Research On Electrical Insulation Properties Of Graphene/polyolefin Composites

Compared with cross-linked polyethylene,polyolefin blends can overcome the disadvantages of cross-linking by-product residues and difficulties in recycles on the premise of a superior insulation performance.Therefore,polyolefin blends have attracted extensive attentions as a potential cable insulating material.In this paper,pure low-density polyethylene(LDPE)was used as the basic resin,whereas 10 wt%high-density polyethylene(HDPE)and polypropylene(PP)were blended with the LDPE respectively.Graphene was added as a new voltage stabilizer in the polyolefin blends.Electrical insulation properties of the graphene/polyolefin composites were experimentally investigated and theoretically analyzed.Graphene/polyolefin composites were prepared by a solution method.Samples were made by a heat pressing method.Thermogravimetric analysis,differential scanning calorimetry and scanning electron microscopy were used to characterize the thermal physics and microscopic morphology of the materials.The electrical insulation properties of the graphene/polyolefin composites were studied by real-time electrical treeing observation and synchronous partial discharge measurements,DC conductivity measurements,dielectric spectrum measurements and pulsed electro-acoustic space charge measurements.The trap energy distribution was estimated by data recorded during the depolarization process in the space charge measurement.The experimental results showed that an addition of 0.002～0.02 wt%graphene could improve the thermal stability of polyolefin blends,but the enhancement of the thermal stability of the material did not related to the amount of the added graphene.Furthermore,graphene could improve the crystallization performance of the polyolefin blends.Results of the electrical treeing initiation at a constant applied voltage presented that 0.2 wt%graphene could significantly prolong the electrical tree initiation time.The addition of the graphene could facilitate the partial discharge process in electrical tree channels of the composites.The results of the electrical treeing initiation at a constant voltage ramping rate demonstrated that the addition of 0.002～0.02 wt%graphene had no significant effect on the electrical tree initiation voltage of the polyolefin blends.DC conductivity test results of the graphene/polyolefin composites at different temperatures showed that the DC conductivity increased with an increase of the temperature.The graphene could significantly reduce the DC conductivity of the LDPE/HDPE.The results of the dielectric spectroscopy measurements illustrated that graphene could increase the relative dielectric constant of the polyolefin blends.Moreover,dielectric losses of the graphene/polyolefin composites were closely related to the dispersion uniformity of the graphene.The space charge measurements results illustrated that the space charge density of the graphene/polyolefin composites increased with the increase of the time.The graphene could suppress the accumulation of the space charge in the materials and evenly distribute electric fields.The graphene could accelerate the space charge attenuation in the polyolefin blends during the depolarization process,whereas the higher the content of the graphene,the more obvious of the space charge attenuation.Theoretical calculation results of the trap energy distribution showed that the graphene/polyolefin composites had high trap energy levels and trap energy density.This would facilitate the space charge suppress in the graphene/polyolefin composites.