This article describes a green approach to the transportation and encapsulation of lauric acid (LA), a natural food-grade phase change material (PCM), in polystyrene (PS) hollow fibers. By simply tuning the temperature, the obtained LAPS composite fibers achieved an unprecedented thermal energy storage capacity up to 81.6% of pristine LA. This capacity was higher than the reported values in the literature which were generally less than 50%. The thermally triggered nanocapillary transportation and encapsulation of LA did not alter the size and morphology of PS hollow fibers. Furthermore, the LA was contained inside PS hollow fibers, leaving the interfiber space and surface free of LA. Direct SEM observation, IR spectra, Raman spectra, XRD diffractograms, and simultaneous TGA–DSC thermograms of LAPS composite fibers proved that the amount of encapsulated LA declined with the elevation of temperature. The distribution of LA in PS hollow fibers was found to be homogeneous across the membrane by TGA and SEM. Further, the LAPS composite fibers demonstrated a robust cycling stability and reusability without notable deterioration of thermal storage capacity during 100 continuous heating–cooling cycles. Also, the composite fibers showed excellent structural stability without any fiber rupture or LA leakage during prolonged and repeated heating–cooling cycles.
This work demonstrates a green method for the encapsulation of a natural phase change material (PCM), lauric acid (LA), in polystyrene (PS) hollow fibers through a solvent-assisted diffusion process inside fiber nanochannels. The obtained LAPS composite fibers had a melting enthalpy of up to 147.8 J/g, which was 82.0% the heat storage capacity of pristine LA (180.2 J/g). This capacity was higher than the values (generally less than 60%) reported in the literature. The LA content in the composite fibers could be controlled by the solution concentration and the solvent. On the contrary, encapsulation time had little effect on the final LA loading beyond 1 h due to the rapid diffusion of the LA solution. The optimal LA loading (82.2%) was achieved in 0.4 g/mL LA ethanol solution for 1 h, which was more than 4 times the weight of PS fibers. Simultaneous TGA−DSC, ATR, Raman, and SEM measurements confirmed the homogeneous distribution of LA inside the fibers across the whole membranes. Further, the LAPS composite fibers showed a long-lasting stability during cycling without storage capacity deterioration, as well as an exceptional structural stability without LA leaking and fiber rupture during 100 heating−cooling cycles. The energy-dense and form-stable LAPS composite fibers have a great potential for various thermal energy storage applications like "temperature-smart" buildings and textiles.
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