Poly(p‐phenylene terephthalamide) films formed from extrusion and coagulation of liquid crystalline sulphuric acid solutions: Characterization of orientation and void structure, annealing, and upgrading of film mechanical properties

Abstract

Poly(p-phenylene terephthalamide) (PPD-T) films have been prepared by continuous extrusion of liquid crystalline 17 percent PPD-T/sulphuric acid solutions through an annular die followed by coagulation. Films extruded without drawdown exhibit some polymer chain orientation in the machine direction. This is increased by uniaxially drawing down films. Films produced with a lubricated conical mandrel sitting between the die and the coagulation bath exhibit an equal biaxial orientation. The uniaxially oriented films exhibit highly anisotropic mechanical properties, while the mandrel-produced film exhibits balanced properties. Heat treatment at 350°C results in significant enhancement of the tensile strength of the mandrel film. Void structures in the films have been investigated by mass density, scanning electron microscopy (SEM), and small-angle X-ray scattering (SAXS). Density measurements indicate a void content decreasing with decreasing film thickness and heat treatment. SEM locates micron-size voids in the thickest films, apparently caused by rapid coagulation. SAXS indicates much smaller void sizes which are roughly prolate ellipsoids (long axis in machine direction) for uniaxial films and oblate ellipsoids (short axis in thickness direction) for the mandrel produced films. Various techniques are used to estimate mean void size.(16) used a lubricated mandrel and developed significant levels of biaxial orientation, i.e., orientation in the transverse as well as the machine direction.In this paper, w e continue our studies of the development of a process for biaxially oriented films of PPD-T and the characterization of such films. W e again consider the mandrel process technology, but include the post-extrusion annealing step. W e compare such films with those of different process histories. The crystalline orientation of the films is carefully characterized. In addition, we will carefully characterize the void sizes/distribution developed in the films.

Gas transport properties of liquid crystalline poly(p-phenyleneterephthalamide)

“…[10][11][12] Films from PPT solutions have also been fabricated and characterized in a few laboratories. [13][14][15][16] The crystalline structure is described as paracrystalline.12 The effects of the type of coagulant and of annealing temperature on the crystal structure of PPT films have been extensively examined by Haraguchi et al14 '15 The well-documented high water sorption capacity of polyamides such as Nylon 6 and 6,6 has been linked closely with the concentration of amide linkages along the polymer chain.17 Despite crystallinity levels near 75%, Kevlar fibers have also been observed to absorb appreciable amounts of water.18 Unlike Nylon 6 and 6,6 materials, the polymeric chains in Kevlar fibers have no isotropic character.10 Thus, it appears as though the ordered (but noncrystalline) regions of the Kevlar fibers behave analogously to the amorphous regions of other polyamides. If this is a characteristic of isotropic and mesomorphic arrangements of chemically similar polymer chains, then one would also expect similar behavior with other penetrants including simple gases.…”

A New Method for Continuous Solid‐State Biaxial Orientation of Polymeric Films

“…A similar approach was used by the researchers at the University of Tennessee to biaxially stretch a film of poly( p ‐phenylene terephthalamide) from liquid crystalline solutions . The process involved the use of extrusion from an annular die over an external mandrel rather than a tubular blowing procedure.…”

“Foil spintrusion” of high‐performance polymer films

“…Attempts have been made to avoid the adversary effects associated with weaving or use of short‐fiber‐reinforced composites and to manufacture high‐performance, biaxially oriented polymer films. Such films have been produced by biaxial deformation in the solid state or, for instance in the case of PPTA, using a mandrel‐guided precipitation process 4–6. Another technique, specifically designed to process thermotropic liquid‐crystalline polymers, such as Vectra®, employs a die with three rotating cylinders to form films 7, 8.…”