Isothermal crystallization kinetics of poly(epsilon-caprolactone) with tetramethyl polycarbonate and poly(styrene-co-acrylonitrile) blends using broadband dielectric spectroscopy

摘要

Phase behavior and isothermal crystallization kinetics of poly(epsilon-caprolactone) (PCL) blends with tetramethyl polycarbonate (TMPC) and poly(styrene-co-acrylonitrile) with 27.5 wt.- acrylonitrile content-have been investigated using broadband dielectric spectroscopy and differential scanning calorimeter. An LCST-type phase diagram has been observed for PCL/SAN blend while all the different blend compositions of PCL/TMPC were optically clear without any phase separation structure even at high temperatures up to 300 degrees C. The composition dependence of T(g)s for both blends has been well described by the Gordon-Taylor equation. The phase diagram of PCL/SAN was theoretically calculated using the Flory-Huggins equation considering that the interaction parameter is temperature and composition dependent. The equilibrium melting point of PCL depressed in the blend and the magnitude of the depression was found to be composition dependent. The interaction parameters of PCL with TMPC and SAN could not be calculated from the melting point depression based on Nishi-Wang approach. The isothermal crystallization kinetics of PCL and in different blends was also investigated as a function of crystallization temperature using broadband dielectric spectroscopy. For pure PCL the rate of crystallization was found to be crystallization temperature (T-c) dependent, i.e., the higher the T-c, the lower the crystallization rate. The crystallization kinetics of PCL/TMPC blend was much slower than that of PCL/SAN at a constant crystallization temperature. This behavior was attributed to the fact that PCL is highly interacted with TMPC than SAN and consequently the stronger the interaction the higher depression in the crystallization kinetics. It was also attributed to the different values of T-g of TMPC (191 degrees C) and SAN (100 degrees C); therefore, the tendency for crystallization decreases upon increasing the T-g of the amorphous component in the blend. The analysis of the isothermal crystallization kinetics was carried out using the theoretical approach of Avrami. The value of Avrami exponent was almost constant in the pure state and in the blends indicating that blending simply retarded the crystallization rate without affecting the crystallization mechanism. Dielectric constant, epsilon', of pure PCL, blends of PCL/TMPC = 80/20 and PCL/SAN = 80/20 as a function of crystallization time at 47 degrees C and 1 kHz.