Polyimides fibers

In addition to carbon and glass fibers ia composites, aramid and polyimide fibers are also used ia conjunction with epoxy resias. Safety requirements by the U.S. Federal Aeronautics Administration (FAA) have led to the development of flame- and heat-resistant seals and stmctural components ia civiUan aircraft cabias. Wool blend fabrics containing aramids, poly(phenylene sulfide), EDF, and other inherently flame-resistant fibers and fabrics containing only these highly heat- and flame-resistant fibers are the types most frequently used ia these appHcations. 

Newer fabrics, not in common use but in development, test, and field trials, are described for higher temperature applications by Reference [50]. Application to 400°F—2100°F are potentially available using ceramic fibers Nextel 312 , laminated membrane of expanded PTFE on a substrate, polyimid fiber P-84, Ryton polyphenylene sulfide, and woven fiberglass. The heat and acid resistance of these new materials... 

The structural anisotropy in crystalline or structurally ordered BPDA-PFMB films was studied in this laboratory with wide-angle X-ray diffraction (WAXD) methods. In brief, WAXD experiments were designed to examine both the reflection and transmission modes of thin-fihn samples. In addition, uniaxially oriented polyimide fiber WAXD patterns were obtained to aid in the identification of the film structure. The film WAXD pattern obtained from the reflection mode corresponded well to the fiber pattern scanned along the equatorial direction (Figure 16.3), " which indicates that the reflection mode pattern represents the (hkQ) diffractions. On the other hand, as shown in Figure 16.4, the (001) diffractions were predominant in the film WAXD pattern obtained via the transmission mode. This pattern corresponded to the fiber pattern scanned along the meridian direction. These experimental observations clearly indicate that the c-axes of the crystals are preferentially oriented parallel to the film surface however, within the film, they are randomly oriented. 4.2 5 j( should be pointed out that the WAXD experiments are only sensitive to crystalline or ordered structures in polyimide films. They do not provide any information on the amorphous regions. 

In most of the previous work with polyimide fibers, the fibers were spun from poly(amic acid) precursors, which were thermally imidized in the fiber form. However, high degrees of imidization were not achieved. Thus, tensile properties of these polymers were not as good as those of high-performance fibers. Work in our laboratories has shown that when the fibers are spun directly from preimidized polymers, it is possible to achieve tensile properties that are as good or even better than those of poly(p-phenyleneterephthalamide) (PPTA or Kevlar ) fibers. For example, fibers have been prepared from m-cresol solutions of BPDA-PFMB using a dry-jet wet-spinning method. The as-spun fibers were then extensively drawn and annealed above 400°C to achieve excellent mechanical properties. 

Polyimide films have excellent electrical properties and a tensile modulus of over 400,000 psi at 25°C. Over 60 percent of this modulis is retained at 200°C. Polyimide wire enamels are stable for up to 100 Oiousand hours at 200°C. Polyimide fibers have a tenacity of 7 g/denier at 25°C and over 1000 hrs at 2833C is required to reduce the value to 1 g/denier. 

Monsanto and Ube (Japan) developed membrane processes for purification of hydrogen gas mixtures. This process is based on the selective diffusion of hydrogen through semi-permeable membranes in the form of hollow fibers. The Monsanto PRISM separator process (owned by Air Products as of 2004) uses a polysulfone fiber whereas Ube uses an aromatic polyimide fiber.46... 

Type R and B fiber trademark of Thermo Electric s Thermoplastic Elastomer and Polyimide fiber, respectively. b Nylon, Teflon, and Kapton are trademarks of the E. I. duPont Co. 

Polyimides have also found a number of specialist applications. Polyimide foams (Skybond by Monsanto) have been used for sound deadening of jet engines. Polyimides fibers have been produced by Upjohn and by Rhone-Poulenc (Kermel). 

The use of swabs for total residue analysis by IMS has been developed for cleaning validation. In this approach, the swabs were 2 x 5 cm strips of polyimide fiber material that were wiped across contaminating surfaces. Figure 15.4 shows the... 

Fibers were spun from poly(amic acid)/dimeihylacetamide solutions and the resultant poly(amic acid) fibers were tlien thermally converted to polyimide fibers under sufficient tension. The polyimide fiber was finally heat treated at 525-575°C. 

The experiments carried out for the non-stressed polyimide fibers (at a = 0) shows that Eq. (18) is valid too. Therefore, excited chemical bonds are generated in the absence of stress. 

In Fig. 18, E and Of are compared with Cd for oriented polyimide fibers in the temperature range from 100 to 750 K. They indeed demonstrate linear dependence as predicted by Eqs. (21) and (22). This result is supposed to prove a correlation between macroscopic processes with the elongation of the excited bonds in macromolecules. 

Weinrotter K, Vodiunig R. Rame retardant high-temperature-resistant polyimide fibers and molded articles manufactured therefrom. US patent 5271889, assigned to Lenzing Aktiengesellschaft, Lenzing, AT 1993. 

Polyimide fiber n. A manufactured fiber formed from the condensation polymer of an aromatic dianhydride and an aromatic diisocyanate. The fiber is produced by dry spinning. It is a high-shrinkage fiber used in the formation of mechanically stable non-woven fabrics. These fabrics are made without binders or resins bonding apparently results from the local temperature and pressure that develop during shrinkage. 

The generic term aramid designates a long chain synthetic polyamide molecule (-CO-NH-) and para-aramids, such as Kevlar , that are wholly aromatic polyamides. DuPont started commercialization of Kevlar as the first high strength aromatic polyimide fiber in 1971. Another fiber with a similar chemical structure is Twaron produced by Akzo Nobel since the late 1970s. 

Schramm C, Rinderer B, Tessadri R (2013) Synthesis and characterization of novel ultrathin polyimide fibers via sol-gel process and electrospinning. J Appl Polym Sci 128 1274-1281... 

Table V makes a comparison of the mechanical properties of Col fibers with those of the pure PI and PBTA fibers. For the sake of possessing poor solubility, polyimide fibers have once generally spun fi-om solutions of their precusor, polyamic acid, following a heat treatment for thermal imidization. In general, micropores and voids exist in polyamic acid fibers. Although many coagulation media have been investigated to prevent this drawback, the production of totally void-fi ee aromatic polyamic add fibers was not found.

Polyimide fibers incorporating the gold salt (HAUCI4 3H2O) were produced by solution electrospinning technique. HAUCI4 blended with PI was electrospun from its DMF solution to form fibers with 0.5-3 wt% HAUCI4 within the fibers. Two different techniques were used in order to reduce the Au to Au . One of them was thermal treatment (200°C for 1, 3, and 6 h) and the other was chanical reduction by the use of ascorbic acid. 

FIGURE 16.10 XPS survey spectra of electrospun PI fibers (PI-3-23 wt%), untreated poly-imide fibers containing H AUCI4 (PI-3-23 wt%/Au 3 wt%), and polyimide fibers containing gold nanoparticles (PI-3-23 wt%/AuNP 3 wt%) at 200°C for 6 h/ascorbic acid. 

Aflori M., Serbezeanu D., Carjal.-D., and Fortunate) G. Gold nanoparticles incorporated into electrospun polyimide fibers. Chem. Lett. 44 no. 10 (2015) 1440-1442. 

Butnaru L, Serbezeanu D., Bruma M., Sava I., Gaan S., and Fortunato G. Physical and thermal properties of poly(ethylene terephthalate) fabric coated with electrospun polyimide fibers. High Perform. Polym. 27 no. 5 (2015) 616-624. 

Liu J., Min Y., Chen J., Zhou H., and Wang C. Preparation of the ultra-low dielectric constant polyimide fiber membranes enabled by electrospinning. Macromol. Rapid Commun. 28 no. 2 (2007) 215-219. 

Zhang, Q. Wu D. Qi S. Wu Z. Yang X. Jin R. (2007). Preparation of ultra-fine polyimide fibers containing silver nanoparticles via in situ technique. Materials Letters. Vol. 61 No. 19-20, (Jan. 2007), pp. 4027-4030, ISSN 0167-577X Zhao Y, Cao X Jiang L, (2007). Bio-mimic Multichannel Microtubes by a Facile Method. J. 

Polyimide fiber is made from an aromatic heterocyclic polymer, and P84 is the brand name of the polyimides manufactured by Evonik Fibers with a trilobal fiber cross section (Fig. 2.25). P84 is a fully imidized polyimide derived from aromatic dianhydrides and aromatic diisocyanates and has a glass transition temperature of 315°C. The fibers start to carbonize at temperatures beyond 370°C. Due to the aromatic structure, the polymer and fibers are inherently nonflammable. An FOl of 38% can be measured. P84 can be used for temperatures up to 260°C, depending on the environment [71]. Typical properties of P84 are introduced in Table 2.67. 

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