Effects of titanium oxide and graphene as nano-fillers on the thermal conductivity of biobased phase change materials as latent thermal heat storage

Biobased phase change materials (BPCMs) have attracted much attention as they offer proper melting temperature, high heat capacity, non-corrosive, low cost, and are abundantly available. However, the BPCMs have a low thermal conductivity which limits their application. To minimise the loss of the overall heat storage enthalpy capacity, nanofillers are added to improve the thermal properties of the BPCMs. This study investigates the thermal conductivity of the BPCMs with nanofillers. The thermal conductivity was calculated using the Maxwell Garnet equation and then compared with the experimental results. The BPCMs such as palm wax, beeswax, and coconut oil were prepared with different weight concentrations of graphene and titanium oxide (0.5 wt%, 1.0 wt%, 1.5 wt%,2.0 wt%). The melting temperature for the BPCMs was between 32 and 60 °C. The thermal conductivity of BPCMs for both fillers increase between 4 and 46 % compared to pure BPCMs. Overall, the titanium oxide shows better improvement in BPCMs’ thermal conductivity compared to graphene. Beeswax gives the highest thermal conductivity of 0.338 W/m.K, while coconut oil is the lowest with 0.232 W/m.K at 2 wt% titanium oxide concentration. The results from the experimental work are in agreement with the calculated value from the Maxwell Garnet model. Overall, the addition of nanofillers in BPCMs offers promising thermal performance making them more attractive to be used as latent thermal heat storage.