Intelligent thermoregulating textiles are gaining significant attention for their potential to minimize energy consumption and provide enhanced thermal comfort. Lightweight and ultrathin fabrics are particularly crucial for applications in aerospace and fire-fighting. Aerogel fibers, with their inherent three-dimensional porous structure and flexibility, offer a promising solution. Their low thermal conductivity, high porosity, and potential for integration with smart materials make them suitable for personal thermal management. While various aerogel fibers have been developed, polyimide (PI) aerogel fibers stand out due to their good temperature resistance and mechanical properties. However, the traditional two-step process involving the sol-gel transition of poly(amic acid) (PAA) followed by imidization is time-consuming and not suitable for continuous spinning. Previous methods, such as sol-gel confined transition and freeze-spinning, have limitations in scalability and continuous production. Recent approaches using organo-soluble PI and freeze-drying still require post-treatment, which is costly and time-consuming. The current research aims to overcome these challenges by developing a fast, scalable, and cost-effective method for producing high-performance PI aerogel fibers suitable for ultrathin, thermoregulating clothing.

The literature extensively covers the development of various aerogel fibers, including silica, graphene, MXene, Kevlar, and polyimide. Polyimide aerogels show promise due to their temperature resistance and mechanical properties. However, traditional production methods for polyimide aerogel fibers, involving a two-step process starting with poly(amic acid) (PAA), are slow and unsuitable for large-scale production. Existing techniques, like sol-gel confined transition and freeze-spinning, have limitations in continuous fiber production and control over pore size. Recent improvements using organo-soluble polyimide and freeze-drying still necessitate energy-intensive post-treatments. This research addresses the need for a fast, scalable, and ambient pressure drying method to produce high-performance polyimide aerogel fibers.

This study introduces a UV-enhanced dynamic gelation strategy for the rapid and scalable production of crosslinked polyimide (CPI) aerogel fibers. Organo-soluble polyimide (PI) was synthesized through a one-pot copolymerization of 4,4'-hexafluoroisopropylidene di(phthalic anhydride) (6FDA) with 4,4'-diaminodiphenyl ether (ODA) and 3,5-diaminobenzoic acid (DABA), followed by imidization. Photosensitive polyimide (PPI) was then synthesized by grafting β-hydroxyethyl methacrylate (HEMA) onto the PI chain via Steglich esterification. The PPI, along with a photoinitiator (Irgacure2100), was dissolved in NMP to create a spinning solution. The wet-spinning process involved extruding the solution through a steel needle (21G) into a NMP bath while irradiating with UV light (2 W cm⁻²) to induce rapid crosslinking and gelation (within 10 seconds). Solvent exchange (ethanol) and ambient pressure drying (25°C, 2h) followed to obtain CPI aerogel fibers. The characterization of the CPI aerogel fibers involved techniques such as FTIR, NMR, SEM, tensile testing, and thermal conductivity measurements. A proof-of-concept intelligent thermally adaptive textile was also fabricated by integrating the CPI aerogel fibers with paraffin wax as a phase change material (PCM). The integration of PCM into CPI aerogel fibers was confirmed using FTIR, XRD, TGA, and DSC.

The UV-enhanced dynamic gelation strategy enabled the fast (10 s) and continuous production of CPI aerogel fibers with lengths of hundreds of meters within 7 hours. The fibers exhibited a typical aerogel morphology with a 3D interconnected nanofiber network and a pore size distribution of 50-250 nm. CPI-100 (with a 100% grafting ratio of HEMA) demonstrated superior properties, including low shrinkage (17.9%), low density (0.55 g cm⁻³), and high specific modulus (390.9 kN m kg⁻¹). The CPI-100 aerogel fabric (0.7 mm thick) showed comparable thermal insulation performance to down (5.4 mm thick), exhibiting a temperature difference of 108 °C on a 200 °C hot stage. The thermal conductivity of the CPI-100 aerogel fabric was 24.2 mW m⁻¹ K⁻¹ at -50 °C and 70.2 mW m⁻¹ K⁻¹ at 150 °C, significantly lower than cotton and commercial PI fabrics at the same temperature. The incorporation of paraffin wax into the CPI aerogel fibers created a shape memory CPI/PCM composite fabric that enabled the development of an intelligent thermally adaptive (ITA) textile. This ITA textile demonstrated reversible shape change and temperature regulation, with shape fixity (Rf) and shape recovery (Rr) values of 77.4% and 89.8%, respectively. The ITA textile showed a decrease in surface temperature from 55.2 °C to 42.1 °C when exposed to 100 °C.

The results demonstrate the successful development of a fast, scalable, and cost-effective method for producing high-performance CPI aerogel fibers. The UV-enhanced dynamic gelation strategy effectively addresses the challenges associated with slow gelation kinetics and weak backbone strength encountered in previous methods. The superior thermal insulation properties of the ultrathin CPI aerogel fabric make it a promising material for lightweight and thermally regulating clothing. The integration of CPI aerogel fibers with PCMs further enhances their functionality, leading to the creation of intelligent thermally adaptive textiles with potential applications in various fields such as protective clothing for firefighters and military personnel. This study significantly advances the field of functional textiles, offering a viable pathway for mass production of high-performance, multifunctional aerogel-based materials.

This research successfully developed a scalable and efficient method for producing high-performance CPI aerogel fibers using a UV-enhanced dynamic gelation strategy. The resulting ultrathin fabrics exhibit excellent thermal insulation, comparable to down but with significantly reduced thickness. Furthermore, the integration of phase-change materials showcases the potential for creating intelligent, thermally adaptive textiles. Future work could explore the incorporation of other functional materials to further enhance the properties of these fibers and expand their applications in diverse areas beyond thermal management.

While the study demonstrates significant progress, limitations include the specific choice of polyimide and the potential scale-up challenges for industrial production. The long-term durability and washing resistance of the CPI aerogel fabrics require further investigation. Additionally, a more comprehensive assessment of the ITA textile's performance under diverse environmental conditions is needed before widespread application.