Polymer encapsulated paraffin wax to be used as phase change material for energy storage
Mochane, Mokgaotsa Jonas
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The study deals with the preparation and characterization of polystyrene (PS) capsules containing M3 paraffin wax as phase change material for thermal energy storage embedded in a polypropylene (PP) matrix. Blends of PP/PS:wax and PP/PS were prepared without and with SEBS as a modifier. The influence of PS and PS:wax microcapsules on the morphology and thermal, mechanical and conductivity properties of the PP was investigated. The SEM images of the microencapsulated PCM show that the capsules were grouped in irregular spherical agglomerates of size 16-24 μm. However, after melt-blending with PP the much smaller, perfectly spherical microcapsules were well dispersed in the PP matrix. The results also show fairly good interaction between the microcapsules and the matrix, even in the absence of SEBS modification. The FT-IR spectrum of the microcapsules is almost exactly the same as that of polystyrene, which indicates that the microcapsules were mostly intact and that the FTIR only detected the polystyrene shell. The amount of wax in the PS:wax microcapsules was determined as 20-30% from the DSC and TGA curves. An increase in PS:wax content resulted in a decrease in the melting peak temperatures of PP for both the modified and the unmodified blends due to the plasticizing effect of the microcapsules. The thermogravimetric analysis results show that the thermal stability of the blends decreased with an increase in PS:wax microcapsules content as a consequence of lower thermal stability of both the wax and PS. The DMA results show a drop in storage modulus with increasing PS:wax microcapsules content. The microcapsules acted as a plasticizer and thus enhanced the mobility of the polymer chains. Generally the thermal conductivity of the unmodified and modified blends decreased with increasing PS:wax microcapsule content when compared to PP. The polystyrene shell has a lower conductivity than the PP matrix, which explains the lower thermal conductivities of the blends with increasing PS content.