Structure And Properties Of Nanofibrous Mats Absorbed With Fatty Acids As Form-Stable Phase Change Materials

The reasonable utilization of energy and new energy development has always been the focus of attention. In order to relieve those contradictions among energy shortage, rapid growth of energy consumption and environmental pollution, it is a novel, environment-friendly and energy-saving technology by using phase change materials(PCMs) for storage and retrieval of thermal energy. It can be used to control the temperatures of system and environment, and has the functions including thermal energy storage and tempearure regulation. Fatty acids are one of important solid-liquid PCMs and have attracted extensive attentions due to the high energy storage capacity and small temperature variation during phase transition process, but they also possess some shortcomings such as large volume variation during phase change and low thermal conductivity. However, electrospun inorganic nanofibrous mats have shown a great potential as supporting materials for form-stable PCMs due to their high specific surface area, unique network structure, rich porosity and high thermal conductivity coefficient, which can effectively solve the leakage problem during phase change process and low thermal conductivity. Therefore, the investigation of preparation, structure and property of nanofibrous mats absorbed with fatty acid eutectics as form-stable PCMs has become an important research direction.In this paper, based on melt-mixing and ultrasonic dispersion methods, CA series fatty acid eutectics(CA-LA, CA-MA, CA-PA and CA-SA) and ternary fatty acids CA-LA-PA were prepared with capric acid(CA), lauric acid(LA), myristic acid(MA), palmitic acid(PA) and stearic acid(SA); and were used as the PCMs, respectively. The Si O2 and Ti O2-doped Si O2 nanofibrous mats were prepared based on the principle and technique which combining sol-gel, electrospinning and high temperature calcination, and both used as the support materials. The structural morphology and property of composite form-stable PCMs made from nanofibrous mats absorbing fatty acids were studied. The major research was divided into the following three sections:1. The Si O2 nanofibrous mats were prepared through calcination of PVP/Si O2 composite nanofibers at different temperatures of 500 oC, 600 oC and 700 oC. TGA was used to evaluate thermal degradation process of PVP/Si O2 composite nanofibers. The composition and changes of functional groups were characterized by FT-IR, confirming the formation of Si O2 nanofibrous mats. The absorption properties of Si O2 nanofibrous mats obtained at different calcination temperatures towards methylene blue and ternary fatty acids CA-LA-PA were compared and analyzed. The result suggested that the Si O2 nanofibrous mats with porous network structure calcinated at 600 oC possessed high absorption capacity.2. The structural morphology of Si O2 nanofibrous mats was further characterized by XRD and SEM. The result showed that Si O2 nanofibrous mats were structurally amorphous and had rough surfaces with partly locations of conglutination. Moreover, the morphological structure, absorption capacity, thermal storage and thermal energy storage/release properties of Si O2-based composite form-stable PCMs were studied by SEM, absorption tests, DSC and self-assembled thermal analyzer, respectively. The results indicated that binary fatty acid euteutics can be well dispersed within the porous network structure of Si O2 nanofibrous mats due to the effect of capillary and surface tension forces between fatty acids and Si O2 nanofibers. Meanwhile, the composite form-stable PCMs possessed appropriate phase transition temperature and higher heat enthalpies. Electrospun Si O2 nanofibrous mats improved thermal energy storage/release rates of composite form-stable PCMs.3. The Ti O2-doped Si O2(Ti O2/Si O2) nanofibrous mats was fabricated via electrospining the composite spin dope containing both Tetraethyl orthosilicate(TEOS) and titanium(IV) n-butoxide(TNBT) followed by high temperature calcinations. The composition, crystalline structures and morphology of Ti O2/Si O2 nanofibers calcinated at different temperatures of 600 oC, 900 oC and 1200 oC were characterized by FT-IR, XRD and SEM, respectively. The results indicated that the structural morphology of Ti O2/Si O2 nanofibers transformed from amorphous structure with smooth surface and cylindrical shape(calcinated at 600 oC) to cystalline structure with calcified shape(calcinated at 1200 oC) with increasing calcination temperature. In addition, SEM, absorption tests and DSC were employed to study structural morphology, absorption capacity and thermal property of Ti O2/Si O2-based composite form-stable PCMs, respectively. The results indicated that binary fatty acid eutectics were absorbed in and/or supported by the porous framework of Ti O2/Si O2 nanofibers. The structural and morphological evolvements of Ti O2/Si O2 nanofibers decreased absorption capacity of nanofibrous mats on binary fatty acid eutectics, leading to a decrease in thermal energy storage performance of composite form-stable PCMs.