CRITICAL ANALYSIS OF THE PHASE-BEHAVIOR OF POLY(EPSILON-CAPROLACTONE) (PCL)/POLYCARBONATE (PC) BLENDS

The phase behavior and miscibility of poly(epsilon-caprolactone) (PCL)/polycarbonate (PC) blends have been investigated with DSC, cloud-point measurement, TGA, FTIR, NMR, and small-angle neutron scattering (SANS). Thermal analysis results indicated that the PCL-rich blends are semicrystalline/semicrystalline at room temperature. At about 30 % PC incorporation, the PCL crystallinity showed a marked reduction, whereas the PC crystallinity approached a maximum. The composition dependence of T(g) exhibited a discontinuity (cusp) and was critically analyzed using the classical equations of Gordon-Taylor and Fox and the free volume theory of Braun-Kovacs. Combination of the Fox and Braun-Kovacs equations accurately reproduced the T(g)-composition dependence. Thermal stability of the blends, as measured by the onset degradation temperature in air, increased with increasing PC. FTIR results coupled with C-13 NMR findings supported the hypothesis that the blends primarily degraded via thermally-induced chain scission of PCL as evidenced by the evolution of CO2. SANS studies on the deuterated PC-rich blends revealed that the scattering intensity first remained fairly constant with increasing temperature and then increased sharply at temperatures above the blend T(g). The sudden rise in the scattering intensity was attributed to crystallization of PC resulting from prolonged annealing. Results derived from the RPA analysis of the SANS profiles measured at 30-degrees-C for the deuterated PC-rich blends and those obtained from the melting point depression analysis of the PCL-rich blends suggested favorable blend interactions as reflected by the negative sign of the X parameter.