**4. Conclusions**

The article presents two methods of obtaining polyacrylonitrile-polyaniline fibers (PAN/PANI), as well as their physicochemical properties. Polyaniline was used to dope the polyacrylonitrile, which was obtained by synthesis in aqueous solution or dimethylformamide during the preparation of the spinning solution.

It should be noted that in the PAN fiber production process that was doped with PANI, an identical polyacrylonitrile amount of 13.5% was assumed in both the non-doped and PANI-doped fibers, which, as a consequence, influenced the spinning process and physical properties of the obtained fibers.

During spinning, an attempt was made to maintain identical solution concentrations, spinning bath temperature and water vapor, as well as the pickup and feed speed at the pickup and delivery points. In turn, this was cause for the PAN/PANI in situ fibers to resist stretching in steam, which, in turn, translated into a lowering of their specific strength. During the spinning of the identical solution concentrations, the spinning bath temperature and water vapor, as well as the pickup and feed speed at the pickup and delivery points were maintained. This was cause for the PAN/PANI in situ fibers to resist stretching in steam, which resulted in a lowering of their specific strength.

The fibers obtained by mixing the previously synthesized polyaniline with the polyacrylonitrile fiber spinning solution (PAN/PANI blended) were characterized by:


Analysis of the above results led to the conclusion that the PANI could be introduced into the fiber in amount and form, which blended well with polyacrylonitrile and formed a homogeneous structure. This additive did not disturb the fiber crystal structure and morphology, but only slightly changed the thermal parameters of the fibers. However, this degree of combination of polymers prevented the transport of electric charges in the fibers; therefore, they remained dielectric. Further research on this modification method will focus on the effective increase of polyaniline content in fibers.

The fibers obtained as a result of the direct synthesis of polyaniline in the spinning solution (PAN/PANI in situ) were characterized by:


The low mechanical strength of the fibers was mainly due to the lack of fiber stretching, their heterogeneous structure, and low degree of crystallinity. The reduced crystal crystallinity in comparison to the PAN fibers resulted from the stiffness of the structure caused by the presence of interactions between the PAN and PANI chains visible on the FTIR spectra. These fibers exhibited electro-conductive properties at the level of 5.47 k Ωg/cm2, which can be used to construct electrical connections in textronic clothing. Moreover, thanks to the reversible color change, which depends on the pH of the environment in which they are found, they can also be used as pH sensors in protective clothing. In further work, the authors will develop research to obtain electro-conducting PAN/PANI fibers with the highest possible mechanical strength. For this purpose, the study will focus primarily on the modification of parameters for obtaining a spinning solution, as well as the spinning itself.

**Author Contributions:** Conceptualization, I.K.; Investigation, O.R.-R. and M.F.-T.; Methodology, I.K. and O.R.-R.; Resources, T.R.; Supervision, H.T.; Visualization, O.R.-R.; Writing—Original Draft, O.R.-R.; Writing—Review & Editing, H.T.

**Funding:** This work was supported by the National Science Centre [decision number DEC-2013/09/B/ST8/03679]; a statutory activity subsidy from the Polish Ministry of Science and Higher Education for the Faculty of Microsystem Electronics and Photonics of Wroclaw University of Science Technology.

**Conflicts of Interest:** The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, or in the decision to publish the results.
