Structure Of Polyacrylonitrile Fibers Research Articles

Effect of graphene oxide coatings on the structure of polyacrylonitrile fibers during pre-oxidation process.

In this paper, graphene oxide (GO) was successfully prepared by the modified Hummers’ method and then uniformly dispersed in an aqueous solution containing a small amount of polyvinyl alcohol (PVA) as an adhesive. The solution was uniformly coated on the surface of polyacrylonitrile (PAN) fibers and then the fibers were pre-oxidized at 240 °C for 20 min in the air. The pre-oxidation degree of PAN fibers and fibers coated with different contents of GO was analyzed by the Fourier transform infrared (FT-IR) spectroscopy, differential scanning calorimetry (DSC), X-ray diffraction (XRD) and thermogravimetric analysis (TGA). In addition, the surface and cross-section of PAN fibers before and after pre-oxidation were observed by scanning electron microscopy (SEM). The experimental results showed that the presence of GO coatings significantly improved the pre-oxidation degree of PAN fibers, at the same time, the pre-oxidation degree of PAN fibers increased with the increase of GO contents from 0.2 to 1.0 mg ml−1. The cross-section morphology of the pre-oxidized PAN fibers revealed that the degree of pre-oxidation inside fibers was uniform. This was because the GO coatings acted as a medium to transfer heat, removing the heat released during the pre-oxidation process and increasing the pre-oxidation degree.

Use of X-Ray Structure Analysis to Study the Fine Structure of Carbon and Polyacrylonitrile Fibers

A procedure for performing x-ray structure analyses that allows data on the fine structure of carbon and polyacrylonitrile fibers to be obtained was described. It was shown that carbon fibers were heterogeneous. Their component composition was determined by the preparation conditions and depended on the orientation angle of the coherent scattering regions relative to the filament axis. The structure of crystalline polyacrylonitrile-fiber components included two types of coherent scattering regions, the average sizes of which differed by an order of magnitude. The change in the fine structure of polyacrylonitrile fibers during thermal stabilization was followed.

Effect of Water on the Modular Structure Conformation of “Polikon K” Material

This paper presents the developed probabilistic spatial model fragments of the structure of polyacrylonitrile fiber, the monomerization composition (condensing components of the polymer matrix), and “Polikon K” – “Polikon K1a” material. The dynamic contact angle of the investigated material was experimentally determined, and the work of adhesion (1.154 mJ/m2) and wetting (73.855 mJ/m2) of the surface material was calculated. The model of the structure of the “Polikon K1a” material indicates the most likely point of interaction of copolymer polyacrylic fiber with reactive CH3– groups of the polymer matrix, namely, the interaction with the C≡N group, by breaking one bond and forming a methylene bridge. The size of the unit cell of the model was estimated: 10.6 × 10.3 × 9.7 A. The dependence of the torsion angle near the methylene bridge on the concentration of water molecules was investigated.

Structure and Properties of Hydrolyzed Cyclization-Crosslinking Flame-Retardant Polyacrylonitrile Fiber

As flame-retardant Polyacrylonitrile (PAN) fibers was one of the most important differential fibers, it was of great importance to make research on the modification of flame-retardant PAN fibers to improve its characteristics. In this present study, the flame-retardant PAN fiber with good moisture absorption and mechanical properties has been prepared treated by blending solution of sodium hydroxide and hydrazine hydrate. FTIR spectra presented that new amide and cyclization-crosslinking pyridine group band peaks appeared. X-ray diffraction showed that the crystal structure of PAN fibers has been converted from quasi-crystalline structure into partially crystallized structure after modification treatment. SEM micrographs indicated that the original longitudinal surface microgroove has changed to layered structure by surficial etchant.

Properties and structure of polyacrylonitrile fibers

With the use of the methods of dynamic mechanical analysis and thermomechanical analysis, the structural transformations of polyacrylonitrile fibers during heating are studied. It is shown that, regardless of the degree of macromolecule orientation, the fibers not exposed to heating are characterized by an amorphous ordered structure with an ordered mesophase. During heating, the fiber acquires a single-phase structure owing to transition of the amorphous component to the mesophase.

The evolution of the core/shell structure of polyacrylonitrile fibers during preoxidation

The core/shell structure of polyacrylonitrile (PAN) fibers formed during preoxidation was investigated by DSC, FT-IR, SEM, optical microscopy and density measurement. Five precursors were used to correlate the core/shell structure with their thermo-chemical reactivity. It was found that the morphologies of the core/shell structures are highly relevant to the reactivity, microstructure and density of PAN fibers, and the quality of the resultant carbon fibers depends strongly on the degree of pre-oxidation.

Effect of the Textile Structure of Polyacrylonitrile Fibres on Formation of a Three-Dimensional Polymer Matrix Network in “Polikon” Materials

The effect of the textile structure of PAN fibre on formation of a three-dimensional network in the polymer matrix in Polikon-A chemisorption material was investigated. The basic process methods and parameters for manufacturing modified Polikon-A materials were developed. Service life tests were performed on experimental-laboratory batches of materials. The effect of the textile structure of the fibre base on the selective power of Polikon-A chemisorption materials was noted.

X-ray studies on the structure of polyacrylonitrile fibers

Using an X-ray fiber diffractometer, 2D intensity distributions of polyacrylonitrile (PAN) fibers are measured in reciprocal space in the plane containing the fiber axis. The equatorial intensity distributions show four relatively sharp reflections and three diffuse maxima. The sharp reflections correspond to a pseudohexagonal 2D lattice of intermolecular packing. The diffuse minima are due to the Laue scattering of a rotational disorder in this lattice. The off-equatorial intensity distribution is mainly determined by intramolecular scattering. A comparison with calculated 2D intensity distributions for various conformations of short PAN chain segments reveals that the predominant conformation is planar zigzag

Change in structure of polyacrylonitrile fibres on treatment with alkali metal salts

Treatment of polyacrylonitrile fibre with alkali metal salts helps to change its supermolecular structure.

Investigation of the structure of polyacrylonitrile fibres modified with sodium salts by the method of water vapor or dye sorption

Figures for the capillary porosity of polyacrylonitrile fibre which has been modified with salts of alkaline metals have been determined.

Change in structure of polyacrylonitrile fibres during the process of giving them ion-exchange properties

Change in structure of polyacrylonitrile fibres during the process of giving them ion-exchange properties

Structure of polyacrylonitrile fibres modified with polyethylenimine

After the treatment of carboxylated PAN with polyethylenimine the fibre center retains the absorption band at 1720 cm-i produced by the free-CO groups and contains new bands at 1410 and 1590 cm-1 (ionized COO-groups), a fact which shows that the sorption of PEI by carboxyl-contain ing PAN fibre proceeds in accordance with an ionic mechanism. Since sorbents of this type contain amino groups as well as carboxyl groups they must be classed as amphoteric ion exchangers, a finding which was corroborated by potentiometric titration. The structural analysis was conducted on a DRON-2.0 x-ray diffraetometer. The original and modified specimens were analyzed in identical conditions. The x-ray diagram of the original PAN fibre (Fig. 2a) contains distinct reflections with interplanar spacings of 5.5 and 5.2 ~, a fact which agrees with earlier findings [4]. The structure of partly carboxlated PAN fibre (Fig. 2b) has undergone a slight rearrangement compared with that of the original fibre. The sharp decrease in the strength of the reflections indicates that the macromolecule chains in the crystalline part of the polymer have become randomized. The degree of order of the structure is lower. After modification with PEI the partly carboxylated PAN fibre (fibre PAN-PEI) is almost wholly amorphous (Fig. 2c). The x-ray diagram contains two very faint reflections with 5.5 and 5.2 ~ against a background of an amorphous halo. The heating of PAN- PEI fibre for 30 rain at 150°C produced no effect on the order of its structure, i.e., the x-ray diagram in Fig. 2d differs sacrcely at all from that in Fig. 2c. TABLE i. Physicomechanica l Properties of PAN Fibres

Relation between the internal stresses and the structure of polyacrylonitrile fibers

The change in the structure of a polyacrylonitrile fiber after various stages of processing has been investigated. The existence of three relaxation processes in isometrically heated polyacrylonitrile fibers is demonstrated.