Cellulose foams as scalable templates for phase change materials

Cellulose foams produced by wet-templating fibers and surfactants offer an unlimited creative space for the design of green functional materials with a wide range of energy-related applications. Aiming to reduce plastic pollution, cellulose foams promise to replace plastic foams after tailoring physical functionalities into their structures. Here, this work demonstrates that cellulose foams made of methylcellulose and cellulose fibers can exhibit a solid–liquid phase change functionality by adding a phase change material (PCM) during the foam-forming process. The resulting foam composites, termed cellulose phase change foams (PCFs), exhibit a tenth of cellulose's density (134.7 kg m⁻³) yet a high Young's modulus (0.42MPa). They are also dimensionally stable over a wide range of temperatures while absorbing up to 108 kJ kg⁻¹ as latent heat when the PCM confined to the foam experiences a solid-to-liquid transition at ∼60 °C, and releasing 108 kJ kg⁻¹ as latent heat when changing from liquid to solid at ∼40 °C. Such phase change transition opens up broad applications for the PCFs as thermal insulators. For example, by further tuning the transition temperature, the PCFs can exploit their phase change and reduce the heat flow rate through their radial direction at specified temperatures. This article showcases the versatility of the foam-forming process of cellulose to accommodate physical functionalities in materials with complex architectures. Furthermore, thanks to the advances in cellulose foam-forming, such foams are recyclable, industrially scalable, and can be exploited as heat storage materials.