Near-infrared reflective materials for textiles

Abstract

In this study, the research work mainly focused on the preparation of near-infrared (NIR) reflective titanium dioxide (TiO₂) particles and their application on cotton fabric to achieve a cooling effect under solar radiation. TiO₂ was selected due to its high refractive index and well-proven NIR reflective properties. All the TiO₂ particles prepared in this work were applied on coloured cotton substrate using a simple pad-dry-cure method.A room-temperature sol-gel route to prepare highly stable TiO₂ colloids was devised. Their temperature reducing effect on cotton fabric, however, was very small due to the deviation of its particle size (42.8 nm) from the optimum range to reflect thermal NIR radiation. Therefore, the synthesis of silica-titania core-shell was carried out. Both the titania and silica were prepared using the sol-gel method. By varying the precursor concentration during the preparation of the silica core, core-shell composites with sizes ranging from 565-1038 nm were synthesised. A maximum temperature reduction of 4.3°C was achieved by applying the core-shell on coloured fabric, being tested under illumination approximating sunlight using a solar simulator.Commercial titania was modified by means of calcination treatments. Phase transition from anatase to rutile and growth in particle size were induced, and both processes resulted in the increase of NIR reflectance of the calcined TiO₂. Irregular-shaped TiO₂ particles with sizes of 293-618 nm were obtained. By applying the NIR reflective coating consisting of calcined TiO₂ on cotton fabric, a lower surface temperature was recorded with a maximum difference of 4.3°C. It was found that a chitosan-TiO₂-chitosan multilayer coating could provide a good wash fastness, with only a solar reflectance decrease of 3.70-6.33% after 50 simulated launderings.