A rotating annular die for control of biaxial orientation in melt processed thermotropic liquid crystalline cellulose derivatives

A rotating annular die was used to control the molecular orientation in melt processed thermotropic liquid crystalline cellulose ethers. The annular die consists of a rotating inner core and a simultaineously counter-rotating outer cylinder. The inner core and outer cylinder rotation speed was used to vary the velocity profile. Nitrogen gas could be fed through the inner core of the die to inflate the tubes and produce thin films.

Mechanical testing, birefringence measurements, and wide angle x-ray diffraction techniques using pole figures in conjunction with orientation functions show that the molecular orientation can be controlled by the rotating annular die. Tubes and films were characterized at various die rotation speeds. White-Spruiell biaxial orientation factors were f B/1 = 0.80 and f B/2 = 0.021 for an extrudate without die rotation. The rotating annular die is capable of changing the biaxial orientation factors to f B/1 = 0.17 and f B/2 = 0.71. The rotating annular die can change the mechanical properties of the hydroxypropyl cellulose films from highly biased in the machine direction to biased in the transverse direction. It is believed that the long relaxation times associated with thermotropic liquid crystalline material are responsible for the high degree to which the orientation can be controlled through the use of a rotating annular die.