Abstract:

Objective For protective materials, excellent protective performance and wearing comfort are both important for their application. Although the nanofiber membrane has excellent protective performance, the small pore size and narrow pore size distribution prone to produce a stuffy feeling when worn for a long time, and would affect air permeability and moisture permeability. The wearing comfort of nanofiber protective materials still needs to be improved. Many ways are proposed to improve the wearing comfort of protective materials. Among them, the infrared radiation transmittance of the material has an important impact on its temperature regulation function, thus affecting the wearing comfort.

Method In order to improve the wearing comfort of nanofiber protective materials, the radiation cooling polyolefin elastomer (POE) nanofiber membrane was prepared by using the melt blended phase separation and subsequent deposition process. The morphology, infrared radiation transmittance, transparency, radiation cooling effect and water vapor transmittance of POE nanofiber membrane were studied and compared with the poly(vinyl alcohol-co-ethylene) (PVA-co-PE) nanofiber membrane and cotton fabric.

Results The morphology of POE nanofiber membrane is uniform, with an average diameter of 570 nm, which is larger than that of PVA-co-PE nanofiber membrane. The POE nanofiber membrane is completely transparent to light in the mid-infrared band (7-14 μm), with a transmittance of almost 100%. This is mainly because the molecular structure of POE has no groups that can absorb mid-infrared light, and its pore size is much smaller than the mid-infrared wavelength, so it does not affect the mid-infrared radiation transmittance. The infrared radiation transmittance is directly related to the thickness of nanofiber membrane, and it decreases significantly with the increases of POE nanofiber membrane thickness. In contrast, the structure of PVA-co-PE contains groups that can absorb mid-infrared light, so that its transmittance in the corresponding band is reduced, while cotton fabric cannot transmit infrared light at all. As the infrared radiation accounts for more than 50% of the total heat loss of the human body, the POE nanofiber membrane has better infrared radiation cooling effect. At room temperature, the temperature of the heating module rises by only 0.5 ℃ after POE nanofiber membrane covering. Under vacuum, the temperature of the heating module remains unchanged after the POE nanofiber membrane is covered. Notably, the infrared transmittance of a material is not related to its transparency. In the visible light band, the transmittance of POE nanofiber membrane and cotton cloth is close to zero, and the transmittance of PVA-co-PE nanofiber membrane is about 30%. This is because the pore size of the POE nanofiber membrane is comparable to the wavelength of visible light, and light scattering makes the POE nanofiber membrane unable to transmit visible light. In addition, although POE is a hydrophobic polyolefin elastomer, it still has good moisture permeability by virtue of its three-dimensional porous structure. The water vapor transmittance of POE nanofiber membrane is 2 845 g/(m²·d), which is just slightly lower than the water vapor transmittance of 3 530 g/(m²·d) of cotton cloth. Therefore, the POE nanofibers can be used as coating materials to be coated on different substrate surfaces to improve the substrate protection performance without affecting its thermal and humid comfort.

Conclusion the prepared radiation cooling POE nanofiber membrane with excellent wearing comfort has a better thermal radiation cooling effect than PVA-co-PE nanofiber membrane and cotton fabric. The temperature change little after POE nanofiber membrane covering, hence maintaining excellent thermal comfort. In addition, the three-dimensional pore structure of POE nanofiber membrane gives it excellent moisture permeability, and its water vapor transmittance is only slightly lower than that of cotton fabric. The results demonstrate that the POE nanofiber membrane has excellent thermal and humid comfort, and it can be used as protective layer for medical use to improve protection without affecting comfort.

Key words: poly(vinyl alconol-co-ethylene), polyolefin elastomer, polyolefin nanofiber, protective material, infrared radiation cooling, moisture-permeable