Acta Polymcriu 42 (1991) Nr. 7 306 PLUTA, MILCZAREK et al. : Strocture reorganiza tion in is0 tactic polypropylene I I I 50 I00 'C 150 T Fig. 4. TSC spectra for the original foil (1) and of the thcrmoelectret (T, = llO°C, ED = 80 MV/m, f, = 1 h) before (2) and after (3) annealing a t T , = 90°C during 1, = 10 min increased dielectric absorption below high temperature anomaly and decreased absorption above this anomaly (curves 4 in Figure 3). Figure 4 presents the temperature dependence of TSC spectra of the copolymer (I), with polarization (2) and additional annealing (3) for the samples analogous to those in Figure 3. The intensity of depolarization current for the thermoelcctret has much higher values than for the original foil. By emptying the low energetic traps, annealing decreases the depolarization current below the annealing temperature. This is accornpanicd by a deepening of local anomalies, whose source is in the ac relasation of the crystalline phase [a].
ConclusionsThe observed dielectric absorption is connected with the ccc relaxation in the antipolar phase of PVDF [3-71. The determined activation energy is consistent with literature data.The decrease of diclcctric absorption under the influence of polarization can be accounted for by induction of the polar phase ,9-PVDF. The decreased value of t a n S a t high temperatures, particularly for low frequencies, is connected with ''purification" of doping ions by the electric field Annealing of the polarized polymer brings about a ,9 -+ a transformation, which is manifested in increased dielectric absorption resulting from a, relaxation. Additional purification by the electric field of thermoelectret causes further decrease of tan 6 a t high temperatures.The influence of annealing is also visible in the dielectric relaxation observed for temperatures below 40°C. Annealing diminishes the frequency of low temperature relaxation, whose source lies in the amorphous phase. Annealing after polarization increases the temperature dependence on the density of depolarization current below annealing temperature. As a result of polarization the value of the current after annealing is by one order of magnitude greater than for the original foil.The increase of temperature sensitivity, monitored by dielectric measurements, in connection with decrease of tan 6, forecasts the improvement of pyro-and piezoelectric properties of annealed polymer thermoelectrets.[41.ikknowledgement The paper was supported by the CPBP 02.03/2.13 Scientific Problem.The effects of modification of polypropylene by liquid styrene are reported. The structural changes in the polymer ar? related to its initial structure and the processes of transformation of the smectic phase into the monoclinic one. The structure reorganization induced by the swelling processes is analyzed and compared will1 analogous effects reported earlier for low density polyethylene.
Uriistrukfiirierungen in isotaktisctieni Polypropylen bei Behandlung niit SfyrenDie Effelite einer XIoclifizierung von I'clypropylcn durcli Ein...
