The Preparation Of Form-Stable Phase Change Materials And Experimental Investigation On The Shape Stability

Phase change materials (PCMs) are substances with a high heat of fusion which, through melting and solidifying at certain temperatures, are capable of storing or releasing large amounts of energy. From the phase transition temperature and latent heat point of view, low temperature solid-liquid PCMs have a better prospect for industrialization. To avoid the leakage of liquid PCMs during applications, some kinds of packing are required. In recent years, there has been growing interest in developing the polymer-based PCMs as a new type of latent heat thermal energy storage materials to resolve the liquid leakage problem.In this work, several kinds of FSPCMs which consist of paraffin astlatent heat storage material and SEBS、HDPE、EPDM as supporting material were prepared and their shape stability and shape stabilizing mechanism were studied from a physical viewpoint. In addition, the thermal stabilities and thermal properties of the composites were also investigated. The main research efforts devoted to the shape stability and shape stabilizing mechanism of polymer-based FSPCMs are summarized as follows.(1) The preparation of SEBS/paraffin form-stable phase changet materials experimental investigation on the shape stability and thermal propertiesSEBS/paraffin composites were prepared as form-stable PCMs in which SEBS serves as supporting material for paraffin. The maximum weight percentage of paraffin could up to90wt%and no leakage of paraffin was observed at a test temperature of100℃, which is higher than the melting point of paraffin. Rheological analysis revealed that the shape stability of these composites came from the formation of SEBS-paraffin reversible physical gel which could prevent the free flowage of the melted paraffin, while the failing to keep their apparent stable shape at a further higher temperature may be ascribed to the liquid like gel-sol transition. In addition, differential scanning calorimetry (DSC) analysis illustrated that the introduction of SEBS did not significantly change the melting and crystallization temperatures of paraffin but the enthalpy of SEBS/paraffin FSPCMs decreased with the increase of SEBS contents. Thermogravimetric analysis (TGA) results suggested that the thermal stability of SEBS/paraffin composites was much better than that of neat paraffin.(2) The selection of supporting material for form-stable phase change materials based on paraffinSeveral kinds of FSPCMs which consist of paraffin as latent heat storage material and SEBS、HDPE、EPDM as supporting material were prepared and the shape stability and shape stabilizing mechanism were studied. When the paraffin weight content of polymer-paraffin FSPCMs were20%, the mass loss rate of SEBS/paraffin was least, the HDPE/paraffin followed by and HDPE/paraffin was maximum. DSC analysis illustrated that the introduction of polymer did not significantly change the melting and crystallization temperatures of paraffin. Scanning electronic microscopy (SEM) images revealed that all of the prepared polymer-paraffin FSPCMs plates have homogeneous constitution. Atomic force microscopy (AFM) microscopic pictures of pure SEBS and SEBS-20sample showed that the shape stability of SEBS/paraffin came from the three-dimensional network of SEBS, and the polarized optical microscopy (POM) photograph of pure paraffin and HDPE-20showed that shape stability of HDPE/paraffin came from the crystallization of HDPE above the melting point of paraffin.(3)The influence on crystallization between high-density polyethylene (HDPE) and paraffinHDPE/paraffin composites with different HDPE weight content were prepared and the influence on crystallization between HDPE and paraffin was studied by DSC.The results showed that the addition of paraffin simultaneously improved the crystallization rate and the melting temperature of HDPE and crystallization temperature decreased with the increased of paraffin content. On the other hand, the isothermal crystallization data of paraffin showed that the addition of HDPE has little effect on the crystallization of paraffin.