Effect Of Shearing Action On The Structure And Electrical Insulation Properties Of Polypropylene

Polypropylene is widely used in the manufacture of insulated cables due to its excellent electrical insulation properties and mechanical properties,as a cable in actual processing and production will inevitably be affected by the shear action,such as extrusion,injection molding,etc.,these processing technology will cause irreversible changes to the structure of the material,and then affect its various properties.There are few studies on the regulation of material structure and properties by shear stress field,by adjusting the shear field indexes during processing,not only can the final performance of the material be improved,but also provide a guarantee for high quality and high efficiency production.From this perspective,this article deeply explores the influence of different degrees of shear on the structural properties,mechanical properties,and electrical properties of polypropylene,as well as the correlation between the three,and explores the effects of adding antioxidants on these changes.In this paper,two types of polypropylene,T30 S and K8003,were used to produce the materials required for the experiments by applying shear to the materials in a dense manner with a torque rheometer and varying the shear strength by changing the shear time and shear temperature.The effect of shearing on the rheological behavior of the material was investigated,and the changes in the structure,mechanical and electrical properties of the material were tested and analyzed,as well as the correlation between them.In terms of rheological properties,when the shear strength increases to a certain extent,the equilibrium torque drops sharply and the viscosity decreases.The stronger the shearing degree,the more the carbonyl content produced by polypropylene,the shorter the oxidation induction period,and the worse the oxidation resistance.The effect of improving the oxidative degradation of the material is the best when the amount of antioxidant is 2wt%.At the time of shearing for 5 min,the crystallinity of orientation increased slightly,as the shear continued to be applied,the crystallinity began to decrease.After increasing the shear temperature,the crystallinity of T30 S will increase,but the crystallinity of K8003 will decrease due to the difference between the two polypropylene structures.With the addition of antioxidant materials,balance torque,resistance to oxidative degradation and crystallinity have been improved.In terms of mechanics,the thermal elongation of the samples after various degrees of shearing is about 5%,indicating that the samples still have excellent mechanical properties after shearing.Short-term shearing can improve the toughness of the material.When the shearing degree continues to increase,the toughness and rigidity of the material are gradually reduced.After shearing,the toughness of the K8003 sample is still better than the T30 S sample under the same conditions.After adding antioxidants,the toughness and rigidity of the material have been improved.From the dynamic relaxation map,the storage modulus of the material after shearing decreases with the increase of the shearing time.The peak change of the loss peak is positively correlated with the crystallinity,and the peak position is related to the flexibility of the molecular chain,and the loss factor is less than 0.2,the loss factor is relatively small.After adding antioxidants,due to the increased crystallinity,the peak-to-peak loss of the loss increases,and the peak position also moves to high temperature.For the study of the electrical properties of materials,when the shear time reaches 45 min,it has a certain inhibitory effect on the accumulation of space charges in the material.The addition of antioxidants can only inhibit the space charge in the sample T30S-190-anti 15 min.As the shear time increases,the current density of the material first increases and then decreases.The nonlinear threshold field strength first decreases and then increases with the increase of the shear time.Regarding the research on the electrical strength of materials,it is concluded that the short-term shearing effect reduces the electrical resistance of the material.When shearing for a long time,the electrical strength of the material can be increased by about 2%,and the material after shearing still It has the same level of electrical resistance as the pure sample.After the shear temperature is increased,the current density,nonlinear threshold field strength,and electric strength of the two types of samples show opposite trends.