Effect of Frequency and Temperature on Dielectric Properties of Polypropylene at X-Band Microwave Region

Abstract

Dielectric behaviour of large-molecular weight, high density, sol vent insoluble, isotactic samples of polypropylene have been studied in the X-band microwave region as a function of frequency (8.4-10.835 GHz) at ambi ent temperature (30 ° C) and as a function of temperature ( —120 ° C to 160 ° C) at three different frequencies by the method of Smith and von Hippel as modified by Dakin and Works. The sample exhibits two types of dispersion/relaxation in the semilog frequency plots of ∈' and ∈". The lower frequency dispersion is asso ciated with the crystalline region of the polymer while the higher frequency dispersion is related to the amorphous region of the polymer. Percent relative dispersions and relaxation magnitudes are found to be small. The values of "a" factors corresponding to the two loss peaks are 0.023 and 0.031, respectively. The most probable relaxation times for the two relaxation processes have also been calculated. Three types of dispersions namely β, γ ₁, and γ₂ have been observed in the ∈" vs. temperature plots at three different frequencies. The av erage apparent energy of a polypropylene molecule associated with its induced dipoles has also been calculated. The average values of the intrinsic activation energy, ΔE', decreases with increase of frequency, changing from 2.764 to 0.886 kcal/mol in the specific frequency region used.