High‐strength–high‐modulus polyimide fibers II. Spinning and properties of fibers

Abstract

SynopsisThe polyimides baaed on 3,3,4,4'-biphenyltetracarboxylic dianhydride (BPDA) described in Part I of this series were dissolved in p-chlorophenol and spun into fibers using a coagulating bath of ethanol. The fibers as spun had in general low tenacities and low moduli, but a heat treatment at 300-5WC under tension produced a remarkable increase in strength and modulus, and fibers with a tensile strength of 26 g/den (3.1 GPa) and an initial modulus higher than 1,ooO g/den (120 GPa) could be obtained. Thus, the annealed fibers of polyimides are comparable to aramid fibers in mechanical properties. To heating in air and in the saturated steam, the polyimide fibers showed higher resistance than the aramid fibers. The polyimide fibers surpassed the aramid fibers in resistance to acid treatment and ultraviolet (UV) irradiation, but were inferior in resistance to alkali treatment. The annealed fibers of polyimides displayed distinct X-ray diffraction patterns. The chain repeat distance of 20.5 8, determined on the fibers of polyimide prepared from BPDA and o-tolidine, and 20.6 8, determined on the fibers of polyimide derived from BPDA and 3,4diamindiphenyl ether are reasonable when the dimensions of monomeric units and the shapes of the molecular chains are considered.The X-ray reflections of both polyimide fibers were indexed satisfactorily on the basis of postulated unit cells.

Structures and properties of polyimide fibers containing ether units

“…By means of the extensive amount of potential monomers and solvents, the industrial level production of PI fibers is more likely to be realized in this method. Nevertheless, in the two-step wet-spinning method, the microvoids and other structural imperfection could generate through the dual-diffusion and imidization & Dezhen Wu wdz@mail.buct.edu.cn process, leading to a negative effect on the mechanical properties of PI fibers [17,18]. To overcome the drawback, some modifications should be done in attempt to improve the mechanical properties.…”

Polyimide Fibers Obtained by Spinning Lyotropic Solutions of Rigid‐Rod Aromatic Poly(amic ethyl ester)s

“…Drawing at 150 8C [fiber (8)] did not change the fiber properties dramatically; this temperature more resembles the pre-bake conditions used in PI precursor chemistry. As expected, imidization of (8) on a metal spool renders a PI fiber (9) with properties close to fiber (6) (see Tables 4 and 5).…”

“…A fiber morphology with large voids prevented the formation of fibers with good mechanical properties. Other research groups [5,8,14,18] favor the spinning of PI solutions directly, without the use of precursor polymer solutions. This route avoids the notorious imidization step, which might be incomplete and is always accompanied by a mass loss, thus impeding the ultimate mechanical properties of fiber.…”

“…In view of commercialized high modulus fibers with excellent performance, such as M5, Zylon, or others (see entries [8][9][10][11][12], the aim of this work was not to attempt to produce yet another high modulus PI fiber. In the course of our studies of order in lyotropic PAEs, [11][12][13] where the orientation in a two-dimensional thin film was investigated, we now want to examine the development of orientation in an elongated, fibrillar geometry.…”

Copolymers derived from bismaleimide oligomer with active solvent

“…[3][4] However, all PIs mentioned above have to be processed in either solution or thermoplastic state. As we know, the tooling costs for fabricating PIs composites can be quite high.…”