Carboxymethyl chitosan/sodium alginate/polyethylene glycol phase-change foams with humidity-adaptive low-temperature buffering performance.

The performance deterioration of phase-change composites in humid environments severely restricts their practical applications. Herein, A novel polysaccharide-based foam with low-temperature buffering properties was fabricated through electrostatic self-assembly of carboxymethyl chitosan and sodium alginate combined with mechanical foaming. This composite process enables the encapsulation of polyethylene glycol while simultaneously stabilizing the foam structure generated by mechanical agitation. Remarkably, without any hydrophobic modification, the phase-change foam exhibits long-term structural stability at up to 74% relative humidity (RH). With increasing humidity, the material undergoes a transition from rigid to flexible behavior, characterized by a decrease in Young's modulus from 48.90 MPa (36% RH) to 1.56 MPa (74% RH). Concurrently, the crystallization and melting enthalpies diminish from 34.8 J/g and 37.7 J/g, respectively, to 0 J/g at 74% RH. Despite this, the foam's overall heat capacity increases due to moisture absorption, enabling it to maintain stable low-temperature buffering performance. This work, for the first time, unveils the humidity-driven evolution of phase transition behavior in hydrophilic phase change composites and proposes a mechanism for humidity-adaptive temperature regulation. These findings offer a new insight for designing moisture-resistant thermal management materials.