| In order to study the feasibility of polypropylene(PP)as a new energy-saving and environment-friendly cable insulation materials,and taking the improvement of dielectric properties brought by nano particles into consideration,nano-MgOs with surface-treated and untreated are added into the base stock PP by different concentration of 0.5wt%、1wt% and 3wt%,respectively.Different nano-MgO/PP composites are prepared.The investigations of transmission electron microscopy(TEM)and differential scanning differential scanning calorimetry(DSC)are carried out to observe the micro and morphological structure of composites;space charge measurement,ac and dc breakdown strengths tests and dielectric spectra tests are investigated to study the dielectric property of PP and nano MgO/PP composites.Dynamic thermo-mechanical analysis(DMA)tests and thermo gravimetric analysis(TGA)tests are carried out to study the dynamic mechanical properties and heat resistance of the new insulation materials.The comprehensive application of PP and its nanocomposites in cable insulation materials are investigated.Results of TEM and DSC tests reveal that,nano-MgO is well dispersed in polymer,and the composites with surface-treated have less agglomeration in particles.Both of crystallization peak temperature and crystallinity of polymer in nano MgO/PP composites are higher than pure PP.It is found in space charge experiment that the amout of charge by cathode electrode is decreased,and hetero-charge by anode electrode almost disappears with the addition of nano MgO during the depolarization process.The average charge density in nanocomposites declines at high electrical field.The nano-composite with surface-untreated performs better in the resistant effect of space charge density and peak charge at high electrical field compared to the nanocomposites with surface-treated,and that with surface-treated has better withstanding effect of electric field distortion.In all the samples,the composite with the concentration of 0.5wt% has the best improvement effect in space charge.Study on breakdown experiments reveal that,ac breakdown strengths and dc breakdown strengths of PP and its nanocomposites are higher than 120 k V/mm and 200 k V/mm,respectively.Breakdown strengths of dc are higher than bds of ac.among the range of the research,the addition of nano-MgO would increase the breakdown strengths of MgO/PP composites;The process of surface treatment would also increase the breakdown strength of corresponding component.The highest breakdown strengths of composites under ac voltage appear in the concentration of 3wt% while the highest breakdown strengths under dc voltage appear in the concentration of 1wt%.Results of dielectric frequency spectra tests at normal temperature show that the addition of nano-filler would decrease the relative permittivity,and the samples with surface-treated have a larger decline;The dielectric loss angel of composites increase compared with PP,and in the meantime,the electrical conductivity has a little rise.Dielectric temperature spectra curves under the power frequency reveal that,with the increase of temperature,the relative permittivity of PP and nano MgO/PP has an increasing trend at first,and then becomes stable or has a slight decline.The dielectric loss angel would rise with the increasing of temperature.The addition of high concentrationnano particles with surface-treated could increase the dielectric loss angel largely.Study on DMA reveals that the glass transition temperature of PP and nano MgO/PP is about 2℃;The addition of nano-filler would improve viscous transition temperature and mechanical loss factor.It is found in TGA test that the low concentration of nano particles could hardly improve the heat resistance of PP.When the concentration of nano-MgO increases to 3wt%,the initial thermal decomposition temperature of the components with surface-untreated and surface-treated have improved 76℃ and 148℃ compared with PP,respectively. |
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