Effect of temperature and crystallinity on the thermal conductivity of semi-crystalline polymers: A case study of polyethylene.

In this work, the effect of temperature and crystallinity on the thermal conductivity was investigated in a series of polyethylenes (PEs) with different crystallinities including high-density polyethylene (HDPE), medium-density polyethylene (MDPE), linear low-density polyethylene (LLDPE) and low-density polyethylene (LDPE). It was found that the applied ambient temperature has a significant effect on the thermal conductivity. At −20~100 °C, the thermal conductivity of PE showed a linearly decline with the increase of temperature. The thermal properties of a series of PE samples were also investigated by differential scanning calorimeter. The results showed that the higher the crystallinity, the higher the thermal conductivity of polyethylene. However, above the melting point, thermal conductivity of all PE samples tended to be the same, with a value of about 0.21 W/m·K. Based on the crystallinity and temperature, an empirical formula was proposed to predict the thermal conductivity of PEs with an error within 3%, which was also consistent with the results of other reported thermal conductivity of PEs. This work can guide the design of thermally conductive polymers in the future. [Display omitted] • Negative T-dependence of PE thermal conductivity is explained by phonon theory. • An empirical formula for calculating the thermal conductivity of PE is proposed. • The formula calculates thermal conductivity of PE within 3% error. [ABSTRACT FROM AUTHOR]