(417b) Thermally Conductive Polyethylene-hBN Nanocomposites for Heat Exchanger Applications

Thermal desalination of seawater remains the primary source of water for the Arabian Gulf countries. The heart of the thermal desalination processes is the heat exchangers (evaporators), which suffer from significant corrosion and scale formation due to the high salinity of the Arabian Gulf water. Therefore, costly metals or metal alloys such as titanium and Cu-Ni are used as the heat transfer surfaces. Polymers are less susceptible to corrosion and scale formation caused by high salinity water compared to metals. Therefore, replacing metals with polymers as heat transfer surfaces in thermal desalination evaporators could result not only in mitigating the corrosion problems but also in substantial cost savings due to the low price, fabrication cost and low density of polymers. However, the intrinsically low thermal conductivity of polymers must be significantly increased to permit their use as heat transfer surfaces. In this presentation, we discuss our approach to enhance the thermal conductivity of polyethylene via nanocompositing with hexagonal boron nitride (hBN) nanosheets. hBN was exfoliated using dry ball milling and the exfoliated hBN nanosheets were characterized using SEM, TEM, and AFM. Nanocomposites with 5-60 wt.% hBN were prepared using melt extrusion and dry ball milling. The impacts of the processing method and hBN exfoliation and loading on the thermal conductivity, thermophysical properties, and mechanical properties are investigated. The thermal conductivity of polyethylene is increased by over 1000% and the mechanical properties (Young modulus and ultimate strength) are simultaneously improved. Moreover, our results indicate that ball milling is viable and benign technique not only for the exfoliation of hBN but also for processing of the polymer nanocomposites. Analysis of the impact of the enhanced thermal conductivity on the cost of evaporators of multi-effect distillation desalination (MED) is presented.