**3. Results and Discussion**

### *3.1. Molecular Weight of Polymers*

Based on the results of exclusion chromatography (GPC) analysis, the molecular weights of the polymers were determined. The average molecular weight of polyacrylonitrile was Mw 644,600 and Mn 177,400. Its polydispersity was 3.6, which indicates a very large weight distribution of molecules in the polymer. On the other hand, the average molecular weight of the PANI obtained in the aqueous solution, which was Mw 12,920 and Mn 4263, respectively, and the degree of polydispersity of PANI were also large, amounting to 3.0.

### *3.2. Rheological Properties of Spinning Solutions*

The basic properties of each spinning solution, which demonstrated its quality, were rheological properties. To modify the composition of these solutions, it was necessary to determine the effect of modifications on these properties. When analyzing the rheological properties of spinning solutions, the dependence of tangential stress on shear rate (A power-law fluid—the Ostwald–de Waele relationship) is analyzed (1):

$$
\pi = \mathbf{k} \gamma^n \tag{1}
$$

where n is the flow behavior index (-), and k is the flow consistency index (Pa·<sup>s</sup>n). These two basic rheological parameters of each spinning solution were determined experimentally (Table 1).

**Table 1.** The value of flow behavior index n and the flow consistency index k of the spinning solutions.


The value of the flow behavior index depended on the way in which polymer macromolecules were placed in motion, and the way they formed a system of mutually sliding layers. The linear polymer chains in the spinning solution (with a sufficiently high concentration) can be highly tangled. The determined value of n (Table 1) indicated that all the obtained spinning solutions were shear thinned liquids. This is desirable for technological reasons (the ease of pressing the solution through the nozzles). The flow rates of solutions containing polyaniline were slightly higher. This means that polyaniline particles minimally affected the orientation of polyacrylonitrile macromolecules. This gentle effect on the *n*-value may be due to the difference in the molecular structure of both polymers. The flow behavior index depended on several factors, e.g., the average molecular weight of the polymer and its degree of polydispersity, the degree of branching of macromolecules, and the content of additional components (especially fillers) and plasticizers. In the studied system, both polymers were linear, but the PAN macromolecules formed entangled structures, and the PANI macromolecules were largely rigid due to the presence of quinone rings in them. This parameter, in addition to temperature, pressure, and concentration, had a significant impact on the value of the flow consistency index k. Taking into account technological requirements, the k value of spinning solutions should be greater than 20 Pa·<sup>s</sup>n. In comparison to changes in the n value, the presence of polyaniline molecules in the spinning solution caused a significant change in the k value. This change was mainly due to the addition of a polymer with a much lower average molecular weight relative to the spinning solution. The average molecular weight of PANI was 50 times less than PAN. Moreover, a significantly lower value of the consistency coefficient of spinning solutions containing PANI may be related to the occurrence of interactions between the PAN and PANI chains [19,20].
