Crystalline morphology in high‐density polyethylene/paraffin blend for thermal energy storage

The durability of high‐density polyethylene (HDPE)/ paraffin blends as a thermal energy storage material was studied by investigation of the seepage behavior of paraffin. The HDPE in the blends serves to prevent paraffin seepage during repeated heating‐cooling cycles; i.e., the HDPE acts as a sealant material. Two representative HDPEs were used for the blends; one was a low molecular weight HDPE (1‐HDPE) and the other was a high molecular weight HDPE (h‐HDPE). Investigation by optical microscopy, scanning electron microscopy and light scattering revealed that the surface area of an injection molded sample in h‐HDPE/paraffin blend had compact spherulites of about 7 μm in radius. On the other hand, the morphology of the coarse spherulite of about 15 μm in radius is observed in the 1‐HDPE/paraffin blend. This crystalline morphological characteristic resulting from the molecular weight difference of the sealant material (HDPE) is responsible for the excellent sealant property of the h‐HDPE/paraffin blend.