Sisal fiber exhibits a fibrous and porous structure with significant surface roughness, making it highly suitable for storing phase change materials (PCMs). Its intricate morphology further aids in mitigating the risk of PCM leakage. This research successfully employs vacuum adsorption to encapsulate paraffin within sisal fiber, yielding a potentially cost-effective, durable, and environmentally friendly phase change energy storage medium. A systematic investigation was carried out to evaluate the effects of sisal-to-paraffin mass ratio, fiber length, vacuum level, and negative pressure duration on the loading rate of paraffin. The experimental results demonstrate that a paraffin loading rate of 8 wt% can be achieved by subjecting a 3 mm sisal fiber to vacuum adsorption with 16 wt% paraffin for 1 h at −0.1 MPa. Through the utilization of nano-CT imaging enhancement technology, along with petrographic microscopy, this study elucidates the mechanism underlying paraffin storage within sisal fiber during vacuum adsorption. The observations reveal that a substantial portion of paraffin is primarily stored within the pores of the fiber, while a smaller quantity is firmly adsorbed onto its surface, thus yielding a durable phase change energy storage medium. The research findings contribute to both the theoretical foundations and the available practical guidance for the fabrication and implementation of paraffin/sisal fiber composite phase change energy storage mediums.

This study incorporated self-prepared paraffin/sisal composite phase change fibers (PCFs) into three-dimensional printed concrete (3DPC) to enhance its thermal properties. The effects of fiber type and dosage on the rheological and thermal properties of 3DPC were systematically investigated. The mechanisms underlying these effects were examined in terms of the internal pore distribution and fiber dispersion. The results indicate that differences in fiber dispersion, which are likely governed by fiber surface characteristics, are closely associated with the pore distribution within the 3DPC and, consequently, with its rheological and thermal properties. Compared with sisal-fiber-reinforced and fiber-free 3DPC, PCF-containing 3DPC exhibited lower thermal conductivity and a slower surface temperature rise under the tested conditions, and its heat-transfer behavior differed among the X, Y, and Z directions. These findings suggest that the incorporation of PCFs can enhance the thermal insulation of 3DPC under the tested conditions.