Crystallization and melting behavior of zenite thermotropic liquid crystalline polymers

The crystallization and melting behavior of a DuPont Zenite™ series, namely, Z 6000 and Z 8000B, thermotropic liquid crystalline polymer (TLCP) have been investigated by differential scanning calorimetry (DSC). Both, non-isothermal and isothermal crystallizations were carried out. From the non-isothermal experiments, the crystallization temperature was found to be 234°C for a cooling rate of 10°C/min whereas it was only 228°C for 40°C/min for Z 8000B, and was found to be 296°C and 290°C, respectively, for Z 6000. In the isothermal experiment both the thermal and crystallization behaviors were studied as a function of the annealing temperature and annealing time. Two types of transition processes were evidenced in the low temperature region of the isothermal crystallization. One is fast transition, which may be regarded as liquid crystal transition, and is characterized by the enthalpy, which is independent of annealing time. The other is slow process, related to crystal perfection, and it shows increases in the transition temperature and enthalpy, which is dependent on annealing time.