Radiative cooling performance analysis of cooling wood with three delignification processes for building applications

The delignification process is essential in the preparation of radiative cooling wood, and optimizing the delignification process is crucial for achieving a balance in the optical, mechanical, and thermal insulation characteristics of the delignify wood. Using the orthogonal experimental method, the study explored the influence of different delignification processes (such as chlorite, sulfite, and hydrogen peroxide methods), treatment duration, temperature, and other factors on wood weight loss rate, infrared spectroscopy, tensile and flexural strength, thermal conductivity, reflectance, and emissivity in order to obtain the best delignification process parameters for preparing radiative cooling wood with the optimal overall performance. The experimental results showed that delignification treatment followed by hot pressing improved the mechanical properties of the wood. As the delignification temperature and duration increased, the wood weight loss rate also increased, the mechanical properties declined, and the thermal insulating properties improved. The comprehensive comparison revealed that using the hydrogen peroxide method with treatment temperature at 80 °C and lasting 4 h can achieve the best overall performance for radiative cooling wood. Compared with Balsa wood, the tensile strength increased by 4.2 times and the flexural strength by 2.3 times, while the thermal conductivity reached 0.08 W/mK. In outdoor experiments, this radiative cooling wood can attain a good cooling effect throughout the day. During the noon hours, its surface temperature was lower than that of cement and the ambient temperature by 11.4℃ and 4.4℃ respectively, and the net radiative cooling power was up to 46 W/m2. The results show broad prospects for its application in building insulation and energy saving.