The study of interreaction of insulating oils with PP film-the effect of impregnant on crystal structure of PP film

The thermal stimulated current (TSC) technique and differential thermal analysis (DTA) were used to investigate the effect of impregnant on the crystal structure of polypropylene (PP) film. PP film samples used in DTA were impregnated in PXE (phenylxylyl ethane) for one day, ten days, and 20 days at 60 degrees C, 80 degrees C, and 100 degrees C, respectively. It is shown that the unstable beta -crystal form in impregnated PP film begins to turn into alpha -crystal form at lower temperature, indicating that the impregnant may penetrate into the imperfect crystal structure and promote the change of the crystal form of the PP film. Experimental results of DTA and TSC are consistent in supporting this conclusion. The TSC peak of impregnated PP film around 75 degrees C is closely related to impregnating temperature and impregnating time; thus, it is possible to study the effect of impregnation on crystal structure of PP film by investigating the change of this peak.<
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