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

Abstract

Polymer composites based on linear low-density polyethylene (LLDPE) and halloysite nanotubes (HNTs) are promising for low fire-hazard cables (LFHC) due to their proven fire-retardant properties. This work aims to describe changes in dielectric, thermal and mechanical parameters for LLDPE/HNT composites that differ in the surface treatment of the incorporated HNT particles. Two sets of LLDPE/HNT composites containing 5 wt% of incorporated HNTs with and without surface treatment by stearic acid were prepared by extrusion. The LLDPE without filler was selected as the reference material. Measurement of selected dielectric properties, tensile tests and thermal properties by simultaneous thermal analysis and differential scanning calorimetry (DSC) were performed. Adding HNTs or their subsequent modification did not significantly affect the mechanical properties. It is also evident that the addition of unmodified HNTs shifted the main thermo-oxidative peak on the DSC signal to the higher temperatures; thus, HNTs positively reduced the maximum heat flow and enthalpy distribution of the whole system. Unfortunately, the effect of surface treatment of HNTs with stearic acid is the opposite. The dissipation factor increases over the range of measured temperatures and frequencies. However, the surface modification of HNTs slightly reduced the dissipation factor for some frequencies and temperatures. It is clear from the presented results that the chosen type of surface modification of HNTs is not as beneficial as the addition of unmodified HNTs.