Design of polyurethane fibers: Relation between the spinning technique and the resulting fiber topology

A review of advanced helical fibers: formation mechanism, preparation, properties, and applications

As a unique structural form, helical structures have a wide range of application prospects. In the field of biology, helical structures are essential for the function of biological macromolecules such as proteins, so the study of helical structures can help to deeply understand life phenomena and develop new biotechnology. In materials science, helical structures can give rise to special physical and chemical properties, such as in the case of spiral nanotubes, helical fibers, etc., which are expected to be used in energy, environment, medical and other fields. The helical structure also has unique charm and application value in the fields of aesthetics and architecture. In addition, helical fibers have attracted a lot of attention because of their tendrils' vascular geometry and indispensable structural properties. In this paper, the development of helical fibers is briefly reviewed from the aspects of mechanism, synthesis process and application. Due to their good chemical and physical properties, helical fibers have a good application prospect in many fields. Potential problems and future opportunities for helical fibers are also presented for future studies.

Water-Based Continuous Fabrication of Highly Elastic Electromagnetic Fibers

Elastic electromagnetic fibers are promising building blocks for next-generation flexible electronics. However, fabrication of elastic fibers is still difficult and usually requires organic solvents or high temperatures, restricting their widespread applications. Furthermore, the continuous production of electromagnetic fibers has not been realized previously. In this study, we propose an ionic chelation strategy to continuously produce electromagnetic fibers with a magnetic liquid metal (MLM) as the core and elastic polyurethane as the sheath in water at room temperature. Sodium alginate (SA) has been introduced to rapidly chelate with calcium ions (Ca2+) in a coagulation bath to support the continuous spinning of waterborne polyurethane (WPU) as a sheath. Meanwhile, WPU-encapsulated MLM microparticles efficiently suppress the fluid instability of MLM for continuous extrusion as the core. The resultant fiber exhibits excellent mechanical performances (tensile strength and toughness up to 32 MPa and 124 MJ/m3, respectively), high conductive stability in large deformations (high conductivity of 7.6 × 104 S/m at 580% strain), and magnetoactive properties. The applications of this electromagnetic fiber have been demonstrated by conductance-stable wires, sensors, actuation, and electromagnetic interference shielding. This work offers a water-based molecular principle for efficient and green fabrication of multifunctional fibers and will inspire a series of applications.

Processing and characterization of aligned electrospun gelatin/polycaprolactone nanofiber mats incorporating borate glass (13-93B3) microparticles

Aligned biodegradable fibers incorporating bioactive glass particles are being highly investigated for tissue engineering applications. In this study, 5, 7 and 10 wt% melt-derived 1393B3 borate glass (BG) microparticles (average size: 3.15 µm) were incorporated in 83 wt% polycaprolactone (PCL) and 17 wt% gelatin (GEL) (83PCL/17GEL) solutions to produce aligned electrospun composite nanofiber mats. Addition of 5 wt% BG particles significantly increased the alignment of the nanofibers. However, further incorporation of BG particles led to reduced degree of alignment, likely due to an increase of viscosity. Mechanical tests indicated a tensile modulus and tensile strength of approximately 51 MPa and 3.4 MPa, respectively, for 5 wt% addition of 1393B3 BG microparticles, values considered suitable for soft tissue engineering applications. However, with the increasing amount of 1393B3 BG, the nanofiber mats became brittle. Contact angle was reduced after the addition of 5 wt% of 1393B3 BG particles from∼45° to∼39°. Cell culture studies with normal human dermal fibroblast (NHDF) cells indicated that 5 wt% 1393B3 BG incorporated nanofiber mats were cytocompatible whereas higher doping with 1393B3 BGs reduced biocompatibility. Overall, 5 wt% 1393B3 BG doped PCL/GEL nanofiber mats were aligned with high biocompatibility exhibiting desirable mechanical properties for soft tissue engineering, which indicates their potential for applications requiring aligned nanofibers, such as peripheral neural regeneration.

Flame-Retarded Rigid Polyurethane Foam Composites with the Incorporation of Steel Slag/Dimelamine Pyrophosphate System: A New Strategy for Utilizing Metallurgical Solid Waste

Rigid polyurethane (RPUF) was widely used in external wall insulation materials due to its good thermal insulation performance. In this study, a series of RPUF and RPUF-R composites were prepared using steel slag (SS) and dimelamine pyrophosphate (DMPY) as flame retardants. The RPUF composites were characterized by thermogravimetric (TG), limiting oxygen index (LOI), cone calorimetry (CCT), and thermogravimetric infrared coupling (TG-FTIR). The results showed that the LOI of the RPUF-R composites with DMPY/SS loading all reached the combustible material level (22.0 vol%~27.0 vol%) and passed UL-94 V0. RPUF-3 with DMPY/SS system loading exhibited the lowest pHRR and THR values of 134.9 kW/m² and 16.16 MJ/m², which were 54.5% and 42.7% lower than those of unmodified RPUF, respectively. Additionally, PO· and PO₂· free radicals produced by pyrolysis of DMPY could capture high energy free radicals, such as H·, O·, and OH·, produced by degradation of RPUF matrix, effectively blocking the free radical chain reaction of composite materials. The metal oxides in SS reacted with the polymetaphosphoric acid produced by the pyrolysis of DMPY in combustion. It covered the surface of the carbon layer, significantly insulating heat and mass transport in the combustion area, endowing RPUF composites with excellent fire performance. This work not only provides a novel strategy for the fabrication of high-performance RPUF composites, but also elucidates a method of utilizing metallurgical solid waste.

Low-Density Silk Nanofibrous Aerogels: Fabrication and Applications in Air Filtration and Oil/Water Purification

A method was developed to fabricate light, water-insoluble silk fibroin nanofibrous aerogels (SNFAs) through solvent welding of lyophilized silk nanofibrous 3D networks at the junction points while converting silk structures from random-coils to β-sheets (water insoluble). Aromatic alcohols, especially phenethyl alcohol (PEA), supported robust solvent welding and the structural conversion of silk. PEA vapor treatment was a better approach than solvent infusion to retain volume, density, and mechanical strength of the SNFAs. The mechanical properties of highly orientated SNFAs were superior to randomly distributed fibers. The SNFAs had a low density (3.5 mg/cm³), high hydrophobicity (140.9°), and a porous surface morphology on the individual nanofibers, resulting in high efficiency and selectivity for absorbing particulate matter and oils. Compared with commonly used inorganic aerogels, the SNFAs developed in this study are biocompatible, easily functionalized, environmentally friendly, and low-cost and therefore have potential for air and water purification, biosensors, drug delivery, and tissue engineering.