Effect Of α/β Nucleating Agent Crystal Phase Regulation On The Mechanical And Electrical Properties Of Polypropylene-Based Polyblends

With the increasing demand for cables,environmentally friendly insulated cables have become the new development trend,and the development of improved polypropylene has become the first choice of dielectric research scholars.However,the large modulus,rigidity,and poor flexibility of polypropylene seriously hinder the application of polypropylene in insulated cables.Usually,polypropylene requires the addition of elastomers to form polyblends for use in cables,and the added elastomers themselves have poor dielectric properties and destroy the crystalline regularity of polypropylene,which reduces the electrical properties of the blended material.Therefore,while toughening and modifying polypropylene,we also need to pay attention to the electrical property changes,which can be further improved by doping the nucleating agent in the polyblend to change its crystalline phase structure,thus further improving the mechanical and electrical properties of the polyblend.In this study,polypropylene and elastomer POE were fused with lamellated αnucleating agent O-MMT and β nucleating agent WBG-II by melt blending method and hot pressing method,respectively,to prepare modified blends with different nucleating agents.X-ray diffraction(XRD),polarizing microscope(PLM)and differential scanning calorimetry(DSC)were used to characterize the melting,crystallization behavior and crystal structure of the blends.Tensile test and dynamic thermomechanical analysis(DMA)test were used to evaluate the relationship between the toughness and rigidity of blends and the type and content of nucleating agents.The dielectric properties,conductance current,space charge,breakdown strength and other electrical properties of the blends were analyzed,and the influence mechanism of α/βnucleating agent on the electrical properties of polypropylene materials was explored in relation to the crystallization characteristics and mechanical properties.The results show that the α/β nucleating agents can increase the crystallization rate,decrease the crystal size,and bring different crystal structure to the polyblends.The samples modified with α nucleating agent have the highest elongation at break,and the storage modulus decreases with the increase of O-MMT content.The small size crystallization caused by the addition of α nucleating agent and the lamellar OMMT work together to improve the mechanical properties of the polyblends.The addition of β nucleating agent reduced the yield strength of the blend from 22.1 MPa to 19.0 MPa,and the storage modulus from 1470.82 MPa to 1117.87 MPa.The βnucleating agent changed the dominant crystal shape of the polypropylene polyblend,which greatly reduced the rigidity of the polyblend.The appropriate amount of αnucleating agent and β nucleating agent can reduce the dielectric constant of the polyblend.The crystallization refinement brought by the nucleating agent can effectively inhibit the electron transition,reduce the current density of the material,improve the charge concentration of the polyblend,and then increase the AC/DC breakdown strength,among which the β nucleating agent has the most prominent effect.The industrial frequency AC breakdown field strength increased from 84.8k V/mm to 102.3 k V/mm,and the DC breakdown field strength increased from 286.5k V/mm to 333.8 k V/mm.The two special nucleating agent modified polyblends both improved the mechanical and electrical properties at the same time,and the appropriate amount of β nucleating agent induced the polypropylene polyblends to produce compact crystal regions.The special crystal structure led to the β nucleating agent modified polyblends to have higher insulation properties,which provided a reference for the modification of polypropylene insulating materials.