Thermal conductivity of highly crystallized polyethylene

We report thermal conductivity (κ) of low-density, high-density and ultra-high density polyethylene (PE) with different crystallinity and microstructures. PE was crystallized under high-pressure and high-temperature conditions which produce extended chain crystals. By applying a two-phase model, we estimate κ of 100% crystallized PE as a function of pressure and temperature. The increased crystallinity and lamellar thickness (fold length) reduce the thermal resistance, which is reflected not only in the absolute value of κ but also in more pronounced pressure and temperature dependencies approaching those of polycrystalline low-molecular weight materials. The results suggest that it is crucial to increase the lamellar thickness to significantly improve κ of PE with randomly oriented lamellae.