A renewable thermochromic phase change material encapsulated within a wood-based cellulose/sodium methylsilicate framework.

Thermochromic phase change material (TC) is a temperature-responsive heat storage material. However, few TCs are renewable. In the present study, a renewable TC (RTC) composed of alizarin, myristyl myristate, and 1-hexadecanol was synthesized, demonstrating a color shift between orange and orange-red during phase transitions. To maintain the shape stability, the RTC was encapsulated within a wood-based cellulose/sodium methylsilicate framework, termed thermochromic wood composite-smart material (TWC-SM). This framework altered the chemical structure of alizarin, resulting in a color shift between greyish-purple (L: 26 ± 1, a: 4 ± 1, b: -6 ± 1) and deep-purple (L: 14 ± 2, a: 1 ± 1, b: -3 ± 1) for TWC-SM during phase changes, indicating a distinct thermochromic mechanism compared to RTC. Specifically, TWC-SM appears greyish-purple below 52 °C, where the benzene ring of alizarin features two fixed O groups and an additional -OH group. At temperatures above 70 °C, it turns deep-purple as the -OH group loses a hydrogen ion. TWC-SM exerts a pronounced thermochromic effect, conferring temperature-responsive functionality. Moreover, the solid-liquid phase-changing enthalpy of RTC is 186.78 J/g, and the wood-based cellulose/sodium methylsilicate framework ensures the shape stability of RTC within TWC-SM. Consequently, the average temperature of TWC-SM is at least 5.56 °C higher than that of untreated wood over 60 min following identical thermal treatment. This finding shows the potential of the framework for practical applications in temperature-responsive heat storage materials. This study reveals the structure-activity relationship between RTC and the framework within TWC-SM, which is key to the development of practical applications of RTCs.