S. Shang, K-L Chiu
The Hong Kong Polytechnic University,
Hong Kong
Keywords: Saharan silver ant, bionic finishing technology, solar heat shielding ability, architextiles, ZnO microrod
Summary:
The global intense heat in summer becomes a grave public health threat and imperils industrial labor productivity and life, and thus can be very detrimental to the wellness and economy of the whole society. With climate change, sustainable green buildings can be a good solution, but the efficient and economical architextile that can provide outdoor solar shielding is lacking. Saharan silver ants (SSAnt), an insect living under extremely high-temperature weather, show their amazing ability to keep cool, benefiting from their microrod shaped hairs [1]. The strategy of mimicking SSAnt hairs on fabrics inspired us to develop functional textiles for efficient thermal management. As a result, we developed a novel bionic finishing technology by fabricating microrods that simulate the SSAnt micro-hair array and coating them on fabrics in an aligned array, which can significantly enhance the solar heat shielding ability of the finished architextiles. The micro-hair array of SSAnt is duplicated on the polyester (PET) fabric by coating the synthesized ZnO microrods on fabric horizontally aligned. The research involved three major steps: 1) synthesis of ZnO microrods as the artificial micro-hair via hydrothermal method; 2) production of the horizontally aligned ZnO microrods membrane on fabric with silicone binder via Meyer rod coating method; 3) characterization of the solar heat shielding ability and other fabric properties of the finished fabric via various test methods. The SEM results show that the synthesized ZnO microrod is about 0.8 - 2.6 μm and its length was about 10 - 40 μm, which is similar to the size of SSAnt micro-hairs. The UV-Vis-NIR spectrum of ZnO microrods shows that it has a higher near-infrared shielding ability than commercial ZnO pigments. The alignment of ZnO microrods on the coated fabric was observed with a scanning electron microscope. As shown in Figure 1, the ZnO microrods were found to be horizontally aligned in the coating along the coating direction. The solar heat gain coefficient of the coated fabric was measured to be 0.29, which was significantly lower than that of the original PET fabric (0.39). The solar heat shielding test was carried out under the sun and the result is shown in Figure 2. The ground temperature in the area covered by the PET fabric coated with the ZnO microrods was found to be up to 10°C lower than that covered by the original PET fabric, and up to 55°C lower than that covered by the transparent polyethylene film. The ground temperature fluctuations are due to changes in the intensity of sunlight. When the sunlight is strong, the coated fabric can immediately cool the ground temperature it covers. This finishing process has no negative impact on the mechanical properties of the PET fabric. Meanwhile, it improves the water repellency and ultraviolet resistance of the coated PET fabric. As a result, our bionic finishing technology is an innovative, economical and practical method to enhance the solar heat shielding ability of architextile.