Dielectric Studies Of Polyester/Polycarbonate Blends
- PDF / 568,103 Bytes
- 6 Pages / 420.48 x 639 pts Page_size
- 23 Downloads / 184 Views
Dielectric Studies of Polyester/Polycarbonate Blends James K. O'Reilly and Joseph S. Sedita, Eastman Kodak Company, Corporate Research Laboratories, Rochester, NY 14650-2110 Abstract: Dielectric and enthalpic relaxation times have been measured as a function of composition and temperature. A fractional exponential (W-W) distribution of relaxation times fits both the dielectric and enthalpic relaxation times with different values which are a function of composition. Free volume parameters calculated using the WLF equation are not simple functions of the composition. Concentration fluctuations are considered to be important in these phenomena. Introduction: There is widespread interest in polymer blends which offer the opportunity to obtain improved properties at lower cost. The class of miscible and immiscible polyester/polycarbonate blends have been extensively studied {1} and reviewed {2}. Copolyesters of ethylene glycol (EG) and cyclohexanedimethanol(CHDM) and terphthalic acid (T) and bisphenol A polycarbonate(PC) blends were studied by Paul and co-workers {3-6}. These blends were miscible under most conditions but because of high temveratures, 250C and higher required for melt blending, transesterification of the polymers may contribute to the miscibility. PET is not miscible with PC in the absence of transesterification. CHDMT is reported to be miscible with PC by Paul(7) We will report dielectric and thermal properties of a20/80 mole% oopolymer of EG/CHDM/T blended in an extruder wlthvarlous amounts of PC. The temperature dependence of the dielectric and thermal relaxation times will be analyzed in termsof the free volume models of relaxation. Experimental: Merlon M40 PC used in these studies has Mw-31,000 and Tg is 140C. The copolyester EG/CHDM 20/80 terphthalate is a commercial product of Eastman Chemicals and has Mw-39,000 and Tg is 85C. The blends were melt extruded at 285C and films were mol ded in compression at 295C. DSC measurements were made using a DSC II. Dielectric measurements were made using a DETA apparatus from Polymer Labs over a temperature range of -100 to 200 C and from 1 to 100 kHz. Only tang measurements are reported here because they show all the interesting behavior and are the most accurate. Dielectric Results: A beta relaxation process is observed in both the polyester (Tmax -- 10C) and polycarbonate homopolymers (Tmax - -50C). The beta process of the blends appears to be an average of the two pure component losses and little additional information is discernible from these measurements. In the Tg region (alpha relaxation) a single narrow peak is observed for each blend and indicates that the blends are miscible (Fig. 1.) For the pure polyester, an additional peak is observed at high temperature which is attributed to recrystallization of the polyester Mat. Res. Soc. Symp. Proc. Vol. 171.
1990 Materials Research Society
226
and leads to an alpha' loss characteristic of semi-crystalline polymers. The intensity of the loss peak is not a linear function of the composition. This may b
Data Loading...
