Development of smart window using an hydroxypropyl cellulose-acrylamide hydrogel and evaluation of weathering resistance and heat shielding effect

Reducing the amount of electricity used by cooling systems is essential for lowering CO2 emissions; therefore suppressing increases in room temperature in an environmentally friendly manner requires the development of heat-shielding materials that autonomously control sunlight without the use of electricity. Hydroxypropyl cellulose (HPC) has attracted attention as a lower critical solution temperature (LCST) type of temperature-responsive polymer. HPC is a thermochromic material that changes its optical properties in response to changes in external temperature. In this study, acrylamide (AAm) and HPC with various molecular weights were used to prepare HPC-AAm hydrogels, and their optical, heat-shielding, and weathering-resistant properties were evaluated. UV–vis–NIR spectroscopy revealed that the solar transmittance (αTsol) of the HPC-AAm hydrogel decreased while its solar reflectance (αRsol) increased with increasing HPC concentration above LCST. The αTsol of low-molecular-weight HPC was found to be lower than that of high-molecular-weight HPC. In addition, the temperature inside a box constructed using an HPC-AAm hydrogel window was approximately 10 °C lower than that constructed using glass alone. Furthermore, the optical properties of the HPC-AAm hydrogel were found to hardly deteriorated even when continuously exposed to heat and UV radiation for 150 h. Therefore, the HPC-AAm hydrogel prepared in this study is expected to be useful as a heat-shielding material.