Wood Template-Supported Phase Change Materials Composites for Durable and Form-Stable Thermal Energy Storage

To reduce building energy consumption, phase change materials (PCMs) with high transition enthalpies and transition temperatures close to the thermal comfort of humans are desirable for thermal energy storage (TES) in building envelope applications. But traditional high-enthalpy solid-to-liquid PCMs suffer from leakage issues during thermal cycling and thus require encapsulation to be form-stable, which reduces the effective transition enthalpy. Polyethylene glycol (PEG) is a compatible PCM with wood templates (WT). Still, we show that with just PEG infiltrated into the wood, 30 wt% of PEG is stored within wood before detectable phase changes occur, indicating inefficiency of PCM usage. We developed a method to (1) improve the leakage stability of balsa and pine composites (BWT+PCMs and PWT+PCMs) under isothermal conditioning for one month at 50 °C and (2) reduce the inefficiency of the unused PCM within the composites to 10 wt% by incorporating a cross-linkable polymer (<10 wt%). These composites exhibit transition properties as high as 114.2 J/g at 25.4 °C, exhibit no shift in properties after 1000 thermal cycles and retain flexural strengths comparable to the raw balsa and pine wood. Our shape-stabilized WT+PCM composites enrich the functionality of wood materials as both ideal TES material candidates and building construction materials.