spinning. The structural, thermal, and mechanical properties of the melt-spun PAN fibers were obtained by a combination of various characterization methods, such as differential scanning calorimetry, thermogravimetric analysis, Fourier transform infrared spectroscopy, scanning electron microscopy, X-ray diffraction, and mechanical testing. These results demonstrated that the IL structure and counteranions influence the PAN fiber formation. More specifically, ILs containing bromide counteranions produced PAN precursor fibers with increased mechanical properties compared to ILs containing chloride anions. Our research can provide a foundation to understand the influence of ILs on melt-spinning of PAN fibers and provides us the guidelines for a higher cost-/energy-efficient production of PAN-based carbon fibers.

Melt-Spun Nanocomposite Fibers Reinforced with Aligned Tunicate Nanocrystals

The fabrication of nanocomposite films and fibers based on cellulose nanocrystals (P-tCNCs) and a thermoplastic polyurethane (PU) elastomer is reported. High-aspect-ratio P-tCNCs were isolated from tunicates using phosphoric acid hydrolysis, which is a process that affords nanocrystals displaying high thermal stability. Nanocomposites were produced by solvent casting (films) or melt-mixing in a twin-screw extruder and subsequent melt-spinning (fibers). The processing protocols were found to affect the orientation of both PU hard segments and the P-tCNCs within the PU matrix and therefore the mechanical properties. While the films were isotropic, both the polymer matrix and the P-tCNCs proved to be aligned along the fiber direction in the fibers, as shown using SAXS/WAXS, angle-dependent Raman spectroscopy, and birefringence analysis. Tensile tests reveal that fibers and films, at similar P-tCNC contents, display Young's moduli and strain-at-break that are within the same order of magnitude, but the stress-at-break was found to be ten-times higher for fibers, conferring them a superior toughness over films.

Electrical Properties of Silver-Attached Amine Functionalized Carbon Black/Polyethylene Terephthalate Fibers Prepared by Melt-Spinning

In this study, amine functionalized carbon black (ABCB) was synthesized using 4-aminobenzoic acid in a phosphoric acid (PPA)/phosphorus pentoxide (P₂O₅) medium, and silver-attached carbon black (Ag-ABCB) was prepared by reducing AgNO₃ with NaBH₄ in the presence of ABCB in ethanol. Elemental, thermogravimetric, and Fourier transform-infrared analyses showed that carbon black (CB) had a well-functionalized 4-aminobenzoic acid. In addition, X-ray photoelectron spectroscopy and X-ray diffraction were used to examine the crystal structure of Ag nanoparticles. Conductive fibers were prepared by melt-spinning using ABCB, Ag-ABCB as a conductive filler, and polyethylene terephthalate (PET) as a polymer matrix. Results confirmed that the fiber that had Ag-ABCB as a conductive filler exhibited the best electrical conductivity. The dispersibility and morphology of the conductive filler in the PET matrix were confirmed through scanning electron microscopy analysis, and Ag-ABCB was the most uniformly dispersed filler in the PET matrix, with good structure.

Structure and Properties of a Metallocene Polypropylene Resin with Low Melting Temperature for Melt Spinning Fiber Application

An isotactic polypropylene (iPP-1) resin with low melting temperature (T_m) is synthesized by a metallocene catalyst and investigated for melt-spun fiber applications. The structure, thermal and mechanical properties, and feasibility of producing fibers of a commercial metallocene iPP (iPP-2) and a conventional Ziegler–Natta iPP (iPP-3) are carefully examined for comparison. T_m of iPP-1 is about 10 °C lower than the other two samples, which is well addressed both in the resin and the fiber products. Besides, the newly developed iPP-1 possesses higher isotacticity and crystallinity than the commercial ones, which assures the mechanical properties of the fiber products. Thanks to the addition of calcium stearate, its crystal grain size is smaller than those of the two other commercial iPPs. iPP-1 shows a similar rheological behavior as the commercial ones and good spinnability within a wide range of take-up speeds (1200–2750 m/min). The tensile property of fibers from iPP-1 is better than commercial ones, which can fulfill the application requirement. The formation of the mesomorphic phase in iPP-1 during melt spinning is confirmed by the orientation and crystallization investigation with wide angle X-ray diffraction (WAXD), which is responsible for its excellent processing capability and the mechanical properties of the resultant fibers. The work may provide not only a promising candidate for the high-performance PP fiber but also a deep understanding of the formation mechanism of the mesomorphic phase during fiber spinning.

The Efficiency of Biobased Carbonization Agent and Intumescent Flame Retardant on Flame Retardancy of Biopolymer Composites and Investigation of their Melt-Spinnability

The objective of this study is to assess the efficiency of biobased carbonization agent in intumescent formulations (IFRs) to examine the flame retardant properties of polylactic acid (PLA) composites and to investigate their melt-spinnability. We used phosphorous-based halogen free flame retardant (FR) and kraft lignin (KL) as bio-based carbonization agent. After melt compounding and molding into sheets by hot pressing various fire related characteristics of IFR composites were inspected and were characterized by different characterization methods. It was fascinating to discover that the introduction of 5–20 wt% FR increased the limiting oxygen index (LOI) of PLA composites from 20.1% to 23.2–33.5%. The addition of KL with content of 3–5 wt% further increased the LOI up to 36.6–37.8% and also endowed PLA/FR/KL composites with improved anti-dripping properties. Cone calorimetry revealed a 50% reduction in the peak heat release rate of the IFR composites in comparison to 100% PLA and confirmed the development of an intumescent char structure containing residue up to 40%. For comparative study, IFR composites containing pentaerythritol (PER) as a carbonization agent were also prepared and their FR properties were compared. IFR composites were melt spun and mechanical properties of multifilament yarns were tested. The analysis of char residues by energy dispersive X-ray spectrometry (EDS) and SEM images confirmed that PLA/FR/KL composites developed a thicker and more homogeneous char layer with better flame retardant properties confirming that the fire properties of PLA can be enhanced by using KL as a carbonization agent.

Melt-Spun Fe-Sb Intermetallic Alloy Anode for Performance Enhanced Sodium-Ion Batteries

Owing to the high theoretical sodiation capacities, intermetallic alloy anodes have attracted considerable interest as electrodes for next-generation sodium-ion batteries (SIBs). Here, we demonstrate the fabrication of intermetallic Fe-Sb alloy anode for SIBs via a high-throughput and industrially viable melt-spinning process. The earth-abundant and low-cost Fe-Sb-based alloy anode exhibits excellent cycling stability with nearly 466 mAh g^-1 sodiation capacity at a specific current of 50 mA g^-1 with 95% capacity retention after 80 cycles. Moreover, the alloy anode displayed outstanding rate performance with ∼300 mAh g^-1 sodiation capacity at 1 A g^-1. The crystalline features of the melt-spun fibers aid in the exceptional electrochemical performance of the alloy anode. Further, the feasibility of the alloy anode for real-life applications was demonstrated in a sodium-ion full-cell configuration which could deliver a sodiation capacity of over 300 mAh g^-1 (based on anode) at 50 mA g^-1 with more than 99% Coulombic efficiency. The results further exhort the prospects of melt-spun alloy anodes to realize fully functional sodium-ion batteries.

Structure and Mechanical Properties of Al-Cu-Fe-X Alloys with Excellent Thermal Stability

In this work, the structure and mechanical properties of innovative Al-Cu-Fe based alloys were studied. We focused on preparation and characterization of rapidly solidified and hot extruded Al-Cu-Fe, Al-Cu-Fe-Ni and Al-Cu-Fe-Cr alloys. The content of transition metals affects mechanical properties and structure. For this reason, microstructure, phase composition, hardness and thermal stability have been investigated in this study. The results showed exceptional thermal stability of these alloys and very good values of mechanical properties. Alloying by chromium ensured the highest thermal stability, while nickel addition refined the structure of the consolidated alloy. High thermal stability of all tested alloys was described in context with the transformation of the quasicrystalline phases to other types of intermetallics.

A Cost-Effective Approach to Optimizing Microstructure and Magnetic Properties in Ce17Fe78B₆ Alloys

Optimizing fabrication parameters for rapid solidification of Re-Fe-B (Re = Rare earth) alloys can lead to nanocrystalline products with hard magnetic properties without any heat-treatment. In this work, we enhanced the magnetic properties of Ce₁₇Fe₇₈B₆ ribbons by engineering both the microstructure and volume fraction of the Ce₂Fe₁₄B phase through optimization of the chamber pressure and the wheel speed necessary for quenching the liquid. We explored the relationship between these two parameters (chamber pressure and wheel speed), and proposed an approach to identifying the experimental conditions most likely to yield homogenous microstructure and reproducible magnetic properties. Optimized experimental conditions resulted in a microstructure with homogeneously dispersed Ce₂Fe₁₄B and CeFe₂ nanocrystals. The best magnetic properties were obtained at a chamber pressure of 0.05 MPa and a wheel speed of 15 m·s^-1. Without the conventional heat-treatment that is usually required, key magnetic properties were maximized by optimization processing parameters in rapid solidification of magnetic materials in a cost-effective manner.

Body-monitoring with photonic textiles: a reflective heartbeat sensor based on polymer optical fibres

Knowledge of an individual's skin condition is important for pressure ulcer prevention. Detecting early changes in skin through perfusion, oxygen saturation values, and pressure on tissue and subsequent therapeutic intervention could increase patients' quality of life drastically. However, most existing sensing options create additional risk of ulcer development due to further pressure on and chafing of the skin. Here, as a first component, we present a flexible, photonic textile-based sensor for the continuous monitoring of the heartbeat and blood flow. Polymer optical fibres (POFs) are melt-spun continuously and characterized optically and mechanically before being embroidered. The resulting sensor shows flexibility when embroidered into a moisture-wicking fabric, and withstands disinfection with hospital-type laundry cycles. Additionally, the new sensor textile shows a lower static coefficient of friction (COF) than conventionally used bedsheets in both dry and sweaty conditions versus a skin model. Finally, we demonstrate the functionality of our sensor by measuring the heartbeat at the forehead in reflection mode and comparing it with commercial finger photoplethysmography for several subjects. Our results will allow the development of flexible, individualized, and fully textile-integrated wearable sensors for sensitive skin conditions and general long-term monitoring of patients with risk for pressure ulcer.

Novel Melt-Spun Polymer-Optical Poly(methyl methacrylate) Fibers Studied by Small-Angle X-ray Scattering

The structural properties of novel melt-spun polymer optical fibers (POFs) are investigated by small-angle X-ray scattering. The amorphous PMMA POFs were subjected to a rapid cooling in a water quench right after extrusion in order to obtain a radial refractive index profile. Four fiber samples were investigated with small-angle X-ray scattering (SAXS). The resulting distance-distribution functions obtained from the respective equatorial and meridional SAXS data exhibit a real-space correlation peak indicative of periodic cross-sectional and axial variations in the scattering density contrast. Simple model calculations demonstrate how the structural information contained particularly in the equatorial distance distribution function can be interpreted. The respective results are qualitatively verified for one of the fiber samples by comparison of the model curve with the measured SAXS data. Eventually, the study confirms that the cross-sectional variation of the (scattering-) density is the main reason for the formation of radial refractive-index profiles in the POFs.

Preparation and Characterization of Modified Soda Lignin with Polyethylene Glycol

Soda lignin does not have thermal flowing characteristics and it is impossible for it to be further thermally molded. To achieve the fusibility of soda lignin for fiber preparation by melt-spinning, an effective method for soda lignin modification was conducted by cooking it with polyethylene glycol (PEG) 400 at various ratios. The higher the ratio of PEG that was used, the more PEG molecular chains were grafted at the alpha carbon of the soda lignin through ether bonds, resulting in lower thermal transition temperatures and more excellent fusibility. The modified soda lignin with a weight ratio of lignin to PEG of 1:4 exhibited a relative thermal stability of molten viscosity at selected temperatures. Thereafter, the resultant fusible soda lignin was successfully melt-spun into filaments with an average diameter of 33 ± 5 μm, which is smaller than that of some industrial lignins. Accordingly, it is possible to utilize soda lignin to produce fibrous carbonaceous materials.

Preparation of melt-spun antimicrobially modified LDH/polyolefin nanocomposite fibers

Layered double hydroxide (LDH) was synthesized and organically modified with camphorsulfonic acid (CSA) and ciprofloxacin. The thermal stability of CSA was improved remarkably under LDH shielding. A minimal inhibitory concentration of free CSA against tested bacteria was determined in order to define the essential quantity in LDH modification. The modified LDHs were melt-compounded with high density polyethylene and the prepared nanocomposites were further melt-spun using a piston-type spinning device. The melt-spun fibers were tested for their antimicrobial activity against Escherichia coli, Proteus vulgaris, Pseudomonas aeruginosa, Enterobacter cloacae, Staphylococcus aureus, Staphylococcus epidermidis, and Streptococcus pyogenes. CSA integrated fibers show susceptibility against Gram-positive bacteria and ciprofloxacin integrated fibers showed activity against both Gram-positive and Gram-negative bacteria.