Effect of Halloysite Nanotubes on the Properties of LLDPE/HNT Composites for the Cable Industry

Polymer composites based on linear low-density polyethylene (LLDPE) with halloysite nanotubes (HNT) offer great promise for developing low-fire hazard cables due to their proven fire-retardant properties. However, incorporating HNT into a non-polar polymer matrix inevitably changes the composites’ polarity, homogeneity, and thermal properties. Consequently, this can lead to a degradation of the dielectric and mechanical properties. This work describes such changes for LLDPE/HNT composites that differ in the amount of HNT present in the LLDPE matrix. A series of LLDPE/HNT composites with filling levels of 1, 3, and 7 wt% of HNT and pure LLDPE as the reference material were prepared by extrusion. Dielectric properties such as volume resistivity, dielectric strength, complex relative permittivity, and dissipation factor were determined. Tensile tests and cone calorimetry were also carried out to enhance the characterization of the tested materials regarding dielectric properties and other parameters necessary for using the tested materials as cable insulation. Adding HNT to LLDPE up to 7 wt% has no substantial effect on the mechanical parameters. However, due to its molecular polarity, HNT significantly deteriorates the dielectric parameters at 7 wt% of HNT. The results obtained using the cone calorimeter show that adding HNT reduces the value of the maximum heat release rate curve and the burning time. Burning of composites with HNT does not produce more smoke than burning of reference LLDPE.