Oxidative stabilization of acrylic fibres

Warner, Steven B.; Uhlmann, D. R.; Peebles, L. H.

doi:10.1007/bf00551029

Cited by 104 publications

(45 citation statements)

References 23 publications

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“…'o-12 Bahl et al13 have concluded that the PAN fibers have either orthorhombic or hexagonal structure that depends on the spinning conditions and the composition. An orthorhombic unit-cell has been proposed to account for the observed reflections obtained by mounting the specimen a t 16.5' and showing the (004) reflection.12 Bohn et al14 and Warner et al 15 have proposed models for the morphological structure of PAN fibers and indicated that the existence of ordered regions was due to the formation of lamellar-like structure. In this work the precursor is found to have similar structure.…”

Section: Effect Of Pretreatment On the Structure Of The Precursormentioning

confidence: 98%

Thermal stabilization of polyacrylonitrile fibers

Ting

Lin

1988

J of Applied Polymer Sci

107

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SynopsisPolyacrylonitrile (PAN) fibers pretreated with potassium permanganate have reduced the activation energy of cyclization and the oxidation time, and also improved the properties of the resultant carbon fibers. The activation energy of cyclization is reduced to 24 5 1 kcal/mol from 30 3 kcal/mol and the tensile strength of the carbon fibers increases by about 20-40%. The method of measuring the "aromatization index" (AI) value is modified and is recommended in checking the oxidation process. All fully stabilized PAN fibers have almost the same A1 value. However, the oxidation time is decreased by 30 min when oxidation temperature is raised by looc. INTRODUCTIONPolyacrylonitrile (PAN) fiber has been used as the precursor for making high-performance carbon fibers. An important step in preparing carbon fiber from the PAN fiber is to heat the precursor from 200 to 300°C in the air. Morita et a1.l and Raskovic and Marinkovic2 stated that treating PAN fiber by sulfur dioxide gas instead of air oxidation, is a better method of stabilizing fiber structure, and results in more economical production of high-performance carbon fibers.It has been established that heat treatment of PAN fiber under a tension load improves fiber quality.3* However, recent trends in developing highperformance carbon fibers from PAN is through chemical modification of the precursor with certain additives before oxidation. Mathur et al.5 and Bahl et a1.6 have pretreated PAN fiber with CuCl to make high-performance carbon fibers. Our previous study7 presented the preliminary results of the process taking place during the pretreatment of PAN fibers with potassium permanganate. This study offers further details of our investigations, the microstructure, physical, and mechanical properties of the oxidized fibers. EXPERIMENTALA special grade acrylic fiber, Courtelle fiber (Courtaulds Limited, Coventry, UK), containing 6% methyl acrylate and 1% (itaconic) acid copolymer was used in our work. Each single tow of the fiber contains 6000 strands of 1.1 denier monofilament. A fiber-wound frame was pretreated by immersing it in a 7% potassium permanganate solution at 85°C for a few minutes, then washed with distilled water and dried to a constant weight in an oven. The color changed from clear white to brown after pretreatment. The manganese content in the prepared carbon fibers was determined by atomic emission spectrometer analysis and found to be 25 ppm for the untreated, and 1630 Oxidized PAN fibers and the pretreated precursor were heat-treated in a constant temperature zone furnace under constant load (0.1 g/denier) a t 230, 250, and 270°C from 1 to 10 h, respectively, in a purified air atmosphere. The oxidized fiber tows were carbonized to 1300°C in a ceramic reaction tube under oxygen-free Ar atmosphere. A heating rate of 250°C/h was carried out up to lOOO"C, then continued a t 6OoC/h until reaching 1300"C, then the specimens were cooled down immediately.Mechanical properties of PAN and stabilized fibers were measured by Instron 1122 tensile-tes...

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Section: Effect Of Pretreatment On the Structure Of The Precursormentioning

confidence: 98%

Thermal stabilization of polyacrylonitrile fibers

Ting

Lin

1988

J of Applied Polymer Sci

107

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“…However, there are more intermolecular and more intramolecular dipolar interactions between the nitrile groups in the molecular rods (ordered phase) of PAN fiber. Warner et al 16 supposed that the amorphous (disordered) phase of PAN fiber was a jumbled molecular chain structure (as shown in Fig. 6), but Gupta and Singhaln considered it to be some kind of random alignment of molecular rods (as shown in Fig.…”

Section: Pan Fibermentioning

confidence: 98%

Structural changes and molecular motion of polyacrylonitrile fibers during pyrolysis

Lin

Ting

1989

J of Applied Polymer Sci

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SynopsisThe stabilization process of polyacrylonitrile (PAN) fiber is necessary to develop high-performance carbon fiber. This work is concerned with studies of the activation energy of PAN fibers during the stabilization process. A wide-angle X-ray diEractometer combined with a fiber specimen holder for heating was used to measure the activation energy of crystal transition E,. E, is almost the same as the activation energy of the cyclization reaction E which is measured by a differential thermal analysis (DTA). The variation of crystal size in PAN fiber and a model of the ladder polymer in stabilized fiber transformed from acrylontrile (AN) units of PAN fiber are discussed also. The crystal size of PAN fiber increases when the thermal treatment temperature is raised. When exposed to temperatures above the crystal degradation temperature Td, the molecular rods of PAN fiber are destroyed completely, and ladder polymer is formed in the ordered phase of the original PAN fiber. The transformation of ladder polymer is initiated in the disordered phase, &d then at the boundaries of the ordered phase.

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“…However, there was lack of fine morphological characterization of this structure. The periodic lamellar structure supports the highly orientated acrylic fibers structural model proposed by Warner, et al [14]. Further looking into Figure 1(d), the exfoliated fibrils with 500-600 nm in diameter were comprised by two microfibrils of 200-350 nm in diameter.…”

Section: Morphology Of Pan Fibrilsmentioning

confidence: 64%

Microstructure of fibrils separated from polyacrylonitrile fibers by ultrasonic etching

Wang

et al. 2010

Sci. China Technol. Sci.

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Polyacrylonitrile (PAN) fiber is an important precursor fiber for high performance carbon fiber. The properties of the final carbon fiber depend strongly on the nature of the PAN fibers. The PAN fibrils were separated successfully from fibers by ultrasonic etching and were systematically investigated by field emission scanning electron microscopy (FESEM) and high resolution transmission electron microscopy (HRTEM). It is found that in certain ultrasonic etching conditions (at 75±2ºC for 6 h with a frequency of 40 kHz) the PAN fibers are dissolved in the 95 wt.% aqueous dimethylsulphoxide (DMSO) solution; the fibrils consisting of numerous periodic lamellae with thickness of 3045 nm and perpendicular to the fiber axis are separated in the 90 wt.% aqueous DMSO solution; and the fibrils with smooth surface exfoliated from the PAN fibers are obtained in the 7090 wt.% aqueous DMSO solutions. Inner periodical structure of fibrils was observed in HRTEM, which indicates that there are different densities and two phases in fibrils. The PAN fibers are dissolved layer by layer with increasing ultrasonic etching time. The fiber surface experiences ultrasonic cleaning, selective etching, excessive etching and dissolution, and then the sublayer experiences the same process. There are numerous periodic lamellae in fibrils of nascent fibers. This means that the fibrils with lamellae are formed by orientation and crystallization in shearing field of spinning pipe and drawing stress field of coagulation bath. carbon fibers, PAN fibers, fibrils, microstructure Citation: Wang Q F, Wang C G, Yu M J, et al. Microstructure of fibrils separated from polyacrylonitrile fibers by ultrasonic etching.

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Oxidative stabilization of acrylic fibres

Cited by 104 publications

References 23 publications

Thermal stabilization of polyacrylonitrile fibers

Thermal stabilization of polyacrylonitrile fibers

Structural changes and molecular motion of polyacrylonitrile fibers during pyrolysis

Microstructure of fibrils separated from polyacrylonitrile fibers by ultrasonic etching

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