Polymer Journal, Vol. 16, No. 7, pp 575-578 (1984)

NOTES Dielectric Properties of Polypropylene/ Polycarbonate Polyblends

P. K. C. PILLAI, G. K. NARULA, and A. K. TRIPATHI

Department of Physics, Indian Institute of Technology, New Delhi-110016, India

(Received February 2, 1984)

KEY WORDS Dielectric Properties I Polypropylene and Polycarbonate Polyblends I AC Measurements I

AC measurements give an important tool in granules were obtained from Sri Ram Institute the study of polarization and dielectric relax• of Industrial Research, Delhi, India and ation in polymer dielectrics. Most of the inter• Bayer, Germany, respectively. The blends were esting properties of polymers are due to the made by taking the two polymers in different molecular motions which are very complex. In weight proportions (10 to 90) in a melt ex• a polymeric system, the molecular relaxations truder and later the films were made by com• correspond to various transitions of the pression moulding. The different blend ratios polymer. The investigation of dielectric dis• used in present studies include. persion of polymers has been popular in (10/90), (40/60), (50/50), (60/40), and (90/10) recent years and considerable literature now weight proportions of PC and PP and are 1 3 exists. - The dielectric relaxation depends designated as PP1 , PP4 , PP5 , PP6 , and PP9, on the total chain length, frequency, tempera• respectively. ture, pressure4 - 6 and in some cases is a func• A sample of (2 x 2) cm2 was cut from each tion of plasticiser concentration,7 curing film for AC dielectric measurements. The agent,8 complex formation and co-polymeri• aluminium electrodes were vacuum deposited zation.9 on both sides of the film on an area of The dielectric measurements made on (1.4x 1.5)cm2 . A 1615 A type General Radio polypropylene (PP)/Polycarbonate (PC) poly• bridge was used for measuring the dielectric blends are reported in this paper in the fre• Permittivity and dielectric loss in the polyblend quency range 1 to 100kHz and temperature systems. Measurements were made in the fre• range 50-170ac. The dielectric constant a' quency range 1 to 100kHz and in the tempera• and dielectric loss a'' were measured as func• ture range from room temperature to 170°C. tions of frequency and temperature. The results have been explained on the basis RESULTS AND DISCUSSION of induced dipole formation. The effect of temperature and frequency EXPERIMENTAL DETAILS variation on c;' and tan b of various poly• blends is shown in Figures 1-3 a' has been PP and PC in the form of transparent found to be independent of frequency of the

575 P. K. C. PILLAI, G. K. NARULA, and A. K. TRIPATHI

3,5r

3.31- .... 5

1- 4 3.1 I• V)z 0 (,) 2.91-

1 10 100 FREQUENCY (KHz)

Figure 1. Permittivity as a function of frequency: 1, PP1; 2, PP4 ; 3, PP5 ; 4, PP6 ; 5, PP9 .

4-0

'w 1-z 3.5 - < 1- VJ z 0 u 5 4 a: 1- u 3.0 aUJ 3 2

I 30 70 110 150 190 TEMP (°C l

Figure 2. Permittivity as a function of temperature: 1, PP1 ; 2, PP4 ; 3, PP5 ; 4, PP6 ; 5, PP9 • applied field for all the polyblends (Figure 1). up to 150°C and after that increased sharply in This is in accordance with the dielectric re• all the systems studied (Figure 2). The tem• sponse of non-polar dielectrics. 10 With an in• perature dependence of tan c5 at fixed fre• crease in temperature a' remained almost con• quency (20 K) is shown in Figure 3 for various stant or decreased slightly in some polyblends polyblends. Here again it is found that tan c5

576 Polymer J., Vol. 16, No. 7, 1984 Dielectric Properties of PP j PC Polyblends

20.0

15.0

X

1. 50 90 130 170 TEMP (°C l

Figure 3. Loss tangent as a function of temperature: 1, PP4 ; 2, PP5 ; 3, PP6 . decreases slightly with temperature up to remained almost constant with frequency and 150oC and then shows a sudden increase also with temperature (or decreased slightly) with further rise in temperature. However, no up to 150ac. Since the applied field in the dependence of tan (J was found on the fre• AC measurements is very weak as compared quency of the AC field. to the field value in TSC or DC conduction The polyblends under study are made up of studies ( 20 k V em -l ), the injected charge one polar (PC) and one non-polar (PP) com• density from the electrodes into the polymer ponent. They are heterogeneous mixtures, and is almost negligible in this case and only the thus contain a large number of trapping sites. thermally generated carriers (bulk generated) As is clear from Figures 1 and 2 the dipolar dominate in the present experiments. On ap• contribution of PC towards the total polari• plication of an AC field at room temperature zation of polyblends is not much because we or 50°C, trapping of charge carriers takes are concerned with the non-polar characteris• place which leads to induced dipole forma• tics. In the case of polar dielectrics, 10 s' de• tion. As the temperature of the system in• creases with an increase in frequency and also creases, the mobility of carriers increases s' increases with an increase in temperature slightly and also the trapping will decrease owing to the increase in polarization in these marginally, leading to a lowering of polariza• materials. But in the present polyblends, s' tion. Owing to this s' decreases slightly

Polymer J., VoL 16, No.7, 1984 577 P. K. C. PILLA!, G. K. NARULA, and A. K. TRIPATHI with temperature initially. At around 150°C REFERENCES the molecular motion increases to such an extent that the induced dipoles which 1. F. E. Karasz, Ed., "Dielectric Properties of Poly• mers," Plenum Press, New York, N.Y., 1972. were formed start orienting under the ap• 2. N. G. McCrum, B. E. Read, and G. Williams, plied field. This gives rise to sudden increases "Anelastic and Dielectric Effects in Polymeric of s' and tan <5 with further increase of tem• Solids," John Wiley, New York, N.Y., 1967. perature. 3. P. Hedvig, "Dielectric Spectroscopy of Polymers," Ademhilger, Bristol, 1977. 11 Our TSC (thermal stimulated current) 4. H. Sasabe and S. Saito, J. Polym. Sci., 6, 1401 (1968). and step response measurement12 studies on 5. G. Williams, Trans. Faraday Soc., 62, 2091 (1966). these polyblends have also suggested charge 6. G. Williams and D. A. Edwards, Trans. Faraday carrier trapping leading to induced dipole Soc., 62, 1329 (1966). 7. R. M. Fuoss, J. Am. Chern. Soc., 63, 378 (1941). formation. 8. J. Gowri Krishna, 0. S. Josyulu, J. Sobhandri, and R. S. Subrahmanian, J. Phys. D, Appl. Phys., 15, 2315 (1982). CONCLUSION 9. P. K. C. Pillai and Rashmi, Int. J. Polym. Mater., 8, 255 (1980). The AC measurements in polyblends of PC 10. B. Tareev, "Physics of Dielectric Materials," Mir and PP show that the dielectric relaxation in Publishers, Moscow, 1979. these systems is due to induced dipoles formed 11. P. K. C. Pillai, G. K. Narula, A. K. Tripathi, and R. as a result of trapping of charge carriers in G. Mendiratta, Phys. Rev., B, 27 2508 (1983). 12. P. K. C. Pillai, G. Narula, A. K. Tripathi, and R. deeper traps and their orientation at higher G. Mendiratta, Phys. Status Solidi (a), 77, 693 temperatures. (1983).

578 Polymer J., Vol. 16, No. 7, 1984