Preparation And Properties Of Polypropylene Grafted 4-acetoxystyrene And Styrene

HVDC power transmission has the advantages of long distance,low loss,and large-capacity power transmission,and has received extensive attention at home and abroad.At present,the most widely used insulation material for high-voltage DC cables is cross-linked polyethylene?XLPE?,but because of the many disadvantages of XLPE materials,such as internal space charge accumulation,complex processing processes and non-recyclable reuse.Therefore,it is of great significance to develop new DC cable insulation materials.Polypropylene?PP?has excellent performance without cross-linking,can be recycled and reused,effectively increases the working temperature of the DC cable,and simplifies the processing process,so it has a good potential application prospect in the field of high-voltage DC cables.However,the insulation material based on PP will generate a large amount of space charge accumulation under the action of DC electric field,which will distort the electric field,cause uneven distribution of the electric field,and cause local area discharge and insulation breakdown problems,reducing the life of the cable.Therefore,it is particularly important to modify the PP to suppress the accumulation of space charges.Based on this,this paper uses PP grafted styrene?St?and 4-acetoxystyrene?AOS?to suppress the accumulation of internal space charge in PP,the preparation and properties of polypropylene-grafted styrene?PP-g-St?and polypropylene-grafted 4-acetoxystyrene?PP-g-AOS?were studied respectively.First,St monomer was grafted on the PP molecular chain by melt grafting,and PP-g-St was successfully prepared.The preparation of PP-g-St was studied by infrared spectrum characterization and external standard curve method.The results show that the optimal process parameters of PP-g-St are the blending temperature of 200?,the rotor speed of 70 r/min,and the blending time of 7min.The blending ratio of the materials is PP:St:DCP=50:8:1.4?mass ratio?.The space charge,breakdown field strength,volume resistivity,dielectric constant,and mechanical properties were tested to investigate the effect of grafting rate on the space charge suppression characteristics,dielectric and mechanical properties of PP-g-St.The results show that the introduction of the St group improves the internal space charge of PP.At a grafting rate of 4.4%,the maximum internal charge density is 0.896 C/m³,which is 79.6%lower than that of pure PP;The breakdown field strength and reliability have also been improved.The characteristic breakdown value is as high as 392.9 k V·mm^-1,which is 1.6times as that of pure PP;At the same time,the volume resistivity has also been improved.Its volume resistivity is as high as 3.6×10¹⁵?·m,which is 2.0 times higher than that of pure PP;The effect of grafting rate on the tensile strength of PP-g-St increased first and then decreased,while the elongation at break showed a decreasing trend.The influence of the grafting rate of St on the thermal properties of PP-g-St was further studied by TG and DSC testing methods.The results show that PP-g-St has better thermal stability than PP.When the grafting rate is 5.7%,Its starts to decompose at 401.17?,which is 97.5?higher than pure PP.With the increase of the grafting rate,the crystallization temperature?Tc?of moves to the high temperature direction,and the melting temperature?Tm?moves to the low temperature direction,and the crystallinity?Xc?shows a downward trend.When the grafting rate was 6.9%,the Tc of PP-g-St is 8.8?higher than that of PP,Tm is 14.8?lower than PP,and Xc is 38.5%,which is 14.7%lower than PP.Then,in this paper,AOS monomer was grafted onto PP to improve the space charge accumulation in PP and to further improve its dielectric properties.AOS monomer was grafted on the PP molecular chain by melt grafting,and it was successfully prepared.The preparation was studied by infrared spectrum characterization and external standard curve method.The results show that the optimal process parameters are the blending temperature of 190?,the rotor speed of 80 r/min,and the blending time of 8 min.The blending ratio of the materials is PP:AOS:DCP=50:1.4:0.08?mass ratio?;The space charge,breakdown field strength,volume resistivity,dielectric constant,and mechanical properties were tested to investigate the effect of grafting rate on the space charge suppression characteristics,dielectric and mechanical properties of PP-g-AOS.The results show that the introduction of AOS groups has effectively improved the internal space charge of PP.When the grafting rate is 1.14%,the maximum internal charge density is 0.076 C/m³,which is 98.3%lower than that of pure PP;The breakdown field strength and reliability have also been effectively improved.the characteristic breakdown value is as high as 487.1 k V·mm^-1,which is twice the characteristic breakdown value of pure PP;At the same time,the volume resistivity has also been improved.When the grafting rate is 1.14%,the volume resistivity of pure PP;The effect of grafting rate on the tensile strength showed a decreasing trend,and the elongation at break showed an increasing trend.The effects of the graft ratio of AOS on the thermal properties of PP-g-AOS were further studied by TG and DSC testing methods.The results show that PP-g-AOS has better thermal stability than PP.When the grafting rate is 1.14%,its starts to decompose at 381.45?,which is 77.78?higher than pure PP,and the thermal stability is the best.With the increase of the grafting rate,the crystallization temperature?Tc?moves to the high temperature direction,and the melting temperature?Tm?moves to the low temperature direction,and the crystallinity?Xc?shows a downward trend.When the grafting rate was 1.21%,the Tc of PP-g-AOS is 17.8?higher than that of PP,Tm is 6.6?lower than PP,and Xc is 41.9%,which is 11.3%lower than PP.Further research shows that PP-g-AOS has a more effective suppression of internal space charges than PP-g-St,and the internal charge density is reduced by91.5%;The highest characteristic breakdown value and maximum form factor of PP-g-AOS are 1.24 and 1.14 times that of PP-g-St,respectively;The maximum volume resistivity of PP-g-AOS is 1.42 times that of PP-g-St;The maximum decomposition temperature of PP-g-St is 19.72?higher than that of PP-g-AOS;At the maximum grafting rate,Tc of PP-g-AOS is 9?higher than PP-g-St,Tm is 4.2?higher than PP-g-St,and Xc is 3.4%larger than PP-g-St.