Fabrication of Biaxially Oriented Films via Poly(P-phenylene Teraphthalamide)/H2SO4 Liquid Crystalline Dopes

摘要

The fundamental innovation arising from this research is that the state of spatial biaxial order in lyotropic Poly(p-phenylene terephthalamide)(PPTA/H2SO4 liquid crystal solutions is strongly controlled by an externally imposed stress field. Also the orientation only relaxes slowly after the stresses are released. This enables processes to b devised that develop biaxial stress on a flowing liquid crystal to cause high levels of molecular orientation. Since the character of the stress, i.e., the magnitude and direction of the sigma ij components, is set by the experimental conditions, then the orientation is also controllable. Thus a process has been developed which takes advantage of the rheological and phase behavior of PPTA/H2SO4 to create films ranging from uniaxial through unequal biaxial to equal biaxial orientation. This and other structural features have been documented by WAXS, pole figure analysis, microscopy and SAXS. Also mechanical property studies show that a range of strengths and moduli can be obtained including a film of equal axial orientation (fzc = 0.45, fyc = 0.50 using the White-Spruiell indices from 0.0 to 0.5 where 0.5 means perfect orientation). Property values for this film are modulus in the machine direction = 700,000 psi and transverse direction = 800,000 psi with tensile strengths in the machine direction = 25,000 psi and transverse direction = 30,000 psi.