High-Throughput Fabrication of Tunable Ethyl Cellulose Hollow Tubes via Triaxial Electrospinning for Superior Thermal Insulation

Buildings account for nearly one-third of global energy consumption, creating an urgent demand for sustainable, low-conductivity insulation derived from renewable feedstocks. Soft polymeric microtubes are attractive candidates because their hollow, low-density architecture suppresses both conductive and convective heat transfer, yet their fabrication from natural polymers has long been hindered by jet instability, low throughput, and difficulty in controlling wall structures. Here, we report a sheath-assisted triaxial electrospinning strategy that overcomes these limitations and enables the high-throughput, eco-friendly fabrication of ethyl cellulose (EC) microtubes with independently tunable diameter, wall thickness, and porosity. An inner oil core, a middle EC solution, and an outer ethanol sheath are co-extruded through concentric needles; the ethanol sheath stabilizes the multilayer jet at flow rates up to 30 mL h –1 per needle—an order of magnitude higher than typical electrospinning throughputs—while preserving structural integrity. By varying the core oil flow rate and viscosity, tube diameter and wall thickness are continuously tuned from 3.0 ± 1.2 to 19.2 ± 7.0 μm and from 1940 ± 300 to 120 ± 30 nm, respectively, with low-viscosity oils favoring the smallest, most uniform tubes. Increasing the EC solution flow rate from 5 to 30 mL h –1 transforms the wall from a dense to a highly porous architecture through accelerated phase separation and solvent evaporation. The resulting hollow, porous EC microtubes deliver low thermal conductivities of 0.130 ± 0.007 W m –1 K –1 (radial) and 0.060 ± 0.003 W m –1 K –1 (axial), reduce surface temperatures by more than 30 °C against a 70 °C heat source, and visibly protect heat-sensitive flowers from thermal damage. Together, these results establish a scalable, solvent-lean platform for converting a renewable polysaccharide into energy-efficient insulation materials for sustainable building applications.