Conversion of acrylonitrile-based precursors to carbon fibres

Jain, Mukesh; Balasubramanian, M.; Desai, Prashant; Abhiraman, A. S.

doi:10.1007/bf01160585

Cited by 93 publications

(41 citation statements)

References 6 publications

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“…The former occurred because of the relaxation of stresses that built up in the amorphous phase during the fiber spinning and drawing, whereas the second step of thermal shrinkage was due to chemical reactions that led to the cyclization of nitrile groups. Jain et al 28 explained the physical shrinkage in the coiling of the oriented chains and the shrinkage at the higher temperature side (250°C) on the basis of chemical reactions associated with the nitrile oligomerization leading to ladder polymer formation.…”

Section: Dichroic Ratiomentioning

confidence: 99%

Structure development during dry–jet–wet spinning of acrylonitrile/vinyl acids and acrylonitrile/methyl acrylate copolymers

Bajaj

Sreekumar

Sen

2002

J of Applied Polymer Sci

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Section: Dichroic Ratiomentioning

confidence: 99%

Structure development during dry–jet–wet spinning of acrylonitrile/vinyl acids and acrylonitrile/methyl acrylate copolymers

Bajaj

Sreekumar

Sen

2002

J of Applied Polymer Sci

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“…When no macroscopic changes in the length of precursor fibers are allowed during heat treatment, stress develops due to the tendency of chains in a disordered phase to undergo entropic relaxation. 6,7 Since the origin of this stress is thermal energy, thus it can be defined as thermal-induced entropic stress. Therefore, in FRT, the fibers are neither shrunk nor elongated; thus thermal-induced entropic stress is equivalent to external imposed stress in this temperature.…”

Section: First Return Behaviormentioning

confidence: 99%

“…The orientation index of crystallite planes parallel to the fiber axis (f crystal ) is calculated by Eq. (6). 23 H is FWHMs (full width at half maximum) of the peaks at 180°from an azimuthal scan.…”

Section: Measurementsmentioning

confidence: 99%

“…5 As a result, thermal-induced stress is developed due to tendency of chains in the disordered phase to undergo entropic relaxation. 6 The entropic stress is generated in chains when molecular motions occur in the paracrystalline region, and the intermolecular bonds break by the heating process in the amorphous phase. 7 As a result, entropic shrinkage in the paracrystalline region takes place sooner.…”

mentioning

confidence: 99%

“…In the first method, fibers are heat treated while constrained to a constant length. 6,[12][13][14][15][16] In the second method, fibers are restrained by a constant force during heat treatment. [17][18][19][20][21] In the third method, stretching force is applied on PAN fibers by controlling the speed differences between the feed rollers and the take-up rollers in the continuous prestabilization process.…”

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confidence: 99%

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A Novel Method for Investigation of Entropic Stress in Prestabilization of PAN‐Based Precursor Fibers

2015

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ABSTRACT:Applying stress in the fiber axis direction during the prestabilization process is the best method to control entropic relaxation. Evaluation of entropic stress is necessary for exact determination of required imposed stress. Accordingly, in this paper three types of special-grade polyacrylonitrile (PAN) fibers with different physical-mechanical properties and morphological characteristic are studied. To determine thermal-induced entropic stresses, we use the thermomechanical analysis method from room temperature to beginning of chemical reactions under certain stresses. It is shown that three thermophysical behaviors including the first return, second return, and sans return occurs under certain stresses during the thermal process. There are distinct temperatures for the first and second return behaviors, in which fibers return to primary length after shrinkage or elongation. These temperatures depend on imposed stress during prestabilization. We found that if no elongation or fiber shrinkage occurs in a specific stress and temperature, it shows that imposed stress is equivalent to thermal entropic stress. Changes in shrinkage as a function of temperature for various external imposed stresses are also observed. According to our findings, the onset of entropic stress strongly depends on the orientation index of the paracrystalline region. The maximum entropic stress occurs in the rubbery flow region in amorphous phases and can be obtained from a derivative of the second-order polynomial trend line of the entropic stress-temperature diagram.

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Investigation of the thermal oxidative stabilization of PAN filaments in carbon fibre processing

Walenta¹,

Fink²

1990

Acta Polymerica

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Investigation of the thermal oxidative stabilization of PAN filamentsFig. 1. Sample 3 c shows a nematic texture, best development a t 257% Poly(oxycarbonylimino-4,4'-azo benzenediyliminocarbonyloxyethyleneoxyethyleneoxyethyleneoxyethylene) ( 3 4 : T h e reaction of 0.66 g (2.5 mmol) 1 and 0.49 g (2.5 mmol) 2 d i n 10 m l diglyme yields 0.65 g 3d (56.7%), mp. 150 t o 156 "C. IR(KBr, cm-l): 3325 (-NH-stretch); 1730, 1710 (C=Ostretch) ; 1535, 1510 (-NH-def.) ; 1 120 (-C-N-stretch) ; 1075 ethylene glycol; 850 aromat. (C22H26N407)n ; (458.2),.Calc.:C 57.64% H 5.72% N 12.22%Found:C 57.29% H 5.83% N 12.90% Results and discussionThe polyurethanes 3a-d prepared b y polyaddition reaction in solution (cf. experimental p a r t ) have high melting points. They have been characterized b y elemental analyses a n d IR-spectral data.One of t h e polyui'ethanes, 3c, exhibits a liquid crystalline state. Figurc 1 shows the t e x t u r e of 3 c in polarized light at microscopic inspection. One can see clearly t h a t a nematic phase exists higher than 225°C (see Figure 1). Phase transition at this temperature can also b e seen in t h e DSC.T h e polyurethanes 3a, 3b, and 3d d o not have mesogenic phases.The thermal oxidative stabiiization of PAN fibres was investigated by small and wide angle X-ray scattering and by measurements of the fibre density. It has been proved that stabilization starts in the less ordered regions and proceeds t o higher ordered domains. Dimensions of these regions were estimated. Untersuchung der thermisch-ozidativen Stabilisierung von PAN-Faden bei der Herstellung yon KohlenstoffasernMittels Rontgenweitwinkel-und Kleinwinkel-Untcrsuchungen einschlieBlich Dichtemessungen wird die thermischoxidative Stabilisierung von PAN-Copolymer-Faden untersucht. Es wird nachgewiesen, daS die Stabilisierung in den ungeordneten Bereichen beginnt und erst danach die lateral geordneten Gebiete erfalt. Die GroSe dieser Bereiche wird angegeben. Hayueiiue mepaoo?cueaumeabwoii cma6uauaayuu IlAH-eoaoicon e npoyecce noayuenus yznepodnaax eonotconMeTOgaMH peHTreHorpa@mm nog 6 0 n b r r r~~ B Mamm y r n a m B n a~e p e~m s IIJIOTHOCTB ~s y s e e a TepMooHHcnaTenbHaa c~a 6~n~a a q~a BOJIOWOH m 3 cononmrepa HAH . H O I E~~~H O , YTO nposecc C T~~A J I H~~~M M HawiHaeTca B Heynopanoo q e m a p a 3~e p o~ 3~mx a6nac~eiX.YeHHbIX 0 6 n a c~a x BOJIOHOH Ei TOJIbHO BaTeM OXBaTbIBaeT O~J I~C T E C IIOnepeqHbIM yIIOpl3nOqeHBeM. npOBeneHa

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Conversion of acrylonitrile-based precursors to carbon fibres

Cited by 93 publications

References 6 publications

Structure development during dry–jet–wet spinning of acrylonitrile/vinyl acids and acrylonitrile/methyl acrylate copolymers

Structure development during dry–jet–wet spinning of acrylonitrile/vinyl acids and acrylonitrile/methyl acrylate copolymers

A Novel Method for Investigation of Entropic Stress in Prestabilization of PAN‐Based Precursor Fibers

Investigation of the thermal oxidative stabilization of PAN filaments in carbon fibre processing

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