Morphology of the structure of polyacrylonitrile fibres

Abstract

Polyacrylonitrile (PAN) has been widely used for a relatively long time for fabrication of fibres. There are many articles and monographs on very different aspects of this polymer and the fibres made from it. The structure and formation of PAN as a function of the fabrication conditions have also been studied repeatedly and in detail, in particular, especially in detail in [1, 2] and monograph [3]. Detailed studies were usually conducted using only one aprotic solvent --dimethylformamide (DMF). At the same time, in addition to DMF, another aprotic solvent --dimethylacetamide (DMAA) --can be used as a solvent for PAN. Despite the fact that these two solvents belong to the same class and that their great similarity is noted in the literature, there are also data on differences in their properties. Convincing data on the important difference in the values of the second virial coefficient (A2), a quantitative measure of the thermodynamic affinity between polyaner and solvent, for PAN in DMF and DMAA solvents, are cited in [4]. For DMAA A9 has a value of 6.1.10 -4 cm 3.mole/e 2 -4 3 2 9 ". .for DMF and 2.5.10 cm .mole/g . This means that DMAA has a lower thermodynamic affimty for PAN than DMF and thus lower solvent power. In consideration of these concrete and other data, the question of the structure of PAN fibres obtained from solutions in DMAA merits separate examination. The results of a study of this question are presented in the present article.Finished PAN fibres spun by the wet method from highly concentrated solutions in DMAA containing a lyophilic salt were investigated. The concentration of solvent in the aqueous spinning bath varied within a wide range --from 40 to 86 wt. %. The structure was studied with a JSM-840A scanning electron microscope by determining the shape and overall character of the structure of the cross section and the morphology of the surface of the fibres.The photomicrographs of the cross section and surface of fibres fabricated with variation of the ratio of spinning bath components are shown in Fig. 1. The shape of the cross section and morphology of the surface of PAN fibres very obviously change with a change in the composition of the spinning bath.For a 45 and 63% concentration of solvent in the spinning bath, the cross section of the fibres is clearly bean-shaped (Fig. la, b). The surface morphology can be characterized as striated, with a furrow width of tenths of a micrometer ( Fig. la', b').Increasing the concentration of solvent in the spinning bath to 70% causes small changes in the bean shape of the cross section of the fibres (Fig. lc). No significant changes were observed in the surface morphology (Fig. lc').The shape of the fibre cross section is totally different with a spinning bath solvent:precipitator ratio of 75:25 (Fig. ld), 82:18 (e), and 85:15 (f). The shape of the fibre cross section in Fig. ld-f is almost romld. As for the surface morphology (Fig. ld', e'), it does not change significantly with respect to the striated morphology in comparison to Fig. la'-c'. Ch...

Analysis of fabrics obtained during the archeological excavation sites in Israel

“…This is an indication that the Fabric 4 is made of PAN polymer. When compared with literature, PAN polymers are soluble in DMSO and DMF 39 …”