Studies On The Relationship Between Morphology And Space Charge In Fluoropolymers

Fluorocarbon polymers are widely used as an insulation material in special cables that are often used in spaceships and aircrafts, because of their outstanding electrical and mechanical properties. However, fluorocarbon polymers tend to store charges and become electrets under certain conditions. In the case of direct current (DC) voltage application, the accumulation of space charges can distort the electric field distribution in the polymer insulation matrix. When the distorted electric field is strong enough, the electrical tree initiation and breakdown will occur in the material. In the case of spacecraft application, the gathering of space charges in dielectric may pose a threat to the safety of satellites. Cosmic rays, high energy protons and electrons can inject into dielectric and form space charges, which usually accumulate in the dielectric and cause high voltage. The discharge of static electricity usually leads to apparatus failure of satellites. Therefore, it is important to understand the mechanism of the formation and accumulation of space charges in fluorocarbon polymers and to explore the means of improvement.In this paper, PTFE, FEP, PVDF are selected. Three different ways, improving processing, blending, adding additive, are employed to decrease the charge amount and improve charge distribution in fluorocarbon polymers. Here we discuss the relationship between charge distribution and morphology of fluorocarbon polymers, and the reason of charge accumulation, transportation and elimination. According to the result of experiment, following conclusion can be made:1. Space charges in PTFE and FEP under DC voltage application can be reduced and the charge distribution can be improved by quenching process. The crystallinities and crystalline sizes decrease and the crystallites become disorderly and imperfect at high cooling rates while the crystalline forms remain the same. The decrease of space charges can be attributed to the decrease of crystallinities and crystalline sizes, which improves the charge transportation both in crystalline regions and in amorphous regions.2. Amount of charges in PVDF under DC voltage application can be reduced and the charge distribution can be improved by blending with PMMA. The decrease of space charges can be attributed to the ability of charge transportation enhanced by PMMA, the weakening of charge attraction ability and the decrease of crystallite sizes of PVDF. Polar groups of PMMA can act as hopping sites to transport the trapped charges. The changes of phase structures influence the ability of charge transportation in the blends. The hydrogen bonds in PVDF/PMMA blends weaken the charge attraction ability of PVDF, which decreases traps. All of these make contributions for the decrease of charges in the blends.3. Amount of charges in PVDF under DC voltage application can be reduced and the charge distribution can be improved by adding anlistatig. the crystalline morphology remain the same as pure PVDF. anlistatig must be pushed out into the amorphous regions during the crystallization of PVDF. Anlistatig can absorb moisture easily and then be dissociated. Thus anlistatig improve the conductivity of PVDF. The charges can easily migrate and the accumulated space charges will dissipate and be neutralizated by heterocharges.