Personal cooling using textiles could help to save energy that is usually required for air-conditioning. It is also useful, e.g., for athletes or outdoor workers. Passive-cooling textiles, for example, draw moisture away from the body and then cool via evaporation. However, this only works well when the person is already sweating. Liquid cooling using, e.g., water is an alternative, but not a very practical one due to high weight and inconvenience.
Cooling by using thermally conductive fabrics that actively transfer heat away from the body is more promising. Boron nitride (BN) nanosheets, for example, can transfer heat well and are low-cost, stable materials. They can, e.g., be used in nanofibrous membranes. However, existing membranes of this type need to be pressed to achieve good heat transfer, which makes them non-breathable.
Yang Si, Bin Ding, Donghua University, Shanghai, China, and colleagues have developed heat-conductive, moisture-permeable, and waterproof nanofibrous membranes via a one-step electrospinning process. The membranes consist of a mixture of polyurethane/hydrophobic fluorinated polyurethane (FPU) and thermally conductive BN nanosheets. The team prepared solutions of polyurethane/fluorinated polyurethane with a weight ratio of 8:1 and BN nanosheets with a weight concentration of 18 % in dimethylacetamide. These solutions were turned into FPU/BN membranes through electrospinning under a relative humidity of 90 %.
The resulting FPU/BN18-RH90 membranes showed a uniform morphology in scanning electron microscopy (SEM) imaging, with the boron nanosheets and the polymer nanofibers forming a porous structure. Higher loadings of BN nanosheets or lower relative humidities led to uneven morphologies. The FPU/BN18-RH9 membranes are superhydrophobic, i.e., water-repellent, due to their rough surface structure and the inclusion of hydrophobic fluorinated polyurethane. However, they remain breathable due to their porous structure, with a high water-vapor transmission. The team tested the active cooling effect of the membranes and found high in-plane and cross-plane thermal conductivities. Due to the resulting effective heat dissipation, the membranes are cool to the touch. These properties show the promise of the material for cooling fabrics.
- Thermoconductive, Moisture-Permeable, and Superhydrophobic Nanofibrous Membranes with Interpenetrated Boron Nitride Network for Personal Cooling Fabrics,
Xi Yu, Yang Li, Xianfeng Wang, Yang Si, Jianyong Yu, Bin Ding,
ACS Appl. Mater. Interfaces 2020, 12, 32078–32089.