Kinetics of isothermal and non-isothermal crystallization of poly(butyleneterephthalate)/liquid crystalline polymer blends

The melting behavior and isothermal and non-isothermal crystallization kine tics of poly(butylene terephthalate) (PBT)/thermotropic liquid crystalline polymer (LCP), Vectra A950 (VA) blends were studied by using differential s canning calorimetry. Isothermal crystallization experiments were performed at crystallization temperatures (T-c), of 190, 195, 200 and 205 degreesC fr om the melt (300 degreesC) and analyzed based on the Avrami equation. The v alues of the Avrami exponent indicate that the PBT crystallization. process in PBT/VA blends is governed by three-dimensional morphology growth preced ed by heterogeneous nucleation. The overall crystallization rate of PBT in the melt blends is enhanced by the presence of VA. However, the degree of P BT crystallinity remains almost the same. The analysis of the melting behav ior of these blends indicates that the stability and the reorganization pro cess of PBT crystals in blends are dependent on the blend compositions and the thermal history. The fold surface interfacial energy of PBT in blends i s more modified than in pure PBT. Analysis of the crystallization data show s that crystallization occurs in Regime Il across the temperature range 190 degreesC-205 degreesC. A kinetic treatment based on the combination of Avr ami and Ozawa equations, known as Liu's approach, describes the non-isother mal crystallization. It is observed that at a given cooling rate the VA ble nding increases the overall crystallization rate of PBT.