Effect of additives on melt viscoelasticity of insulating materials used in high voltage crosslinked polyethylene cables

Low-density polyethylene (LDPE) is widely used in insulating materials for high voltage (HV) crosslinked polyethylene (XLPE) cables and its viscoelastic properties are important factors for the extrusion molding of insulating materials. However, the effect of additives such as crosslinking agent and antioxidant on melt viscoelasticity of LDPE-based insulating materials is not comprehensively studied. In this work, the varieties and content of additives are analyzed by infrared spectrum test. Moreover, the molecular chain structure of different LDPE is measured by gel permeation chromatography. Besides, the influence of additives on melt viscoelasticity of LDPE-based insulating materials is discussed. The results show that additives has plasticizing effect on uncross-linked LDPE-based insulating materials, which reduces the complex viscosity and zero shear viscosity of insulating materials melts. Meanwhile, the storage modulus (G') and loss modulus (G'') also have the same trend. The main reason is that small molecular additives enter into the molecular chain segments of LDPE, which can weaken the interaction force between LDPE molecular chains and change the molecular conformation under the shear action. This study reveals that the reasonable additive formula is beneficial to improving the extrusion molding of LDPE-based insulating materials used in HV XLPE cables.