Crystallization Behavior And DC Electrical Properties Of Polypropylene Modified By ? Nucleating Agent

Recyclable insulation materials have recently gained more attention.Polypropylene has long been used in the manufacture of power capacitors as a thermoplastic insulating material with excellent insulation properties.However,it is prone to poor impact strength and difficult to apply to power cables.The crystal types of polypropylene are complicated.The ? crystal form which is a dense and regular crystal structure is usually formed in polypropylene.It makes the material have a large modulus and poor toughness.The blending of elastomers can destroy the regularity of the ? crystal form and significantly improve the impact resistance of the material,but its electrical properties have decreased significantly.Compared with the ? crystal form,the ? crystal form in PP exhibits a slightly loose structural feature.It has been confirmed that the ? crystal form can improve the impact resistance of the material,but there are few reports on its electrical properties.This paper proposes to use rare earth ? nucleating agent to modify polypropylene to study the relationship between nucleation efficiency and ? crystal form content,and to study the crystalline characteristics,mechanical characteristics and direct current performance of?-PP.The main results obtained are as follows: the rare earth ? nucleating agent WBG-? can efficiently induce the formation of ? crystal form in polypropylene,and increasing the filling amount of the nucleating agent helps to induce more ? crystal formation.Decreasing the cooling rate of crystallization increases the relative content of ? crystals of the material;? spherulites exhibit a typical bundle structure with a size below 10 ?m.DSC test found that ? crystal PP has two melting peaks,and the temperature of melting peak is at 150 ?,the high-temperature melting peak is near 165 ?,corresponding to the crystallization melting process of ? crystal phase and ? crystal phase respectively;tensile test shows that the introduction of ? nucleating agent can increase the fracture elongation of the material and improve the system toughness Although slow cooling increases the relative content of ? crystal form,the elongation at break is actually lower than that under rapid cooling conditions.The possible reason may be the more regular the crystal,the more structural defects in the amorphous region are,which is very likely to cause deformation stress concentration leads to fracture;?-crystal form PP has stronger space charge suppression ability with the increase of nucleating agent loading,the structure of ?-crystal form induced by nucleating agent is loose,and the crystal phases are not compact enough.The free volume of the amorphous region is large,thus giving space for space charge migration and release;when the nucleating agent filling amount is 0.1%,the highest breakdown strength is obtained,and the filling amount can be obtained The space charge suppression capability can also have a relatively small free volume content,and when the filling amount is too much,although the space charge suppression effect becomes better and the field strength in the body is more uniform,the free volume content increases,more The high-energy electrons are generated to counteract the positive effect,and the breakdown strength of the material decreases instead.