Study on the water‐tree ageing characteristics of polyethylene/organic montmorillonite and crosslinked polyethylene/organic montmorillonite nanocomposites

Abstract

The dispersion state of nanoparticles affects the properties of composites, and the crosslinking process of polymers affects the dispersion state of nanoparticles. In order to investigate the effects of crosslinking behaviour on the water-tree ageing characteristics of nanocomposite dielectrics at the molecular level, polyethylene/organic-montmorillonite (PE/organic montmorillonite (OMMT)) and crosslinked polyethylene/organic-montmorillonite (XLPE/OMMT) nanocomposites were prepared by the melt blending method, after which the accelerated water-tree ageing experiments were conducted using a needle electrode. Fourier transform infrared spectroscopy, differential scanning calorimetry, successive self-nucleation annealing and scanning electron microscope (SEM) tests were conducted to characterise the properties of the samples before and after watertree ageing. The results indicate that the initiation probability and the length of water trees in XLPE/OMMT are less than those in PE/OMMT. The carbonyl index in the watertree area of the two nanocomposites increases, indicating that the water-tree ageing is the result of electrochemical degradation. The crystallisability of the water-tree area degrades, decreasing the crystallinity and the lamellar thickness. The growth of water trees destroys molecular chains and crystal structures, which results in local cracks. There are many holes for the water tree growth in the PE/OMMT specimen. However, the crosslinked meshwork not only restricts the movement of macromolecular chains but also increases the stability of the lamellar barrier effect of OMMT. The combination of the two effects significantly improves the water-tree resistance of the XLPE/OMMT nanocomposite.