Search

In this study, a transient viscosity adjustment method using a coaxial nozzle was explored to fabricate nanofibers from non-spinnable m-poly(hydroxyamide) (m-PHA). Unlike conventional electrospinning methods that often require additives to induce fiber formation, this approach relies on a sheath-core configuration, introducing tetrahydrofuran (THF) to the sheath to temporarily adjust solution viscosity. The diffusion of THF into the core m-PHA solution resulted in momentary solidification at the interface, promoting nanofiber formation without compromising polymer solubility. SEM and rheological analyses confirmed that optimized sheath-to-core flow ratios yielded nanofibers with significantly reduced particle formation. Notably, increasing the THF flow rate facilitated a faster solidification rate, enhancing jet elongation and resulting in uniform nanofibers with diameters of approximately 180–190 nm. Although complete nanofibers without beads were not achieved in this study, this coaxial electrospinning approach presents a possible pathway for fabricating nanofibers from polymers with limited spinnability, potentially expanding the application scope of electro-spun materials in high-performance fields. [ABSTRACT FROM AUTHOR]

Smart color‐changing fibers attract much attention owing to their importance as a component of flexible electronics. A facile and scalable method of multicolor reversible electro–thermochromic Ag nanoparticles/reduced graphene oxide/polyurethane conductive fiber (ETC AgNPs/rGO/PU conductive fiber) is fabricated, which contains the polyurethane (PU) as the inner layer, reduced graphene oxide (rGO) with Ag nanoparticles (AgNPs) as the conductive layer, and thermochromic paste as the outermost layer. It possesses excellent electrothermal and color‐changing properties and rapidly generates Joule heat at 0.5 V, which makes the fiber surface temperature reach 39.81 °C rapidly. The color switching rate is fast and changes from green to yellow within 2 s. During the process of 250 times on/off voltage, ETC AgNPs/rGO/PU conductive fibers still maintain excellent electrical and thermal properties and color change stability; even in the washing, strong acid, and strong alkali environment, they still have excellent durability. This human subjective adjustable electrical–thermal–color multi‐level induced modulation makes it possible to be applied to smart wearable fields such as visual camouflage, personal thermal management, and active information transfer. [ABSTRACT FROM AUTHOR]

The formation of stereocomplex crystalline domains in the bicomponent fiber melt spinning of enantiomeric polylactic acids (PLAs) is systematically explored and enhanced. Here we report a polycrystalline morphology where distinctly different crystalline regions are formed and aligned along the longitudinal direction of the fiber. This approach employs side-by-side and sheath-core bicomponent melt spinning configurations where the two components are the enantiomeric pairs of poly(L-lactic acid) (PLLA) and poly(D-lactic acid) (PDLA). We demonstrate the formation of the PLA stereocomplexes at the junction interphase through the melt spinning process which subsequently crystallize into a round fibers with stereocomplex and homogeneous crystal lamella morphologies. The fiber morphologies and crystallinities of the melt processed fiber are substantially different from the solution based bicomponent spinning system reported in the prior literature. Furthermore, the different molecular weight in the PLLA/PDLA pairing are found to be crucial to the structural development and properties of the PLA polycrystalline materials. The solid-state annealing does not change the crystal distribution of the crystalline domains and stereocomplex crystalline state, it just enhances the homo-crystallinity in the peripheral of the bicomponent fibers. [ABSTRACT FROM AUTHOR]

Abstract: Polypropylene (PP) loaded with copper‐exchanged montmorillonite (Cu‐MMT) nanocomposite filaments and films with excellent antimicrobial activity have been reported for the first time. A sheath–core morphology filament in which only the sheath contains Cu‐MMT was prepared for maximizing bioactivity. Sodium MMT clay was modified to acid‐activated MMT and further to Cu‐MMT via an ion exchange process. The exchange operation was confirmed using wide‐angle X‐ray diffraction and energy‐dispersive X‐ray spectroscopy (EDX) which suggested increased interlayer spacing and confirmed the loading of copper in Cu‐MMT. Further, Cu‐MMT was melt‐mixed in PP in the form of PP/Cu‐MMT nanocomposite filament, film and sheath–core morphology PP/Cu‐MMT nanocomposite filament. The surface morphology and elemental composition of the nanocomposites were studied using scanning electron microscopy coupled with EDX. Transmission electron micrographs were obtained to understand the dispersion characteristics of Cu‐MMT phase in PP. X‐ray diffraction analysis of nanocomposites suggested increased crystallinity at lower loading due to heterogeneous nucleating action of MMT. The PP nanocomposite filaments and films were tested for antimicrobial activity against Gram‐negative bacterium Escherichia coli, which is the main pathogenic bacterium found abundantly in water, and were found to exhibit excellent antimicrobial activity. © 2018 Society of Chemical Industry [ABSTRACT FROM AUTHOR]

The axial orientation of molecular chains always results in an increase in fiber strength and a decrease in toughness. Here, taking inspiration from the skin structure, artificial spider silk with a buckled sheath-core structure is developed, with mechanical strength and toughness reaching 1.61 GPa and 466 MJ m -3 , respectively, exceeding those of Caerostris darwini silk. The buckled structure is achieved by nano-pulley combing of polyrotaxane hydrogel fibers through cyclic stretch-release training, which exhibits axial alignment of the polymer chains in the fiber core and buckling in the fiber sheath. The artificial spider silk also exhibits excellent supercontraction behavior, achieving a work capacity of 1.89 kJ kg -1 , and an actuation stroke of 82%. This work provides a new strategy for designing high-performance and intelligent fiber materials., (© 2023 Wiley-VCH GmbH.)

A novel sheath-core poly(ethylene terephthalate) (PET)/poly(ethylene-co-vinyl alcohol) (EVOH) composite fiber was designed and manufactured to improve the hydrophilicity of the PET fibers. The thermal stability of EVOH was first examined to determine the possible processing temperature. Second, the rheological characteristics of EVOH were measured to obtain the appropriate spinning parameters. Then, PET/EVOH composite fibers with various sheath-core ratios were manufactured and the effect of sheath-core ratio on the stable spinning process was investigated. Scanning electron microscopy (SEM) shows that the PET/EVOH fibers possess a round sheath-core cross-section and a smooth surface, indicating successful spinning. Finally, the mechanical properties and moisture absorption of the PET/EVOH composite fibers were measured. For PET/EVOH composite fibers, the PET content contributes to the mechanical properties and the EVOH content contributes to the moisture absorption. For the PET/EVOH composite fibers with a sheath-core ratio of 50:50, the moisture regains at room conditions reach to 2.8% and the breaking strength is 2.53 cN/dtex. These good mechanical and moisture properties attract good application prospects. [ABSTRACT FROM AUTHOR]

A method for manufacturing sheath-core structured fibers was developed using wet spinning techniques. The core portion of a fiber was prepared using a carbon nanotube (CNT) solution while the sheath used a fiber-forming polymer such as polyvinyl alcohol (PVA). Preparation methods of CNT solutions were investigated and it was found that dispersivity and concentration played an important role in the formation and spinning of fiber's core. CNT solution prepared using a surfactant with high molecular weight such as sodium lignosulfonate (SLS) was most effective and the CNT concentration was as high as 30 g/ l. Fiber processing conditions were optimized and it was determined that stretching fibers in the coagulation bath was a significant step in the formation of a solid and well structured core. Drawn fibers were so strong and flexible that they could be woven into a fabric for potential use as a pressure sensor. These results are relevant for practical applications, such as the development of large-area fabric sensors. Furthermore, the described procedure to produce sheath-core CNT fibers is scalable as wet spinning methods have been widely used in the fiber industry. [ABSTRACT FROM AUTHOR]

• A sheath-core shaped ZrO 2 -SiC/SiO 2 fiber felt with continuously distributed rod-like SiC was successfully constructed. • The continuous distribution of SiC absorber was designed and realized. • The maximum EAB of ZrO 2 -SiC/SiO 2 fiber felt reaches 5.52 GHz and the bandwidth with RL less than −8 dB attains 13.50 GHz. • The excellent performance is attributed to continuous distribution of absorber and the matched impedance. • The EM absorption mechanism was analyzed according to the characterization results. Silicon carbide (SiC), has been considered as one of the most suitable options for high-temperature electromagnetic absorption materials (EAMs), and it's still a challenge to achieve the broad-band absorption performance for SiC-based EAMs. In this work, according to the impedance matching principle, a kind of ZrO 2 -SiC/SiO 2 fiber felt was prepared by combining chemical vapor infiltration (CVI) and oxidation treatment. SiC, as the electromagnetic (EM) absorber, was deposited continuously along the EM transparent ZrO 2 fibers, and the SiO 2 covered on SiC surface in the oxidation process, forming the unique sheath-core structure. It can form a large amount of interfaces to enhance the polarization loss, leading to excellent EM absorption performance with the reflection loss (RL) smaller than −8 dB at 4.50–18 GHz. The exploration results provide design inspiration to SiC-based EAMs with wide bandwidth strong absorption performance. [ABSTRACT FROM AUTHOR]