Research On DC Dielectric And Thermal Aging Properties Of Polyethylene Grafted With Antioxidant MC

The space charge problem of insulating materials under high-voltage DC electric fields has become the main factor restricting the development of high-voltage DC cables,which will cause the internal electric field of the insulating materials to distort,produce partial discharges and even breakdown,and seriously affect the service life of the cables.In addition,PE inclines thermal oxidation aging in the process of production,storage and use,which can bring out the deterioration of physicochemical,thermal,mechanical and electrical properties,and then reduce the cable operation stability and service life.In order to suppress space charge accumulation,delay the oxidation process of polymers and minimize the antioxidants migration,polyethylene(PE)grafted with reactive antioxidant containing polar groups was prepared,and the DC dielectric and thermal aging properties are studied.First,low-density polyethylene(LDPE)grafted with reactive hindered amine antioxidant MC was prepared by melt radical grafting using Dicumyl peroxide(DCP)as an initiator.Fourier transform infrared(FTIR)spectroscopy is used to investigate the grafting reaction,which shows that the antioxidant MC is successfully introduced onto LDPE.Space charge distribution,DC conductivity,DC breakdown strength and thermal stimulated current are measured and the electronic structure is calculated from first-principles.The results show that LDPE grafted with antioxidant MC can effectively suppress space charge accumulation,reduce DC electrical conductivity and enhance DC breakdown strength.The polar functional groups of antioxidant MC anchored on LDPE macromolecular chain form immobile deep traps at the grafted MC sites,which can capture space charges and scatter charge carriers to reduce the amount,mobility and energy of charge carriers.The results of the oxidative induction time(OIT)show that the LDPE grafted with antioxidant MC has strong thermal oxidation stability.Seen from the oxidative induction time of the specimens before and after acetone extraction,the level of retention of the grafted antioxidant MC are significantly higher than those of conventional antioxidant 300 and antioxidant 4020,which indicates that LDPE grafted with antioxidant MC has excellent long-term thermal oxidation stability.Among them,the LDPE grafted with0.5 phr MC has the best overall performance.Next,the crosslinked polyethylene(XLPE)grafted with 0.5 phr MC was prepared.FTIR spectroscopy shows that the antioxidant MC is successfully introduced onto XLPE.Gel extraction experiments and thermal extension experiments show that MC graft modification has no significant effect on the degree of crosslinking of XLPE materials.The DC dielectric properties test results show that compared with pure XLPE,the XLPE grafted with 0.5 phr MC can still suppress space charge accumulation,reduce DC electrical conductivity and enhance DC breakdown strength at high temperatures.The results of the oxidative induction time show that the XLPE grafted with antioxidant MC has strong thermal oxidation stability and excellent long-term thermal oxidation stability.The change rates of tensile strength and elongation at break of the XLPE grafted with MC are less than20% after thermal aging at 135℃ for 168 h,the mechanical properties meet the standards of JB/T 10437-2004 cross-linkable polyethylene insulation material for wire and cable after air thermal aging.