A kinematic approach to the formation and characterization of biaxially oriented poly (p-phenylene terephthalamide) films

Poly (p-phenylene terephthalamide), PPTA, in the form of quarter inch staple fiber is redissolved in 99% sulfuric acid in concentrations of 17% by weight. The solution is than extruded over an oil coated mandrel into a methanol coagulation bath. From there the film is taken up through nip rollers into a water coagulation bath. The films are then washed using water, carbon tetrachloride, and a weak sodium hydroxide solution. The polymer solution in the concentration range used is liquid crystalline. The liquid crystal nature of the solution is believed to aid the orientation process on the mandrel.

Several different mandrel shapes were used. Molecular orientation as well as mechanical properties were found to be dependent on mandrel shape. Wide angle X-ray diffraction, WAXS, techniques using orientation functions, pole figures and WAXS patterns were used to characterize the films. Mechanical properties as well as the above techniques indicate that a high degree of biaxial orientation can be obtained with a bias in certain film directions dependent on the mandrel used. Tensile strength and initial modulus values were found to be on the order of 30,000 psi and one million psi respectively for mandrel films. They also can be equally distributed in the film plane dependent on mandrel shape. Orientation function values as high as 0.49 and 0.5 for f_x and f_y respectively were also 3 obtained. Film density was on the order of 1.44 g/cm³.

Different drying techniques such as compression and tension drying at temperatures as high as 300°C were used in an attempt to remove wrinkles and increase the modulus. Though the above techniques were successful in removing wrinkles they were not very effective in increasing the modulus. Uniaxially drawn films, made without the mandrel, were found to be susceptible to tension drying and demonstrated a marked increase in modulus.

There was also an attempt to quantify mandrel design so that one could predict the type of molecular orientation that a particular mandrel shape would develop. Thin Shell Theory as well as the mandrel kinematics were used in this analysis.