Thermally conductive h-BN/polymer composites for textiles thermal management Chengning Yao , Sihui Liu, Felice Torrisi 1 Molecular Sciences Research Hub, Department of Chemistry, Imperial College London, W12 0BZ, UK Heat stress affects personal thermal comfort and can be the main source of cardiovascular disease. Textile materials with high thermal conductivity are ideal for personal cooling by accelerating the heat dissipation between the human body and hot atmosphere. Current works on advanced textiles for thermal management adopted thermally reinforced composites to form nanofibers using carbon-based or boron-based nanofillers, achieving an in-plane and out-of-plane thermal conductivities (κ) of 13.1 W m −1 K −1 and 1.9 W m −1 K −1 , respectively 1 . However, the complex fabrication and the insufficient thermal conductivity of nanofiber composites impede their use in applications such as sportswear. Hexagonal boron nitride (h-BN) is a promising candidate as thermal conductive filler, with a bandgap of 5.6 eV and electrically insulating properties. Being a layered material h-BN can be exfoliated into single and few layer form showing highly thermal-conducting properties, with an in-plane thermal conductivity value of up to 370 W m −1 K −1 for bulk 2 and of up to 751 W m −1 K −1 for a single layer 3 . In this work we demonstrate a thermally conductive polymer composite embedded with exfoliated h-BN suitable for textile coating, achieving κ ~ 21.7 W m −1 K −1 , (Figure 1) about 5-fold higher than bulk h-BN embedded composites (κ ~ 4.5 W m −1 K −1 ). Exfoliated h-BN inks were produced via probe sonication of bulk h-BN powders mixed with carboxymethyl cellulose in deionized water and subsequently purified via centrifugation. Atomic Force Microscopy characterisation revealed that lateral size and thickness of the exfoliated h-BN flakes both follow log-normal distributions peaked at 352 nm and 6 nm, respectively. The h-BN/CMC aqueous composite is then drop-casted onto a commercial textile (non-woven fabric) and dried in the air to prepare a thermally conducting textile. Comparative temperature measurements by infrared camera (Figure 2) between the composite coated textile and the uncoated textile under the same heating conditions, at the thermal equilibrium show that the h-BN/ CMC coated textile reaches a higher temperature than the uncoated textile by 1 ℃ when the heater is 56 ℃ hot, indicating that the exfoliated h-BN-assisted composite improved the heat amount dissipated from the heater to the environment 4 . The cooling effect of the exfoliated h-BN-assisted composite textile is calculated to be 5.5% greater than the commercial textile under natural air convection, which displays a better thermal management capacity of the textile for applications in active thermal management clothing for sportswear, aerospace, or heavy-duty industries.
References 1. Ouyang T, Chen Y, Xie Y, et al. Thermal transport in hexagonal boron nitride nanoribbons. Nanotechnology. 2010;21(24):245701. 2. Sichel E, Miller R, Abrahams M, et al. Heat capacity and thermal conductivity of hexagonal pyrolytic boron nitride. Physical review B. 1976;13(10):4607. 3. Cai Q, Scullion D, Gan W, et al. High thermal conductivity of high-quality monolayer boron nitride and its thermal expansion. Science advances. 2019;5(6):eaav0129. 4. Guo Y, Dun C, Xu J, et al. Ultrathin, Washable, and Large ‐ Area Graphene Papers for Personal Thermal Management. Small. 2017;13(44):1702645.
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