Compared to phase-change fibers with hydrophilic polymer shell, those with hydrophobic polymer are more stable in water and moist environments. However, their fabrication processes are involved in some toxic organic solvents. Here, the nanofibers with phase-change material (PCM, i.e., octadecane) as core and hydrophobic shell (i.e., polyvinyl butyral) are fabricated via coaxial electrospinning using environmental friendly ethanol as solvent. Effects of the polyvinyl butyral concentration in ethanol solution as well as the flow rates of core and shell fluids on the morphology of octadecane/polyvinyl butyral (PCM/PVB) nanofibers are systematically investigated. The thermo-regulating capability of PCM/PVB nanofibers is demonstrated by observing the surface and inner temperatures of model houses covered with fibers. The higher the PVB concentration and the shell flow rate are, the better the morphology of core/shell PCM/PVB nanofibers becomes, leading to higher encapsulation efficiency. At a constant shell flow rate, the encapsulation ratio of PCM/PVB nanofibers increases with the core flow rate. The encapsulation ratio of the PCM/PVB nanofibers, which fabricated with PVB concentration of 20 % (w/v) and at the core flow rate of 0.60 ml h−1 and the shell flow rate of 3.0 ml h−1, respectively, reaches to the maximum of 46.4 %. The corresponding melting enthalpy (ΔHm) and the crystallization enthalpy (ΔHc) of these PCM/PVB nanofibers are 105.9 and 106.5 J g−1, respectively. The PCM/PVB nanofibers exhibit good thermo-regulating capability under the simulated solar irradiation, regulating the temperature at around 28 °C. The resultant PCM/PVB nanofibers exhibit satisfactory stability and repeatability in the thermo-regulating capability during repeated heating/cooling cycles. The results provide valuable guidance for environmental friendly preparation of phase-change nanofibers with satisfactory and stable thermal characteristics.
Encapsulation Efficiency Octadecane Model House Shell Matrix High Encapsulation Efficiency
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The authors gratefully acknowledge support from the National Natural Science Foundation of China (21136006), the Program for New Century Excellent Talents in University (NCET-11-0352), and the State Key Laboratory of Polymer Materials Engineering (sklpme2014-1-01).
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