Natural Microtubule-Encapsulated Phase-Change Material with Simultaneously High Latent Heat Capacity and Enhanced Thermal Conductivity

It is of critical importance to exploit high-performance phase-change materials (PCM) for thermal energy storage. Present form-stable PCM suffer from the defects in low PCM loading, poor form stability, low thermal conductivity, and complicated approaches. We prepared a novel microtubule-encapsulated phase-change material (MTPCM) by encapsulating lauric acid (LA) into kapok fiber (KF) microtubules that had been precoated with silver nanoparticles. The measured melting and freezing temperatures were 43.9 and 41.3 °C for the LA/KF MTPCM and 44.1 and 42.1 °C for the LA/KF@Ag MTPCM, respectively. After being heated, the MTPCM can retain its original solid state without leaking, even under a pressure of 500 times the gravity of MTPCM itself, which shows that the encapsulated phase-change material can undergo a solid–liquid transition microscopically while retaining its macroscopic solid state. The latent heats of fusion were found to be 153.5 J/g for the LA/KF MTPCM and 146.8 J/g for the LA/KF@Ag MTPCM, which is up to 86.5% and 82.7% that of pristine LA, respectively. This thermal energy storage capacity is much higher than reported values in recent literature, which tend to be ≤60%. In contrast with the penalty of a 3.8% decrease in latent heat capacity, the remarkable 92.3% increase in thermal conductivity caused by the introduction of silver nanoparticles is more pronounced. The thermoregulatory capacity analysis results show that the thermal transfer efficiency of LA/KF@Ag MTPCM has been enhanced significantly by 15.8% and 23.5% in terms of thermal energy storage and release compared to that of the LA/KF MTPCM. Moreover, the LA/KF@Ag MTPCM exhibits a robust thermal, chemical, and morphological reliability after 2000 thermal cycles, which makes it favorable for repetitive thermal energy storage/retrieval applications. The high latent heat, suitable phase-change temperature, outstanding form stability, robust thermal reliability, enhanced thermal transfer efficiency, and the inherited advantages of KF and nanosilver provide potential for the novel application of MTPCM in solar thermal energy storage, waste heat recovery, intelligent thermoregulated textiles, and infrared stealth of important military targets.