The effect of peroxide cross-linking on the thermal conductivity and crystallinity of low-density polyethylene

In this work, the thermal conductivity of a series of low-density polyethylene (LDPE) with different degrees of cross-linking was measured by the transient hot-wire method at different temperatures. It was found that the thermal conductivity of LDPE samples with different degrees of cross-linking decreased smoothly with increasing temperature at temperatures ranging from -20 to 80 degrees C. The higher the degree of cross-linking, the smaller the negative temperature dependence of the cross-linked LDPE samples. The decrease of negative temperature dependence of LDPE was explained by the thermal vibration of molecular chains. Meanwhile, the crystallinity and melting point of a series of LDPE samples with different degrees of cross-linking were determined by differential scanning calorimetry (DSC), and the crystallization process of LDPE samples with different degrees of cross-linking was investigated using the Jeziorny method with a modification of the Avrami equation. The results show that the thermal conductivity of cross-linked LDPE is directly proportional to the crystallinity and inversely proportional to the gel content. This work provides a basis for the future design of semi-crystalline polymers with no temperature dependence of thermal conductivity.