Phase diagram for liquid crystalline polymer/polycarbonate blends

Blends containing a thermotropic liquid crystalline polymer and an engineering thermoplastic polymer have recently received considerable attention, because liquid crystalline polymers display low melt viscosity, excellent chemical resistance, thermal stability and mechanical performance. A novel mechanism to form binary polymer blends is through phase separation by spinodal decomposition in the unstable region of the phase diagram. The overall objective of this work is to investigate the effects of thermally induced phase separation by spinodal decomposition on the morphology development of liquid crystalline polymer/polycarbonate blends and to obtain a thermodynamic binary phase diagram. The blends were obtained using a twin-screw extruder at various processing melt temperatures. To study miscibility of the blends and the resulting morphology, techniques such as differential scanning calorimetry and scanning electron microscopy were used. The liquid crystalline polymer/polycarbonate blend undergoes phase separation during thermally induced spinodal decomposition exhibiting a miscibility window reminiscent of a lower critical solution temperature. The blend is found to be miscible, when blend Tg slightly decreases. On the other hand, the blend is found to be immiscible as blend Tg increases. A thermodynamic two-phase transition curve phase diagram was obtained using an innovative practical experimental technique in conjunction with twin screw extrusion and scanning electron microscopy.