Preparation, Structure And Property Of Ternary Fatty Acid Eutectics/Cellulose Acetate As Form-stable Phase Change Materials

Phase change energy storage as a kind of latent heat energy storage, it utilize phase transition of phase change material (PCM) itself for storage and release of energy. It can effectively alleviate the imbalance between supply and demand of energy, and play an important role in the energy-saving and thermal energy storage aspects. Fatty acids as a kind of commonly used solid-liquid PCMs are widely used because of its appropriate phase transition temperature, high phase change latent heat, little or no super-cooling, non-toxicity, non-corrosion, cost-effectiveness, good chemical and thermal stability, etc. However, phase transition temperatures of individual fatty acids are typically higher than what would be preferred upon climatic requirements. Fortunately, the phase transition temperatures can be tailored/adjusted into suitable range through preparing the eutectic mixtures of fatty acids.In this paper, fatty acids (capric acid (CA), lauric acid (LA), myristic acid (MA), palmitic acid (PA) and stearic acid (SA)) were firstly chosen as raw materials, the thermal performance parameters were characterized. Based on the lowest eutectic point theory and Schrader equation, the mass proportion of ternary fatty acid eutectic mixture was calculated, and thermal property of fabricated ternary fatty acid eutectic mixture was analyzed by using differential scanning calorimeter (DSC). Then, the fabricated CA-MA-SA (CMS) ternary eutectic mixture was chosen as model PCM. Three different methods were taken to preparing form-stable composite PCMs:(1) one-step electrospining CMS/cellulose acetate (CA) form-stable composite PCMs; (2) form-stable composite PCMs were fabricated by incorporating CMS ternary eutectic mixture with CA nanofibrous mat that was derived from electrospinning a binary mixture of CA/polyvinylpyrrolidone (PVP) and subsequent selective dissolution of PVP component from the obtained bicomponent nanofibrous mat; (3) form-stable composite PCMs were fabricated by absorbing CMS with phase inversion membrane including different concent of SiO2 nanoparticles that was prepared by using immersion precipitation phase inversion method. The structural morphology, thermal energy storage and temperature control performances of form-stable composite PCMs were studied. The major researchs included the following three sections:1. Preparation and property of electrospun CMS/CA form-stable composite PCMsTen kinds of ternary fatty acid eutectic mixtures were prepared by combing melting blend and ultrasonic dispersion method, and its thermal performance was characterized by DSC. The results showed that the prepared ternary fatty acid eutectic mixtures had appropriate phase transition temperatures and high phase change latent heat. Spin dope for electrospinning was prepared by dissolving ternary fatty acid eutectic (CMS) and cellulose acetate (CA) in acetone/DMAc mixture solvents. The form-stable composite PCMs with different CMS amounts was obtained by electrospinning technique. The morphological structure, thermal energy storage and temperature control performances of fabricated CMS/CA form-stable composite PCMs were characterized by Scanning Electron Microscopy (SEM), DSC and self-assembled thermal performance tester. The result indicated that CMS/CA form-stable composite PCMs possessed good morphological structure. The fiber diameter increased, rough fiber surface and partial conglutination of fiber occurred with increasing CMS amounts. The latent heat of form-stable composite PCMs increased with the increases of CMS content. The temperature control time of composite PCMs (mass ratio of CMS:CA=4:1) increased to 44.5 min from 28.5 min of neat CA nanofirous mat.2. Structural modification of CA nanofibrous mat, and preparation and property of form-stable composite PCMsThe CA/PVP bicomponent nanofibrous mats with different PVP amounts were firstly prepared by electrospinning. The form-stable composite PCMs were prepared by incorporating CMS with modified CA nanofibrous mat that was derived from selective dissolution of PVP component from the obtained CA/PVP bicomponent nanofibrous mat. The morphological structure and absorption property of CA mat before and after modification were studied by Fourier transform infrared (FTER) spectra, SEM and absorption capacity. The results showed that the PVP components PVP component was effectively removed from CA/PVP bicomponent nanofibrous mat. The groove structure nanoporous features on the resultant CA nanofiber surface was created. The maximum absorption capacity of modified CA mats was～83.3 wt.% when mass ratio of CA/PVP was 3:4.Structural morphology, as well as the properties of thermal energy storage, thermal cycle stability and temperature control, of form-stable composite PCMs were investigyed. The result indicated that CMS was uniformly distributed in the porous structure of nanofibrous mats. The form-stable composite PCMs demonstrated high latent heat, good thermal reliability after multiple thermal cycle and temperature regulation ability.3. Preparation, structure and property of CA-SiO2 phase inversion membranes and form-stable composite PCMs incorporating with CMSSiO2 nanoparticles were incorporated into CA membranes for preparing a new supporting material through phase inversion method. The form-stable composite PCMs were fabricated by absorbing CMS with phase inversion membrane. The influences of different nano SiO2 amounts on morphological structue and absorption performance of CA phase inversion membrane were investigated by SEM, Atomic force microscope (AFM), Brunauer-Emmett-Teller (BET) surface area analyzer and absorption capacity. The results showed that the addition of SiO2 nanoparticles resulted in the porpus structure on and/or within CA-SiO2 phase inversion membrane, and increased surface roughness and specific surface area of CA-SiO2 membrane. The maximum absorption capacity of CA-SiO2 phase inversion membrane with 10 wt.% nano SiO2 on CMS was 80.3 wt.%. The structural morphology, thermal energy storage and temperature control properties of the developed form-stable composite PCMs were characterized. The results demonstrated that CMS was absorbed in and/or supported by the network porous structure of CA-SiO2 phase inversion membranes. The melting/crystallization heat enthalpies of form-stable composite PCMs were 99.8kJ/kg and 96.7 kJ/kg, respectively. The temperature control time of form-stable composite PCMs increased to 26.3 min from 13.3 min of CA phase inversion membranes.