Large-Scale Nanofiber Manufacturing| Sustainable aramid filaments generated from waste aramid viaproton-donor-regulated wet spinning strategy

Wei Qufu's Team from Jiangnan University: Wet Spinning Regulation Strategy Achieves High-Performance Recycling of Waste Aramid

With the widespread application of high-performance fibers in aerospace, protective clothing, rail transportation and other fields, aramid materials have become key industry materials due to their excellent thermal stability, flame retardancy and mechanical properties. However, the high crystallinity and strong intermolecular hydrogen bonding of aramid materials also bring a serious problem - difficulty in degradation and recycling. Currently, large amounts of waste aramid materials are incinerated or landfilled, causing both resource waste and environmental pressure. How to recycle waste aramid fibers to regenerate aramid nanofibers remains an urgent challenge.

Recently, Professor Wei Qufu, Professor Lü Jing and Associate Professor Wang Qingqing from Jiangnan University published their latest research "Sustainable aramid filaments generated from waste aramid via proton-donor-regulated wet spinning strategy" in Chemical Engineering Journal. The study efficiently prepared novel sustainable regenerated aramid nanofibers through a proton-donor-regulated wet spinning strategy. Rigid aramid nanofibers (ANF) construct a dense "scaffold network", while flexible polyvinyl alcohol (PVA) serves as a "binding phase" to form a biomimetic "brick-mortar" structure, achieving synergistic enhancement of high strength and high toughness in the fibers.The ANF/PVA composite fibers prepared based on this strategy not only exhibit excellent sewing and weaving properties, but can also be processed into various forms such as colored fibers, conductive fibers, hydrogel fibers and aerogel fibers through dyeing, silver plating, freeze-drying and other methods, widely applicable in cutting-edge fields including thermal protection, artificial ligaments, smart textiles and conductive fabrics.

Figure 1: Preparation of regenerated ANF fibers and various post-processing applications

Waste aramid fibers were chemically disassembled into aramid nanofibers (ANF), then polyvinyl alcohol (PVA) capable of forming hydrogen bond networks was introduced to construct a "brick-mortar" biomimetic structure, and finally continuous stretchable regenerated ANF/PVA composite fibers were obtained through wet spinning, achieving fiber-level recycling and structural reconstruction.

Figure 2: Formation process of ANF/PVA hydrogel fibers and their supporting role in continuous wet spinning

During wet spinning, the ANF/PVA mixed solution undergoes sol-gel transition after injection into the coagulation bath: DMSO solvent gradually diffuses out while water molecules penetrate, inducing protonation reconstruction of ANF chain segments and hydrogen bond networks, while synergizing with PVA to form a densely crosslinked hydrogel structure. This hydrogel fiber possesses excellent initial strength and flexibility, effectively withstanding drawing tension and preventing filament breakage, significantly improving the stability and efficiency of continuous spinning.Moreover, the relatively slow gelation rate provides sufficient time for ANF chain segments to achieve orderly arrangement and orientation rearrangement, further enhancing fiber structural density and mechanical properties, which is key to achieving high-performance regenerated aramid fibers.

Figure 3: Mechanical properties and regulation mechanism of regenerated ANF/PVA fibers

The dried ANF/PVA fibers exhibit excellent mechanical properties, with tensile strength up to 546.5 MPa, Young's modulus of 23.3 GPa, and toughness reaching 21.1 MJ/m³. This performance improvement benefits from the multiple hydrogen bond crosslinked networks formed between rigid ANF nanofibers and flexible PVA chain segments in the "brick-mortar" biomimetic structure, which not only enhances fiber structural integrity but also effectively alleviates microcrack propagation.Meanwhile, by regulating proton donor concentration in the coagulation bath, precise control of sol-gel transition rate was achieved, enabling sufficient orientation and alignment of ANF chain segments during spinning. Small-angle X-ray scattering results further confirmed changes in fiber orientation under different pH conditions, with higher orientation leading to better dry fiber strength, revealing the microscopic mechanism of fiber reinforcement.

Figure 4: Performance analysis and multifunctional applications of regenerated aramid nanofibers

On the basis of excellent mechanical properties, the regenerated ANF/PVA fibers also demonstrate broad potential for functional expansion. Through dyeing coagulation bath treatment, colored fibers can be obtained for aesthetic and identification needs; freeze-drying treatment can prepare aerogel fibers with excellent thermal insulation performance, showing significant advantages in thermal protective fabrics; hydrogel fibers, soft and elastic, show promise for biomedical applications such as artificial ligaments and tissue scaffolds.Additionally, through chemical reduction of silver ammonia solution, conductive networks can be constructed on fiber surfaces to obtain conductive ANF fibers, which can stably drive LED lighting, possess good electrothermal conversion capability and resistance to repeated bending, suitable for wearable smart textiles, electrothermal temperature-regulating fabrics and other fields.

Figure 5: Recycling process of regenerated ANF fibers

The prepared ANF/PVA composite fibers exhibit good recyclability and reprocessing capability. After multiple dissolution-spinning cycles, their mechanical properties only slightly decrease, with tensile strength still maintained at 428 MPa, demonstrating good structural stability and significant potential for sustainable utilization. Thermogravimetric analysis and infrared spectroscopy comparisons further confirm the preservation of material structure and thermal stability.

Paper link: https://www.sciencedirect.com/science/article/pii/S1385894725048405