Study on synthesis and hygrothermal performance of calcium alginate-based moisture-adsorbing phase change composite

Building materials with capabilities of thermal and moisture regulations can effectively mitigate the fluctuations of indoor temperature and humidity, improve the living comfort, and reduce the energy consumption of buildings. However, existing hygroscopic phase change composites (HPCC) often suffer from low latent heat, insufficient moisture adsorption capacity, or the difficulty in achieving both high values simultaneously. The present study focuses on the preparation of the novel HPCC with both high saturated moisture adsorption capacity and large phase-change latent heat. The material was prepared from calcium alginate samples integration with binary phase change materials (PCMs) at various CaCl₂ concentrations. Initially, a series of calcium alginate samples with different CaCl₂ concentrations were prepared, and freeze-drying was utilized to enhance the porosity of samples. Subsequently, the calcium alginate was combined with the PCMs using an ultrasonic impregnation method. The thermal and hygroscopic properties of HPCC were experimentally investigated. Considering the balance of latent heat, thermal conductivity, and moisture adsorption capacity, composite material at 15 wt% CaCl2 (SACP-15) was identified as the optimal composite through the normalized weighting method. The results indicate that the latent heat and thermal conductivity of SACP-15 are measured to be 88.75 kJ/kg and 1.62 W/(m·K) respectively, and its maximum saturated moisture adsorption capacity is 0.470 g/g at 24 °C and 70 % relative humidity. Additionally, the moisture adsorption capacity of SACP-15 decreases when the temperature exceeds the phase change temperature. Furthermore, SACP-15 exhibits a desorption and regeneration efficiency of approximately 88 % at high temperature and low humidity, indicating broad application potential for SACP-15 in improving indoor temperature and humidity control as well as enhancing building energy efficiency.