Manufacturing of Continuous Core–Shell Hydrated Salt Fibers for Room Temperature Thermal Energy Storage

The encapsulation ofsalt hydrate phase change materials (PCMs) in uniform microscale bodies has yetbeen reported in research due in part to the delicate relationship betweenthermal performance and water-to-salt ratios which are easily altered duringmanufacturing. Herein, core–shell composite fibers comprised of a salt hydratePCM core and a poly(acrylonitrile) (PAN) shell are wet spun in a continuousprocess using a syringe pump and coaxial die. The PCM phase comprises calciumchloride hexahydrate (CaCl₂·6H₂O) with strontium chloride hexahydrate(SrCl₂·6H₂O) (3 wt%) and fumed silica(SiO₂) (2 wt%) as additive, acomposition that is prepared from homogenous melt at 40 °C. 15 wt% PAN indimethylsulfoxide solvent is used to prepare the shell-forming polymer gel. PCM and polymer gel injectionrates of 10–40 mL h⁻¹ are used tospin coaxial fibers through a coagulation bath, yielding continuousmicrotubules with diameters in the range of 850–1500 μm. Cyclic testing showsthat after 1000 cycles, melting enthalpies incurred only a 3.5% decline from 131.46 to 126.9 J g⁻¹. Success hereovercomes several coincidental drawbacks of PCM fiber performance andmanufacturing and delivers the first example of scalable roll-to-roll PCM fiber produced by wet spinning forbuilding material applications.