The Shape Stabilization of Paraffin PCM to Reduce Graphite Nanofiber Settling During the Phase Change Process


Graphite nanofibers (GNFs) embedded in paraffin phase change material (PCM) are found to settle to the bottom of the sample when subjected to repeated thermal cycling. The majority of this settling is found to occur over the first heating/cooling cycle. A method is developed to prevent GNF settling by creating a shape stabilized phase change material using high density polyethylene (HDPE) as a stabilizing polymer. The shape stabilized samples reduced or eliminated GNF settling over repeated thermal cycles with as little as 10% HDPE by weight.

Shape-stabilization of PCM is done using a polymeric stabilizing agent to eliminate  the contraction  of the sample during solidification. The resulting  material,  referred  to as shape-stable PCM (SS-PCM) is a polymer/paraffin  blend. When a SS-PCM sample is heated  above the PCM melt point, the paraffin liquefies but remains  encapsulated within  a solid  polymeric  matrix much like water in a sponge. It is proposed that the addition of GNFs to a shape-stabilized PCM will fix the location of the graphite  nanofibers and prevent their migration  during  the  phase change. This study examines the development of SS-PCM using high density polyethylene  (HOPE) with embedded  GNF. Any addition of HDPE to the paraffin reduces the overall energy storage of the system, so samples with varying levels of HDPE are studied  to determine the minimum  necessary level of polymeric addition.